Separation of mainlobe and sidelobe contributions to B-mode ultrasound images based on the aperture spectrum.

Purpose: Isolating the mainlobe and sidelobe contribution to the ultrasound image can improve imaging contrast by removing off-axis clutter. Previous work achieves this separation of mainlobe and sidelobe contributions based on the covariance of received signals. However, the formation of a covariance matrix at each imaging point can be computationally burdensome and memory intensive for real-time applications. Our work demonstrates that the mainlobe and sidelobe contributions to the ultrasound image can be isolated based on the receive aperture spectrum, greatly reducing computational and memory requirements. Approach: The separation of mainlobe and sidelobe contributions to the ultrasound image is shown in simulation, in vitro, and in vivo using the aperture spectrum method and multicovariate imaging of subresolution targets (MIST). Contrast, contrast-to-noise-ratio (CNR), and speckle signal-to-noise-ratio are used to compare the aperture spectrum approach with MIST and conventional delay-and-sum (DAS) beamforming. Results: The aperture spectrum approach improves contrast by 1.9 to 6.4 dB beyond MIST and 8.9 to 13.5 dB beyond conventional DAS B-mode imaging. However, the aperture spectrum approach yields speckle texture similar to DAS. As a result, the aperture spectrum-based approach has less CNR than MIST but greater CNR than conventional DAS. The CPU implementation of the aperture spectrum-based approach is shown to reduce computation time by a factor of 9 and memory consumption by a factor of 128 for a 128-element transducer. Conclusions: The mainlobe contribution to the ultrasound image can be isolated based on the receive aperture spectrum, which greatly reduces the computational cost and memory requirement of this approach as compared with MIST.

Contrast-Enhanced Ultrasound as a Problem-Solving Modality: Tips and Tricks.

ABSTRACT: Contrast-enhanced ultrasound (CEUS) continues to be an ever-growing tool in radiation-free imaging. While it has been widely used in cardiac imaging, CEUS has only recently become an Food and Drug Administration-approved and viable modality for evaluation of abdominal structures. Ultrasound contrast agents are nontoxic, microbubble-based vascular agents and can be used to reliably assess enhancement patterns of various lesions in real time. In particular, it's non nephrotoxic nature makes CEUS a particularly important tool in renal failure patients requiring serial follow-up. This review provides a comprehensive discussion on the utility of CEUS agents, imaging techniques, comparison with traditional cross-sectional imaging modalities, and its application in diagnosing kidney and liver lesions. This pictorial review is illustrated with cases of renal and hepatic lesions that the practicing radiologist should become familiar with as CEUS becomes increasingly popular.

Do Not Get It Twisted: Common and Uncommon Manifestations of Testicular Torsion.

Color flow and spectral Doppler ultrasound are the backbone of scrotal imaging when evaluating acute scrotal pain. Testicular Torsion is one of the most common causes of acute scrotal pain but can be a challenging diagnosis both clinically and sonographically. This article will review the pertinent Doppler ultrasound findings that can help make the diagnosis of both complete and partial torsion. A review of other causes of testicular ischemia will also be included as these pathologies can mimic Testicular Torsion.

Vascular Imaging in the Asymptomatic High-risk Cancer Population: A Role for Thrombosis Screening and Therapy Management.

OBJECTIVES: We retrospectively examined the venous thromboembolism (VTE) events diagnosed in the Prophylaxis of High-Risk Ambulatory Cancer Patients Study (PHACS), a multi-center randomized trial, to assess the value of screening vascular imaging for the diagnosis of incidental VTE in high-risk cancer patients. METHODS: A total of 117 asymptomatic cancer patients with a Khorana score ≥3 starting a new systemic chemotherapy regimen were enrolled in a prospective randomized control trial. Patients underwent baseline venous ultrasound (US) of the lower extremities (LEs) and screening contrast-enhanced chest computed tomography (CT). Those without preexisting VTE were then randomized into observation or dalteparin prophylaxis groups and were screened with serial US every 4 weeks for up to 12 weeks and imaged with contrast-enhanced chest CT at 12 weeks. Any additional imaging performed during the study period was also evaluated for VTE. RESULTS: Baseline prevalence of incidental VTE was 9% (n = 10) with 58% percent of VTEs diagnosed by screening US. Incidence of VTE in the randomized phase of the trial was 16% (n = 16) with 21% (n = 10) of patients in the control arm and 12% (n = 6) of patients in the dalteparin arm developing VTE, a non-significant 9% absolute risk reduction (HR = 0.69, 95% CI 0.23-1.89). Sixty-nine percent of these patients were asymptomatic with 31% of patients diagnosed by screening US. CONCLUSIONS: Adding screening US to routine oncologic surveillance CT in high-risk ambulatory cancer patients with a Khorana score ≥3 can lead to increased VTE detection, with potential for decreased morbidity, mortality, and health care spending.

Lung ultrasound volume sweep imaging for respiratory illness: a new horizon in expanding imaging access.

BACKGROUND: Respiratory illness is a leading cause of morbidity in adults and the number one cause of mortality in children, yet billions of people lack access to medical imaging to assist in its diagnosis. Although ultrasound is highly sensitive and specific for respiratory illness such as pneumonia, its deployment is limited by a lack of sonographers. As a solution, we tested a standardised lung ultrasound volume sweep imaging (VSI) protocol based solely on external body landmarks performed by individuals without prior ultrasound experience after brief training. Each step in the VSI protocol is saved as a video clip for later interpretation by a specialist. METHODS: Dyspneic hospitalised patients were scanned by ultrasound naive operators after 2 hours of training using the lung ultrasound VSI protocol. Separate blinded readers interpreted both lung ultrasound VSI examinations and standard of care chest radiographs to ascertain the diagnostic value of lung VSI considering chest X-ray as the reference standard. Comparison to clinical diagnosis as documented in the medical record and CT (when available) were also performed. Readers offered a final interpretation of normal, abnormal, or indeterminate/borderline for each VSI examination, chest X-ray, and CT. RESULTS: Operators scanned 102 subjects (0-89 years old) for analysis. Lung VSI showed a sensitivity of 93% and a specificity of 91% for an abnormal chest X-ray and a sensitivity of 100% and a specificity of 93% for a clinical diagnosis of pneumonia. When any cases with an indeterminate rating on chest X-ray or ultrasound were excluded (n=38), VSI lung ultrasound showed 92% agreement with chest X-ray (Cohen's κ 0.83 (0.68 to 0.97, p<0.0001)). Among cases with CT (n=21), when any ultrasound with an indeterminate rating was excluded (n=3), there was 100% agreement with VSI. CONCLUSION: Lung VSI performed by previously inexperienced ultrasound operators after brief training showed excellent agreement with chest X-ray and high sensitivity and specificity for a clinical diagnosis of pneumonia. Blinded readers were able to identify other respiratory diseases including pulmonary oedema and pleural effusion. Deployment of lung VSI could benefit the health of the global community.

Testing telediagnostic right upper quadrant abdominal ultrasound in Peru: A new horizon in expanding access to imaging in rural and underserved areas.

BACKGROUND: Hepatic and biliary diseases are prevalent worldwide, but the majority of people lack access to diagnostic medical imaging for their assessment. The liver and gallbladder are readily amenable to sonographic examination, and ultrasound is a portable, cost-effective imaging modality suitable for use in rural and underserved areas. However, the deployment of ultrasound in these settings is limited by the lack of experienced sonographers to perform the exam. In this study, we tested an asynchronous telediagnostic system for right upper quadrant abdominal ultrasound examination operated by individuals without prior ultrasound experience to facilitate deployment of ultrasound to rural and underserved areas. METHODS: The teleultrasound system utilized in this study employs volume sweep imaging and a telemedicine app installed on a tablet which connects to an ultrasound machine. Volume sweep imaging is an ultrasound technique in which an individual scans the target region utilizing preset ultrasound sweeps demarcated by easily recognized external body landmarks. The sweeps are saved as video clips for later interpretation by an experienced radiologist. Teleultrasound scans from a Peruvian clinic obtained by individuals without prior ultrasound experience were sent to the United States for remote interpretation and quality assessment. Standard of care comparison was made to a same-day ultrasound examination performed by a radiologist. RESULTS: Individuals without prior ultrasound experience scanned 144 subjects. Image quality was rated "poor" on 36.8% of exams, "acceptable" on 38.9% of exams, and "excellent" on 24.3% of exams. Among telemedicine exams of "acceptable" or "excellent" image quality (n = 91), greater than 80% of the liver and gallbladder were visualized in the majority of cases. In this group, there was 95% agreement between standard of care and teleultrasound on whether an exam was normal or abnormal, with a Cohen's kappa of 0.84 (95% CI 0.7-0.98, p <0.0001). Finally, among these teleultrasound exams of "acceptable" or "excellent" image quality, the sensitivity for cholelithiasis was 93% (95% CI 68.1%-99.8%), and the specificity was 97% (95% CI 89.5%-99.6%). CONCLUSION: This asynchronous telediagnostic system allows individuals without prior ultrasound experience to effectively scan the liver, gallbladder, and right kidney with a high degree of agreement with standard of care ultrasound. This system can be deployed to improve access to diagnostic imaging in low-resource areas.

Lung Ultrasound: The Essentials.

Although US of the lungs is increasingly used clinically, diagnostic radiologists are not routinely trained in its use and interpretation. Lung US is a highly sensitive and specific modality that aids in the evaluation of the lungs for many different abnormalities, including pneumonia, pleural effusion, pulmonary edema, and pneumothorax. This review provides an overview of lung US to equip the diagnostic radiologist with knowledge needed to interpret this increasingly used modality. Supplemental material is available for this article. © RSNA, 2021.

New Ultrasound Telediagnostic System for Low-Resource Areas: Pilot Results From Peru.

Billions of people around the world lack access to diagnostic imaging. To address this issue, we piloted a comprehensive ultrasound telediagnostic system, which uses ultrasound volume sweep imaging (VSI) acquisitions capable of being performed by operators without prior traditional ultrasound training and new telemedicine software capable of sending imaging acquisitions asynchronously over low Internet bandwidth for remote interpretation. The telediagnostic system was tested with obstetric, right upper quadrant abdominal, and thyroid volume sweep imaging protocols in Peru. Scans obtained by operators without prior ultrasound experience were sent for remote interpretation by specialists using the telemedicine platform. Scans obtained allowed visualization of the target region in 96% of cases with diagnostic imaging quality. This telediagnostic system shows promise in improving health care disparities in the developing world.

Update to the Society of Radiologists in Ultrasound Liver Elastography Consensus Statement.

This multidisciplinary update of the Society of Radiologists in Ultrasound consensus statement on liver elastography incorporates the large volume of new information available in the literature since the initial publication. The recommended procedure for acquiring stiffness measurements is reviewed. There has been substantial improvement in the acoustic radiation force impulse (ARFI) technology-most notably the addition of a quality assessment of the shear wave propagation. Due to the efforts of the Quantitative Imaging Biomarkers Alliance, or QIBA, the variability of liver stiffness measurements between systems had decreased. There are now effective treatments for hepatitis B and hepatitis C, and follow-up after effective treatment should be based on the use of the delta change of the value obtained at viral eradication or suppression. Because the detection of compensated advanced chronic liver disease (cACLD) is very important, the new guidelines are made based on the probability of cACLD for given stiffness values. The panel recommends a vendor-neutral rule of four for interpretation for ARFI techniques. This new method simplifies interpretation of liver stiffness results and is more clinically relevant.

Sonography of Acute Cholecystitis and Its Mimics.

Right upper quadrant (RUQ) abdominal pain is a common complaint. Acute cholecystitis (AC) is the primary diagnostic consideration in most adults presenting with acute onset RUQ abdominal pain; however, a variety of other conditions can mimic AC. Abdominal ultrasound (US) receives the highest score for imaging appropriateness for these patients. This article reviews the sonographic findings of uncomplicated and complicated AC and provides practical technical tips. The radiologist should be familiar with conditions that can mimic AC, be able to suggest these alternative diagnoses when findings are present on US, and recommend additional tests or procedures, if needed.

Attenuation of Shear Waves in Normal and Steatotic Livers.

Shear wave propagation in the liver has been a robust subject of research, with shear wave speed receiving the most attention. The correlation between increased shear wave speed and increased fibrosis in the liver has been established as a useful diagnostic tool. In comparison, the precise mechanisms of shear wave attenuation, and its relation to diseased states of the liver, are less well-established. This study focused on the hypothesis that steatosis adds a viscous (lossy) component to the liver, which increases shear wave attenuation. Twenty patients' livers were scanned with ultrasound and with induced shear wave propagation, and the resulting displacement profiles were analyzed using recently developed estimators to derive both the speed and attenuation of the shear waves within 6-cm2 regions of interest. The results were compared with pathology scores obtained from liver biopsies taken under ultrasound guidance. Across these cases, increases in shear wave attenuation were linked to increased steatosis score. This preliminary study supports the hypothesis and indicates the possible utility of the measurements for non-invasive and quantitative assessment of steatosis.

Dalteparin thromboprophylaxis in cancer patients at high risk for venous thromboembolism: A randomized trial.

BACKGROUND: Ambulatory cancer patients at high-risk for venous thromboembolism (VTE) can be identified using a validated risk score (Khorana score). We evaluated the benefit of outpatient thromboprophylaxis with dalteparin in high-risk patients in a multicenter randomized study. METHODS: Cancer patients with Khorana score≥3 starting a new systemic regimen were screened for VTE and if negative randomized to dalteparin 5000units daily or observation for 12weeks. Subjects were screened with lower extremity ultrasounds every 4weeks on study and with chest CT at 12weeks. The primary efficacy endpoint was all VTE over 12weeks and primary safety endpoint was clinically relevant bleeding events over 13weeks. The study was terminated early due to low accrual. RESULTS: Of 117 enrolled patients, 10 (8.5%) had VTE on baseline screening and were not randomized. Of 98 randomized patients, VTE occurred in 12% (N=6/50) of patients on dalteparin and 21% (N=10/48) on observation (hazard ratio, HR 0.69, 95% CI 0.23-1.89). Major bleeding was similar (N=1) in each arm but clinically relevant bleeding was higher in dalteparin arm (N=7 versus 1 on observation) (HR=7.0, 95% CI 1.2-131.6). There was no difference in overall survival. CONCLUSIONS: Thromboprophylaxis is associated with a non-significantly reduced risk of VTE and significantly increased risk of clinically relevant bleeding in this underpowered study. The Khorana score successfully identifies patients with high incidence of VTE both at baseline and during treatment. Future studies should continue to focus on risk-adapted approaches to reduce the burden of VTE in cancer. TRIAL REGISTRATION: clinicaltrials.gov identifier: NCT00876915.

Methodology to study the three-dimensional spatial distribution of prostate cancer and their dependence on clinical parameters.

A methodology to study the relationship between clinical variables [e.g., prostate specific antigen (PSA) or Gleason score] and cancer spatial distribution is described. Three-dimensional (3-D) models of 216 glands are reconstructed from digital images of whole mount histopathological slices. The models are deformed into one prostate model selected as an atlas using a combination of rigid, affine, and B-spline deformable registration techniques. Spatial cancer distribution is assessed by counting the number of tumor occurrences among all glands in a given position of the 3-D registered atlas. Finally, a difference between proportions is used to compare different spatial distributions. As a proof of concept, we compare spatial distributions from patients with PSA greater and less than [Formula: see text] and from patients older and younger than 60 years. Results suggest that prostate cancer has a significant difference in the right zone of the prostate between populations with PSA greater and less than [Formula: see text]. Age does not have any impact in the spatial distribution of the disease. The proposed methodology can help to comprehend prostate cancer by understanding its spatial distribution and how it changes according to clinical parameters. Finally, this methodology can be easily adapted to other organs and pathologies.

Elastography Assessment of Liver Fibrosis: Society of Radiologists in Ultrasound Consensus Conference Statement.

The Society of Radiologists in Ultrasound convened a panel of specialists from radiology, hepatology, pathology, and basic science and physics to arrive at a consensus regarding the use of elastography in the assessment of liver fibrosis in chronic liver disease. The panel met in Denver, Colo, on October 21-22, 2014, and drafted this consensus statement. The recommendations in this statement are based on analysis of current literature and common practice strategies and are thought to represent a reasonable approach to the noninvasive assessment of diffuse liver fibrosis.

Shear wave dispersion in lean versus steatotic rat livers.

OBJECTIVES: The precise measurement of fat accumulation in the liver, or steatosis, is an important clinical goal. Our previous studies in phantoms and mouse livers support the hypothesis that, starting with a normal liver, increasing accumulations of microsteatosis and macrosteatosis will increase the lossy viscoelastic properties of shear waves in a medium. This increase results in an increased dispersion (or slope) of the shear wave speed in the steatotic livers. METHODS: In this study, we moved to a larger animal model, lean versus obese rat livers ex vivo, and a higher-frequency imaging system to estimate the shear wave speed from crawling waves. RESULTS: The results showed elevated dispersion in the obese rats and a separation of the lean versus obese liver parameters in a 2-dimensional parameter space of the dispersion (slope) and shear wave speed at a reference frequency of 150 Hz. CONCLUSIONS: We have confirmed in 3 separate studies the validity of our dispersion hypothesis in animal models.

What do we know about shear wave dispersion in normal and steatotic livers?

A number of new approaches to measure the viscoelastic properties of the liver are now available to clinicians, many involving shear waves. However, we are at an early stage in understanding the physical processes that govern shear wave propagation in normal liver, with more unknowns added when pathologies such as steatosis are present. This technical note focuses on what is known about the characterization of normal and steatotic (or fatty) livers, with a particular focus on dispersion. Some studies in phantoms and mouse livers support the hypothesis that, starting with a normal liver, increasing accumulations of micro- and macrosteatosis will increase the lossy viscoelastic properties of shear waves in a medium. This results in an increased dispersion (or slope) of shear wave speed and attenuation in the steatotic livers. Theoretical and empirical findings across a number of studies are summarized.

The essentials of extracranial carotid ultrasonographic imaging.

In this article, the standard ultrasonographic scanning techniques and Doppler settings necessary to produce reliable and reproducible carotid imaging are discussed. The normal carotid anatomy is reviewed, including grayscale, color Doppler, and spectral Doppler imaging appearances, is reviewed. The vascular abnormalities caused by atherosclerosis are examined, including plaque morphology characterization as well as waveform and velocity changes caused by stenosis, are examined. In addition, special situations are explored, such as imaging in the presence of an arrhythmia or cardiac assist devices. Imaging after carotid intervention is discussed, including the complications associated with these procedures.