ultrasound research topics

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Ultrasonography articles from across Nature Portfolio

Ultrasonography is an imaging technique that uses the reflections of high-frequency sound waves to create an image of a structure located within the body.

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• Echocardiography

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Audio-visual modelling in a clinical setting

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Ensemble learning for fetal ultrasound and maternal–fetal data to predict mode of delivery after labor induction

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Clinical evaluation of AI-assisted muscle ultrasound for monitoring muscle wasting in ICU patients

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Clinical experience with shear wave elastography (SWE) for assessing healthy uterus in a transabdominal approach

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A fully autonomous robotic ultrasound system for thyroid scanning

Current thyroid ultrasounds rely heavily on the experience and skills of the sonographer and of the radiologist, and the process is physically and cognitively exhausting. Here, the authors show a fully autonomous robotic ultrasound system, which is able to scan thyroid regions without human assistance and identify malignant nodules.

• Jingwei Liu
• Peter Xiaoping Liu

Transthoracic ultrasound localization microscopy of myocardial vasculature in patients

Transthoracic ultrasound localization microscopy enables super-resolution imaging of myocardial microvasculature and haemodynamics in patients with impaired myocardial function using data acquired within a breath hold.

• Meng-Xing Tang

News and Comment

Adapting vision–language AI models to cardiology tasks

Vision–language models can be trained to read cardiac ultrasound images with implications for improving clinical workflows, but additional development and validation will be required before such models can replace humans.

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Factors identified that predict resolution of subclinical synovitis

New findings provide insight into the natural history of subclinical synovitis, a reported predictor of the development of rheumatoid arthritis, and identify various factors associated with its reversal.

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AI outperforms sonographers at diagnosing cardiac function on echocardiography

An artificial intelligence-guided workflow for initial evaluation of left ventricular ejection fraction in echocardiography is non-inferior to initial assessment by a sonographer, according to findings from a blinded, randomized, non-inferiority clinical trial.

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A wearable ultrasonic device to image cardiac function

Researchers have engineered a wearable device that adheres to the skin and uses ultrasound imaging and a deep learning model to produce a dynamic, real-time assessment of cardiac function.

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Secukinumab reduces synovitis in PsA

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Deep learning for detecting congenital heart disease in the fetus

New advances in machine learning could facilitate and reduce disparities in the prenatal diagnosis of congenital health disease, the most common and lethal birth defect.

• Shaine A. Morris
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Home > Books > Medical Imaging

Ultrasound Imaging - Current Topics

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Ultrasound Imaging - Current Topics presents complex and current topics in ultrasound imaging in a simplified format. It is easy to read and exemplifies the range of experiences of each contributing author. Chapters address such topics as anatomy and dimensional variations, pediatric gastrointestinal emergencies, musculoskeletal and nerve imaging as well as molecular sonography. The book is...

Ultrasound Imaging - Current Topics presents complex and current topics in ultrasound imaging in a simplified format. It is easy to read and exemplifies the range of experiences of each contributing author. Chapters address such topics as anatomy and dimensional variations, pediatric gastrointestinal emergencies, musculoskeletal and nerve imaging as well as molecular sonography. The book is a useful resource for researchers, students, clinicians, and sonographers looking for additional information on ultrasound imaging beyond the basics.

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Ultrasound has potential to damage coronaviruses, study finds

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The coronavirus’ structure is an all-too-familiar image, with its densely packed surface receptors resembling a thorny crown. These spike-like proteins latch onto healthy cells and trigger the invasion of viral RNA. While the virus’ geometry and infection strategy is generally understood, little is known about its physical integrity.

A new study by researchers in MIT’s Department of Mechanical Engineering suggests that coronaviruses may be vulnerable to ultrasound vibrations, within the frequencies used in medical diagnostic imaging.

Through computer simulations, the team has modeled the virus’ mechanical response to vibrations across a range of ultrasound frequencies. They found that vibrations between 25 and 100 megahertz triggered the virus’ shell and spikes to collapse and start to rupture within a fraction of a millisecond. This effect was seen in simulations of the virus in air and in water.

The results are preliminary, and based on limited data regarding the virus’ physical properties. Nevertheless, the researchers say their findings are a first hint at a possible ultrasound-based treatment for coronaviruses, including the novel SARS-CoV-2 virus. How exactly ultrasound could be administered, and how effective it would be in damaging the virus within the complexity of the human body, are among the major questions scientists will have to tackle going forward.

“We’ve proven that under ultrasound excitation the coronavirus shell and spikes will vibrate, and the amplitude of that vibration will be very large, producing strains that could break certain parts of the virus, doing visible damage to the outer shell and possibly invisible damage to the RNA inside,” says Tomasz Wierzbicki, professor of applied mechanics at MIT. “The hope is that our paper will initiate a discussion across various disciplines.”

The team’s results appear online in the Journal of the Mechanics and Physics of Solids . Wierzbicki’s co-authors are Wei Li, Yuming Liu, and Juner Zhu at MIT.

A spiky shell

As the Covid-19 pandemic took hold around the world, Wierzbicki looked to contribute to the scientific understanding of the virus. His group’s focus is in solid and structural mechanics, and the study of how materials fracture under various stresses and strains. With this perspective, he wondered what could be learned about the virus’ fracture potential.

Wierzbicki’s team set out to simulate the novel coronavirus and its mechanical response to vibrations. They used simple concepts of the mechanics and physics of solids to construct a geometrical and computational model of the virus’ structure, which they based on limited information in the scientific literature, such as microscopic images of the virus’ shell and spikes.

From previous studies, scientists have mapped out the general structure of the coronavirus — a family of viruses that s HIV, influenza, and the novel SARS-CoV-2 strain. This structure consists of a smooth shell of lipid proteins, and densely packed, spike-like receptors protruding from the shell.

With this geometry in mind, the  team modeled the virus as a thin elastic shell covered in about 100 elastic spikes. As the virus’ exact physical properties are uncertain, the researchers simulated the behavior of this simple structure across a range of  elasticities for both the shell and the spikes.

“We don’t know the material properties of the spikes because they are so tiny — about 10 nanometers high,” Wierzbicki says. “Even more unknown is what’s inside the virus, which is not empty but filled with RNA, which itself is surrounded by a protein capsid shell. So this modeling requires a lot of assumptions.”

“We feel confident that this elastic model is a good starting point,” Wierzbicki says. “The question is, what are the stresses and strains that will cause the virus to rupture?”

A corona’s collapse

To answer that question, the researchers introduced acoustic vibrations into the simulations and observed how the vibrations rippled through the virus’ structure across a range of ultrasound frequencies.

The team started with vibrations of 100 megahertz, or 100 million cycles per second, which they estimated would be the shell’s natural vibrating frequency, based on what’s known of the virus’ physical properties.

When they exposed the virus to 100 MHz ultrasound excitations, the virus’ natural vibrations were initially undetectable. But within a fraction of a millisecond the external vibrations, resonating with the frequency of the virus’ natural oscillations, caused the shell and spikes to buckle inward, similar to a ball that dimples as it bounces off the ground.

As the researchers increased the amplitude, or intensity, of the vibrations, the shell could fracture — an acoustic phenomenon known as resonance that also explains how opera singers can crack a wineglass if they sing at just the right pitch and volume. At lower frequencies of 25 MHz and 50 MHz, the virus buckled and fractured even faster, both in simulated environments of air, and of water that is similar in density to fluids in the body.

“These frequencies and intensities are within the range that is safely used for medical imaging,” says Wierzbicki.

To refine and validate their simulations, the team is working with microbiologists in Spain, who are using atomic force microscopy to observe the effects of ultrasound vibrations on a type of coronavirus found exclusively in pigs. If ultrasound can be experimentally proven to damage coronaviruses, including SARS-CoV-2, and if this damage can be shown to have a therapeutic effect, the team envisions that ultrasound, which is already used to break up kidney stones and to release drugs via liposomes, might be harnessed to treat and possibly prevent coronavirus infection. The researchers also envision that miniature ultrasound transducers, fitted into phones and other portable devices, might be capable of shielding people from the virus.

Wierzbicki stresses that there is much more research to be done to confirm whether ultrasound can be an effective treatment and prevention strategy against coronaviruses. As his team works to improve the existing simulations with new experimental data, he plans to zero in on the specific mechanics of the novel, rapidly mutating SARS-CoV-2 virus.

“We looked at the general coronavirus family, and now are looking specifically at the morphology and geometry of Covid-19,” Wierzbicki says. “The potential is something that could be great in the current critical situation.”

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Vibrations of coronavirus proteins may play a role in infection

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What is medical ultrasound?

How does it work, what is ultrasound used for, are there risks, what are examples of nibib-funded projects using ultrasound.

Medical ultrasound falls into two distinct categories: diagnostic and therapeutic.

Diagnostic ultrasound can be further sub-divided into anatomical and functional ultrasound. Anatomical ultrasound produces images of internal organs or other structures. Functional ultrasound combines information such as the movement and velocity of tissue or blood, softness or hardness of tissue, and other physical characteristics, with anatomical images to create “information maps.” These maps help doctors visualize changes/differences in function within a structure or organ.

Therapeutic ultrasound also uses sound waves above the range of human hearing but does not produce images. Its purpose is to interact with tissues in the body such that they are either modified or destroyed. Among the modifications possible are: moving or pushing tissue, heating tissue, dissolving blood clots, or delivering drugs to specific locations in the body. These destructive, or ablative, functions are made possible by use of very high-intensity beams that can destroy diseased or abnormal tissues such as tumors. The advantage of using ultrasound therapies is that, in most cases, they are non-invasive. No incisions or cuts need to be made to the skin, leaving no wounds or scars.

Ultrasound waves are produced by a transducer, which can both emit ultrasound waves, as well as detect the ultrasound echoes reflected back. In most cases, the active elements in ultrasound transducers are made of special ceramic crystal materials called piezoelectrics. These materials are able to produce sound waves when an electric field is applied to them, but can also work in reverse, producing an electric field when a sound wave hits them. When used in an ultrasound scanner, the transducer sends out a beam of sound waves into the body. The sound waves are reflected back to the transducer by boundaries between tissues in the path of the beam (e.g. the boundary between fluid and soft tissue or tissue and bone). When these echoes hit the transducer, they generate electrical signals that are sent to the ultrasound scanner. Using the speed of sound and the time of each echo’s return, the scanner calculates the distance from the transducer to the tissue boundary. These distances are then used to generate two-dimensional images of tissues and organs.

During an ultrasound exam, the technician will apply a gel to the skin. This keeps air pockets from forming between the transducer and the skin, which can block ultrasound waves from passing into the body.

Click here to watch a short video about how ultrasound works.

Diagnostic ultrasound. Diagnostic ultrasound is able to non-invasively image internal organs within the body. However, it is not good for imaging bones or any tissues that contain air, like the lungs. Under some conditions, ultrasound can image bones (such as in a fetus or in small babies) or the lungs and lining around the lungs, when they are filled or partially filled with fluid. One of the most common uses of ultrasound is during pregnancy, to monitor the growth and development of the fetus, but there are many other uses, including imaging the heart, blood vessels, eyes, thyroid, brain, breast, abdominal organs, skin, and muscles. Ultrasound images are displayed in either 2D, 3D, or 4D (which is 3D in motion).

Functional ultrasound. Functional ultrasound applications include Doppler and color Doppler ultrasound for measuring and visualizing blood flow in vessels within the body or in the heart. It can also measure the speed of the blood flow and direction of movement. This is done using color-coded maps called color Doppler imaging. Doppler ultrasound is commonly used to determine whether plaque build-up inside the carotid arteries is blocking blood flow to the brain.

Another functional form of ultrasound is elastography, a method for measuring and displaying the relative stiffness of tissues, which can be used to differentiate tumors from healthy tissue. This information can be displayed as either color-coded maps of the relative stiffness; black-and white maps that display high-contrast images of tumors compared with anatomical images; or color-coded maps that are overlayed on the anatomical image. Elastography can be used to test for liver fibrosis, a condition in which excessive scar tissue builds up in the liver due to inflammation.

Ultrasound is also an important method for imaging interventions in the body. For example, ultrasound-guided needle biopsy helps physicians see the position of a needle while it is being guided to a selected target, such as a mass or a tumor in the breast. Also, ultrasound is used for real-time imaging of the location of the tip of a catheter as it is inserted in a blood vessel and guided along the length of the vessel. It can also be used for minimally invasive surgery to guide the surgeon with real-time images of the inside of the body.

Therapeutic or interventional ultrasound. Therapeutic ultrasound produces high levels of acoustic output that can be focused on specific targets for the purpose of heating, ablating, or breaking up tissue. One type of therapeutic ultrasound uses high-intensity beams of sound that are highly targeted, and is called High Intensity Focused Ultrasound (HIFU). HIFU is being investigated as a method for modifying or destroying diseased or abnormal tissues inside the body (e.g. tumors) without having to open or tear the skin or cause damage to the surrounding tissue. Either ultrasound or MRI is used to identify and target the tissue to be treated, guide and control the treatment in real time, and confirm the effectiveness of the treatment. HIFU is currently FDA approved for the treatment of uterine fibroids, to alleviate pain from bone metastases, and most recently for the ablation of prostate tissue. HIFU is also being investigated as a way to close wounds and stop bleeding, to break up clots in blood vessels, and to temporarily open the blood brain barrier so that medications can pass through.

Diagnostic ultrasound is generally regarded as safe and does not produce ionizing radiation like that produced by x-rays. Still, ultrasound is capable of producing some biological effects in the body under specific settings and conditions. For this reason, the FDA requires that diagnostic ultrasound devices operate within acceptable limits. The FDA, as well as many professional societies, discourage the casual use of ultrasound (e.g. for keepsake videos) and recommend that it be used only when there is a true medical need.

The following are examples of current research projects funded by NIBIB that are developing new applications of ultrasound that are already in use or that will be in use in the future:

3D printing through the skin : Researchers at Duke University have developed a method to 3D print biocompatible structures through thick, multi-layered tissues. The approach entails using focused ultrasound to solidify a special ink that has been injected into the body to repair bone or repair soft tissues, for example. Initial experiments in animal tissue suggest the method could turn highly invasive surgical procedures into safer, less invasive ones. (Image on left courtesy of Junjie Yao (Duke University) and Yu Shrike Zhang (Harvard Medical School and Brigham and Women’s Hospital)). 

Inducing a hibernation-like state : Researchers at Washington University in St. Louis used ultrasound waves directed into the brain to lower the body temperature and metabolic rates of mice, inducing a hibernation-like state, called torpor. The researchers replicated some of these results in rats, which, like humans, don’t naturally enter torpor. Inducing torpor could help minimize damage from stroke or heart attack and buy precious time for patients in critical care. (Image on right courtesy of  Yang et al./Washington University in St. Louis).

High-quality imaging at home : Brigham and Women’s Hospital researchers compared ultrasound scans acquired by experts with those taken by inexperienced volunteers, finding little difference in the image quality of the two groups. The unconventional approach of having patients take ultrasound images of themselves at home and share them with healthcare professionals could allow for remote monitoring and reduce the need for hospitalization. (Image on right courtesy of Duggan et al./Brigham and Women's Hospital). 

Reviewed December 2023

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Volume 5 Supplement 1

Topics in emergency abdominal ultrasonography

Edited by Luca Brunese and Antonio Pinto

Publication of this suppement has been funded by the University of Molise, Universiy of Siena, University of Cagliari, University of Ferrara and University of Turin. The Supplement Editors declare that they have no competing interests.

Sources of error in emergency ultrasonography

To evaluate the common sources of diagnostic errors in emergency ultrasonography.

• View Full Text

Accuracy of ultrasonography in the diagnosis of acute appendicitis in adult patients: review of the literature

Ultrasound is a widely used technique in the diagnosis of acute appendicitis; nevertheless, its utilization still remains controversial.

US detection of renal and ureteral calculi in patients with suspected renal colic

The purpose of this study was to determine whether the color Doppler twinkling sign could be considered as an additional diagnostic feature of small renal lithiasis (_5mm).

Gastrointestinal perforation: ultrasonographic diagnosis

Gastrointestinal tract perforations can occur for various causes such as peptic ulcer, inflammatory disease, blunt or penetrating trauma, iatrogenic factors, foreign body or a neoplasm that require an early re...

Sigmoid diverticulitis: US findings

Acute diverticulitis (AD) results from inflammation of a colonic diverticulum. It is the most common cause of acute left lower-quadrant pain in adults and represents a common reason for acute hospitalization, ...

The role of US examination in the management of acute abdomen

Acute abdomen is a medical emergency, in which there is sudden and severe pain in abdomen of recent onset with accompanying signs and symptoms that focus on an abdominal involvement. It can represent a wide sp...

Intestinal Ischemia: US-CT findings correlations

Intestinal ischemia is an abdominal emergency that accounts for approximately 2% of gastrointestinal illnesses. It represents a complex of diseases caused by impaired blood perfusion to the small and/or large ...

US in the assessment of acute scrotum

The acute scrotum is a medical emergency . The acute scrotum is defined as scrotal pain, swelling, and redness of acute onset. Scrotal abnormalities can be divided into three groups , which are extra-testicula...

Contrast enhanced ultrasound ( CEUS ) in blunt abdominal trauma

In the assessment of polytrauma patient, an accurate diagnostic study protocol with high sensitivity and specificity is necessary. Computed Tomography (CT) is the standard reference in the emergency for evalua...

Abdominal vascular emergencies: US and CT assessment

Acute vascular emergencies can arise from direct traumatic injury to the vessel or be spontaneous (non-traumatic).

Accuracy of ultrasonography in the diagnosis of acute calculous cholecystitis: review of the literature

To evaluate the accuracy of ultrasonography in the diagnosis of acute calculous cholecystitis in comparison with other imaging modalities.

Ultrasonography (US) in the assessment of pediatric non traumatic gastrointestinal emergencies

Non traumatic gastrointestinal emergencies in the children and neonatal patient is a dilemma for the radiologist in the emergencies room and they presenting characteristics ultrasound features on the longitudi...

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59 Ultrasound Essay Topic Ideas & Examples

🏆 best ultrasound topic ideas & essay examples, ✅ good essay topics on ultrasound, 📑 interesting topics to write about ultrasound.

• The Biological Effects of Ultrasound The paper also evaluates the physical mechanisms for the biological effects of ultrasound and the effects of ultrasound on living tissues in vivo and vitriol.
• MRI and Ultrasound for Determining Abnormalities in Preterm Infants Neonatal cranial ultrasound is used in detecting brain injury in preterm infants and can be used repetitively without harming the infant.
• Benefits of 3D Ultrasound to Pregnant Mothers This is coherent to the 3D planar imaging are improved technology previously applied in the 2D ultrasound technology. As an extrapolation from 3D technology, 3D ultrasound is applied as a medical diagnostic technique that utilizes […]
• The Recent Advances in Real Time Imaging in Ultrasound In point of fact, Medical imaging provides the most perfect task of diagnostic to Ultrasound, whereas, the main usage of therapeutic Ultrasound is to treat the numerous types of diseases and disorders in human beings.
• Comparison of MRI and Ultrasound for Determining Abnormalities in Preterm Infants Medical Imaging helps in detecting and diagnosing diseases at its earliest and treatable stage and helps in determining most appropriate and effective care for the patient.”Medical imaging provides a picture of the inside of the […]
• Ultrasound Techniques Applied to Body Fat Measurement in Male and Female The main objective of this paper is to evaluate the accuracy of body fat by using portable ultra sound device which results are reliable and authentic. The ultra sound technique is widely used to measure […]
• Benefits of 3D/4D Ultrasound in Prenatal Care The information that is obtained from this exam assists the health care providers in counseling parents on the development of the fetus especially in the nature of anomalies, prognosis, and the postnatal consideration of the […]
• Biologic Effects of Ultrasound in Healthcare Setting The instrument performing the emission of the sound waves and the recording of their bouncing back is referred to as the transducer and the medical practitioner generally gently presses the transducer against the skin of […]
• Mammography vs. Ultrasound for Breast Tissue Analysis Mammography screening is one of the most recognized options for analyzing breast tissue in adult women. In contrast, the accuracy of this procedure allows it to be an alternative for women who cannot undergo mammography […]
• Ultrasound Physics and Instrumentation The camera is often not in harmony with the perception of the depth of a human vision. The level of such an acoustic signal distortion within a tissue is dependent on the emitted pulse’s amplitude […]
• Low-Back Pain and Ultrasound Therapy In the meantime, their opponents highlight that the beneficial aspects of the treatment course outweigh the risks related to the use of ultrasound equipment.
• Ultrasound in Treatment and Side-Effect Reduction Within the framework of the research project conducted by Ebadi et al, the research problem consisted in the fact that the effects of continuous ultrasound were underresearched.
• Ultrasound in Achilles Tendinitis Diagnosis In this research, the case study approach is applicable due to the fact that various patients suffering from tendon Achilles problem will be used as a basis for gauging the effectiveness of the method of […]
• Ultrasound Technology in Podiatry Surgery First, it is important to briefly outline the peculiarities of the RCT to understand the researchers’ point. They will be able to use the technology in numerous settings.
• Abdominal Ultrasound and Diagnoses The examiner explains to the patient how the procedure will be performed and how much time is necessary to finish the examination.
• Ultrasound and Color Doppler-Guided Surgery The purpose of the study is to examine the opinions of the trainees attending a training course concerning the use of technology.
• Contrast-Enhanced Ultrasound in Focal Liver Lesions In addition, inaccessibility to the eighth of the liver is a major setback in detecting lesions in the segment. With the advent of Doppler ultrasound, more insight in the diagnosis of liver lesions has been […]
• Ultrasound in Chemistry: Sonochemistry
• Intravascular Ultrasound: Current Role and Future Perspectives
• The Difference Between an Echocardiogram and an Ultrasound of the Heart
• Cooperative Control With Ultrasound Guidance for Radiation Therapy
• Optically Generated Ultrasound: A New Paradigm for Intracoronary Imaging
• Nondestructive Testing: Principle of Flaw Detection With Ultrasound
• Closed-Loop Transcranial Ultrasound Stimulation for Real-Time Non-invasive Neuromodulation
• Consumer Application of Ultrasound: A Television Remote
• Roles of Low-Intensity Ultrasound in Differentiating Cell Death
• High-Intensity Focused Ultrasound Development: Destroying the Target Tissue
• Using Ultrasound to Enhance the Mechanical and Physical Properties of Metals
• The Security Implications of the Machine-Learning Supply Chain: Professionalism in the Ultrasound Department
• Ultrasound Neuromodulation: Mechanisms and the Potential of Multimodal Stimulation for Neuronal Function Assessment
• How Ultrasound Can Produce Sonoluminescence
• Preparation for an Ultrasound of a Gallbladder and a Pelvic
• Endorectal and Endoanal Ultrasound Technique
• Transvaginal Ultrasound: Is It Painful, Purpose, and Results
• Endoscopic Ultrasound in Diagnosing Cancer: One of the Most Common Imaging Procedures
• Ultrasound Skin Imaging in Dermatology, Aesthetic Medicine, and Cosmetology
• Ultrasound Physical Medical Treatment in Healing Following an Acute Injury or a Chronic Condition
• How Do Ultrasound Scans Work
• Americas Ultrasound Systems Market: From USD 7.9 Billion to USD 10.23 Billion
• How Ultrasound Imaging Helps Us Understand Speech and Accent Variation
• Cerebral Ultrasound Time-Harmonic Elastography: Softening of the Human Brain Due to Dehydration
• Wireless Communication in “Audio Beacons” Using Ultrasound
• Low-Intensity Focused Ultrasound for Posttraumatic Stress Disorder
• Thyroid Ultrasound: Purpose, Procedure, Benefits
• Blood Pressure Modulation With Low-Intensity Focused Ultrasound
• Accuracy of Ultrasounds in Diagnosing Birth Defects
• Functional Ultrasound During Awake Brain Surgery
• Live Animal Ultrasound Explained by Dr. Allen Williams
• Ultrasound Waves in Acoustic Microscopy
• Chemical and Physical Effects of Ultrasound: Sonoluminescence and Materials
• Focused Ultrasound for Noninvasive, Focal Pharmacologic Neurointervention
• Lung Ultrasound Findings in COVID-19 Pneumonia
• High-Power Ultrasound in Dry Corn Milling Plants
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MIT’s Ultrasound Breakthrough: A New Era in Non-Invasive Brain Healing

By Anne Trafton, Massachusetts Institute of Technology June 30, 2024

The ImPULS device contains ultrasound transducers and electrodes (gold) encapsulated within a polymer. Credit: Courtesy of the researchers

MIT ’s implantable ImPULS device could become an alternative to the electrodes now used to treat Parkinson’s and other diseases.

MIT engineers developed a hair-thin ultrasound device that offers a potential breakthrough in treating neurological disorders by providing precise, minimally invasive deep brain stimulation. This technology, known as ImPULS, could replace traditional electrode-based methods, promising reduced tissue damage and increased efficacy.

Deep brain stimulation, by implanted electrodes that deliver electrical pulses to the brain, is often used to treat Parkinson’s disease and other neurological disorders. However, the electrodes used for this treatment can eventually corrode and accumulate scar tissue, requiring them to be removed.

Researchers at the Massachusetts Institute of Technology have now developed an alternative approach that uses ultrasound instead of electricity to perform deep brain stimulation, delivered by a fiber about the thickness of a human hair. In a study of mice, they showed that this stimulation can trigger neurons to release dopamine , in a part of the brain that is often targeted in patients with Parkinson’s disease.

“By using ultrasonography, we can create a new way of stimulating neurons to fire in the deep brain,” says Canan Dagdeviren, an associate professor in the MIT Media Lab and the senior author of the new study. “This device is thinner than a hair fiber, so there will be negligible tissue damage, and it is easy for us to navigate this device in the deep brain.”

Advantages of Ultrasound-Based Stimulation

In addition to offering a potentially safer way to deliver deep brain stimulation, this approach could also become a valuable tool for researchers seeking to learn more about how the brain works.

MIT graduate student Jason Hou and MIT postdoc Md Osman Goni Nayeem are the lead authors of the paper, along with collaborators from MIT’s McGovern Institute for Brain Research, Boston University, and Caltech. The study was published on June 4 in the journal Nature Communications .

Deep in the Brain

Dagdeviren’s lab has previously developed wearable ultrasound devices that can be used to deliver drugs through the skin or perform diagnostic imaging on various organs . However, ultrasound cannot penetrate deeply into the brain from a device attached to the head or skull.

“If we want to go into the deep brain, then it cannot be just wearable or attachable anymore. It has to be implantable,” Dagdeviren says. “We carefully customize the device so that it will be minimally invasive and avoid major blood vessels in the deep brain.”

Deep brain stimulation with electrical impulses is FDA-approved to treat symptoms of Parkinson’s disease. This approach uses millimeter-thick electrodes to activate dopamine-producing cells in a brain region called the substantia nigra. However, once implanted in the brain, the devices eventually begin to corrode, and scar tissue that builds up surrounding the implant can interfere with the electrical impulses.

The new approach uses ultrasound delivered by a fiber about the thickness of a human hair. Credit: Courtesy of the researchers

New Design and Application of Ultrasound in the Brain

The MIT team set out to see if they could overcome some of those drawbacks by replacing electrical stimulation with ultrasound. Most neurons have ion channels that are responsive to mechanical stimulation, such as the vibrations from sound waves, so ultrasound can be used to elicit activity in those cells. However, existing technologies for delivering ultrasound to the brain through the skull can’t reach deep into the brain with high precision because the skull itself can interfere with the ultrasound waves and cause off-target stimulation.

“To precisely modulate neurons, we must go deeper, leading us to design a new kind of ultrasound-based implant that produces localized ultrasound fields,” Nayeem says. To safely reach those deep brain regions, the researchers designed a hair-thin fiber made from a flexible polymer. The tip of the fiber contains a drum-like ultrasound transducer with a vibrating membrane. When this membrane, which encapsulates a thin piezoelectric film, is driven by a small electrical voltage, it generates ultrasonic waves that can be detected by nearby cells.

“It’s tissue-safe, there’s no exposed electrode surface, and it’s very low-power, which bodes well for translation to patient use,” Hou says.

Implications and Future Directions

In tests in mice, the researchers showed that this ultrasound device, which they call ImPULS (Implantable Piezoelectric Ultrasound Stimulator), can provoke activity in neurons of the hippocampus. Then, they implanted the fibers into the dopamine-producing substantia nigra and showed that they could stimulate neurons in the dorsal striatum to produce dopamine.

“Brain stimulation has been one of the most effective, yet least understood, methods used to restore health to the brain. ImPULS gives us the ability to stimulate brain cells with exquisite spatial-temporal resolution and in a manner that doesn’t produce the kind of damage or inflammation as other methods. Seeing its effectiveness in areas like the hippocampus opened an entirely new way for us to deliver precise stimulation to targeted circuits in the brain,” says Steve Ramirez, an assistant professor of psychological and brain sciences at Boston University, and a faculty member at B.U.’s Center for Systems Neuroscience, who is also an author of the study.

In the new system, transducers (silver) are powered by wires (gold) that deliver electrical stimulation. Credit: Courtesy of the researchers

Customizable and Scalable Technology

All of the components of the device are biocompatible, including the piezoelectric layer, which is made of a novel ceramic called potassium sodium niobate, or KNN. The current version of the implant is powered by an external power source, but the researchers envision that future versions could be powered a small implantable battery and electronics unit.

The researchers developed a microfabrication process that enables them to easily alter the length and thickness of the fiber, as well as the frequency of the sound waves produced by the piezoelectric transducer. This could allow the devices to be customized for different brain regions.

“We cannot say that the device will give the same effect on every region in the brain, but we can easily and very confidently say that the technology is scalable, and not only for mice. We can also make it bigger for eventual use in humans,” Dagdeviren says.

Conclusion and Future Research Goals

The researchers now plan to investigate how ultrasound stimulation might affect different regions of the brain, and if the devices can remain functional when implanted for year-long timescales. They are also interested in the possibility of incorporating a microfluidic channel, which could allow the device to deliver drugs as well as ultrasound.

In addition to holding promise as a potential therapeutic for Parkinson’s or other diseases, this type of ultrasound device could also be a valuable tool to help researchers learn more about the brain, the researchers say.

“Our goal to provide this as a research tool for the neuroscience community, because we believe that we don’t have enough effective tools to understand the brain,” Dagdeviren says. “As device engineers, we are trying to provide new tools so that we can learn more about different regions of the brain.”

Reference: “An implantable piezoelectric ultrasound stimulator (ImPULS) for deep brain activation” by Jason F. Hou, Md Osman Goni Nayeem, Kian A. Caplan, Evan A. Ruesch, Albit Caban-Murillo, Ernesto Criado-Hidalgo, Sarah B. Ornellas, Brandon Williams, Ayeilla A. Pearce, Huseyin E. Dagdeviren, Michelle Surets, John A. White, Mikhail G. Shapiro, Fan Wang, Steve Ramirez and Canan Dagdeviren, 4 June 2024, Nature Communications . DOI: 10.1038/s41467-024-48748-6

The research was funded by the MIT Media Lab Consortium and the Brain and Behavior Foundation Research (BBRF) NARSAD Young Investigator Award.

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Whale sharks given a health check with ultrasound imaging technique

by Annelies Gartner, University of Western Australia

An international team of researchers has discovered a new method of imaging free-swimming whale sharks using underwater ultrasound.

The research, published in Frontiers in Marine Science , was led by the Australian Institute of Marine Science (AIMS) in collaboration with The University of Western Australia, WA's Mira Mar Veterinary Hospital, Okinawa Churaumi Aquarium in Japan, and Georgia Aquarium in the U.S.

Lead author Dr. Mark Meekan, from UWA's Oceans Institute, has been running a monitoring program at Ningaloo Reef with AIMS for the past 20 years.

"Whale sharks are large filter feeders, which makes them vulnerable to consuming plastics and man-made chemicals in the water, so we want to know if they're healthy," Dr. Meekan said.

As part of the program the researchers have been collecting tiny parasites called copepods, a small shrimp-like animal, from the whale sharks ' lips and edges of their fins.

"We found when we started to scrape the copepods off their lips, the whale sharks slowed down, hung vertically in the water and treated us like a giant cleaner fish," Dr. Meekan said.

While the whale sharks were in this position, the researchers were able to use an underwater ultrasound to capture images of the internal organs to help to assess their condition and reproductive status.

"Underwater ultrasounds have been used before to look at reproductive status of sharks in aquariums or caught on drumlines, but this method is not viable with whale sharks," Dr. Meekan said.

Kim Brooks was AIMS' senior field technician during the expedition and operated the hand-held ultrasound unit while free diving with a dozen whale sharks.

"We began by trying to find landmarks inside the body, starting with the heart and from there tried to work out where we were in relation to the rest of the organs," Brooks said.

"It was both an awesome and challenging experience because whale sharks are the largest fish in the ocean, and I was able to watch a live screen view of their beating heart while holding my breath underwater."

Dr. Meekan said the ultrasound imaging showed that whale sharks have a very slow heart rate—just 12 to 16 beats per minute.

The researchers then started to map the internal organs and at first were interested in the liver, where oil is stored to keep the whale shark buoyant.

"We also imaged the back of the shark and could clearly see the skin thickness and muscle bundles," Dr. Meekan said.

"They have a layer of hard denticles at the skin surface that feels rough like sandpaper and below that connective tissue up to 20cm deep, making their skin one of the thickest of any animal.

"We found whale sharks that were skinny and in poor condition had thinner skins."

Scuba diving around whale sharks is not permitted at Ningaloo and touching whale sharks is illegal.

Journal information: Frontiers in Marine Science

Provided by University of Western Australia

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Ultrasound in Radiology: from Anatomic, Functional, Molecular Imaging to Drug Delivery and Image-Guided Therapy

Alexander l. klibanov.

1 Cardiovascular Division; Robert M. Berne Cardiovascular Research Center, University of Virginia School of Medicine, Charlottesville VA 22908

2 Department of Biomedical Engineering, University of Virginia, Charlottesville VA 22908

John A. Hossack

During the past decade, ultrasound has expanded medical imaging well beyond the “traditional” radiology setting - a combination of portability, low cost and ease of use makes ultrasound imaging an indispensable tool for radiologists as well as for other medical professionals who need to obtain imaging diagnosis or guide a therapeutic intervention quickly and efficiently. Ultrasound combines excellent ability for deep penetration into soft tissues with very good spatial resolution, with only a few exceptions (i.e. those involving overlying bone or gas). Real-time imaging (up to hundreds and thousands frames per second) enables guidance of therapeutic procedures and biopsies; characterization of the mechanical properties of the tissues greatly aids with the accuracy of the procedures. The ability of ultrasound to deposit energy locally brings about the potential for localized intervention encompassing: tissue ablation, enhancing penetration through the natural barriers to drug delivery in the body and triggering drug release from carrier micro- and nanoparticles. The use of microbubble contrast agents brings the ability to monitor and quantify tissue perfusion, and microbubble targeting with ligand-decorated microbubbles brings the ability to obtain molecular biomarker information, i.e., ultrasound molecular imaging. Overall, ultrasound has become the most widely used imaging modality in modern medicine; it will continue to grow and expand.

Introduction

Over the decade 2000–2011, the annual global per-procedure usage of X-Ray Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) doubled [ 1 ]. Meanwhile, the number of ultrasound imaging procedures increased more than tenfold [ 1 ]. It is clear to practicing radiologists that this increase in ultrasound imaging usage has not occurred in the traditional medical imaging settings - radiology and cardiology departments in hospitals. In this review, we will examine recent developments and potential future directions in ultrasound imaging instrumentation that will explain the rapid changes in the practice of medical ultrasound imaging.

Similar to the other imaging modalities, ultrasound is approaching limits imposed by the underlying physics (e.g. wavelength) and regulatory tolerance for patient exposure to any form of energy transmitted into the body. Therefore, it becomes interesting to speculate how the different modalities may evolve in the coming years in the face of fundamental physics-origin limitations. As in other imaging modalities, application of contrast agents may assist in overcoming some of the limitations, and brings ultrasound imaging to the areas where its application was not feasible earlier, such as molecular imaging, therapy and drug delivery. In a short manuscript format it is not possible to provide an exhaustive review of literature; we provide examples of the specific trends of highest interest.

Fragmentation of the Practice of Ultrasound Imaging

Until the early 2000s, ultrasound imaging was dominated by cart-based systems priced in the ∼$100–200K range. Physicians, or specialized imaging technicians, in hospital radiology and cardiology departments operated these instruments. More recently, ultrasound imaging has proliferated in the form of hand-held and laptop-size instruments that are finding use in a range of settings beyond conventional large hospital imaging-focused departments. By extension, the reduced size, reduced cost and perceived reduced training requirement of these smaller devices make them feasible options for overseas and underserved communities, as well as ambulance and house call scenarios. This change has been enabled by the Moore’s Law [ 2 ] related improvement in the performance of electronics. Specialized, single purpose, signal processing hardware has been replaced by systems in which software controls a range of functions implemented on powerful, versatile, digital processors with very high data bandwidths [ 3 , 4 ]. Today’s hand carried instruments can essentially achieve functionality and imaging performance similar to the earlier cart-based instruments [ 5 ]. Small-scale instruments are finding uses that include guiding vascular access [ 6 ], emergency room assessment for conditions such as chest pain [ 7 ], detecting blood pooling or foreign object identification / removal [ 8 ]. Significantly, these instruments are primarily operated by healthcare workers for whom imaging is not their primary clinical specialty. Medical ultrasound has been taken to the International Space Station [ 9 ] and to the battlefield [ 10 ]. Remote real-time image viewing (i.e. “telemedicine”) has been demonstrated in both scenarios [ 9 , 10 ].

Figure 1 illustrates two recently commercialized handheld ultrasound scanners. It is clear that we are approaching a scenario in which size of the device is not limited by electronics but by the need for a transducer of a specific aperture according to the clinical necessity and the requirement for a usefully dimensioned image display. Currently, battery dimension and charge duration are also significant considerations but progress in battery technology and processor efficiency provide optimism for continued improvement towards a widespread use of handheld and laptop-based ultrasound.

Portable ultrasound equipment. (Left) “SonicWindow” Handheld C-scan device (Reprinted with permission, image courtesy of Analogic, Copyright, 2014) (Right) “V-Scan” Handheld B-scan device (Reprinted with permission, image courtesy of GE Healthcare, Copyright 2013)

In essence, the Moore’s Law contribution to the field is greatest in areas where massive computational processing requirements are most relevant. Until recently, many of signal / image processing algorithms that existed only in research laboratories could not be translated to widespread clinical usage. Now, however, progressively more complex signal and image processing tasks come within the realm of practicality and viable cost.

Each imaging modality is capable of anatomic, functional and molecular imaging – with varying degrees of performance and limitation. Anatomic imaging remains the dominant application even as the increasing values of functional and molecular imaging become more evident. Unfortunately, ultrasound imaging does not reliably perform well at anatomic imaging. Ultrasound relies on weak reflections and low rates of beam refraction. Generally, in soft tissue, the weak reflection requirement is met. The weak reflection requirement is not met when there is an interface involving materials possessing significantly different acoustic impedances. In ultrasound, bones and air volumes (in lungs, esophagus, and the gastrointestinal tract) present challenges and give rise to limited “acoustic windows” in some applications. For example, cardiac imaging relies on a relatively small number of acoustic windows between or below the ribs. The weak reflection requirement is not met in some other scenarios giving rise to either, or both, acoustic shadowing and acoustic reverberation. In the former, ultrasound does not reach underlying tissue regions and no echo signal is received resulting in a black region. A typical example involves the inability to “see” below an overlying rib. Reverberation typically occurs between overlying layers of muscle and fat and causes multi-path reflection [ 11 ]. This is projected as a phantom, static, echo haze-like image appearing at a greater depth than the actual source of the initial reflection. In radiology applications, the “haze” obscures the tissue of interest to varying degrees contributing to reduced image contrast and less reliable diagnosis.

This phenomenon occurs in cardiac imaging and may cause a static haze over the superficial moving cardiac muscle or appears, for example, as a static object within a heart chamber. Another important class of ultrasound artifact frequently encountered relates to “phase aberration”. Ultrasound beam formation relies on assumed tissue velocity. Since fat possesses a significantly lower sound speed (1478m/s) than muscle tissue (1547 m/s) [ 12 ], a layer of non-uniformly thick superficial fat, or distributed fat, can give rise to refractive errors in the beam focusing process. This results in a degraded beam resolution that has impact on both image spatial (“detail”) resolution and image contrast quality. These artifact mechanisms give rise to a variety of opportunities in research and point towards areas of probable progress in the coming decade.

Phase aberration correction

Phase aberration has been extensively studied since the late 1980s [ 13 ]. Flax and O’Donnell’s work represented a major early contribution towards a practical solution in that it was the first to not require a “beacon” or ideal point source. During the 1990s, efforts were made to implement phase aberration correction on clinical scanners but cost and technical complexity impeded progress. Additionally, it was realized that ideal phase aberration correction requires aberration delay correction in both elevational and azimuthal dimensions on an array surface [ 14 , 15 ]. Building from the concept of receive direction phase distortion, Liu and Waag proposed a “back propagation” approach in which compensatory delay corrections are made on the transmit direction [ 16 ]. A closely related technique involves the use of “time reversal” which also uses received phase errors to guide subsequent transmitted waves [ 17 ]. This technique works optimally with a well defined point source or point scatterer. More recently, Pernot [ 18 ] proposed the generation of cavitation bubbles to provide a nearly ideal source for the time reversal approach. Considerable work over many years has resulted in progressively more sophisticated algorithms with improved performance versus the earlier element signal cross correlation approaches. These include development of a new generalized coherence factor (GCF) [ 19 ] in which the lower frequencies correspond to the phase aligned components of received echo data, and the higher frequencies correspond to the poorly phase aligned echo signals. Additionally, new applications are being proposed that include, for example, phase aberration correction to improve the performance of therapeutic transcranial focused ultrasound [ 20 – 23 ].

“Tissue Harmonic Imaging” (THI)

Nonlinear ultrasonic propagation effects have been studied for several decades. During propagation at high pressure levels, local sound speed changes between compressional and rarefactional phases giving rise to distortion of the wavefront. This progressive increase in signal distortion gives rise to the presence of harmonics of the transmitted signal and these harmonics can be isolated for imaging purposes. Christopher, in 1997 [ 24 ], focused attention on the potential impact of imaging using the tissue harmonic signal and, in particular, it was noted that the nonlinear tissue signal would have reduced sidelobes and improved performance when propagating through typical abdominal wall sections. Within a few months following this paper, all major ultrasound imaging equipment vendors offered some variant on tissue harmonic imaging. In current imaging usage, THI, rather than conventional fundamental mode imaging, is frequently the default operating mode [ 25 ]. Initially, it had been assumed that the low signal level of the nonlinear signal would be objectionable but practical experience indicates that the level of performance achieved in practical settings vastly outweighs a relatively modest impact on maximum imaging depth. One minor drawback of tissue harmonic imaging is that it has motivated widespread use of higher peak power intensity in order to generate the greatest nonlinear signal and to minimize the impact of reduced SNR. Tissue harmonic imaging has proven to be one of the major contributions towards improved clinical B-Mode ultrasound quality [ 26 , 27 ]. Significantly, tissue harmonic imaging made the greatest clinical impact in imaging through the abdominal wall of patients with thicker abdominal walls – i.e. it has made the most impact in the population most likely to benefit from diagnostic ultrasound. It is only in recent years that comprehensive simulations, enabled by high power computation, have elucidated the underlying roles of phase aberration and nonlinear signal generation in the remarkable improvements in image quality observed in clinical THI imaging [ 28 ].

Model-based segmentation and imaging

Frequently, in radiology it is desirable to assess the shape or volume of a particular tissue region. In the case of objects with well-constrained shapes it becomes feasible to eliminate imaging deficiencies (overlying noise, speckle effects, etc.) by fitting a model to the acquired data and presenting to the user a model closely fitted to the acquired image data. For example, a tumor mass or the left ventricle of the heart is known to possess a convex shape that can be fitted and presented to the user as a perfectly “clean” representation of the ventricle – with a seemingly realistic smooth surface and no overlying clutter. Once the model is determined, clinically important linear, area and volume dimensions may be reliably generated. The primary limitation of any model-based fitting approach is that if the model is poorly selected then the method will fail to obtain an accurate fit to the actual available image data. In cancer radiology, there is interest in following the serial evolution of a tumor to assess growth or regression. The most reliable measure of tumor size is a determination of volume (3D) rather than a linear dimension (1D) or maximal cross-sectional area (2D). These two latter measurements are susceptible to error, due to incorrect slice plane selection and both implicitly rely on simplistic geometric assumptions relating linear dimension, or area, to volume. Unfortunately, tumors and other masses can take a number of shapes making model fitting challenging. One of the most versatile fitting models in image processing involves “snakes” or “active contours” [ 29 ]. Although originally developed as a 2D model, the snake is readily extensible to 3D [ 30 ]. The snake formulation involves the use of “internal energy” and “external energy” [ 29 ]. “Internal energy”, which can be user refined, forces the fitted closed line (or volume) shape to adopt a controlled degree of smoothness. (Technically, this involves a constraint on the second derivative along the resulting snakes contour.) In the case of a noisy ultrasound image, this parameter is particularly important. “External energy” is the parameter that forces the fitted line to best conform to the underlying image data. This is most frequently derived from the image gradient (i.e. image feature edges). Since the purpose is to find the underlying feature gradient, uncontaminated by ultrasound image speckle, snake processing on ultrasound data frequency involves a speckle reducing pre-processing step [ 31 , 32 ]. There are a number of frequently encountered speckle reducing algorithms [ 33 – 38 ]. Among these algorithms, Yu’s Speckle Reducing Anisotropic Diffusion (SRAD) is the most commonly encountered and has been extended to 3D [ 39 ]. Several examples of the use of snakes in ultrasound feature segmentation exist for both 2D [ 40 ] and 3D [ 41 , 42 ].

Artifact reduction

One of ultrasound’s primary weaknesses as an anatomic imaging modality, in comparison with MRI and CT, is its susceptibility to artifacts. This motivates a range of efforts to solve ultrasound’s artifact problems. Fortunately, evolving processing speed enables the clinical realization of progressively more complex algorithms. Except in the case of tissue harmonic imaging, in which the nonlinear second harmonic of the transmitted fundamental is isolated (i.e. filtered) for image formation, the challenge in ultrasound image data processing is that desired signals and artifacts (e.g. reverberations) cannot be isolated by simple frequency domain filtering.

Frequently, the contrast qualities of an image can be improved by spatial compounding in which a common tissue region is viewed from independently oriented transmit beam angles [ 43 ]. Spatial compounding has been shown to reduce speckle, clutter and improve image qualities and the ability to differentiate tissues [ 43 ]. In particular, it has proven successful in breast ultrasound: increased conspicuity of lesions, improved margin delineation and clearer cystic imaging have been reported [ 44 ]. A limitation, however, of transmit beam spatial compounding is that the aperture must be divided to yield independent apertures and this results in reduced resolution on a per aperture basis.

In the case of moving tissue one can, in principle, differentiate the desired moving signal from an overlying static haze artifact [ 45 – 47 ]. While most of these algorithms are computationally intensive, they have the potential for widespread incorporation into the future generation of clinical scanners. This class of artifact reduction has more utility in cardiology than in radiology.

Quantification – tissue tracking

Within the past decade regional tissue tracking (“speckle tracking”) has rapidly evolved from a research topic to a commonly implemented clinical ultrasound feature. Although most applications of speckle tracking are in cardiology [ 48 – 50 ], there are a number of radiology applications. Golemati et al [ 51 ] discussed the utility of speckle tracking for assessing elastic properties of the arterial wall and plaque in carotid arteries.

Advances in Doppler

Traditional Color Doppler processing is limited to detecting the 1D component of motion aligned with the ultrasound beam axis. Kasai’s [ 52 ] 1D autocorrelation-based method formed the basis of the vast majority of early clinical scanner implementations for Color Doppler. Kasai’s approach is computationally very efficient but involves a narrow signal bandwidth assumption. Kasai’s approach was largely supplanted by Loupas’ [ 53 ] 2D method which estimates the Doppler value using explicit estimates of both mean Doppler frequency and mean RF frequency at each range segment. It is also possible to estimate velocities using time domain cross-correlation [ 54 ] but this method is less frequently encountered in clinical implementations. However, all these early methods extract only the Doppler component aligned with the ultrasound beam axis. Given that vessels are frequently parallel to the skin surface (e.g. carotid artery), this represents a major limitation. In principle, this problem can be addressed using speckle tracking [ 55 ] but this typically requires high signal to noise ratio and, thus, is limited to shallow vessels like the carotid artery. Speckle tracking is also a relatively computationally intensive process. Another solution for enabling Doppler detection of transverse motion is to introduce oscillation into the transverse direction [ 56 – 58 ]. Using this approach, true “vector Doppler” (i.e. 2D Doppler) is achievable. Synthetic aperture-based approaches have also been proposed that transmit across all directions simultaneously and consequently can form images across the entire field of view at once [ 59 ]. By stepping the aperture source element across the array aperture, and combining the results from multiple transmit events, a high resolution wide-field Doppler image is acquired. More recently, there has been growth in the area of plane wave Doppler processing [ 60 , 61 ]. Multiple acquisitions are obtained from multiple angles and these are combined. This approach provides for very high frame rates (>1000 fps vs. 10’s fps in conventional Color Doppler) across wide fields of view (see Figure 2 ). Significantly, Bercoff notes that real-time implementation of this Doppler processing places very high demands on processor speed and data bandwidth [ 61 ]. Bercoff’s work was implemented on the Aixplorer ultrasound system (SuperSonic Imagine, France). This is the first clinical system with the required processing capability for this new Doppler method and suggests where the “high end” of clinical ultrasound is evolving. Since kHz Color Doppler has only recently become available, we are only now learning about its value in diagnoses. It is also noteworthy that these frame rates place them well beyond the foreseeable capabilities of competing imaging modalities even as frame improvements in competing modalities are enabled by significant technical advances.

Selected frames from a cardiac cycle obtained with using ultrafast compound Doppler. (a) Average flow in the artery indicating the selected frames. (b) Before the opening of the aortic valve, there is a minimal laminar flow. (c) and (d) Acceleration of the flow. (e) Inversion of the parabolic profile in the deceleration. (f) Local turbulence is present and propagates in the artery. (g) and (h) Laminar flows in diastole. Reprinted with permission from [ 61 ], Copyright, 2011, IEEE.

Catheter-based ultrasound

Intravascular Ultrasound (IVUS) has been available clinically for more than two decades. Although the majority of IVUS applications are in cardiology, there are a number of uses within interventional radiology. IVUS technology generally divides into those based on mechanically scanned single transducer element and those comprising a solid-state circumferential array [ 62 ]. IVUS provides cross-sectional vessel anatomic structural information that is not obtained using only X-Ray angiography – which gathers information from a projection across the vessel lumen. IVUS also provides greater imaging depth than Optical Coherence Tomography (OCT); the latter is limited to ∼1 mm [ 63 , 64 ]. IVUS can provide a range of functional information about the vessel wall health and function [ 63 ], yet OCT is frequently presented as a technology that may potentially supplant IVUS based on its superior spatial resolution. Recently, there has been significant progress in the area of pairing IVUS and photoacoustic imaging [ 65 – 68 ]. IVUS can provide excellent anatomic information and some functional information. Photoacoustic imaging provides superior information on vessel wall composition [ 66 , 67 ] and can perform molecular imaging using appropriately targeted light absorbing nanoparticles [ 69 ] (see below).

Elastography

Early versions of elastography primarily relied upon an external application of force during which tissue motion was tracked in using phase sensitive approaches applied to the beamformed radio frequency (RF) line data [ 70 , 71 ]. Over the years, many improvements have been proposed to the underlying algorithms to improve precision and accuracy [ 72 – 74 ][ 75 – 77 ]. The method has found application in a range of settings that include: breast [ 78 , 79 ], prostate [ 80 ] and thyroid [ 81 ]. The approach has been scaled down and performed using IVUS to assess vessel wall elasticity [ 82 – 84 ]. A major contribution in the field of elasticity involved the realization that acoustic radiation force could be used to project the force from within the body at a precise location instead of relying on an external force that rapidly decays with depth and is susceptible to artifacts due to intervening inhomogeneities [ 85 – 87 ]. This version of elasticity imaging is now in clinical usage [ 88 ]. More recently, considerable interest has arisen in shear wave elasticity imaging. Since a shear wave propagates slowly in tissue, the wavelength is low, which improves spatial resolution. Among the various implementations, supersonic shear imaging [ 89 ] appears to be the most promising and has yielded very encouraging early results. In this approach, a supersonic wavefront is created by rapid sequencing of pulses through depth, taking advantage of the fact that the shear wave velocity is just a few m/s. The method also relies on an ultrasfast scanner capable of full field imaging in response to a single transmit burst – i.e. similar to the Aixplorer ultrasound system previously mentioned. Promising results involving characterizing breast lesions have been reported using this approach [ 90 ]. It would appear that full frame, very high frame rate, systems like the Aixplorer most closely suggest the direction in which the “high end” ultrasound imaging field is going. It is also probable that a number of signal processing techniques, yet to be invented, will be enabled by this versatile high performance architecture.

Photoacoustic imaging

Photoacoustic (or optoacoustic) imaging involves the use of short duration laser pulses to induce transient thermal expansions giving rise to emitted ultrasound pulses emanating from the point of light absorption. The received ultrasound pulses are processed in a manner analogous to conventional ultrasound receive signal processing. The receive path may involve either a mechanically scanned single element ultrasound transducer or a phased ultrasound array. Photoacoustic imaging has experienced an extraordinarily rapid rate of technical development in the past decade. Consequently, it should be viewed as a completely new imaging modality as opposed to a subset of ultrasound imaging. Photoacoustic imaging is discussed only briefly in this review. The reader is referred to the review article by Xu and Wang [ 91 ] for a more extensive discussion.

Anatomic ultrasound image contrast is a function of tissue mechanical properties, tissue interfaces and backscatter density. Image contrast in photoacoustic imaging is determined by local light absorption conditions and this will typically also vary with optical wavelength. Thus, it is feasible to image and differentiate between oxygenated and deoxygenated blood [ 91 ], differentiate lipid-dominant versus water-dominant tissue signals and detect other light-absorbing chomophores (endogenous and exogenous). Traditional optical imaging is sensitive to these parameters but possesses extremely limited penetration due to light scattering at any significant depth. Photoacoustic imaging is projected to contribute across a wide range of clinical areas that include: endoscopic imaging, mapping of metabolic rate of oxygen, melanoma, breast cancer, brain pathologies, and mapping of sentinel lymph nodes [ 92 ]. Photoacoustic tomography, using reconstruction principles similar to those used in Computed Tomography, has extended the technical frontier in terms of very high resolution photoacoustic imaging [ 93 – 95 ]. Using these approaches, small animal whole body photoacoustic imaging systems have become developed [ 96 ] and are available commercially [ 97 ].

Photoacoustic imaging divides broadly into two modes of operation. In acoustic resolution photoacoustics, it is not necessary for the input light to be focused to a single point. Because of rapid light scattering in tissue, in any event the light signal becomes defocused beyond approximately 1 mm of depth. In this scenario, photoacoustic imaging resolution is determined by the focusing performance of the receive ultrasound beamformation process. It is a common misperception to believe that light cannot penetrate deep into tissue. By choosing the correct light wavelength (i.e. using Near Infra-Red (NIR: ∼700 to ∼900 nm) [ 91 ], several cm of imaging depth is achievable. Additionally, photoacoustics has extensive applications in catheter-based applications where it can be paired with conventional IVUS [ 65 , 66 , 98 ]. Photoacoustics can also be paired with

Optical Coherence Tomography (OCT) [ 99 ].

Figure 3 , from Hu et al, [ 100 ] illustrates a range of resolutions and sources of contrast that include optical resolution photoacoustic microscopy of sO2 in a mouse ear, acoustic resolution photoacoustic microscopy of hemoglobin concentration in a human palm, photoacoustic CT of Methylene Blue concentration in a rat sentinel lymph node, photoacoustic CT of cerebral hemodynamic changes in response to whisker stimulation in a rat and Photoacoustic endoscopy of a rabbit esophagus and adjacent tissue.

Components of Photoacoustic Tomography, with representative in vivo images across multiple resolution scales (A) Optical Resolution Photoacoustic Microscopy of sO2 in a mouse ear. (B) Acoustic Resolution Photoacoustic Microscopy of normalized total hemoglobin concentration, [hemoglobin], in a human palm. (C) Linear-array Photoacoustic Computed Tomography of normalized Methylene Blue concentration, [dye], in a rat sentinel lymph node (SLN). (D) Circular-array Photoacoustic Computed Tomography of cerebral hemodynamic changes, Δ [hemoglobin], in response to one-sided whisker stimulation in a rat. (E) Photoacoustic endoscopy of a rabbit esophagus and adjacent internal organs, including the trachea and lung. UST, ultrasonic transducer. Reprinted with permission from [ 100 ]; Copyright, 1012, American Association for the Advancement of Science.

Contrast agents in ultrasound imaging

Contrast materials are applied in all imaging modalities, and ultrasound is not an exception. Early ideas of blood pool contrast ultrasound imaging (first discovered by serendipity) [ 101 ] come from the use of air bubbles generated in saline, serum albumin solutions or viscous X-ray contrast media. Unlike water (or most of biological tissues), gas bubbles are very compressible; thus, in response to the passage of the ultrasound wave as the cycles of positive and negative pressure, microbubbles rapidly compress and expand about their equilibrium (ambient) pressure setting, with the particle diameter variation reaching several fold [ 102 ]; movement of gas-liquid interface creates secondary pressure waves, i.e., ultrasound scattering. Luckily for this field, relatively small bubbles, with the diameter somewhat less than of a red blood cell, can scatter MHz ultrasound very efficiently, and can be detected by ultrasound imaging, with excellent sensitivity. A single microbubble, with a sub-picogram mass, can be observed at multi-cm depth, with abundant clinical imaging systems, in real time (at 20–30 frames/s or faster) [ 103 ]. Thus, the dose of the administered ultrasound contrast material can be in the single milligram or sub-milligram range, of which most material is either fully natural (e.g., human serum albumin in Optison microbubbles [ 104 ], or synthetic fully biocompatible, such as phospholipids, e.g., in Definity [ 105 ] and Sonovue microbubbles [ 106 ]). Non-microbubble ultrasound contrast agents were tested widely at the preclinical stage, but have not yet made it to the clinical application level, perhaps due to the larger required dose and lower acoustic backscatter.

Ultrasound contrast is used as a general radiology intravascular agent worldwide (so far the USA is an exception, where only cardiac ultrasound contrast imaging is approved in the clinic). Worldwide, several million ultrasound contrast exams take place every year; due to the low dose of the contrast material, serious side effects are infrequent; for the patients with kidney impairment, where X-ray contrast or Gd-based MRI contrast agents are undesirable, microbubble contrast exam may become the preferred option [ 107 ].

In order to observe microbubble particles in the bloodstream, contrast-specific detection schemes and pulse sequences have been implemented, with multi-pulse detection schemes being the most efficient. A combination of phase inversion (i.e., compression-first and rarefaction-first pulses) and power modulation (i.e., pulses with varying ultrasound transmit amplitude) provides the best sensitivity to contrast along with an excellent suppression of the background tissue signal [ 108 ]; see accompanying video of microbubbles influx into the tumor vasculature in a murine model. Contrast mode is often used in combination with regular grayscale B-mode imaging for anatomy positioning (see Figure 4 ). It is important that microbubble detection in the tissues can be achieved at low acoustic power levels, i.e., without destroying the microbubbles.

Ultrasound imaging of subcutaneneous tumor in a murine model. Top Left: B-mode grayscale imaging (anatomy). Top Right: contrast mode (Cadence CPS), prior to microbubble administration. Bottom Left: contrast mode (Cadence CPS), following microbubble administration (at peak, ∼5 sec following iv bolus). Bottom Right: contrast mode (Cadence CPS), following microbubble administration (at peak, ∼30 sec following iv bolus). Imaging performed with Sequoia 512 scanner equipped with 15L8 probe.

Real-time ultrasound contrast imaging capability is often used for characterization of cancerous nodules: after an intravenous bolus injection, tissue arrival time for normal tissues, benign and malignant tumors may differ significantly [ 109 ]. Modern imaging equipment has a color-coded arrival time routine, which allows a distinct presentation of the contrast arrival time differential between the tumor and surrounding tissues.

Destruction-replenishment as a tool for perfusion contrast imaging

In the 1990s, at the time when microbubble detection was not as sensitive, the most efficient way to monitor microbubble contrast in the bloodstream was to destroy them by higher acoustic pressure of ultrasound. Typically, with mechanical index (MI) in excess of 0.3, and up to 1.9 (as allowed for the diagnostic imaging scanners) destruction is achieved within just one imaging frame. Therefore, taking advantage of this targeted microbubble destruction in the interrogated volume with intermittent timed frame collection, Kaul et al [ 110 ] devised a tool to monitor myocardial perfusion, with the aim to observe perfusion defects in heart muscle following myocardial infarction. Intermittent imaging was performed in synchrony with heart pulses, triggered by EKG, typically at end-systole. Following microbubble infusion, when microbubbles concentration in the vasculature reached a constant level, ultrasound imaging was initiated and performed at every heart beat, then at every other heartbeat, then every third, fourth and fifth heartbeat. Microbubbles from outside of the insonated field (typically, a thin slice, 1–5 mm thick and up to 5 −15 cm long and wide) start to refill the vasculature, larger arteries first, followed by arterioles, capillaries, postcapillary venules and veins. It has been suggested that by timing the interval of ultrasound pulses, the fraction of the blood in the particular portion of the vasculature (e.g., capillaries) can be estimated [ 111 ].

Lately, with the advent of high-sensitivity multipulse detection schemes, ultrasound contrast imaging does not require microbubble destruction anymore. Therefore, after a single destructive pulse, replenishment of microbubbles into the interrogated volume can be monitored in real time, with the traditional clinical imaging equipment at 20–50 frames per second [ 112 ], (see Figure 5 and accompanying video) and with the most modern equipment at 10 3 Hz or even faster [ 113 , 114 ].

Contrast ultrasound imaging of tumor vasculature perfusion in destruction-replenishment mode in a subcutaneous murine tumor model. Top Left: microbubbles within the tumor vasculature after intravenous administration, prior to the destructive pulse. Top Center: immediately after 2 s destructive pulse. Top Right: 2 s after cessation of the destructive pulse. Bottom Right: 6 s after destructive pulse. Bottom Center: 10 s after destructive pulse. Bottom Right: 20 s after destructive pulse. Imaging performed with Sequoia 512 scanner equipped with 15L8 probe (7 MHz, MI 0.2 for imaging, MI 1.9 for destruction).

Overall, perfusion studies with microbubble contrast are now routinely used in the clinical setting worldwide (except USA as of now); they can provide blood flux information in the settings where Doppler imaging is not useful due to smallest size of the vessels in the tissue (e.g., in a transplanted skin flap [ 115 ]). An unfortunate limitation of this technique is in the inability of ultrasound at imaging frequencies to transit through the human skull without attenuation; thus, brain perfusion studies that are routinely performed with functional MRI cannot be performed with contrast ultrasound unless there is a burr hole present [ 116 ].

Molecular (Targeted) Contrast Ultrasound Imaging

Expanding the ability of ultrasound imaging to collect information on the biological processes at the molecular and cellular level requires the use of a specialized contrast agents, targeted microbubbles [ 117 ]. The general idea is traditional for targeted contrast imaging: a contrast particle is conjugated with the targeting ligand that possesses affinity towards the disease marker. The particles are administered in vivo (e.g., intravenously), circulate in the body, and accumulate in the area of disease.

As the typical mean size of microbubble contrast agents is several micrometers, these agents are unable to probe the receptors located outside of the vascular bed. Although nanobubble studies have been repeatedly reported in the literature over the past decade [ 118 , 119 ]), the acoustic backscatter and particle lifetime are both rather low and these agents have not approached practical application; therefore, ultrasound contrast imaging of leaky neovasculature (e.g., as in enhanced permeability and retention effect, EPR, [ 120 ]) is most likely going to be limited to the phase-shift liquid fluorocarbon nanodroplet formulations [ 121 ].

Current progress of molecular imaging with micrometer-sized targeted bubbles has been significant. It started with a model ultrasound imaging study in vitro, in petri dishes, avidin-biotin targeting [ 117 ], and progressed rapidly towards the use of cell cultures and antibody-mediated targeting [ 122 ], followed by in vivo studies. Several targets were investigated with significant detail: thrombi, markers of inflammation, and markers of angiogenesis.

The simplest targeted contrast agent is already in clinical use: Sonazoid (perflubutane) formulation is approved for liver imaging in Japan and South Korea [ 123 ]. Targeting specificity of this agent is based on its lipid shell composition, phosphatidylserine. This phospholipid is a natural marker of apoptosis and a powerful driver for the phagocytic uptake of apoptotic cells [ 124 , 125 ], cell fragments and other particles [ 126 ] by the cells of reticuloendothelial system (RES) and any other phagocytic cells, e.g., leukocytes, specifically, neutrophils. The latter cell is the first to adhere to vascular endothelium in the acute inflammatory response to ischemia-reperfusion injury, e.g., in an experimental myocardial infarction [ 127 ], or in the acute kidney injury scenario [ 128 ], which allows targeted microbubble ultrasound imaging.

More specific endothelial markers of interest to microbubble targeting include selectins (P- and E-) and integrins, such as VCAM-1 and ICAM-1, which are expressed on the surface of vascular endothelium in response to inflammatory stimuli. Microbubble targeting of these molecules is achieved either via antibody placement on the bubble shell [ 129 ] or the use of smaller molecules, such as peptides [ 130 ], nanobodies [ 131 ] or carbohydrates [ 132 ]. The latter molecule, sialyl Lewis X (or A), is present on the business end of a natural leukocyte membrane protein P-selectin glycoprotein ligand −1 (PSGL-1), a ligand for P- and E-selectin, so it is suitable for microbubble targeting to the sites of inflammation [ 133 , 134 ] and to activated platelets [ 135 ].

Another significant application area for microbubble targeting is tumor vasculature: specific markers of vascular endothelium in the areas of malignant tumors can be successfully imaged by ligand-carrying microbubbles. Initially an antibody against the tumor vasculature biomarker α v β 3 was applied [ 136 ], later followed by targeting with other ligand molecules, such as modified RGD peptides [ 137 ]. VEGF Receptor 2 is another important biomarker of the malignant tumor vasculature; this molecule is already a popular target for tumor detection with other imaging modalities [ 138 ] as well as with ultrasound molecular imaging, via microbubbles decorated with anti-VEGFR2 antibodies, [ 139 ], or single-chain VEGF [ 140 ], which has been shown to achieve selective accumulation of microbubbles in the tumor neovasculature in a murine model (see Figure 6 ). A synthetic heterodimeric peptide combination was discovered as a smaller molecule combination tool for VEGFR2 targeting [ 141 ]. The latter microbubble formulation, BR55, is in the ongoing Phase 1/2clinical trial, (see {"type":"clinical-trial","attrs":{"text":"NCT02142608","term_id":"NCT02142608"}} NCT02142608 ). Prior to this, an early-phase BR55 clinical trial for prostate cancer patients with scheduled radical prostatectomy compared VEGFR2 histology with targeted ultrasound imaging. This early study suggested co-location of the tumor nodules by both methods [ 142 ]. Molecular ultrasound imaging may be used to assist with image-guided biopsy (e.g., in the breast and prostate cancer setting) and targeted therapeutic interventions.

Ultrasound Molecular Imaging of VEGFR2 with scVEGF-decorated microbubbles. Ultrasound imaging of subcutaneous colon adenocarcinoma. A, B-mode US image of tumor tissue marked by dotted line. B, Contrast US image of nontargeted MB after 6-minute dwell time. C, Contrast US image illustrates higher pixel intensity because of adherent scVEGF-MB. Copyright, 2010, Lippincott, Williams and Wilkins, reprinted with permission from reference [ 140 ].

Overall, a combination of targeted contrast ultrasound agents with the wide availability of contrast imaging modalities on the ultrasound imaging equipment may result in the use of ultrasound molecular imaging for targeted diagnostics, image-guided biopsy and therapy.

Ultrasound in therapy: thermal and mechanical

Focused ultrasound has been suggested as a therapeutic modality decades ago [ 143 ], although wider clinical use of this approach started much later [ 144 ]. Induction of local hyperthermia by focused ultrasound is based on localized energy deposition. MRI can serve as a tool for precise temperature monitoring in the target tissue, although ultrasound imaging is used for ultrasound therapy guidance in the clinic widely outside of US. Maintaining tissue temperature of ∼45°C for 30–60 minutes (or much higher temperatures, for just a few seconds) is sufficient to kill the cells in the focal zone. Ultrasound of 0.6–1 MHz frequency is often used; from many cm away, a focal zone with the size and shape of a grain of rice can be formed using a focused transducer [ 145 ]. KW power of the therapeutic apparatus can achieve the desired temperature in the focal zone within seconds. Multi-element arrays (optimally, with thousands of elements) allow rapid electronic steering of the focal spot to accelerate the procedure and completely cover the desired treatment zone [ 146 ]. Approved indications include uterine fibroid therapy [ 147 ] and palliative treatment of bone metastases [ 148 ]. Lower frequency ultrasound (220 KHz, necessary for penetrating human skull without heating it significantly) is now being investigated as a tool for ultrasound therapy in the brain [ 149 ]. Focused ultrasound heating is now being tested as a non-invasive replacement of neurosurgical/electrode placement approach for treatment of essential tremor [ 150 ]. We can hope that tumor therapy will be successful in clinical trials in the bone metastasis setting (beyond palliation), as well as for treatment of brain tumors (e.g., {"type":"clinical-trial","attrs":{"text":"NCT01698437","term_id":"NCT01698437"}} NCT01698437 ) or prostate cancer (e.g., {"type":"clinical-trial","attrs":{"text":"NCT02265159","term_id":"NCT02265159"}} NCT02265159 ). Success of this non-invasive therapeutic modality is supported by the ability to focus ultrasound tightly and rapidly deep within the body (even through the skull). Limitations are also based on physical constraints: ultrasound energy is attenuated and absorbed by the bones (thus, brain treatment requires an additional CT or MRI study to adjust the ultrasound pulse sequences to compensate for the shape and thickness of the skull). Ultrasound cannot efficiently travel through the gas phase, so lung treatment can only be performed for liquid-filled lungs [ 151 ]. In some instances, ribcage obscures access to the target (e.g., certain areas of the liver). There have been reports that ribs in the way of ultrasound beam had been resected prior to the treatment with a large aperture single element transducer [ 152 ]. However, more appropriate would be to use multi-element array and adjust the transmit power for the elements which are obscured by the ribs [ 153 ].

Histotripsy implies high-power pulverization of the tissues: a water fountain generated on the air-water interface in the focal zone of an ultrasound transducer is recreated by cavitation in vivo within the therapeutic target tissues, if peak negative acoustic pressure reaches 10 MPa [ 154 ]. Following this treatment, a void in the biological tissue is created: target tissue (e.g., tumor nodule) is destroyed to subcellular level and liquefied [ 155 ].

Thrombolysis with ultrasound

Enhancing the rate of thrombolysis with ultrasound has been suggested more than a decade ago [ 156 , 157 ]. The idea is quite similar to tissue ablation, as described in the previous section; the acoustic energy applied for thrombolysis may be significantly lower, often within the limits of diagnostic ultrasound imaging. Ultrasound pressure wave provides mechanical action on the biological tissues (including the clot and surrounding blood). Liquid media streaming improves convection of the participants of the thrombolytic cascade in proximity and within the clot structure, resulting in thrombolysis acceleration. Presence of even small doses of thrombolytic agents and/or microbubbles (micro-foci of energy deposition and microstreaming) further accelerates thrombolysis. We can hope that ultrasound-assisted thrombolysis, if applied quickly (e.g., in an ambulance setting) will aid in reduction of the clot size, which in turn may help save brain tissue following stroke or myocardium following myocardial infarction [ 158 ]. Ultrasound can be applied non-invasively [ 159 ], or via a catheter [ 160 ].

Ultrasound-microbubble combination as a tool for targeted drug and gene delivery

Ultrasound has been investigated as a tool for microbubble-assisted drug delivery for almost two decades. Initially [ 161 ] model drugs were incorporated into the bubble shell. Later, tumor therapy in response to insonation was achieved in animal models [ 162 , 163 ] - but that was feasible mostly for rather hydrophobic drugs, e.g., paclitaxel. Plasmid DNA could be attached onto the bubble shell electrostatically, and ultrasound-assisted transfection enhancement was observed with such constructs [ 164 ]. Attachment of drug-loaded liposomes onto the surface of microbubbles allows ultrasound-triggered drug delivery capability: in response to microbubble insonation the drug is released from the liposome core [ 165 ]. This has been shown to work with widely used anticancer drugs, e.g., doxorubicin [ 166 ] and paclitaxel [ 167 ].

A combination approach, where existing drug is simply co-administered along with clinical grade approved microbubbles and focused ultrasound, will obviously get to clinical trials faster. In this approach, stable cavitation of microbubbles within the vasculature is used to transiently alter permeability of blood-brain barrier [ 168 ]. The disruption of the barrier is mild and transient (permeability enhancement ceases within hours). However, large items, such as liposomes [ 169 ] and other nanoparticles [ 170 ] can be delivered into the brain tissue as efficiently as smaller items, such as antibodies [ 171 ], other drugs [ 172 ], or even Gd-based MRI contrast agents [ 173 ] (See Figure 7 as an example of penetration enhancement of Gd-DTPA across blood-brain barrier in a rat model). This approach has already led to an exciting demonstration of glioma treatment in a rodent model (curative in a significant fraction of animals) with a simple combination of long-circulating doxorubicin liposomes (doxil) and clinical perflutren microbubbles [ 174 ]. Success of therapy can be explained by the ability of PEG-coated liposomes to stay in the bloodstream for many hours, recirculate through the insonated area vasculature and extravasate for many hours, as long as the drug remains in the bloodstream and the barrier remains open. Expansion of this technique towards clinical applications could be predicted, ranging from tumor therapy [ 174 ] to Alzheimer treatment [ 175 , 176 ].

Ultrasound-induced opening of blood brain barrier in a rat model. Decafluorobutane microbubbles (stabilized with DSPC and PEG Stearate) were injected intravenously, immediately followed by focused ultrasound treatment (IGT, 1 Hz, 20ms pulses, 1–2 min treatment duration) and intravenous administration of Gd-DTPA. MRI contrast extravasation and accumulation (white focal spots in the center of the image) observed minutes after ultrasound treatment and Gd-DTPA administration. Imaging performed at UVA Molecular Imaging Center (7T MRI Clinscan, Bruker/Siemens). Copyright, Max Wintermark, 2014, reprinted with permission.

Similar therapeutic approach can be applied in the situations other than the blood-brain barrier, to any endothelial lining in the vasculature that precludes entry of the drug into the diseased tissue. This approach has been applied to deliver particles of adeno-associated virus to the insonated myocardium [ 177 ], as well as for the treatment of pancreatic cancer in an orthotopic xenograft mouse model, by a combination of anticancer drug gemcitabine and Sonovue microbubbles [ 178 ]. The latter combination has demonstrated interesting data in a clinical trial setting, initially showing the suppression of tumor growth in response to intravenous administration of gemcitabine, immediately followed by injections of Sonovue microbubbles every 3.5 min and continuous insonation of the primary tumor with an ultrasound imaging system during the next half hour [ 179 ], with repeated ultrasound/microbubble treatment cycles administered with every scheduled administration of gemcitabine, up to 32 weeks. Expansion of this trial to a larger group of patients now points towards the beneficial extension of life for the patients undergoing this treatment, with 60% surviving 12 months [ 180 ].

Bioeffects of ultrasound in therapeutic applications

Therapeutic applications of ultrasound may span beyond thermal or mechanical disruption of the tissues or drug delivery. Action of ultrasound on the tissues, possibly in combination with microbubbles, may lead to manifestation of a variety of therapeutic bioeffects, spanning from therapeutic angiogenesis [ 181 ] to inhibiting blood flow in the tumors [ 182 – 184 ], to targeting therapeutic stem cells following intravenous administration [ 185 ], bone fracture healing [ 186 ], and, surprisingly, ultrasound action on splenic nerve to mitigate acute kidney injury [ 187 , 188 ]. Non-invasive brain stimulation by ultrasound is also quite intriguing [ 189 ].

All these techniques are based on the ability of ultrasound (as a pressure wave) to provide guided energy deposition in the treatment area; in some instances the ultrasound action is further enhanced by the presence of vibrating microbubbles. Physiological effects demonstrated by ultrasound application are quite diverse and will definitely lead to the development of new therapeutic approaches and modalities.

Ultrasound has become an indispensable tool of modern medicine that helps expand the borders of radiology. Hardware improvements, based on continuous acceleration of data processing rate, lower cost and smaller size of the electronic devices, are combined with smart transducer design, pulse sequences and novel data processing and analysis schemes. Hand-held and laptop ultrasound is already in wide use, soon to replace cart-based systems. Ultrasound contrast agents bring the ability to monitor tissue perfusion, and targeted agents enable molecular ultrasound imaging of the vascular biomarkers of angiogenesis or inflammation. The ability to direct ultrasound to the desired areas of the body opens up direct therapeutic applications of this modality, including targeted drug and gene delivery, and thrombolytic therapy enhancement. Overall, ultrasound is rapidly developing both as an imaging and a therapeutic modality.

Acknowledgments

NIH EB016752, EB001826, EB002349, HL090700, HL111077, CA102880, DK093841.

Reply to letter to the Editor: “Percutaneous ultrasound‐guided needle tenotomy for treatment of chronic tendinopathy and fasciopathy: a meta‐analysis”

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Firoozeh Shomal Zadeh & Majid Chalian

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Shomal Zadeh, F., Chalian, M. Reply to letter to the Editor: “Percutaneous ultrasound‐guided needle tenotomy for treatment of chronic tendinopathy and fasciopathy: a meta‐analysis”. Eur Radiol (2024). https://doi.org/10.1007/s00330-024-10877-3

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ORIGINAL RESEARCH article

Non-destructive testing technology for corrosion wall thickness reduction defects in pipelines based on electromagnetic ultrasound.

• Saint-Petersburg Mining University, Saint Petersburg, Russia

Pipeline transportation is the main means of transportation of oil, natural gas and other energy sources. During transportation, corrosive substances in oil and natural gas can cause damage to the pipeline structure. A non-destructive testing technology for pipeline corrosion based on electromagnetic ultrasound technology was proposed to improve the stability and safety of energy pipeline transportation systems. This technology utilized empirical mode decomposition and singular spectrum analysis to denoise electromagnetic ultrasound signals. The designed electromagnetic signal denoising algorithm completely removed mild noise pollution. When using this method to detect pipeline corrosion, the maximum calculation error of pipeline wall thickness was 0.1906 mm, and the lowest was 0.0015 mm. When detecting small area corrosion deficiency, the amplitude of the detection signal increased with the depth, up to a maximum of around 24 V, which accurately reflected small area defects. This non-destructive testing technology for pipelines can effectively detect the pipeline corrosion, which is helpful for the regular maintenance of pipeline energy transmission systems.

1 Introduction

Pipelines have the characteristics of low cost and high convenience in transporting energy such as natural gas and oil, making them the main mode of energy transportation ( Sampath et al., 2021 ). Oil and natural gas energy pipelines are mostly made of alloys or plastics, Natural gas and oil contain a large amount of substances such as carbon dioxide and hydrogen sulfide, which can mix or react during transportation, causing corrosion to the inner walls of pipelines ( Marinina et al., 2022 ). Pipeline corrosion is a major threat to the safe operation of pipelines. There are various forms of corrosion defects, including localized pitting, which refers to strong corrosion in small areas of the material surface ( Islamov et al., 2019 ). Sedimentary corrosion is caused by sediment coverage ( Litvinenko et al., 2022b ). Large area corrosion refers to uniform corrosion that covers a large surface area ( Da et al., 2020 ). The accumulation of corrosion on the inner wall of pipelines can lead to a decrease in wall thickness and strength. This may ultimately lead to pipeline leakage or rupture, causing serious economic losses, or causing serious environmental damage ( Litvinenko et al., 2022a ). Therefore, it is crucial to regularly inspect and maintain the inner walls of pipelines. Non-destructive testing technology can complete regular inspections of corrosion on the inner walls of pipelines ( Karyakina et al., 2021 ). Electromagnetic ultrasonic non-destructive testing is a commonly used non-destructive testing technique that is sensitive to various defects in the detection target ( Pryakhin and Azarov, 2024 ). However, this technology has low conversion efficiency during the detection process and is susceptible to interference, resulting in significant errors in the detection results ( Fetisov et al., 2023 ). Therefore, a noise suppression algorithm and different defect feature recognition algorithm for electromagnetic ultrasonic non-destructive testing are designed. Improvements are made to improve the detection accuracy of electromagnetic ultrasonic non-destructive testing (EUT) technology.

Non-destructive testing technology is widely applied in many fields ( Lucas et al., 2022 ). Olisa et al. proposed a non-destructive evaluation method based on guided wave ultrasonic testing to investigate the impact of composite damage on metal structures. Guided wave ultrasonic testing had the ability to remotely detect metal damage. However, parameter characteristics were influenced by structure and environment ( Ren et al., 2022 ). The existing research had not fully explored the correlation between composite damage and guided wave ultrasonic detection parameter characteristics, and further research was needed ( Olisa et al., 2021 ). Garcia Marquez and Gomez Munoz proposed a new method based on cross-correlation and wavelet transform to detect delamination faults in wind turbine blades. This experiment was conducted on real blades, using ultrasonic guided waves to analyze faulty and non-faulty blades. This method effectively identified signal energy mutations and locate faults ( Garcia Marquez and Gomez Munoz, 2020 ). Chabot et al. proposed a multi-sensor monitoring method based on phased array ultrasonic detection technology. This overcame the challenge of lack of structural health control in direct energy deposition processes in additive manufacturing. Phased array ultrasonic testing could detect defects in directly deposited energy manufactured components online and quantitatively predict their size ( Safiullin and Tian, 2023 ). This detection method opened the way for in-situ control of direct energy deposition ( Chabot et al., 2020 ). Gupta et al. further explored the application and advantages of non-destructive testing technology in various industries. They conducted an investigation and analysis of various commonly used non-destructive testing technologies. Most non-destructive testing techniques could be used not only for structural integrity testing, but also for quality analysis and casting process improvement ( Gupta et al., 2022 ). Chen et al. proposed a method using nonlinear ultrasonic testing technology to accurately measure fatigue cracks. Traditional C-scan imaging reduced accuracy when crack directionality was poor or gaps were narrow. However, finite amplitude nonlinear ultrasonic testing was sensitive to micro damage at the optimal voltage and was not affected by macroscopic crack states, which effectively tested fatigue damage ( Chen et al., 2020 ).

Pipeline transportation is currently the mainstream way of transporting various types of energy ( Korobov and Podoprigora, 2019 ). How to improve the quality and service life of pipelines is also the main research direction of pipeline transportation at present. Parlak et al. investigated and analyzed intelligent cleaning devices used for steel pipelines to ensure the safety and integrity of oil and gas pipelines. They classified and discussed its working principle and application. They studied multiple sensor technologies and compared their accuracy in anomaly detection. Intelligent pipeline cleaners not only maintained pipeline safety, but also had environmental benefits ( Parlak and Yavasoglu, 2023 ). Karkoub et al. proposed a new method for pipeline detection using small mobile robots and a reflective omnidirectional vision system to reduce maintenance costs for oil and gas pipelines. The system parameters were optimized using simulated annealing optimization method, proving the feasibility of this technology. This robot system could be used for pre-scanning, reducing the need for expensive tools, thereby reducing inspection time and cost ( Karkoub et al., 2020 ). Ma et al. explored non-destructive testing methods to ensure the safe operation of pipelines in energy transportation. They compared the advantages and disadvantages of non-destructive testing technology and non-cleaning robot detection systems. In addition, the application of data models and management in defect quantification, classification, fault prediction, and maintenance was studied. These results revealed the importance and development trend of non-destructive testing technology in pipeline maintenance ( Ma et al., 2021 ). Daniyan et al. designed a robot inspection system for non-destructive testing of pipelines to improve pipeline quality and reduce pipeline obsolescence caused by cracks, corrosion, and other factors. The inspection robot used ultrasonic detection technology and color perception to inspect pipelines. This robot could not only determine the corrosion situation of pipelines, but also detect the occurrence and growth of cracks in pipelines ( Daniyan et al., 2022 ). Elankavi et al. developed pipeline inspection robots and classified them based on their movement types. This overcame the inconvenience of manual intervention in the internal repair and maintenance of pipelines. By designing and validating different models, their performance was compared. These different types of robots had different functions in pipeline internal maintenance, providing important insights for selection, development, and research ( Elankavi et al., 2020 ). Wang et al. proposed a new type of transducer that generates spiral Lamb waves in pipelines to study the mechanism of transducer action in electromagnetic ultrasonic testing, and established a finite element model to simulate the wave generation and propagation of the transducer. The results show that existing transducers with winding coils are not suitable for generating spiral waves ( Wang et al., 2020 ). In order to solve the problems of poor accuracy and high noise in electromagnetic ultrasonic testing technology in pipeline inspection, Li et al. designed a pipeline crack quantitative detection device consisting of three uniformly distributed probes on the circumference. The results showed that the positioning error of the crack was less than 6.75%. Based on the characteristic coefficient method, the quantitative error of crack size is less than 8.75% ( Li et al., 2022 ).

In summary, the inner wall of the pipeline will come into direct contact with the conveyed content. Corrosion or damage can easily occur under the impact of conveyed content, leading to leakage and loss of conveyed content. Regular inspection and maintenance of the inner wall of pipelines can effectively improve their service life and prevent losses in a timely manner. However, the inner wall of the pipeline cannot be directly inspected. Non-destructive testing technology can complete the detection of targets without causing damage. Therefore, this study proposes to use ultrasonic testing technology to detect and analyze the corrosion of the inner wall of pipelines.

The innovation of this study lies in the design of a signal denoising method based on Empirical Mode Decomposition (EMD) and Singular Spectrum Analysis (SSA) to denoise EUT signals. This study also proposes a defect signal feature extraction algorithm based on signal envelope, which further improves the detection accuracy of EUT. The main contribution of this study is to design a new signal denoising method and a signal feature extraction method for processing detection signals. This improves the target of EUT detection accuracy and enhances the stability and safety of energy transportation.

2 Pipeline inner wall corrosion defect detection technology based on electromagnetic ultrasonic testing

The research on pipeline inner wall corrosion defect detection technology based on EUT includes two parts. Section 1 is the study of EUT from signal preprocessing and noise cancellation. Section 2 is the study of EUT based on defect signal feature recognition and extraction.

2.1 Signal preprocessing of electromagnetic ultrasonic testing based on empirical mode decomposition

EUT combines the principles of electromagnetics and ultrasound to detect defects, foreign objects, or other structural issues in materials. This technology applies electromagnetic fields to the tested material during detection and uses ultrasound to detect changes in the internal structure of the target for structural detection ( Deepak et al., 2021 ; Nikolaev et al., 2018 ). The ultrasonic excitation force mechanism of this method in detection will change according to the material of the detection target. The mechanism of electromagnetic ultrasonic excitation force includes Lorentz force, magnetization force, and magnetostrictive force ( Fetisov, 2024 ). Oil and natural gas transmission pipelines are iron pipelines made of ferromagnetic materials. The mechanisms of ultrasonic excitation in these materials include Lorentz force, magnetization force, and magnetostrictive force. Figure 1 shows the detection principle.

Figure 1 . Principle of electromagnetic ultrasonic detection of pipeline inner wall.

During EUT, the permanent magnet will generate a bias magnetic field around it. This magnetic field will interact with the excitation coil to generate an alternating magnetic field. The particles on the pipe wall will begin to vibrate and form ultrasonic waves. The echo signal is the key signal for EUT to achieve non-destructive testing. However, the echo signal is susceptible to various types of pollution interference, resulting in a significant decrease in detection accuracy. EMD is a time series data processing technique used for analyzing nonlinear and non-stationary signals ( Zhou et al., 2021 ). This technology can segment complex echo signal data into a series of intrinsic mode functions. The number of extremes and zeros in all intrinsic mode function signals is basically the same, with a difference of no more than 1. At any position of the intrinsic mode function signal, the mean of the maximum and minimum envelope lines of the signal is 0. Figure 2 shows the EMD steps.

Figure 2 . The empirical mode decomposition and the echo signal processing.

The steps for processing electromagnetic ultrasound detection echo signals using EMD are as follows: Firstly, signal preprocessing. Necessary preprocessing is performed on the collected electromagnetic ultrasound detection echo signals, such as filtering to remove noise ( Shi et al., 2023a ; Shi et al., 2023b ; Shi et al., 2023c ). Secondly, EMD decomposition involves inputting the preprocessed signal into the EMD algorithm and iteratively decomposing the signal into several IMFs and residual signals ( Wu et al., 2020 ; Wu et al., 2022 ; Wu et al., 2024 ; Zheng et al., 2024 ). Each IMF represents an inherent oscillation mode of the signal. Thirdly, screen IMFs, analyze the obtained IMFs, identify which ones contain useful signal features, and which ones may contain noise or irrelevant information. Fourthly, signal reconstruction can selectively reconstruct certain IMFs as needed to obtain signals that remove noise or highlight specific features. Fifth, post-processing, further processing of the reconstructed signal, such as wavelet transform denoising, feature extraction, etc., to meet specific analysis needs. Fifth, result analysis: Analyze the processed signal, extract useful information such as defect size, position, etc., and provide explanations ( Towsyfyan et al., 2020 ; Stroykov et al., 2021 ). This study assumes that the original signal is s t and solves for all extreme points of s t . The average envelope of the original signal is calculated using a cubic spline function ( Shammazov et al., 2022 ). Cubic spline function is currently a commonly used interpolation method. At this point, the intrinsic mode function can be calculated according to Eq. 1 ( Bolobov et al., 2022 ).

In Eq. 1 , x 1 t represents the first candidate intrinsic mode function. a 1 t represents the average envelope of the original signal. If x 1 t meets the two basic requirements of the intrinsic mode function, it is defined as the first intrinsic mode function. If it does not meet the requirements, the above steps are repeated using x 1 t as the source signal, represented by Eq. 2 .

In Eq. 2 , k represents the repeated operations number. If the candidate intrinsic mode function satisfies the standard deviation condition in Eq. 3 after k operations, the first intrinsic mode function component c 1 t can be decomposed.

In Eq. 3 , T represents the duration of the source signal. c 1 t is separated from s t to generate a new raw signal, represented by Eq. 4 .

In Eq. 4 , r 1 t represents the original signal after removing the first intrinsic mode function. After generating a new original signal r 1 t , the above steps are repeated by replacing s t with r 1 t until the newly generated original signal can no longer extract the intrinsic mode function. After completing EMD, the original signal s t can be expressed as Eq. 5 .

In Eq. 5 , c i represents the intrinsic mode function component of the decomposed signal. n represents the quantity of repetitions. r n represents the residual component of the original signal. After completing the EMD of the original signal, the original signal is reconstructed based on these results. Based on the frequency of the reconstructed signal, EMD can be considered as a high-pass, low-pass, and band-pass filter. When reconstructing the high-frequency intrinsic mode function components, it can be regarded as a high-pass filter ( Pshenin and Zakirova, 2023 ). When reconstructing the low-frequency intrinsic mode function components, it can be regarded as a low-pass filter, removing the high-frequency and low-frequency intrinsic mode components. When only reconstructing the intrinsic mode components of the middle part, it can be regarded as a band-pass filter ( Kumavat et al., 2021 ; Aleksander et al., 2023 ). The signal features obtained by different filtering methods are different ( Tian et al., 2024 ). In the echo signal, the energy of the noise signal is significantly lower than that of the characteristic signal. Therefore, the energy method can be used to screen the intrinsic mode components of the signal. However, this method is prone to losing a large amount of useful information during the screening process. There is no correlation between the noise in the echo signal, while the correlation between the feature signals is strong. Therefore, this study proposes to use the signal feature similarity method to screen the components of the intrinsic mode function. The correlation evaluation method used is a similarity comparison method. The similarity between different components is calculated using Euclidean distance. The correlation between different components is judged. The similarity is represented by Eq. 6 ( Vasiliev et al., 2021 ).

In Eq. 6 , D i represents the Euclidean distance of different components.

2.2 Noise reduction processing of electromagnetic ultrasound signals based on singular spectrum analysis

After filtering and reconstructing the signal using EMD, it is not possible to completely eliminate the noise in the original signal. SSA is a non-parametric statistical method used for analyzing time series data. This method can effectively extract trends, periodic components, noise, etc. from time series. SSA also has good processing ability for non-stationary and nonlinear data. Figure 3 shows the basic process of SSA ( Nikolaev and Zaripova, 2021 ).

Figure 3 . Analysis of the signal singular spectrum detected by electromagnetic ultrasound.

When performing SSA on EUT signals, it is necessary to first convert the original sequence into a trajectory matrix. When embedding the original sequence of ultrasound detection signals, it is necessary to first decompose the original sequence number s t into an L × K dimensional matrix, represented by Eq. 7 .

In Eq. 7 , L and K are parameters that determine the window size in SSA. X represents the transformed trajectory matrix. After converting the original time series into a trajectory matrix, singular value decomposition is also required. The trajectory matrix is decomposed into singular values and singular vectors, represented by Eq. 8 .

In Eq. 8 , X T represents the transpose of matrix X . λ i represents the characteristic value. U i represents the feature vector. It is assumed the singular spectrum d of the original signal in the time series and the right eigenvector V i of the singular spectrum, denoted by Eq. 9 ( Nüßler and Jonuscheit, 2021 ).

Then, matrix X is represented by Eq. 10 .

After completing singular value decomposition on the original sequence, grouping can begin. Grouping is the process of dividing the trajectory matrix into R different groups based on the different characteristics of the signal. After completing the grouping, the singular vectors after grouping can be converted into time series to complete the SSA of the original signal sequence. When performing SSA on the original signal, window size and reconstruction order are two very important parameters. The window size is generally determined by L and K , represented by Eq. 11 .

In Eq. 11 , N represents the length of the original signal. When performing SSA on the original signal, the window must be large enough to decompose subtle noise signals. When the window size is too large, it can lead to a significant increase in the computational cost of SSA ( Baktizin et al., 2020 ). The reconstruction order is selected through the singular spectral inflection point method. Feature signals and noise are distinguished based on the magnitude of singular values. The characteristic signal corresponds to a large singular value and exhibits a curved variation. The noise corresponds to small singular values and the curve is smooth. The inflection point marks the transition from feature signals to noise. When the difference in singular values is large, the inflection point is obvious. The inflection point is not significant when the difference is small. When selecting the window size of SSA, it should first obtain the frequency domain characteristics of the signal. However, electromagnetic ultrasound signals are time-domain signals. Therefore, this study uses the fast Fourier transform to perform time-frequency domain conversion on EUT signals, which is represented by Eq. 12 .

In Eq. 12 , X k represents the discrete signal after fast Fourier transform. x n represents the signal to be converted. j represents the index of parameter K . In SSA, the single component corresponding to each singular value is usually arranged according to frequency. The first singular value usually corresponds to the main trend or lowest frequency component of the time series. This means that the components obtained through the first singular value reconstruction can well preserve the main features and trends of the entire sequence in both the time and frequency domains. Therefore, by analyzing the performance of the first reconstruction component, it is possible to evaluate whether the selected window size is reasonable ( Abed and de Brito, 2020 ). The Hurst exponent is a statistical index used to analyze time series data, quantifying the long-term memory or trend regression of the data. Therefore, when selecting the reconstruction order of SSA, this study uses the Hurst exponent as the evaluation indicator, represented by Eq. 13 ( Kruschwitz et al., 2023 ).

In Eq. 13 , s i represents the cumulative value of the original signal at time [1, t]. s ¯ N represents the mean of the original signal. c is a constant usually taken as 0.5. After preprocessing the electromagnetic supermarket detection data through EMD, preliminary signal noise reduction can be achieved, but small noise cannot be processed. Therefore, this study proposes to use SSA for secondary processing of EUT signals. Figure 4 shows the designed electromagnetic ultrasound signal denoising processing technology based on EMD-SSA.

Figure 4 . Research on signal noise reduction treatment based on empirical mode decomposition and singular spectrum analysis.

When using this technology to process EUT signals, it is necessary to first use EMD to decompose the original signal. Intrinsic mode components are extracted and qualified intrinsic mode function components are selected for SSA, further eliminating small noise in the original signal. After secondary noise reduction processing, the intrinsic mode function component signal can be reconstructed.

2.3 Identification and extraction of defect signal features in electromagnetic ultrasonic testing

After denoising the electromagnetic ultrasonic signal, the changes in ultrasonic waveform under different degrees of corrosion can be analyzed. Corresponding features can be extracted, and the corrosion situation of pipelines can be determined. Pipeline corrosion is usually divided into large area and small area corrosion based on the corrosion area. The changes in ultrasonic waveform under different corrosion areas are inconsistent. Figure 5 shows the specific changes.

Figure 5 . Detection of pipeline corrosion and waveform change.

In Figure 5 , T represents the head wave generated by electromagnetic ultrasonic excitation pulse, F 1 represents the primary echo; F 2 , F 2 ′ and F 2 ″ represents the secondary echo without corrosion, large area corrosion and small area corrosion; F 3 represents the tertiary echo of small area corrosion. When there is no corrosion phenomenon in the pipeline, the time difference between the primary echo formed by ultrasound on the inner side of the pipeline wall and the secondary echo formed on the outer wall of the pipeline is small. When large-scale corrosion occurs in pipelines, the time difference between the primary and secondary echoes will further decrease. When small-scale corrosion occurs in pipelines, electromagnetic ultrasonic waves will form three echoes between the pipe walls. The time difference between the first and second echoes is consistent with the time difference when large-scale corrosion occurs. The time difference between the second and third echoes is extremely short. To identify the degree of corrosion on the inner wall of the pipeline, it is necessary to extract and analyze the features of the echo signals during detection. In corrosion detection, the time difference of echo occurrence is the most direct feature. Therefore, this study uses the arrival time of echoes as the determination method. Common time difference analysis methods include threshold method, peak envelope method, etc. The peak envelope method is a technique used for analyzing and processing signals. The core of this method is to identify and utilize the peak value of the signal to construct an envelope and describe the main characteristics of the signal. This method has a good processing effect on nonlinear and non-stationary signals. Therefore, this study analyzes the EUT echo signal using this method. When extracting the features of EUT echo signals using this method, the analytical signal of the real signal can be defined as Eq. 14 .

In Eq. 14 , a t represents the real signal. a ^ t represents the parsing signal. a t ¯ represents the Hilbert transform of the real signal, represented by Eq. 15 .

In Eq. 15 , τ represents the echo delay time. When using the Hilbert transform to extract the features of the echo signal, the amplitude and phase of the echo signal can be synchronously understood. The peak envelope curve can be calculated by amplitude. The signal frequency can be calculated based on the phase. Signal energy spectrum can be drawn through energy calculation. A three-dimensional time-frequency map can be drawn through the above three dimensions. The localization of pipeline corrosion defects can be completed based on the three-dimensional time-frequency map of the echo signal.

3 Experimental results analysis of non-destructive testing technology for corrosion defects on pipeline inner walls

The experimental results analysis of non-destructive testing technology for corrosion defects on pipeline inner walls includes three parts. Firstly, an experimental platform for detecting corrosion defects on the inner wall of pipelines was established. Secondly, the feasibility of signal denoising processing technology was verified. Finally, the effectiveness of pipeline corrosion detection was analyzed.

3.1 Experimental setup and experimental design

In this study, MATLAB was used to analyze the performance of the model noise reduction algorithm, and to analyze the treatment effect of different degrees of noise pollution. During the experimental verification of the pipeline inner wall corrosion defect detection technology, three experimental scenarios are designed. The first is used for the simulation detection of large area corrosion defects, the second is used for the simulation detection of small area corrosion defects, and the third is the actual detection of the pipeline inner wall. In the detection of large area corrosion defect, RAM-5000-SNAP device was used for ultrasonic excitation and reception. In the detection of small area corrosion defect, RAM-4000-SNAP device was used for the experiment, and the actual detection of the pipeline is the detection device in the pipeline. The experimental devices of the three experiments are shown in Figure 6 .

Figure 6 . Experimental platform and experimental setup. (A) Large area defect detection. (B) Small area defect detection. (C) Actual pipeline detection device.

Figure 6A is a large area corrosion defect detection device, including load ohm, oscilloscope, amplifier and impedance matching equipment. Figure 6B is the actual detection device of the pipeline, which consists of three parts, including the driving section on both sides and the detection section of the intermediate part. Figure 6C shows the in-line detector.

3.2 Analysis of the experimental results

3.2.1 analysis of simulation test results for echo signal noise elimination.

Wavelet Soft Threshold (WST) and Wavelet Hard Threshold (WDT) are two common techniques for denoising ultrasound signals. To verify the feasibility of the EMD-SSAEUT signal denoising algorithm designed, MATLAB was used as the experimental platform to compare and analyze the denoising processing effects of the three methods mentioned above. Figure 7 shows the signal processing effects of three methods.

Figure 7 . Comparison of the noise signal processing effect. (A) Original noise signal. (B) Signal after noise reduction.

Figure 7A shows the original noise signal. Figure 7B shows the signal processed by WST. Figure 7 shows the signal processed by WDT. Figure 7 shows the signal processed by EMD-SSA. After WST processing, the fluctuation amplitude of the original noise signal was significantly reduced. However, there were still significant fluctuations in the stable signal region. The processing effect of WDT method was worse than that of WST. The fluctuation in stable areas was more significant. After being processed by EMD-SSA, the original noise signal still had a certain noise interference at the signal’s stable point. To further verify the signal denoising effect of EMD-SSA, the Signal-to-noise Ratio (SNR) and Mean Squared Error (MSE) processed by three processing methods were compared in Figure 8 .

Figure 8 . SNR and MSE comparison results. (A) SNR comparison results. (B) MSE comparison results.

Figure 8A shows the SNR comparison results of three processing methods. As the SNR of the original signal increased, the SNR of the denoised signal also gradually increased. When the original SNR was 0, the SNR of the signal processed by WST was about 5 dB. The SNR processed by WDT and WST was consistent. The SNR after EMD-SSA processing was approximately 12 dB. When the original SNR increased to 20 dB, the SNR after WST processing was about 17 dB, the SNR after WDT processing was about 23 dB, and the SNR after EMD-SSA processing was about 30 dB. Figure 8B shows the MSE comparison results of three processing methods. With the increase of MSE, the MSE processed by these three processing methods was also increasing. The MSE after EMD-SSA treatment was consistently lower than the other two methods. When the initial MSE was 0.005 dB, the MSE after EMD-SSA processing was about 0.5 dB, while the MSE after WST and WDT processing are both above 1.0 dB. When the initial MSE was 0.007 dB, the MSE after WST and WDT processing was basically the same. The MSE after EMD-SSA treatment was much lower than that after WST and WDT treatment.

3.2.2 The treatment effect of EMD-SSA on different levels of pollution

In the detection of large-scale corrosion defects, firstly, this study compared the effectiveness of this noise reduction method on different noises under the same parameters. Figure 9 shows the processing effect of mild noise.

Figure 9 . Treatment effect of light noise pollution. (A) Mild noise pollution signal. (B) Mild noise pollution signal after processing.

Figure 9A shows the original noise signal with mild pollution. The voltage amplitude of the original noise signal reached 4 V. The amplitude fluctuation of the original noise signal was irregular, and the signal was relatively chaotic, but the signal extremum could still be observed. Figure 9B shows the noise signal after EMD-SSA processing. After EMD-SSA processing, there was a very clear pattern of signal fluctuations. There were three significant peaks in a sampling length of 600. EMD-SSA effectively removed mild noise pollution. Figure 10 shows the treatment effect of moderate pollution.

Figure 10 . Treatment effect of mild noise pollution. (A) Mild noise pollution signal. (B) Mild noise pollution signal after treatment.

Figure 10A shows the raw noise signal with mild noise pollution. The original noise signal had no pattern. The effective signal band was basically completely covered, and the magnitude of the extreme value of the effective signal could not be determined. Figure 10B shows the signal after EMD-SSA denoising processing. After denoising, the effective signal bands were completely separated. However, the amplitude of the effective signal band was also significantly reduced. Figure 11 shows the treatment effect of severe noise pollution.

Figure 11 . Treatment effect of severe noise pollution. (A) Severe noise pollution signal. (B) Severe noise pollution signal after treatment.

Figure 11A shows the original noise signal with severe noise pollution. The effective band and noise signal in the original noise signal completely covered each other, making it difficult to distinguish them. Figure 11B shows the signal after EMD-SSA denoising processing. EMD-SSA can remove most of the noise in severe noise pollution, completely distinguishing the effective band from the noise signal. However, the noise removal effect near the effective band was poor, and significant noise phenomena could still be observed.

3.2.3 Detection of different corrosion defect areas and practical application of pipelines

This study also compared the signal processing effects of large-area corrosion defects under different thicknesses of steel plates in Table 1 .

Table 1 . Treatment effect of large-area corrosion defects of different thickness steel plates.

In Table 1 , when the thickness of the steel plate was 19 mm, the SNR after signal processing reaches the highest value of 16.1354 dB. The SNR gain at this time was 3.859. The SNR of the signal at this thickness was also the lowest before denoising, only 1.1846 dB. When the thickness of the steel plate was 48 mm, the SNR gain after signal denoising was the highest, reaching 12.011. At this point, the SNR of the signal before denoising was 1.2515 dB. The SNR after signal denoising was 15.0648 dB. When the thickness of the steel plate was 36 mm, the SNR after signal denoising was the lowest, only 12.6526 dB. The SNR before signal denoising at this thickness was 2.9784 dB, and the SNR gain was 4.251. This study also compared the pipeline thickness values calculated from the processed signals in Table 2 .

Table 2 . Pipeline wall thickness calculation results and actual results of the denoised signal.

In Table 2 , when the pipe wall thickness was 48 mm, the error between the calculated pipe wall thickness and the actual thickness based on the processed signal was the highest, reaching 0.1906 mm. When the wall thickness was 12 mm, the calculated wall thickness based on the processed signal had the smallest error with the actual thickness, only 0.0015 mm. Among the 8 different thicknesses of pipe walls, only three thicknesses had a calculation error greater than 0.1000 mm. When the thickness of the pipe wall was 19 mm, the calculation error was 0.1452 mm. When the thickness of the pipe wall was 24 mm, the calculation error was 0.1258 mm. Figure 12 shows the time-domain envelope spectrum and energy spectrum changes when there is a small area of corrosion defect.

Figure 12 . Time-domain envelope spectrum and energy spectrum changes of small-area defects. (A) Time domain envelope spectrum variation. (B) Changes in energy spectrum.

Figure 12A shows the variation of the time-domain envelope spectrum of small area defects. As the depth of the defect increased, the fluctuation and amplitude of the time-domain envelope spectrum gradually increased. When the defect depth was 1.5 mm, the amplitude was about 4.5 V. When the defect depth was 3.0 mm, the voltage amplitude was about 5.2 mm. Figure 12B shows the energy spectrum of small area defects. As the defect increased, the signal energy value also continued to increase. When there was no defect, the energy was about 14. After the defect depth increased to 3.0 mm, the energy value rose to about 25. Table 3 shows the pipeline’s actual inspection results.

Table 3 . Test results of the pipeline detection device.

In Table 3 , the calculation results of the wall thickness of the detection pipeline for probes 1 and 3 were basically consistent, indicating that there were no corrosion defects on the wall of probes 1 and 3. In the detection channel of probe 2, the thickness of the detection tube wall was about 7.0 mm, which was significantly lower than the 9.0 mm thickness at probes 1 and 3. There was severe corrosion on the pipe wall at probe 2 of the detection device. By detecting the axial and circumferential positions of the device, the location of pipeline corrosion defects could be determined.

4 Conclusion

A pipeline corrosion detection technology based on electromagnetic ultrasonic non-destructive testing technology has been studied and designed. This can improve the stability of the energy delivery system and reduce the paralysis of the pipeline energy delivery system caused by pipeline corrosion and damage. This study utilized EMD and SSA to denoise EUT signals and improve the accuracy of EUT in pipeline corrosion detection. When the initial MSE was 0.005 dB, the MSE after EMD-SSA processing was about 0.5 dB, while the MSE after WST and WDT processing were both above 1.0 dB. The EMD-SSA signal denoising method effectively removed mild noise pollution, completely separating the effective signal band from noise pollution. When the thickness of the pipe wall was 19 mm, the SNR difference before and after processing of the electromagnetic ultrasound signal was the largest, increasing by a total of 14.9508 dB. When the thickness of the pipe wall was 48 mm, the error between the calculated pipe wall thickness and the actual thickness based on the processed signal was the highest, reaching 0.1906 mm. When the wall thickness was 12 mm, the calculated wall thickness based on the processed signal had the smallest error with the actual thickness, only 0.0015 mm. As the depth of small area defects increased, the signal amplitude gradually increased. When there were no defects, the maximum amplitude was only about 14 V. When the defect depth increased to 3.0 mm, the amplitude increased to above 20 V. The research and design of a pipeline corrosion defect detection technology based on electromagnetic ultrasonic non-destructive testing technology can accurately locate the location of corrosion defects in pipelines and determine the degree of corrosion when the pipe wall thickness is less than 48 mm. The design results of the study contribute to improving the transportation safety of energy sources such as oil and gas. The EUT signal denoising technology designed can effectively eliminate noise interference in pipeline detection. However, the signal denoising method designed has a poor denoising effect on severe noise pollution, resulting in the loss of effective signals. In the future, the noise resistance of electromagnetic ultrasonic pipeline non-destructive testing technology can be further improved to increase the corrosion detection accuracy of pipeline non-destructive testing technology.

Data availability statement

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Author contributions

YT: Conceptualization, Data curation, Formal Analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing–original draft, Writing–review and editing. AP: Conceptualization, Data curation, Investigation, Methodology, Software, Supervision, Writing–review and editing. IS: Formal Analysis, Methodology, Project administration, Supervision, Validation, Visualization, Writing–review and editing. YR: Conceptualization, Data curation, Formal Analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing–review and editing.

The author(s) declare that no financial support was received for the research, authorship, and/or publication of this article.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

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Keywords: electromagnetic ultrasound, pipeline inner wall, non-destructive testing, empirical mode decomposition, singular spectrum analysis

Citation: Tian Y, Palaev AG, Shammazov IA and Ren Y (2024) Non-destructive testing technology for corrosion wall thickness reduction defects in pipelines based on electromagnetic ultrasound. Front. Earth Sci. 12:1432043. doi: 10.3389/feart.2024.1432043

Received: 13 May 2024; Accepted: 17 June 2024; Published: 05 July 2024.

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*Correspondence: Yifan Tian, [email protected]

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.