Comparative Assessment of Real-Time and Offline Short-Lag Spatial Coherence Imaging of Ultrasound Breast Masses

OBJECTIVE

To perform the first known investigation of differences between real-time and offline B-mode and short-lag spatial coherence (SLSC) images when evaluating fluid or solid content in 60 hypoechoic breast masses.

METHODS

Real-time and retrospective (i.e., offline) reader studies were conducted with three board-certified breast radiologists, followed by objective, reader-independent discrimination using generalized contrast-to-noise ratio (gCNR).

RESULTS

The content of 12 fluid, solid and mixed (i.e., containing fluid and solid components) masses were uncertain when reading real-time B-mode images. With real-time and offline SLSC images, 15 and 5, respectively, aggregated solid and mixed masses (and no fluid masses) were uncertain. Therefore, with real-time SLSC imaging, uncertainty about solid masses increased relative to offline SLSC imaging, while uncertainty about fluid masses decreased relative to real-time B-mode imaging. When assessing real-time SLSC reader results, 100% (11/11) of solid masses with uncertain content were correctly classified with a gCNR<0.73 threshold applied to real-time SLSC images. The areas under receiver operator characteristic curves characterizing gCNR as an objective metric to discriminate complicated cysts from solid masses were 0.963 and 0.998 with real-time and offline SLSC images, respectively, which are both considered excellent for diagnostic testing.

CONCLUSION

Results are promising to support real-time SLSC imaging and gCNR application to real-time SLSC images to enhance sensitivity and specificity, reduce reader variability, and mitigate uncertainty about fluid or solid content, particularly when distinguishing complicated cysts (which are benign) from hypoechoic solid masses (which could be cancerous).

Cystic Breast Lesions: Diagnostic Approach and US Assessment

Various cystic breast lesions are encountered during screening and diagnostic breast imaging. According to the Breast Imaging Reporting and Data System (BI-RADS) from the American College of Radiology, cystic breast lesions can be classified into the following categories based on sonographic findings: simple cysts, complicated cysts, clustered microcysts, and complex cystic and solid masses. With appropriate technique, simple cysts can be diagnosed easily by satisfying the diagnostic criteria, which include anechoic round or oval lesions with circumscribed margins and posterior enhancement on US images. Simple cysts are categorized as BI-RADS category 2, benign. Complicated cysts contain debris and satisfy all other sonographic criteria for simple cysts, except they are not anechoic. Clustered microcysts are defined as lesions comprising a cluster of small anechoic masses without a solid component. Based on recent investigations, complicated cysts are categorized as BI-RADS category 3, probably benign, whereas clustered microcysts are categorized as BI-RADS category 2. Complex cystic and solid masses contain fluid and solid components and include those with a thick wall, thick septations, an intracystic or mural mass, and both cystic and solid components. They usually are considered BI-RADS category 4, suspicious, and are accompanied by a biopsy recommendation. Radiologists must evaluate cystic lesions carefully, with meticulous technique, and provide appropriate assessment and management recommendations, thereby reducing unnecessary follow-up and biopsies while preventing cancers from being missed or dismissed. ©RSNA, 2025 Supplemental material is available for this article.

Harmonic imaging for nonlinear detection of acoustic biomolecules

Gas vesicles (GVs) based on acoustic reporter genes have emerged as potent contrast agents for cellular and molecular ultrasound imaging. These air-filled, genetically encoded protein nanostructures can be expressed in a variety of cell types in vivo to visualize cell location and activity or injected systemically to label and monitor tissue function. Distinguishing GV signal from tissue deep inside intact organisms requires imaging approaches such as amplitude modulation (AM) or collapse-based pulse sequences. However, these approaches have limitations either in sensitivity or require the destruction of GVs, restricting the imaging of dynamic cellular processes. To address these limitations, we developed harmonic imaging to enhance the sensitivity of nondestructive GV imaging. We hypothesized that harmonic imaging, integrated with AM, could significantly elevate GV detection sensitivity by leveraging the nonlinear acoustic response of GVs. We tested this hypothesis by imaging tissue-mimicking phantoms embedded with purified GVs, mammalian cells genetically modified to express GVs, and mice liver in vivo post-systemic infusion of GVs. Our findings reveal that harmonic cross-propagating wave AM (HxAM) imaging markedly surpasses traditional xAM in isolating GVs' nonlinear acoustic signature, demonstrating significant (p < 0.05) enhancements in imaging performance. HxAM imaging improves detection of GV producing cells up to three folds in vitro, enhances in vivo imaging performance by over 10 dB, while extending imaging depth by up to 20%. Investigation into the backscattered spectra further elucidates the advantages of harmonic imaging. These advancements bolster ultrasound's capability in molecular and cellular imaging, underscoring the potential of harmonic signals to improve GV detection.

Revealing physical interactions of ultrasound waves with the body through photoelasticity imaging

Ultrasound is a ubiquitous technology in medicine for screening, diagnosis, and treatment of disease. The functionality and efficacy of different ultrasound modes relies strongly on our understanding of the physical interactions between ultrasound waves and biological tissue structures. This article reviews the use of photoelasticity imaging for investigating ultrasound fields and interactions. Physical interactions are described for different ultrasound technologies, including those using linear and nonlinear ultrasound waves, as well as shock waves. The use of optical modulation of light by ultrasound is presented for shadowgraphic and photoelastic techniques. Investigations into shock wave and burst wave lithotripsy using photoelastic methods are summarized, along with other endoscopic forms of lithotripsy. Photoelasticity in soft tissue surrogate materials is reviewed, and its deployment in investigating tissue-bubble interactions, generated ultrasound waves, and traumatic brain injury, are discussed. With the continued growth of medical ultrasound, photoelasticity imaging can play a role in elucidating the physical mechanisms leading to useful bioeffects of ultrasound for imaging and therapy.

Factors Influencing the Visualization of Fallopian Tubes in Hysterosalpingo-Contrast Sonography (HyCoSy)-The Value of Multimodal HyCoSy in Visualizing the Fallopian Tubes

BACKGROUND

Four-dimensional hysterosalpingo-contrast sonography (4D-HyCoSy) can non-invasively evaluate the patency of the fallopian tubes and is increasingly used in clinical practice. However, some factors may lead to false-positive diagnoses. This study aims to analyze the factors affecting clear imaging of the fallopian tubes in 4D-HyCoSy and explore methods to improve the quality of fallopian tube imaging.

METHODS

A total of 118 patients were enrolled in this retrospective study. After injecting the SonoVue into the uterine cavity, three modes of HyCoSy were completed in sequence: 4D-HyCoSy, 2D-HyCoSy, and second harmonic imaging (SHI). Participants were divided into two groups: the easy visualization group (fallopian tubes could be visualized using only 4D-HyCoSy) and the difficult visualization group (a multimodal combination was required for visualization). The position of the uterus, the relationship between the ovaries and the uterus, endometrial thickness, time of catheterization in the uterine cavity, presence or absence of lesions in the uterine cavity, whether intestinal gas covers the fallopian tubes and the imaging effect of different modes on the fallopian tubes was analyzed, to determine the key factors affecting the clear imaging of the fallopian tubes.

RESULTS

The positional relationship between the ovary and the uterus (OR = 4.711, 95% CI: 1.322-19.77, P = 0.023), the positioning of the uterus (OR = 3.843, 95% CI: 1.129-15.26, P = 0.04), endometrial thickness (OR = 3.985, 95% CI: 1.168-15.99, P = 0.036), and the duration of intrauterine catheter placement (OR = 3.547, 95% CI: 1.042-13.52, P = 0.05) were independent factors that affecting difficulty in visualizing the fallopian tubes.

CONCLUSION

Uterine position, the positional relationship between the ovary and the uterus, endometrial thickness, and the time of catheter insertion are factors that affect visualizing the fallopian tubes during 4D-HyCoSy. The combination of multimodal imaging, especially the combination of 4D-HyCoSy with SHI mode, can help improve the quality of fallopian tube visualization.

Harmonic imaging for nonlinear detection of acoustic biomolecules

Gas vesicles (GVs) based on acoustic reporter genes have emerged as potent contrast agents for cellular and molecular ultrasound imaging. These air-filled, genetically encoded protein nanostructures can be expressed in a variety of cell types in vivo to visualize cell location and activity or injected systemically to label and monitor tissue function. Distinguishing GVs from tissue signal deep inside intact organisms requires imaging approaches such as amplitude modulation (AM) or collapse-based pulse sequences, however they have limitations in sensitivity or require irreversible collapse of the GVs that restricts its scope for imaging dynamic cellular processes. To address these limitations, this study explores the utility of harmonic imaging to enhance the sensitivity of non-destructive imaging of GVs and cellular processes. Traditional fundamental-frequency imaging utilizing cross-wave AM (xAM) sequences has been deemed optimal for GV imaging. Contrary to this, we hypothesize that harmonic imaging, integrated with xAM could significantly elevate GV detection sensitivity. To verify our hypothesis, we conducted imaging on tissue-mimicking phantoms embedded with purified GVs, mammalian cells genetically modified to express GVs, and live mice after systemic GV infusion. Our findings reveal that harmonic xAM (HxAM) imaging markedly surpasses traditional xAM in isolating GVs' nonlinear acoustic signature, showcasing significant enhancements in signal-to-background and contrast-to-background ratios across all tested samples. Further investigation into the backscattered spectra elucidates the efficacy of harmonic imaging in conjunction with xAM. HxAM imaging enables the detection of lower concentrations of GVs and cells with ultrasound and extends the imaging depth in vivo by up to 20% and imaging performance metrics by up to 10dB. These advancements bolster the capabilities of ultrasound for molecular and cellular imaging, underscoring the potential of using harmonic signals to amplify GV detection.

Transcranial volumetric imaging using a conformal ultrasound patch

Accurate and continuous monitoring of cerebral blood flow is valuable for clinical neurocritical care and fundamental neurovascular research. Transcranial Doppler (TCD) ultrasonography is a widely used non-invasive method for evaluating cerebral blood flow1, but the conventional rigid design severely limits the measurement accuracy of the complex three-dimensional (3D) vascular networks and the practicality for prolonged recording2. Here we report a conformal ultrasound patch for hands-free volumetric imaging and continuous monitoring of cerebral blood flow. The 2 MHz ultrasound waves reduce the attenuation and phase aberration caused by the skull, and the copper mesh shielding layer provides conformal contact to the skin while improving the signal-to-noise ratio by 5 dB. Ultrafast ultrasound imaging based on diverging waves can accurately render the circle of Willis in 3D and minimize human errors during examinations. Focused ultrasound waves allow the recording of blood flow spectra at selected locations continuously. The high accuracy of the conformal ultrasound patch was confirmed in comparison with a conventional TCD probe on 36 participants, showing a mean difference and standard deviation of difference as -1.51 ± 4.34 cm s-1, -0.84 ± 3.06 cm s-1 and -0.50 ± 2.55 cm s-1 for peak systolic velocity, mean flow velocity, and end diastolic velocity, respectively. The measurement success rate was 70.6%, compared with 75.3% for a conventional TCD probe. Furthermore, we demonstrate continuous blood flow spectra during different interventions and identify cascades of intracranial B waves during drowsiness within 4 h of recording.

[Technical innovations to optimize ultrasound imaging]

Due to the high incidence of thyroid disease, ultrasound examination of the neck has high priority in many nuclear medicine departments. A precise sonogram with high spatial resolution and image sharpness over the entire imaging area, combined with minimal artifacts, is the prerequisite for meeting the demand for high diagnostic accuracy in modern medicine. In the last 20-30 years, a number of significant technical innovations have been implemented, such as the development of the matrix array, electronic image focusing, realtime compound imaging, artifact limitation by speckle reduction and harmonic imaging, as well as the possibility to extend the field of view.

A Backing-Layer-Shared Miniature Dual-Frequency Ultrasound Probe for Intravascular Ultrasound Imaging: In Vitro and Ex Vivo Validations

Intravascular ultrasound (IVUS) imaging has been extensively utilized to visualize atherosclerotic coronary artery diseases and to guide coronary interventions. To receive ultrasound signals within the vessel wall safely and effectively, miniaturized ultrasound transducers that meet the strict size constraints and have a simple manufacturing procedure are highly demanded. In this work, the first known IVUS probe that employs a backing-layer-shared dual-frequency structure and a single coaxial cable is introduced, featuring a small thickness and easy interconnection procedure. The dual-frequency transducer is designed to have center frequencies of 30 MHz and 80 MHz, and both have an aperture size of 0.5 mm × 0.5 mm. The total thickness of the dual-frequency transducer is less than 700 µm. In vitro phantom imaging and ex vivo porcine coronary artery imaging experiments are conducted. The low-frequency transducer achieves spatial resolutions of 40 µm axially and 321 µm laterally, while the high-frequency transducer exhibits axial and lateral resolutions of 17 µm and 247 µm, respectively. A bandpass filter is utilized to separate the ultrasound images. Combining in vitro phantom imaging analysis with ex vivo imaging validation, a comprehensive demonstration of the promising application of the proposed miniature ultrasound probe is established.

The Ultrasound Window Into Vascular Ageing: A Technology Review by the VascAgeNet COST Action

Non-invasive ultrasound (US) imaging enables the assessment of the properties of superficial blood vessels. Various modes can be used for vascular characteristics analysis, ranging from radiofrequency (RF) data, Doppler- and standard B/M-mode imaging, to more recent ultra-high frequency and ultrafast techniques. The aim of the present work was to provide an overview of the current state-of-the-art non-invasive US technologies and corresponding vascular ageing characteristics from a technological perspective. Following an introduction about the basic concepts of the US technique, the characteristics considered in this review are clustered into: 1) vessel wall structure; 2) dynamic elastic properties, and 3) reactive vessel properties. The overview shows that ultrasound is a versatile, non-invasive, and safe imaging technique that can be adopted for obtaining information about function, structure, and reactivity in superficial arteries. The most suitable setting for a specific application must be selected according to spatial and temporal resolution requirements. The usefulness of standardization in the validation process and performance metric adoption emerges. Computer-based techniques should always be preferred to manual measures, as long as the algorithms and learning procedures are transparent and well described, and the performance leads to better results. Identification of a minimal clinically important difference is a crucial point for drawing conclusions regarding robustness of the techniques and for the translation into practice of any biomarker.

Usefulness of contrast-enhanced ultrasonography for biliary tract disease

Conventional ultrasonography (US) for biliary tract disease shows high time and spatial resolution. In addition, it is simple and minimally invasive, and is selected as a first-choice examination procedure for biliary tract disease. Currently, contrast-enhanced US (CEUS), which facilitates the more accurate assessment of lesion blood flow in comparison with color and power Doppler US, is performed using a second-generation ultrasonic contrast agent. Such agents are stable and provide a timeline for CEUS diagnosis. Gallbladder lesions are classified into three types: gallbladder biliary lesion (GBL), gallbladder polypoid lesion (GPL), and gallbladder wall thickening (GWT). Bile duct lesions can also be classified into three types: bile duct biliary lesion (BBL), bile duct polypoid lesion (BDPL), and bile duct wall thickening (BDWT). CEUS facilitates the differentiation of GBL/BBL from tumorous lesions based on the presence or absence of blood vessels. In the case of GPL, it is important to identify a vascular stalk attached to the lesion. In the case of GWT, the presence or absence of a non-contrast-enhanced area, the Rokitansky-Aschoff sinus, and continuity of a contrast-enhanced gallbladder wall layer are important for differentiation from gallbladder cancer. In the case of BDWT, it is useful to evaluate the contour of the contrast-enhanced medial layer of the bile duct wall for differentiating IgG4-related sclerosing cholangitis from primary sclerosing cholangitis. CEUS for ampullary carcinoma accurately reflects histopathological findings of the lesion. Evaluating blood flow in the lesion, continuity of the gallbladder wall, and contour of the bile duct wall via CEUS provides useful information for the diagnosis of biliary tract disease.

Second-Generation Differential Tissue Harmonic Imaging Improves the Visualization of Renal Lesions

OBJECTIVES

To compare to three nonlinear imaging techniques to conventional, grayscale ultrasound imaging of renal lesions.

METHODS

Twenty adults with a known renal lesion and a body mass index >25 kg/m² were enrolled in this prospective, institutional review board approved study. Each subject was imaged with an Aplio 500 scanner (Canon Medical Systems, Tokyo, Japan) using grayscale ultrasound, tissue harmonic imaging (THI) and two dual-frequency, differential tissue harmonic imaging modes (DTHI and DTHI-II, respectively). In total 184 images were scored by three independent and blinded observers for detail resolution, image quality, margin delineation, and depth penetration. Quantitative contrast-to-noise ratios (CNRs) were also calculated.

RESULTS

Readers and CNR values showed that nonlinear imaging was superior to grayscale ultrasound (P < .0014). DTHI-II outperformed DTHI, THI, and grayscale ultrasound with respect to detail resolution, image quality, and margin delineation (P < .012). The depth penetration of DTHI and DTHI-II was similar (P = .16), but superior to grayscale ultrasound and THI (P < .001). Two observers saw improvements in detail resolution with DTHI-II over DTHI (P < .05), while image quality and margin delineation were considered similar by two readers (P > .07) and improved with DTHI-II by one (P < .017).

CONCLUSIONS

DTHI-II improves the imaging of renal lesions compared to DTHI, THI, and grayscale ultrasound, albeit based on a limited sample size.

Recent Advances in Attenuation Estimation

This chapter reviews some of the recent advances in the estimation of the local and the total attenuation, with an emphasis on reducing the bias and variance of the estimates. A special focus is put on describing the effect of power spectrum estimation on bias and variance, the introduction of regularization strategies, as well as on eliminating the need to use reference phantoms for compensating for system dependent effects.

Coherence Metrics for Reader-Independent Differentiation of Cystic From Solid Breast Masses in Ultrasound Images

Traditional breast ultrasound imaging is a low-cost, real-time and portable method to assist with breast cancer screening and diagnosis, with particular benefits for patients with dense breast tissue. We previously demonstrated that incorporating coherence-based beamforming additionally improves the distinction of fluid-filled from solid breast masses, based on qualitative image interpretation by board-certified radiologists. However, variable sensitivity (range: 0.71-1.00 when detecting fluid-filled masses) was achieved by the individual radiologist readers. Therefore, we propose two objective coherence metrics, lag-one coherence (LOC) and coherence length (CL), to quantitatively determine the content of breast masses without requiring reader assessment. Data acquired from 31 breast masses were analyzed. Ideal separation (i.e., 1.00 sensitivity and specificity) was achieved between fluid-filled and solid breast masses based on the mean or median LOC value within each mass. When separated based on mean and median CL values, the sensitivity/specificity decreased to 1.00/0.95 and 0.92/0.89, respectively. The greatest sensitivity and specificity were achieved in dense, rather than non-dense, breast tissue. These results support the introduction of an objective, reader-independent method for automated diagnoses of cystic breast masses.

Effects of acoustic nonlinearity on communication performance in soft tissues

Acoustic communication has been gaining traction as an alternative communication method in nontraditional media, such as underwater or through tissue. Acoustic propagation is known to be a nonlinear phenomenon; nonlinear propagation of acoustic waves in soft tissues at biomedical frequencies and intensities has been widely demonstrated. However, the effects of acoustic nonlinearity on communication performance in biological tissues have not yet been examined. In this work, nonlinear propagation of a communication signal in soft tissues is analyzed. The relationship between communication parameters (signal amplitude, bandwidth, and center frequency) and nonlinear distortion of the communication signal propagating in soft tissues with different acoustic properties is investigated. Simulated experiments revealed that, unlike linear channels, bit error rates increase as signal amplitude and bandwidth increase. Linear and decision feedback equalizers fail to address the increased error rates. When tissue properties and transmission parameters can be estimated, receivers based on maximum likelihood sequence estimation approach the performance of an ideal receiver in an ideal additive white Gaussian noise channel.

Ultrasound Molecular Imaging and Its Applications in Cancer Diagnosis and Therapy

Ultrasound imaging is regarded as a highly sensitive imaging modality used in routine clinical examinations. Over the last several decades, ultrasound contrast agents have been widely applied in ultrasound molecular cancer imaging to improve the detection, characterization, and quantification of tumors. To date, a few new potential preclinical and clinical applications regarding ultrasound molecular cancer imaging are being investigated. This review presents an overview of the various kinds of ultrasound contrast agents employed in ultrasound molecular imaging and advanced imaging techniques using these contrast agents. Additionally, we discuss the recent enormous development of ultrasound contrast agents in the relevant preclinical and clinical applications, highlight the recent challenges which need to be overcome to accelerate the clinical translation, and discuss the future perspective of ultrasound molecular cancer imaging using various contrast agents. As a highly promising and valuable tumor-specific imaging technique, it is believed that ultrasound molecular imaging will pave an accurate and efficient way for cancer diagnosis.

Enhanced endoscopic ultrasound imaging for pancreatic lesions: The road to artificial intelligence

Early detection of pancreatic cancer has long eluded clinicians because of its insidious nature and onset. Often metastatic or locally invasive when symptomatic, most patients are deemed inoperable. In those who are symptomatic, multi-modal imaging modalities evaluate and confirm pancreatic ductal adenocarcinoma. In asymptomatic patients, detected pancreatic lesions can be either solid or cystic. The clinical implications of identifying small asymptomatic solid pancreatic lesions (SPLs) of < 2 cm are tantamount to a better outcome. The accurate detection of SPLs undoubtedly promotes higher life expectancy when resected early, driving the development of existing imaging tools while promoting more comprehensive screening programs. An imaging tool that has matured in its reiterations and received many image-enhancing adjuncts is endoscopic ultrasound (EUS). It carries significant importance when risk stratifying cystic lesions and has substantial diagnostic value when combined with fine needle aspiration/biopsy (FNA/FNB). Adjuncts to EUS imaging include contrast-enhanced harmonic EUS and EUS-elastography, both having improved the specificity of FNA and FNB. This review intends to compile all existing enhancement modalities and explore ongoing research around the most promising of all adjuncts in the field of EUS imaging, artificial intelligence.

Detection of a pituitary macroadenoma with transcranial ultrasonography: Principles and potential clinical applications

Transcranial color-coded duplex sonography (TCCS) allows to study intracranial vessels through the intact skull, but the visualization of normal and pathologic brain structures in adults is often suboptimal due to inadequate acoustic window. The full potential of TCCS for clinical practice remains unfulfilled. Here, we describe the ability of TCCS to detect a non-functioning pituitary macroadenoma in a 58-year-old man affected by headache. The macroadenoma was visualized as a roundish, well-defined mass, mildly hyperechogenic compared to the hypoechogenic mesencephalic brainstem but mainly hypoechogenic compared to the surrounding intracranial structures. Intracranial vessels represented useful landmarks. Using tissue harmonic imaging mode, the borders of the macroadenoma were visualized more clearly. Macroadenoma characteristics were confirmed by magnetic resonance imaging. Neurosonologists should be aware of the possibility to incidentally find, during routinary TCCS, pituitary macroadenomas or other brain tumors (as incidentalomas), worthy to be recognized and referred for further investigations.

Polarization Inverted Ultrasound Transducer Based on Composite Structure for Tissue Harmonic and Frequency Compound Imaging

Ultrasound transducer with polarization inversion technique (PIT) can provide dual-frequency feature for tissue harmonic imaging (THI) and frequency compound imaging (FCI). However, in the conventional PIT, the ultrasound intensity is reduced due to the multiple resonance characteristics of the combined piezoelectric element, and it is challenging to handle the thin piezoelectric layer required to make a PIT-based acoustic stack. In this study, an improved PIT using a piezo-composite layer was proposed to compensate for those problems simultaneously. The novel PIT-based acoustic stack also consists of two piezoelectric layers with opposite poling directions, in which the piezo-composite layer is located on the front side and the bulk-type piezoelectric layer is located on the back side. The thickness ratio between two piezoelectric layers is 0.5:0.5, but unlike a typical PIT model, it can generate dual-frequency spectrum. A finite element analysis (FEA) simulation was conducted, and subsequently, the prototype transducer was fabricated for performance demonstration. In the simulation and experiment, the intensity was increased by 56.76% and 30.88% compared to the conventional PIT model with the thickness ratio of 0.3:0.7. Thus, the proposed PIT-based transducer is expected to be useful in implementation of THI and FCI.

Ultrasound Image Optimization for the Interventional Radiologist

Understanding the basics and nuances of the functionality of ultrasound (US) equipment and of its various knobs and modes will enable the interventional radiologist to acquire higher quality US images. This, in turn will potentially allow US-guided procedures to be performed safely, and with greater operator confidence, and may also allow certain procedures to be performed with US instead of CT or fluoroscopic guidance. In this article, we review the practical aspects of US image optimization for the interventional radiologist, including equipment and transducer selection, depth, focal zone and gain setting adjustment, as well as special considerations for imaging the obese patient. Color Doppler image optimization and recent developments in ultrasound imaging are briefly discussed.

How to Improve TRUS-Guided Target Biopsy following Prostate MRI

TRUS is a basic imaging modality when radiologists or urologists perform cognitive fusion or image fusion biopsy. This modality plays the role of the background images to add to an operator's cognitive function or MRI images. Operators need to know how to make TRUS protocols for lesion detection or targeting. Tumor location, size, and shape on TRUS are different from those on MRI because the scan axis is different. TRUS findings of peripheral or transition tumors are not well known to radiologists and urologists. Moreover, it remains unclear if systematic biopsy is necessary after a tumor is targeted. The purpose of this review is to introduce new TRUS protocols, new imaging features, new biopsy techniques, and to assess the necessity of systematic biopsy for improving biopsy outcomes.

New frontiers in liver ultrasound: From mono to multi parametricity

Modern liver ultrasonography (US) has become a "one-stop shop" able to provide not only anatomic and morphologic but also functional information about vascularity, stiffness and other various liver tissue properties. Modern US techniques allow a quantitative assessment of various liver diseases. US scanning is no more limited to the visualized plane, but three-dimensional, volumetric acquisition and consequent post-processing are also possible. Further, US scan can be consistently merged and visualized in real time with Computed Tomography and Magnetic Resonance Imaging examinations. Effective and safe microbubble-based contrast agents allow a real time, dynamic study of contrast kinetic for the detection and characterization of focal liver lesions. Ultrasound can be used to guide loco-regional treatment of liver malignancies and to assess tumoral response either to interventional procedures or medical therapies. Microbubbles may also carry and deliver drugs under ultrasound exposure. US plays a crucial role in diagnosing, treating and monitoring focal and diffuse liver disease. On the basis of personal experience and literature data, this paper is aimed to review the main topics involving recent advances in the field of liver ultrasound.

Ultrasound Liver Imaging Reporting and Data System (US LI-RADS): An Overview with Technical and Practical Applications

The Ultrasound Liver Imaging Reporting and Data System (US LI-RADS), introduced in 2017 by the American College of Radiology, standardizes the technique, interpretation, and reporting of screening and surveillance ultrasounds intended to detect hepatocellular carcinoma in high-risk patients. These include patients with cirrhosis of any cause as well as subsets of patients with chronic hepatitis B viral infection. The US LI-RADS scheme is composed of an ultrasound category and a visualization score: ultrasound categories define the exam as negative, subthreshold, or positive and direct next steps in management; visualization scores denote the expected sensitivity of the exam, based on adequacy of liver visualization with ultrasound. Since its introduction, multiple institutions across the United States have implemented US LI-RADS. This review includes a background of hepatocellular carcinoma and US LI-RADS, definition of screening/surveillance population, recommendations and tips for technique, interpretation, and reporting, and preliminary outcomes analysis.

Imaging Techniques as an Aid in the Early Detection of Cardiac Amyloidosis

The idea that performing a proper succession of imaging tests and techniques allows an accurate and early diagnosis of cardiac amyloidosis, avoiding the need to perform the myocardial biopsy, is becoming increasingly popular. Furthermore, being imaging techniques non-invasive, it is possible to perform the follow-up of the pathology through repeated image acquisitions. In the present review, the various innovative imaging methodologies are presented, and it is discussed how they have been applied for early diagnosis of cardiac amyloidosis (CA), also to distinguish the two most frequent subtypes in CA: immunoglobulin light chain amyloidosis (AL) and transthyretin amyloidosis (ATTR); this allows to perform the therapy in a targeted and rapid manner.

Recent Advances in Transducers for Intravascular Ultrasound (IVUS) Imaging

As a well-known medical imaging methodology, intravascular ultrasound (IVUS) imaging plays a critical role in diagnosis, treatment guidance and post-treatment assessment of coronary artery diseases. By cannulating a miniature ultrasound transducer mounted catheter into an artery, the vessel lumen opening, vessel wall morphology and other associated blood and vessel properties can be precisely assessed in IVUS imaging. Ultrasound transducer, as the key component of an IVUS system, is critical in determining the IVUS imaging performance. In recent years, a wide range of achievements in ultrasound transducers have been reported for IVUS imaging applications. Herein, a comprehensive review is given on recent advances in ultrasound transducers for IVUS imaging. Firstly, a fundamental understanding of IVUS imaging principle, evaluation parameters and IVUS catheter are summarized. Secondly, three different types of ultrasound transducers (piezoelectric ultrasound transducer, piezoelectric micromachined ultrasound transducer and capacitive micromachined ultrasound transducer) for IVUS imaging are presented. Particularly, the recent advances in piezoelectric ultrasound transducer for IVUS imaging are extensively examined according to their different working mechanisms, configurations and materials adopted. Thirdly, IVUS-based multimodality intravascular imaging of atherosclerotic plaque is discussed. Finally, summary and perspectives on the future studies are highlighted for IVUS imaging applications.

General principles of image optimization in EUS

With the development of modern EUS, multiple imaging functions, transducer settings, and examination modes have become available for clinical settings. While the major determinants of the ultrasound beam are still comprised of the signal wavelength, its frequency range, and its amplitude, other modifications and calculations have gained more interest for advanced users, such as tissue harmonic imaging (THI), spatial and frequency compounding, certain versions of speckle reduction, and various Doppler/duplex settings. The goal of such techniques is a better, perhaps more realistic image, with reduced artifacts (such as speckle), better image contrast, and an improved signal-to-noise ratio. In addition, "add-ons" such as THI, which is based on the phenomenon of nonlinear distortion of acoustic signals as they travel through tissues, provide greater contrast and an enhanced spatial resolution than conventional EUS. Finally, optimization of spectral and color Doppler imaging in EUS requires experience and knowledge about the basic principles of Doppler/duplex phenomena. For these purposes, factors such as adjustment of Doppler controls, Doppler angle, color gain, spectral wall filters, and others require special attention during EUS examinations. Incorporating these advanced techniques in EUS examinations may be time-consuming and cumbersome. Hence, practical guidelines enabling endosonographers to steer safely through the large quantity of technological properties and settings (knobology) are appreciated. This review provides an overview of the role of important imaging features to be adjusted before, during, and after EUS procedures.

Closed-Loop Low-Rank Echocardiographic Artifact Removal

Echocardiographic image sequences are frequently corrupted by quasi-static artifacts ("clutter") superimposed on the moving myocardium. Conventionally, localized blind source separation methods exploiting local correlation in the clutter have proven effective in the suppression of these artifacts. These methods use the spectral characteristics to distinguish the clutter from tissue and background noise and are applied exhaustively over the data set. The exhaustive application results in high computational complexity and a loss of useful tissue signal. In this article, we develop a closed-loop algorithm in which the clutter is first detected using an adaptively determined weighting function and then removed using low-rank estimation methods. We show that our method is adaptable to different low-rank estimators, by presenting two such estimators: sparse coding in the principal component domain and nuclear norm minimization. We compare the performance of our proposed method (CLEAR) with two methods: singular value filtering (SVF) and morphological component analysis (MCA). The performance was quantified in silico by measuring the error with respect to a known "ground truth" data set with no clutter for different combinations of moving clutter and tissue. Our method retains more tissue with a lower error of 3.88 ± 0.093 dB (sparse coding) and 3.47 ± 0.78 (nuclear norm) compared with the benchmark methods 8.5 ± 0.7 dB (SVF) and 9.3 ± 0.5 dB (MCA) particularly in instances where the rate of tissue motion and artifact motion is small (≤0.25 periods of center frequency per frame) while producing comparable clutter reduction performance. CLEAR was also validated in vivo by quantifying the tracking error over the cardiac cycle on five mouse heart data sets with synthetic clutter. CLEAR reduced the error by approximately 50%, compared with 25% for the SVF.

Effects of ultrasound technology advances on measurement of carotid intima-media thickness: A review

In this review, we describe how technological advances in ultrasound imaging related to transducer construction and image processing fundamentally alter generation of ultrasound images to produce better quality images with higher resolution. However, carotid intima-media thickness (IMT) measurements made from images acquired on modern ultrasound systems are not comparable to historical population nomograms that were used to determine wall thickness thresholds that inform atherosclerotic cardiovascular disease risk. Because it is nearly impossible to replicate instrumentation settings that were used to create the reference carotid IMT nomograms and to place an individual's carotid IMT value in or above a clinically relevant percentile, carotid IMT measurements have a very limited role in clinical medicine, but remain a useful research tool when instrumentation, presets, image acquisition, and measurements can be standardized. In addition to new validation studies, it would be useful for the ultrasound imaging community to reach a consensus regarding technical aspects of ultrasound imaging acquisition, processing, and display for blood vessels so standard presets and imaging approaches could reliably yield the same measurements.

Intravascular Ultrasound Transducer by Using Polarization Inversion Technique for Tissue Harmonic Imaging: Modeling and Experiments

Intravascular ultrasound (IVUS) tissue harmonic imaging (THI) is a useful vessel imaging technique that can provide deep penetration depth as well as high spatial and contrast resolution. Typically, a high-frequency IVUS transducer for THI requires a broad bandwidth or dual-frequency bandwidth. However, it is very difficult to make an IVUS transducer with a frequency bandwidth covering from the fundamental frequency to the second harmonic or a dual-peak at the desired frequency. To solve this problem, in this study, we applied the polarization inversion technique (PIT) to the IVUS transducer for THI. The PIT makes it relatively easy to design IVUS transducers with suitable frequency characteristics for THI depending on the inversion ratio of the piezoelectric layer and specifications of the passive materials. In this study, two types of IVUS transducers based on the PIT were developed for THI. One is a front-side inversion layer (FSIL) transducer with a broad bandwidth, and the other is a back-side inversion layer (BSIL) transducer with a dual-frequency bandwidth. These transducers were designed using finite element analysis (FEA)-based simulation, and the prototype transducers were fabricated. Subsequently, the performance was evaluated by not only electrical impedance and pulse-echo response tests but also B-mode imaging tests with a 25 μm tungsten wire and tissue-mimicking gelatin phantoms. The FEA simulation and experimental results show that the proposed scheme can successfully implement the tissue harmonic IVUS image, and thus it can be one of the promising techniques for developing IVUS transducers for THI.

Toward the Clinical Development and Validation of a Thy1-Targeted Ultrasound Contrast Agent for the Early Detection of Pancreatic Ductal Adenocarcinoma

Early detection of pancreatic ductal adenocarcinoma (PDAC) represents the most significant step toward the treatment of this aggressive lethal disease. Previously, we engineered a preclinical Thy1-targeted microbubble (MBThy1) contrast agent that specifically recognizes Thy1 antigen overexpressed in the vasculature of murine PDAC tissues by ultrasound (US) imaging. In this study, we adopted a single-chain variable fragment (scFv) site-specific bioconjugation approach to construct clinically translatable MBThy1-scFv and test for its efficacy in vivo in murine PDAC imaging, and functionally evaluated the binding specificity of scFv ligand to human Thy1 in patient PDAC tissues ex vivo.

MATERIALS AND METHODS

We recombinantly expressed the Thy1-scFv with a carboxy-terminus cysteine residue to facilitate its thioether conjugation to the PEGylated MBs presenting with maleimide functional groups. After the scFv-MB conjugations, we tested binding activity of the MBThy1-scFv to MS1 cells overexpressing human Thy1 (MS1Thy1) under liquid shear stress conditions in vitro using a flow chamber setup at 0.6 mL/min flow rate, corresponding to a wall shear stress rate of 100 seconds, similar to that in tumor capillaries. For in vivo Thy1 US molecular imaging, MBThy1-scFv was tested in the transgenic mouse model (C57BL/6J - Pdx1-Cre; KRas; Ink4a/Arf) of PDAC and in control mice (C57BL/6J) with L-arginine-induced pancreatitis or normal pancreas. To facilitate its clinical feasibility, we further produced Thy1-scFv without the bacterial fusion tags and confirmed its recognition of human Thy1 in cell lines by flow cytometry and in patient PDAC frozen tissue sections of different clinical grades by immunofluorescence staining.

RESULTS

Under shear stress flow conditions in vitro, MBThy1-scFv bound to MS1Thy1 cells at significantly higher numbers (3.0 ± 0.8 MB/cell; P < 0.01) compared with MBNontargeted (0.5 ± 0.5 MB/cell). In vivo, MBThy1-scFv (5.3 ± 1.9 arbitrary units [a.u.]) but not the MBNontargeted (1.2 ± 1.0 a.u.) produced high US molecular imaging signal (4.4-fold vs MBNontargeted; n = 8; P < 0.01) in the transgenic mice with spontaneous PDAC tumors (2-6 mm). Imaging signal from mice with L-arginine-induced pancreatitis (n = 8) or normal pancreas (n = 3) were not significantly different between the two MB constructs and were significantly lower than PDAC Thy1 molecular signal. Clinical-grade scFv conjugated to Alexa Fluor 647 dye recognized MS1Thy1 cells but not the parental wild-type cells as evaluated by flow cytometry. More importantly, scFv showed highly specific binding to VEGFR2-positive vasculature and fibroblast-like stromal components surrounding the ducts of human PDAC tissues as evaluated by confocal microscopy.

CONCLUSIONS

Our findings summarize the development and validation of a clinically relevant Thy1-targeted US contrast agent for the early detection of human PDAC by US molecular imaging.

Interleaved Array Transducer with Polarization Inversion Technique to Implement Ultrasound Tissue Harmonic Imaging

In ultrasound tissue harmonic imaging (THI), it is preferred that the bandwidth of the array transducer covers at least the fundamental frequency f₀ for transmission and the second harmonic frequency 2f₀ for reception. However, it is challenging to develop an array transducer with a broad bandwidth due to the single resonance characteristics of piezoelectric materials. In this study, we present an improved interleaved array transducer suitable for THI and a dedicated transducer fabrication scheme. The proposed array transducer has a novel structure in which conventional elements exhibiting f₀ resonant frequency and polarization-inverted elements exhibiting 2f₀ resonant frequency are alternately located, and the thicknesses of all piezoelectric elements are identical. The performance of the proposed method was demonstrated by finite element analysis (FEA) simulations and experiments using a fabricated prototype array transducer. Using the proposed technique, f₀ and 2f₀ frequency ultrasounds can be efficiently transmitted and received, respectively, resulting in a 90% broad bandwidth feature of the transducer. Thus, the proposed technique can be one of the potential ways to implement high resolution THI.

MimickNet, Mimicking Clinical Image Post- Processing Under Black-Box Constraints

Image post-processing is used in clinical-grade ultrasound scanners to improve image quality (e.g., reduce speckle noise and enhance contrast). These post-processing techniques vary across manufacturers and are generally kept proprietary, which presents a challenge for researchers looking to match current clinical-grade workflows. We introduce a deep learning framework, MimickNet, that transforms conventional delay-and-summed (DAS) beams into the approximate Dynamic Tissue Contrast Enhanced (DTCE™) post-processed images found on Siemens clinical-grade scanners. Training MimickNet only requires post-processed image samples from a scanner of interest without the need for explicit pairing to DAS data. This flexibility allows MimickNet to hypothetically approximate any manufacturer's post-processing without access to the pre-processed data. MimickNet post-processing achieves a 0.940 ± 0.018 structural similarity index measurement (SSIM) compared to clinical-grade post-processing on a 400 cine-loop test set, 0.937 ± 0.025 SSIM on a prospectively acquired dataset, and 0.928 ± 0.003 SSIM on an out-of-distribution cardiac cine-loop after gain adjustment. To our knowledge, this is the first work to establish deep learning models that closely approximate ultrasound post-processing found in current medical practice. MimickNet serves as a clinical post-processing baseline for future works in ultrasound image formation to compare against. Additionally, it can be used as a pretrained model for fine-tuning towards different post-processing techniques. To this end, we have made the MimickNet software, phantom data, and permitted in vivo data open-source at https://github.com/ouwen/MimickNet.

Ultrasound Image Optimization ("Knobology"): B-Mode

Ultrasound is a ubiquitous and indispensable diagnostic and therapeutic tool in medicine. Due to modern equipment and automatic image optimization, the introduction of ultrasound imaging currently requires only little technical and physical knowledge. However, in-depth knowledge of the device functions and underlying mechanisms is essential for optimal image adjustment and documentation. From a medical as well as an aesthetic point of view, the goal should always be to achieve the best possible image quality. The first part of this article provides an overview of the handling of ultrasound systems, fundamental adjustments, and their optimization in B-mode ultrasound.

Techniques for Improving Ultrasound Visualization of Biopsy Markers in Axillary Lymph Nodes

Objective:

Biopsy markers are often placed into biopsy-proven metastatic axillary lymph nodes to ensure later accurate node excision. Ultrasound is the preferred imaging modality in the axilla. However, sonographic identification of biopsy markers after neoadjuvant therapy can be challenging. This is due to poor conspicuity relative to surrounding parenchymal interfaces, treatment-related alteration of malignant morphology during neoadjuvant chemotherapy, or extrusion of the marker from the target. To the authors’ knowledge, the literature provides no recommendations for ultrasound scanning parameters that improve the detection of biopsy markers. The purpose of this manuscript is 3-fold: (1) To determine scanning parameters that improve sonographic conspicuity of biopsy markers in a phantom and cadaver model; (2) to implement these scanning parameters in the clinical setting; and (3) to provide strategies that might increase the likelihood of successful ultrasound detection of biopsy markers in breast imaging practices.

Materials and Methods:

An ex vivo study was performed using a phantom designed to simulate the heterogeneity of normal mammary or axillary soft tissues. A selection of available biopsy markers was deployed into this phantom and ultrasound (GE LOGIQ E9) was performed. Scanning parameters were adjusted to optimize marker conspicuity. For the cadaver study, the biopsy markers were deployed using ultrasound guidance into axillary lymph nodes of a female cadaver. Adjustments in transducer frequency, dynamic range, cross-beam (spatial compound imaging), beam steering, speckle reduction imaging, harmonic imaging, colorization, and speed of sound were evaluated. Settings that improved marker detection were used clinically for a year.

Results:

Sonographic scanning settings that improved biopsy marker conspicuity included increasing transducer frequency, decreasing dynamic range, setting cross-beam to medium hybrid, turning on beam steering, and setting speckle reduction imaging in the mid-range. There was no appreciable improvement with harmonic imaging, colorization, or speed of sound.

Conclusion:

On a currently available clinical ultrasound scanning system, ultrasound scanning parameters can be adjusted to improve the conspicuity of biopsy markers. Overall, optimization requires a balance between techniques that clinically increase contrast (dynamic range, harmonic imaging, and steering) and those that minimize graininess (spatial compound imaging, speckle reduction imaging, and steering). Additional scanning and procedural strategies have been provided to improve the confidence of sonographic detection of biopsy markers closely associated with the intended target.

"I can see clearly now." fundamentals of breast ultrasound optimization

Unlike other modalities in breast imaging, breast ultrasound is very operator dependent. Proper characterization and management of breast lesions depends on the knowledge and skill of the radiologist performing the exam. Breast ultrasound optimization continues to evolve as the technology of ultrasound machines improves. The American College of Graduate Medical Education (ACGME) program requirements for graduate medical education in diagnostic radiology recently updated requirements to include competency in ultrasound physics, knobology, and image generation. As trainees are held to high ultrasound optimization standards, practicing radiologists who perform breast ultrasound exams must keep up to date on current breast ultrasound optimization techniques to avoid mischaracterizing and mismanaging breast ultrasound findings. In this paper, ultrasound optimization techniques, including patient positioning, transducer frequency, transducer contact and pressure, depth, gain, focus, tissue harmonic imaging, spatial compounding, dynamic range, speed of sound imaging, Doppler evaluation, and elastography will be described. Multiple ultrasound case examples will be used to illustrate application of these skills. After reading this paper, the reader will be able to apply these techniques to their own breast ultrasound practice, improving characterization and management of breast lesions in their patients.

Adaptive Ultrasound Tissue Harmonic Imaging Based on an Improved Ensemble Empirical Mode Decomposition Algorithm

Complete and accurate separation of harmonic components from the ultrasonic radio frequency (RF) echo signals is essential to improve the quality of harmonic imaging. There are limitations in the existing two commonly used separation methods, that is, the subjectivity for the high-pass filtering (S_HPF) method and motion artifacts for the pulse inversion (S_PI) method. A novel separation method called S_CEEMDAN, based on the complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) algorithm, is proposed to adaptively separate the second harmonic components for ultrasound tissue harmonic imaging. First, the ensemble size of the CEEMDAN algorithm is calculated adaptively according to the standard deviation of the added white noise. A set of intrinsic mode functions (IMFs) is then obtained by the CEEMDAN algorithm from the ultrasonic RF echo signals. According to the IMF spectra, the IMFs that contain both fundamental and harmonic components are further decomposed. The separation process is performed until all the obtained IMFs have been divided into either fundamental or harmonic categories. Finally, the fundamental and harmonic RF echo signals are obtained from the accumulations of signals from these two categories, respectively. In simulation experiments based on CREANUIS, the S_CEEMDAN-based results are similar to the S_HPF-based results, but better than the S_PI-based results. For the dynamic carotid artery measurements, the contrasts, contrast-to-noise ratios (CNRs), and tissue-to-clutter ratios (TCRs) of the harmonic images based on the S_CEEMDAN are averagely increased by 31.43% and 50.82%, 18.96% and 10.83%, as well as 34.23% and 44.18%, respectively, compared with those based on the S_HPF and S_PI methods. In conclusion, the S_CEEMDAN method provides improved harmonic images owing to its good adaptivity and lower motion artifacts, and is thus a potential alternative to the current methods for ultrasonic harmonic imaging.

Application of 14-MHz Ultrasonography with Tissue Harmonic Imaging to Determine Posterior Capsule Integrity in Traumatic Cataract

Purpose

To report the application of 14-MHz ultrasonography with tissue harmonic imaging (14 MHz + THI) to determine the integrity of the posterior capsule (PC) in traumatic cataract (TC).

Methods

Patients with TC who were scheduled to undergo cataract extraction and whose PC could not be observed by slit lamp examination were included in the study. The status of the PC was determined by 14 MHz + THI before cataract extraction and confirmed during surgery. The results regarding PC integrity obtained from 14 MHz + THI and intraoperative direct observation were compared.

Result

The study enrolled 52 eyes of 52 patients (49 men and 3 women), with a mean age of 42.15 years ± 11.23 (SD). The nature of the trauma was blunt (3 eyes) or sharp (49 eyes). The 14 MHz + THI method showed 21 PCs to be intact and 31 to have ruptured before cataract surgery. During surgery, 23 PCs were observed to be intact, while 29 PCs were ruptured. 27 PCs were ruptured and 19 were intact, as determined by the two methods. The 14 MHz + THI observations were consistent with the intraoperative observations of the PC (kappa = 0.764), with no significant difference between the two methods (P=0.687). The sensitivity, specificity, and accuracy of 14 MHz + THI for observation of the PC were 93.10%, 82.60%, and 88.46%, respectively.

Conclusion

The 14 MHz + THI method can accurately reveal the integrity of the PC in TC. It has important clinical value in the selection of cataract surgery methods and the prediction of complications during TC surgery.

Perinatal post mortem ultrasound (PMUS): a practical approach

Declining rates of consent for standard perinatal autopsy has led to a rise in interest for postmortem imaging as an alternative, non-invasive method for investigation of childhood and perinatal deaths. Whilst much interest has focussed on cross-sectional techniques such as postmortem CT (PMCT) or MRI (PMMR), other modalities including postmortem ultrasound (PMUS) have been shown to have reasonable diagnostic accuracy rates, with the added benefit of being more readily accessible and affordable. There is little published information or formal guidance available on preparation for postmortem perinatal ultrasound, views to be obtained and differentiating normal postmortem change from potential abnormalities.

This article will focus on the role of perinatal postmortem ultrasound as an alternative imaging method for non-invasive autopsy, with emphasis on imaging technique, practical considerations and commonly encountered case examples.

Dual-Element Intravascular Ultrasound Transducer for Tissue Harmonic Imaging and Frequency Compounding: Development and Imaging Performance Assessment

OBJECTIVE

For accurate diagnosis of atherosclerosis, the high spatial and contrast resolutions of intravascular ultrasound (IVUS) images are a key requirement. Increasing the center frequency of IVUS is a simple solution to meet this requirement. However, this leads to a reduction in imaging depth due to the frequency-dependent attenuation of ultrasound. Here, we report a recently developed dual-element IVUS transducer for tissue harmonic imaging (THI) and frequency compounding to increase the spatial and contrast resolutions of IVUS images, while maintaining the imaging depth to assess the overall morphological change of blood vessels.

METHODS

One 35-MHz element is used for producing general IVUS images and the other 70-MHz element is for receiving the second harmonic signals induced by the 35-MHz ultrasound. The fundamental and second harmonic signals can also be used for frequency compound imaging to further improve contrast resolution. The spatial and contrast resolutions achieved by the developed transducer were evaluated through wire and tissue-mimicking phantom imaging tests. Additionally, the images of a stent deployed in a tissue-mimicking phantom and an excised pig artery were acquired to assess clinical usefulness of the transducer.

RESULTS

The results demonstrated that the developed IVUS transducer enables us to simultaneously examine the overall morphological change of blood vessels by the 35-MHz ultrasound images and the near vessel layers such as the intima, the media, and the adventitia by either THI or compound images with high spatial and contrast resolutions. In addition, the developed transducer facilitates the simultaneous acquisition of 35- and 70-MHz fundamental images when needed.

CONCLUSION

The developed dual-element IVUS transducer makes it possible to fully realize the potential benefits of IVUS in the diagnosis of atherosclerosis.

Reader agreement and accuracy of ultrasound features for hepatic steatosis

PURPOSE

The purpose of the study is to assess the reader agreement and accuracy of eight ultrasound imaging features for classifying hepatic steatosis in adults with known or suspected hepatic steatosis.

METHODS

This was an IRB-approved, HIPAA-compliant prospective study of adult patients with known or suspected hepatic steatosis. All patients signed written informed consent. Ultrasound images (Siemens S3000, 6C1HD, and 4C1 transducers) were acquired by experienced sonographers following a standard protocol. Eight readers independently graded eight features and their overall impression of hepatic steatosis on ordinal scales using an electronic case report form. Duplicated images from the 6C1HD transducer were read twice to assess intra-reader agreement. Intra-reader, inter-transducer, and inter-reader agreement were assessed using intraclass correlation coefficients (ICC). Features with the highest intra-reader agreement were selected as predictors for dichotomized histological steatosis using Classification and Regression Tree (CART) analysis, and the accuracy of the decision rule was compared to the accuracy of the radiologists' overall impression.

RESULTS

45 patients (18 males, 27 females; mean age 56 ± 12 years) scanned from September 2015 to July 2016 were included. Mean intra-reader ICCs ranged from 0.430 to 0.777, inter-transducer ICCs ranged from 0.228 to 0.640, and inter-reader ICCs ranged from 0.014 to 0.561. The CART decision rule selected only large hepatic vein blurring and achieved similar accuracy to the overall impression (74% to 75% and 68% to 72%, respectively).

CONCLUSIONS

Large hepatic vein blurring, liver-kidney contrast, and overall impression provided the highest reader agreement. Large hepatic vein blurring may provide the highest classification accuracy for dichotomized grading of hepatic steatosis.

A 35 MHz/105 MHz Dual-Element Focused Transducer for Intravascular Ultrasound Tissue Imaging Using the Third Harmonic

The superharmonic imaging of tissue has the potential for high spatial and contrast resolutions, compared to the fundamental and second harmonic imaging. For this technique, the spectral bandwidth of an ultrasound transducer is divided for transmission of ultrasound and reception of its superharmonics (i.e., higher than the second harmonic). Due to the spectral division for the transmission and reception, transmitted ultrasound energy is not sufficient to induce superharmonics in media without using contrast agents, and it is difficult that a transducer has a −6 dB fractional bandwidth of higher than 100%. For the superharmonic imaging of tissue, thus, multi-frequency array transducers are the best choice if available; transmit and receive elements are separate and have different center frequencies. However, the construction of a multi-frequency transducer for intravascular ultrasound (IVUS) imaging is particularly demanding because of its small size of less than 1 mm. Here, we report a recently developed dual-element focused IVUS transducer for the third harmonic imaging of tissue, which consists of a 35-MHz element for ultrasound transmission and a 105-MHz element for third harmonic reception. For high quality third harmonic imaging, both elements were fabricated to have the same focus at 2.5 mm. The results of tissue mimicking phantom tests demonstrated that the third harmonic images produced by the developed transducer had higher spatial resolution and deeper imaging depth than the fundamental images.

Imaging of suspected pulmonary embolism and deep venous thrombosis in obese patients

Obesity is a growing problem around the world, and radiology departments frequently encounter difficulties related to large patient size. Diagnosis and management of suspected venous thromboembolism, in particular deep venous thrombosis (DVT) and pulmonary embolism (PE), are challenging even in some lean patients, and can become even more complicated in the setting of obesity. Many obstacles must be overcome to obtain imaging examinations in obese patients with suspected PE and/or DVT, and to ensure that these examinations are of sufficient quality to diagnose or exclude thromboembolic disease, or to establish an alternative diagnosis. Equipment limitations and technical issues both need to be acknowledged and addressed. Table weight limits and scanner sizes that readily accommodate obese and even morbidly obese patients are not in place at many clinical sites. There are also issues with image quality, which can be substantially compromised. We discuss current understanding of the effects of patient size on imaging in general and, more specifically, on the imaging modalities used for the diagnosis and treatment of DVT and PE. Emphasis will be placed on the technical parameters and protocol nuances, including contrast dosing, which are necessary to refine and optimize images for the diagnosis of DVT and PE in obese patients, while remaining cognizant of radiation exposure. More research is necessary to develop consistent high-level evidence regarding protocols to guide radiologists, and to help them effectively utilize emerging technology.

Clinical Significance of US Artifacts

Artifacts are frequently encountered at clinical US, and while some are unwanted, others may reveal valuable information related to the structure and composition of the underlying tissue. They are essential in making ultrasonography (US) a clinically useful imaging modality but also can lead to errors in image interpretation and can obscure diagnoses. Many of these artifacts can be understood as deviations from the assumptions made in generating the image. Therefore, understanding the physical basis of US image formation is critical to understanding US artifacts and thus proper image interpretation. This review is limited to gray-scale artifacts and is organized into discussions of beam- and resolution-related, location-related (ie, path and speed), and attenuation-related artifacts. Specifically, artifacts discussed include those related to physical mechanisms of spatial resolution, speckle, secondary lobes, reflection and reverberation, refraction, speed of sound, and attenuation. The underlying physical mechanisms and appearances are discussed, followed by real-world strategies to mitigate or accentuate these artifacts, depending on the clinical application. Relatively new US modes, such as spatial compounding, tissue harmonic imaging, and speckle reduction imaging, are now often standard in many imaging protocols; the effects of these modes on US artifacts are discussed. The ability of a radiologist to understand the fundamental physics of ultrasound, recognize common US artifacts, and provide recommendations for altering the imaging technique is essential for proper image interpretation, troubleshooting, and utilization of the full potential of this modality. ^©RSNA, 2017.