Artifacts in contrast-enhanced ultrasound: a pictorial essay

Tips and tricks for a correct interpretation of contrast-enhanced ultrasound

Although contrast-enhanced ultrasound (CEUS) is a widespread and easily manageable technique, image interpretation errors can occur due to the operator's inexperience and/or lack of knowledge of the frequent pitfalls, which may cause uncertain diagnosis and misdiagnosis. Indeed, knowledge of the basic physical and technical principles of ultrasound is needed both to understand sonographic image findings and to evaluate the potential and limits of the method. Like the B-mode ultrasound, the quality of the CEUS examination is also subject not only to the adequate manual skill of the operator but also to his/her deep knowledge of the technique which improves the quality of the image helping avoid misleading artifacts. In this review, the main parameters influencing a CEUS examination will be described by taking into account the most common errors and pitfalls and their possible solutions.

Contrast-Enhanced Ultrasound of the Indeterminate Renal Mass, From the AJR "How We Do It" Special Series

Contrast-enhanced ultrasound (CEUS) is distinguished from CT and MRI by the use of microbubble ultrasound contrast agents (UCAs) with intravascular blood pool distribution. When performing CEUS, low-intensity ultrasound allows real-time tissue subtraction imaging, whereas high-intensity ultrasound leads to microbubble destruction, enabling visualization of the contrast inflow pattern. CEUS has exceptional contrast resolution that enables the detection of even minimal blood flow, achieving very high NPV for ruling out vascular perfusion and providing high frame rates in the evaluation of tissue perfusion dynamics. UCAs undergo hepatic metabolism and pulmonary clearance, ensuring safety in patients with renal impairment. CEUS excels in distinguishing solid from cystic renal masses, with higher sensitivity than CT or MRI for detection of lesion enhancement. CEUS can aid the further characterization of both solid and cystic lesions and may have particular applications in the surveillance of cystic masses and surveillance after renal cell carcinoma ablation. This review describes the use of CEUS to help characterize indeterminate renal masses, based on the authors' institutional experience. The article highlights key differences between CEUS and CT or MRI, and provides practical insights for performing and interpreting CEUS of renal masses.

Contrast-Enhanced Ultrasound Feasibility in Assessing Carotid Plaque Vulnerability-Narrative Review

The risk assessment for carotid atherosclerotic lesions involves not only determining the degree of stenosis but also plaque morphology and its composition. Recently, carotid contrast-enhanced ultrasound (CEUS) has gained importance for evaluating vulnerable plaques. This review explores CEUS's utility in detecting carotid plaque surface irregularities and ulcerations as well as intraplaque neovascularization and its alignment with histology. Initial indications suggest that CEUS might have the potential to anticipate cerebrovascular incidents. Nevertheless, there is a need for extensive, multicenter prospective studies that explore the relationships between CEUS observations and patient clinical outcomes in cases of carotid atherosclerotic disease.

Contrast-Enhanced Ultrasound in Distinguishing between Malignant and Benign Peripheral Pulmonary Consolidations: The Debated Utility of the Contrast Enhancement Arrival Time

Background. Limited studies and observations conducted on a too small number of patients prevent determining the actual clinical utility of pulmonary contrast-enhanced ultrasound (CEUS). The aim of the present study was to examine the efficacy of contrast enhancement (CE) arrival time (AT) and other dynamic CEUS findings for differentiating between malignant and benign peripheral lung lesions. Methods. 317 inpatients and outpatients (215 men, 102 women; mean age: 52 years) with peripheral pulmonary lesions were included in the study and underwent pulmonary CEUS. Patients were examined in a sitting position after receiving an intravenous injection of 4.8 mL of sulfur hexafluoride microbubbles stabilized by a phospholipid shell as ultrasound contrast agent (SonoVue-Bracco; Milan, Italy). Each lesion was observed for at least 5 min in real-time and the following temporal characteristics of enhancement were detected: the arrival time (AT) of microbubbles in the target lesion; the enhancement pattern; the wash-out time (WOT) of microbubbles. Results were then compared in light of the definitive diagnosis of community acquired pneumonia (CAP) or malignancies, which was not known at the time of CEUS examination. All malignant cases were diagnosed by histological results, while pneumonia was diagnosed on the basis of clinical and radiological follow-up, laboratory findings and, in some cases, histology. Results. CE AT has not been shown to differ between benign and malignant peripheral pulmonary lesions. The overall diagnostic accuracy and sensibility of a CE AT cut-off value < 10 s in discriminating benign lesions were low (diagnostic accuracy: 47.6%; sensibility: 5.3%). Poor results were also obtained in the sub-analysis of small (mean diameter < 3 cm) and large (mean diameter > 3 cm) lesions. No differences were recorded in the type of CE pattern showed between benign and malignant peripheral pulmonary lesions. In benign lesions we observed a higher frequency of delayed CE wash-out time (WOT) > 300 s. Anyhow, a CE WOT cut-off value > 300 s showed low diagnostic accuracy (53.6%) and sensibility (16.5%) in discriminating between pneumonias and malignancies. Similar results were also obtained in the sub-analysis by lesion size. Squamous cell carcinomas showed a more delayed CE AT compared to other histopathology subtypes. However, such a difference was statistically significant with undifferentiated lung carcinomas. Conclusions. Due to an overlap of CEUS timings and patterns, dynamic CEUS parameters cannot effectively differentiate between benign and malignant peripheral pulmonary lesions. Chest CT remains the gold standard for lesion characterization and the eventual identification of other pneumonic non-subpleural localizations. Furthermore, in the case of malignancy, a chest CT is always needed for staging purposes.

Artifacts and Technical Considerations at Contrast-enhanced US

Contrast-enhanced US (CEUS), similar to other radiologic modalities, requires specific technical considerations and is subject to image artifacts. These artifacts may affect examination quality, negatively impact diagnostic accuracy, and decrease user comfort when using this emerging technique. Some artifacts are related to commonly known gray-scale US artifacts that can also appear on the contrast-only image (tissue-subtracted image obtained with the linear responses from background tissues nulled). These may include acoustic shadowing and enhancement; reverberation, refraction, and reflection; and poor penetration. Other artifacts are exclusive to CEUS owing to the techniques used for contrast mode image generation and the unique properties of the microbubbles that constitute ultrasound-specific contrast agents (UCAs). UCA-related artifacts may appear on the contrast-only image, the gray-scale image, or various Doppler mode images. Artifacts related to CEUS may include nonlinear artifacts and unintentional microbubble destruction resulting in pseudowashout. The microbubbles themselves may result in specific artifacts such as pseudoenhancement, signal saturation, and attenuation and shadowing and can confound the use of color and spectral Doppler US. Identifying and understanding these artifacts and knowing how to mitigate them may improve the quality of the imaging study, increase user confidence, and improve patient care. The authors review the principles of UCAs and the sound-microbubble interaction, as well as the technical aspects of image generation. Technical considerations, including patient positioning, depth, acoustic window, and contrast agent dose, also are discussed. Specific artifacts are described, with tips on how to identify and, if necessary, apply corrective measures, with the goal of improving examination quality. ^© RSNA, 2022 Online supplemental material and the slide presentation from the RSNA Annual Meeting are available for this article.

Contrast-enhanced US Evaluation of Endoleaks after Endovascular Stent Repair of Abdominal Aortic Aneurysm

Ruptured abdominal aortic aneurysm (AAA) carries high morbidity and mortality. Elective repair of AAA with endovascular stent-grafts requires lifetime imaging surveillance for potential complications, most commonly endoleaks. Because endoleaks result in antegrade or retrograde systemic arterialized flow into the excluded aneurysm sac, patients are at risk for recurrent aneurysm sac growth with the potential to rupture. Multiphasic CT has been the main imaging modality for surveillance and symptom evaluation, but contrast-enhanced US (CEUS) offers a useful alternative that avoids radiation and iodinated contrast material. CEUS is at least equivalent to CT for detecting endoleak and may be more sensitive. The authors provide a general protocol and technical considerations needed to perform CEUS of the abdominal aorta after endovascular stent repair. When there are no complications, the stent-graft lumen has homogeneous enhancement, and no contrast material is present in the aneurysm sac outside the stented lumen. In patients with an antegrade endoleak, contrast material is seen simultaneously in the aneurysm sac and stent-graft lumen, while delayed enhancement in the sac is due to retrograde leak. Recognition of artifacts and other potential pitfalls for CEUS studies is important for examination performance and interpretation. Online supplemental material is available for this article. ^©RSNA, 2022.

Microbubbles in the belly: optimizing the protocol for contrast-enhanced ultrasound of the pediatric abdomen

Intravenous contrast-enhanced ultrasound (CEUS) can serve as a diagnostic or problem-solving tool in pediatric imaging. CEUS of abdominal solid organs has been reported for a number of indications. The approach to the examination broadly falls into two categories: evaluation of a focal lesion or surveillance of an organ or organs for lesions or perfusion abnormalities. A consistent, technical imaging protocol for both of these clinical scenarios facilitates integration of routine use of CEUS in an imaging department. Here we review the CEUS imaging protocols for abdominal organs in children, including technical and solid-organ-specific considerations.

Pediatric contrast-enhanced ultrasound: optimization of techniques and dosing

When performing contrast-enhanced ultrasound (CEUS), ultrasound (US) scanner settings, examination technique, and contrast agent dose and administration must be optimized to ensure that high-quality, diagnostic and reproducible images are acquired for qualitative and quantitative interpretations. When carrying out CEUS in children, examination settings should be tailored to their body size and specific indications, similar to B-mode US. This review article details the basic background knowledge that is needed to perform CEUS optimally in children, including considerations related to US scanner settings and US contrast agent dose selection and administration techniques.

Experimental acoustic characterization of an endoskeletal antibubble contrast agent: First results

Purpose

An antibubble is an encapsulated gas bubble with an incompressible inclusion inside the gas phase. Current‐generation ultrasound contrast agents are bubble‐based: they contain encapsulated gas bubbles with no inclusions. The objective of this work is to determine the linear and nonlinear responses of an antibubble contrast agent in comparison to two bubble‐based ultrasound contrast agents, that is, reference bubbles and SonoVueTM.

Methods

Side scatter and attenuation of the three contrast agents were measured, using single‐element ultrasound transducers, operating at 1.0, 2.25, and 3.5 MHz. The scatter measurements were performed at acoustic pressures of 200 and 300 kPa for 1.0 MHz, 300 kPa, and 450 kPa for 2.25 MHz, and 370 and 560 kPa for 3.5 MHz. Attenuation measurements were conducted at pressures of 13, 55, and 50 kPa for 1.0, 2.25, and 3.5 MHz, respectively. In addition, a dynamic contrast‐enhanced ultrasound measurement was performed, imaging the contrast agent flow through a vascular phantom with a commercial diagnostic linear array probe.

Results

Antibubbles generated equivalent or stronger harmonic signal, compared to bubble‐based ultrasound contrast agents. The second harmonic side‐scatter amplitude of the antibubble agent was up to 3 dB greater than that of reference bubble agent and up to 4 dB greater than that of SonoVueTM at the estimated concentration of 8×104 bubbles/mL. For ultrasound with a center transmit frequency of 1.0 MHz, the attenuation coefficient of the antibubble agent was 8.7 dB/cm, whereas the attenuation coefficient of the reference agent was 7.7 and 0.3 dB/cm for SonoVueTM. At 2.25 MHz, the attenuation coefficients were 9.7, 3.0, and 0.6 dB/cm, respectively. For 3.5 MHz, they were 4.4, 1.8, and 1.0 dB/cm, respectively. A dynamic contrast‐enhanced ultrasound recording showed the nonlinear signal of the antibubble agent to be 31% greater than for reference bubbles and 23% lower than SonoVueTM at a high concentration of 2×106 bubbles/mL.

Conclusion

Endoskeletal antibubbles generate comparable or greater higher harmonics than reference bubbles and SonoVueTM. As a result, antibubbles with liquid therapeutic agents inside the gas phase have high potential to become a traceable therapeutic agent.

Tumor perfusion evaluation using dynamic contrast-enhanced ultrasound after electrochemotherapy and IL-12 plasmid electrotransfer in murine melanoma

Electrochemotherapy with bleomycin (ECT BLM) is an effective antitumor treatment already used in clinical oncology. However, ECT alone is still considered a local antitumor therapy because it cannot induce systemic immunity. When combined with adjuvant gene electrotransfer of plasmid DNA encoding IL-12 (GET pIL-12), the combined therapy leads to a systemic effect on untreated tumors and distant metastases. Although the antitumor efficacy of both therapies alone or in combination has been demonstrated at both preclinical and clinical levels, data on the predictors of efficacy of the treatments are still lacking. Herein, we evaluated the results of dynamic contrast-enhanced ultrasound (DCE-US) as a predictive factor for ECT BLM and GET pIL-12 in murine melanoma. Melanoma B16F10 tumors grown in female C57Bl/6NCrl mice were treated with GET pIL-12 and ECT BLM. Immediately after therapy, 6 h and 1, 3, 7 and 10 days later, tumors were examined by DCE-US. Statistical analysis was performed to inspect the correlation between tumor doubling time (DT) and DCE-US measurements using semilinear regression models and Bland-Altman plots. Therapeutic groups in which DCE-US showed reduced tumor perfusion had longer tumor DTs. It was confirmed that the DCE-US parameter peak enhancement (PE), reflecting relative blood volume, had predictive value for the outcome of therapy: larger PE correlated with shorter DT. In addition, perfusion heterogeneity was also associated with outcome: tumors that had more heterogeneous perfusion had faster growth, i.e., shorter DTs. This study demonstrates that DCE-US can be used as a method to predict the efficacy of electroporation-based treatment.

Refraction artifact on abdominal sonogram

Ultrasonography (US) is the first-line diagnostic tool for observing the whole abdomen. Unfortunately, a wide spectrum of refraction-related artefactual images is very frequently encountered in routine US examinations. In addition, most practitioners currently perform abdominal US examinations without sufficient knowledge of refraction artifacts (RAs). This review article was designed to present many representative RA images seen in the clinical setting, with a brief explanation of the mechanism of these images, in certain cases through an analyzed and reconstructed method using computer simulation that supports clinical observations. RAs are encountered not only with B-mode US but also with Doppler US, contrast-enhanced US, and shear wave elastography. RAs change their appearance according to the situation, but they always have a significant effect on detailed interpretation of abdominal US images. Correct diagnosis of abdominal US relies on a deep understanding of each characteristic artifactual finding, which necessitates knowledge of basic US physics. When analyzing mass lesions, computer simulation analysis helps to reveal the global images of RAs around a lesion.

Results of Dynamic Contrast-Enhanced Ultrasound Correlate With Treatment Outcome in Canine Neoplasia Treated With Electrochemotherapy and Interleukin-12 Plasmid Electrotransfer

Electrochemotherapy (ECT) and/or gene electrotransfer of plasmid DNA encoding interleukin-12 (GET pIL-12) are effective treatments for canine cutaneous, subcutaneous, and maxillofacial tumors. Despite the clinical efficacy of the combined treatments of ECT and GET, data on parameters that might predict the outcome of the treatments are still lacking. This study aimed to investigate whether dynamic contrast-enhanced ultrasound (DCE-US) results of subcutaneous tumors differ between tumors with complete response (CR) and tumors without complete response (non-CR) in dogs treated with ECT and GET pIL-12. Eight dogs with a total of 12 tumor nodules treated with ECT and GET pIL-12 were included. DCE-US examinations were performed in all animals before and immediately after therapy as well as 8 h and 1, 3, and 7 days later. Clinical follow-up examinations were performed 7 and 14 days, 1 and 6 months, and 1 year after treatment. Numerous significant differences in DCE-US parameters were noted between tumors with CR and non-CR tumors; perfusion and perfusion heterogeneity were lower in CR tumors than in non-CR tumors. Therefore, studies with larger numbers of patients are needed to investigate whether DCE-US results can be used to predict treatment outcomes and to make effective decisions about the need for repeated therapy or different treatment combinations in individual patients.

Contrast-Enhanced Ultrasound in Children: Implementation and Key Diagnostic Applications

Contrast-enhanced ultrasound (CEUS) utilization is expanding rapidly, particularly in children, in whom the modality offers important advantages of dynamic evaluation of the vasculature, portability, lack of ionizing radiation, and lack of need for sedation. Accumulating data establish an excellent safety profile of ultrasound contrast agents in children. Although only FDA-approved for IV use in children for characterizing focal liver lesions and for use during echocardiography, growing off-label applications are expanding the diagnostic potential of ultrasound. Focal liver lesion evaluation is the most common use of CEUS, and the American College of Radiology Pediatric LI-RADS Working Group recommends including CEUS for evaluation of a newly discovered focal liver lesion in many circumstances. Data also support the role of CEUS in hemodynamically stable children with blunt abdominal trauma, and CEUS is becoming a potential alternative to CT in this setting. Additional potential applications that require further study include evaluation of pathology in the lung, spleen, brain, pancreas, bowel, kidney, female pelvis, and scrotum. This review explores the implementation of CEUS in children, describing basic principles of ultrasound contrast agents and CEUS technique and summarizing current and potential IV diagnostic applications based on pediatric-specific supporting evidence.

Artifacts in Contrast-Enhanced Ultrasound during Follow-up after Endovascular Aortic Repair: Impact on Endoleak Detection in Comparison with Computed Tomography Angiography

The study described here systematically analyzed how specific artifacts in contrast-enhanced ultrasound (CEUS) can affect the detection of endoleaks during follow-up after endovascular aortic repair (EVAR). Patients undergoing EVAR of atherosclerotic or mycotic abdominal aortic aneurysms using various standard and branched stent-graft material for visceral and iliac preservation were enrolled over 5 y and followed up with computed tomography angiography (CTA) and CEUS simultaneously. CEUS artifacts were frequently identified after EVAR procedures (59% of examinations) and were caused mainly by contrast agent, different prosthesis or embolization material and postinterventional changes in the aneurysm sac. This article describes how to identify important artifacts and how to avoid false-negative or false-positive interpretations of endoleaks. Despite artifacts, CEUS had higher sensitivity for endoleak detection after EVAR than CTA. CEUS was superior to CTA in the identification of late endoleaks type II and in follow-up examinations after embolization procedures, where beam-hardening artifacts limited CTA.

Contrast-enhanced ultrasound applications in liver transplant imaging

Contrast-enhanced ultrasound (CEUS) is gaining ever-increasing acceptance in the preoperative and postoperative evaluation of liver-transplanted patients. While indications are still a matter of research, CEUS is used in tertiary centers to supplement ultrasound (US) and Color Doppler US examination, with the potential of providing a comprehensive first-line ultrasound-based diagnosis. Alternatively, CEUS is used as a problem-solving tool when previous cross-sectional or US imaging was inconclusive, especially in assessing hepatocellular carcinoma, parenchymal perfusion abnormalities, the vascular status, and even the biliary tree. This review describes the potential use for CEUS in the setting of orthotopic liver transplantation (OLT).

Quality Assessment of CEUS in Individuals with Small Renal Masses-Which Individual Factors Are Associated with High Image Quality?

Obesity and bowel gas are known to impair image quality in abdominal ultrasound (US). The present study aims at identifying individual factors in B-mode US that influence contrast-enhanced US (CEUS) image quality to optimize further imaging workup of incidentally detected focal renal masses. We retrospectively analyzed renal CEUS of focal renal masses ≤ 4 cm performed at our center in 143 patients between 2016 and 2020. Patient and lesion characteristics were tested for their influence on focal and overall image quality assessed by two experienced radiologists using Likert scales. Effects of significant variables were quantified by receiver operating characteristics (ROC) curve analysis with area under the curve (AUC), and combined effects were assessed by binary logistic regression. Shrunken kidney, kidney depth, lesion depth, lesion size, and exophytic lesion growth were found to influence focal renal lesion image quality, and all factors except lesion size also influenced overall image quality. Combination of all parameters except kidney depth best predicted good CEUS image quality showing an AUC of 0.91 (p < 0.001, 95%-CI 0.863–0.958). The B-mode US parameters investigated can identify patients expected to have good CEUS image quality and thus help select the most suitable contrast-enhanced imaging strategy for workup of renal lesions.

Guidelines and Good Clinical Practice Recommendations for Contrast Enhanced Ultrasound (CEUS) in the Liver - Update 2020 - WFUMB in Cooperation with EFSUMB, AFSUMB, AIUM, and FLAUS

The present, updated document describes the fourth iteration of recommendations for the hepatic use of contrast enhanced ultrasound (CEUS), first initiated in 2004 by the European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB). The previous updated editions of the guidelines reflected changes in the available contrast agents and updated the guidelines not only for hepatic but also for non-hepatic applications.The 2012 guideline requires updating as previously the differences of the contrast agents were not precisely described and the differences in contrast phases as well as handling were not clearly indicated. In addition, more evidence has been published for all contrast agents. The update also reflects the most recent developments in contrast agents, including the United States Food and Drug Administration (FDA) approval as well as the extensive Asian experience, to produce a truly international perspective.These guidelines and recommendations provide general advice on the use of ultrasound contrast agents (UCA) and are intended to create standard protocols for the use and administration of UCA in liver applications on an international basis to improve the management of patients.

Guidelines and Good Clinical Practice Recommendations for Contrast-Enhanced Ultrasound (CEUS) in the Liver-Update 2020 WFUMB in Cooperation with EFSUMB, AFSUMB, AIUM, and FLAUS

The present, updated document describes the fourth iteration of recommendations for the hepatic use of contrast-enhanced ultrasound, first initiated in 2004 by the European Federation of Societies for Ultrasound in Medicine and Biology. The previous updated editions of the guidelines reflected changes in the available contrast agents and updated the guidelines not only for hepatic but also for non-hepatic applications. The 2012 guideline requires updating as, previously, the differences in the contrast agents were not precisely described and the differences in contrast phases as well as handling were not clearly indicated. In addition, more evidence has been published for all contrast agents. The update also reflects the most recent developments in contrast agents, including U.S. Food and Drug Administration approval and the extensive Asian experience, to produce a truly international perspective. These guidelines and recommendations provide general advice on the use of ultrasound contrast agents (UCAs) and are intended to create standard protocols for the use and administration of UCAs in liver applications on an international basis to improve the management of patients.

Pathologic Hepatic Contrast-Enhanced Ultrasound Pattern in Patients Undergoing Allogeneic Stem Cell Transplantation

Veno-occlusive disease (VOD) is a severe complication of allogeneic stem cell transplantation (allo-SCT). Its diagnosis is difficult, and ultrasound (US) has not been proven to be of additional diagnostic value. In the work described here, we prospectively analyzed the hepatic contrast-enhanced ultrasound (CEUS) pattern before and after allo-SCT and correlated these results with the pre-allo-SCT VOD risk factors, clinical VOD findings and conventional US findings. Thirty consecutive patients who underwent allo-SCT and had at least one VOD risk factor were studied. B-Mode US and CEUS were longitudinally performed at defined time points before and after allo-SCT. The 1-min hepatic enhancement (OMHE) in CEUS was standardized to splenic enhancement and quantified using optical density (OD) measurement software. A hypo-OMHE was arbitrarily defined as pathologic (pOMHE) if the OD of the liver was less than 90% compared with the mean splenic OD. Twenty-one patients (70%) had a pOMHE, the occurrence of which peaked at day 10 after allo-SCT. The number of pre-treatment VOD risk factors significantly differed between the pathologic and non-pathologic OD groups. Together, patients undergoing allo-SCT frequently exhibit a pathologic hepatic CEUS pattern, which can be quantified by OD measurement and is suggestive of pre-clinical VOD or other hepatic pathologies.

Contrast imaging ultrasound for the detection and characterization of carotid vulnerable plaque

Not only the degree of luminal narrowing but also the plaque morphology and composition play an important role in risk stratification of carotid atherosclerotic lesions. During the last few years, carotid contrast-enhanced ultrasound (CEUS) has emerged as a valuable imaging tool to assess such vulnerable carotid plaques. This review article discussed the use of CEUS for the detection of carotid plaque irregularities and ulcerations as well as the quantification of intraplaque neovascularization and its correlation with histology and inflammatory biomarkers. Apart from evaluating for markers of vulnerable carotid plaques, CEUS enhancement is directly associated with past cerebrovascular events. More importantly, preliminary evidence has shown that CEUS could be used to predict future cerebrovascular and cardiovascular events. Despite the progress in CEUS imaging for carotid atherosclerotic disease, past studies still suffer from the retrospective nature, small sample size, and a lack of matched, well controlled prospective studies. In the future, large multi-center prospective studies addressing the relationship between CEUS findings and patient clinical outcomes in carotid atherosclerotic disease are warranted.

Use of contrast ultrasound in differentiating thrombosed pseudoaneurysm from sarcoma, prior to surgery

We describe a case of a 69-year-old male with a right-sided popliteal mass following a motor vehicle accident 15 years ago. The mass was indeterminate via multiple modalities (magnetic resonance imaging, digital subtraction angiography, and vascular ultrasound) with biopsy requested prior to surgical removal to determine the appropriate surgical team – vascular versus sarcoma oncologic surgery. Contrast ultrasound was utilized to determine if biopsy was indicated and if so, to determine the most appropriate target. Contrast ultrasound showed no areas of enhancement, therefore biopsy was not performed and the patient safely proceeded to vascular surgery. Pathology confirmed the mass to be a thrombosed pseudoaneurysm of the popliteal artery. We present the benefits of using contrast ultrasound in the work up and diagnosis of a popliteal neoplasm versus suspected vascular complication.

The AFSUMB Consensus Statements and Recommendations for the Clinical Practice of Contrast-Enhanced Ultrasound using Sonazoid

The first edition of the guidelines for the use of ultrasound contrast agents was published in 2004, dealing with liver applications. The second edition of the guidelines in 2008 reflected changes in the available contrast agents and updated the guidelines for the liver, as well as implementing some nonliver applications. The third edition of the contrast-enhanced ultrasound (CEUS) guidelines was the joint World Federation for Ultrasound in Medicine and Biology-European Federation of Societies for Ultrasound in Medicine and Biology (WFUMB-EFSUMB) venture in conjunction with other regional US societies such as Asian Federation of Societies for Ultrasound in Medicine and Biology, resulting in a simultaneous duplicate on liver CEUS in the official journals of both WFUMB and EFSUMB in 2013. However, no guidelines were described mainly for Sonazoid due to limited clinical experience only in Japan and Korea. The new proposed consensus statements and recommendations provide general advice on the use of Sonazoid and are intended to create standard protocols for the use and administration of Sonazoid in hepatic and pancreatobiliary applications in Asian patients and to improve patient management.

The AFSUMB Consensus Statements and Recommendations for the Clinical Practice of Contrast-Enhanced Ultrasound using Sonazoid

The first edition of the guidelines for the use of ultrasound contrast agents was published in 2004, dealing with liver applications. The second edition of the guidelines in 2008 reflected changes in the available contrast agents and updated the guidelines for the liver, as well as implementing some nonliver applications. The third edition of the contrast-enhanced ultrasound (CEUS) guidelines was the joint World Federation for Ultrasound in Medicine and Biology-European Federation of Societies for Ultrasound in Medicine and Biology (WFUMB-EFSUMB) venture in conjunction with other regional US societies such as Asian Federation of Societies for Ultrasound in Medicine and Biology, resulting in a simultaneous duplicate on liver CEUS in the official journals of both WFUMB and EFSUMB in 2013. However, no guidelines were described mainly for Sonazoid due to limited clinical experience only in Japan and Korea. The new proposed consensus statements and recommendations provide general advice on the use of Sonazoid and are intended to create standard protocols for the use and administration of Sonazoid in hepatic and pancreatobiliary applications in Asian patients and to improve patient management.

Imaging Methods for Ultrasound Contrast Agents

Microbubble contrast agents were introduced more than 25 years ago with the objective of enhancing blood echoes and enabling diagnostic ultrasound to image the microcirculation. Cardiology and oncology waited anxiously for the fulfillment of that objective with one clinical application each: myocardial perfusion, tumor perfusion and angiogenesis imaging. What was necessary though at first was the scientific understanding of microbubble behavior in vivo and the development of imaging technology to deliver the original objective. And indeed, for more than 25 years bubble science and imaging technology have evolved methodically to deliver contrast-enhanced ultrasound. Realization of the basic bubbles properties, non-linear response and ultrasound-induced destruction, has led to a plethora of methods; algorithms and techniques for contrast-enhanced ultrasound (CEUS) and imaging modes such as harmonic imaging, harmonic power Doppler, pulse inversion, amplitude modulation, maximum intensity projection and many others were invented, developed and validated. Today, CEUS is used everywhere in the world with clinical indications both in cardiology and in radiology, and it continues to mature and evolve and has become a basic clinical tool that transforms diagnostic ultrasound into a functional imaging modality. In this review article, we present and explain in detail bubble imaging methods and associated artifacts, perfusion quantification approaches, and implementation considerations and regulatory aspects.

Diagnostic accuracy of contrast-enhanced ultrasound for detecting bland thrombus from inferior vena cava tumor thrombus in patients with renal cell carcinoma

PURPOSE

To evaluate the role of contrast-enhanced ultrasound (CEUS) in differentiating bland thrombus from tumor thrombus of the inferior vena cava (IVC) in patients with renal cell carcinoma (RCC).

MATERIALS AND METHODS

We retrospectively investigated 30 consecutive patients who underwent robot-assisted radical nephrectomy with IVC thrombectomy and had pathologically confirmed RCC. All patients underwent US and CEUS examination. Two offline readers observed and recorded thrombus imaging information and enhancement patterns. Sensitivity, specificity, accuracy, positive predictive value and negative predictive value for bland thrombus were assessed.

RESULTS

Of the 30 patients, no adverse events occurred during administration of the contrast agent. Early enhancement of the mass within the IVC lumen on CEUS was na indicator of tumor thrombus. Bland thrombus showed no intraluminal flow on CEUS. There were eight (26.7%) patients with bland thrombus, including three level II, two level III, and three level IV. There were three cases with cephalic bland thrombus and five cases with caudal bland thrombus. Three caudal bland thrombi extended to the iliac vein and underwent surgical IVC interruption. Based on no intraluminal flow, for bland thrombus, CEUS had 87.5% sensitivity, 100% specificity, 96.7% accuracy, 100% positive predictive value and 95.6% negative predictive value.

CONCLUSION

Our study demonstrates the potential of CEUS in the differentiation of bland and tumor thrombus of the IVC in patients with RCC. Since CEUS is an effective, inexpensive, and non-invasive method, it could be a reliable tool in the evaluation of IVC thrombus in patients with RCC.

Contrast-enhanced ultrasound of liver lesions in children

Initial pediatric imaging of the liver heavily relies on ultrasonography (US) because it is free of ionizing radiation, easily portable and readily available. Although conventional US (gray-scale and color Doppler) is often an excellent screening tool, its relative low specificity compared to CT/MRI limits liver lesion characterization. The United States Food and Drug Administration's recent approval of an intravenous US contrast agent for pediatric liver lesion characterization (sulfur hexafluoride lipid-type A microspheres) and its excellent safety profile have spurred increased interest in contrast-enhanced US for definitive diagnosis of pediatric liver lesions. This review focuses on the safety of contrast-enhanced US, role of contrast-enhanced US in the evaluation of focal liver lesions, basic contrast-enhanced US technique for liver imaging, and interpretation principles. The authors review common focal liver lesions, with special attention to the role of contrast-enhanced US in the pediatric oncology population.

Comparison of contrast-enhanced CT and contrast-enhanced ultrasound for assessing residual status of primary hepatocellular carcinoma after transcatheter arterial chemoembolization

BACKGROUND

Transcatheter arterial chemoembolization (TACE) can inactivate tumors by embolizing the main blood supply arteries of tumors through selectively inserting microcatheters into the arteries and injecting chemotherapy drugs. Effective TACE treatment will inevitably lead to changes of the microcirculation perfusion state of tumors. Contrast-enhanced ultrasound can accurately reflect the perfusion process of tumors to accurately evaluate the efficacy of TACE.

AIM

To evaluate the clinical value of contrast-enhanced CT (CECT) and contrast-enhanced ultrasound (CEUS) in determining the residual status of hepatocellular carcinoma (HCC) after TACE.

METHODS

Seventy-one HCC patients with a total of 125 lesions who underwent TACE were selected as study subjects during September 2016 and March 2019. One month after TACE, all patients were examined by CEUS and CECT. The results of digital subtraction angiography (DSA) were used as the ¡°gold standard¡± to compare the value of CEUS and CECT in evaluating the efficacy of TACE.

RESULTS

DSA found 97 residual lesions and 28 non-residual lesions. The accuracy, sensitivity, and specificity of CEUS in determining residual lesions were 96.00%, 96.91%, and 92.86%, respectively, and the corresponding values for CECT were 88.00%, 87.63%, and 89.29%. The sensitivity and accuracy of CEUS in determining residual lesions were higher than those of CECT (P < 0.05).

CONCLUSION

CEUS can show the blood perfusion status of HCC after TACE, and is superior to CECT in determining residual lesions, thus providing a new and effective method for clinical evaluation of the efficacy of TACE.

General principles and overview of vascular contrast-enhanced ultrasonography

Ultrasonography (US) is the first-line modality for the evaluation of vascular pathology. Although well-established for many diseases, US has inherent limitations that can occasionally hinder an accurate diagnosis. The value of US was improved by the introduction of microbubbles as ultrasonographic contrast agents (UCAs) and the emergence of contrast-enhanced ultrasonography (CEUS), following the introduction of second-generation UCAs and the emergence of modern contrast-specific techniques. CEUS offers valuable information about vascular disease, both on a macrovascular and a microvascular level, with well-established applications for carotid disease, post-interventional follow-up of abdominal aortic aneurysms, and the assessment of portal vein thrombosis. The purpose of this review is to discuss the principles of CEUS and to present an overview of its vascular applications.

Ultrasound Evaluation in Patients at Risk for Hepatocellular Carcinoma

In the context of chronic liver disease (CLD), sonographic features of hepatic steatosis, cirrhosis, and portal hypertension are discussed and examples are provided. The impact of CLD and hepatocellular carcinoma (HCC) is introduced, providing the rationale for a robust HCC screening and surveillance program for at-risk patients. The American College of Radiology Liver Imaging Reporting and Data System algorithms for screening and surveillance by ultrasound and for the definitive diagnosis of HCC by contrast-enhanced ultrasound are explained, with imaging examples provided. Contrast-enhanced ultrasound technique, limitations, and pitfalls also are introduced.

Contrast-Enhanced Ultrasound-Guided Radiofrequency Ablation of Renal Tumors

Although only limited long-term studies evaluating thermal ablation of renal masses have been performed, it appears that thermal ablation has a comparable 5-year success rate to that of partial or total nephrectomy. This technique is often used in patients who are not good candidates for partial or total nephrectomy. Contrast-enhanced ultrasound (CEUS) has been recently approved by the Food and Drug Administration for characterization of focal liver lesions in adults and pediatric patients. CEUS can be used off label for renal applications and has been used for years in Europe and Asia. It has several advantages over contrast-enhanced computed tomography for use as the technique to guide and evaluate efficacy of thermal ablation of renal masses. These include the ability to visualize small amounts of enhancement, repeat dosing to evaluate efficacy of an ablation during a procedure, thin slice thickness, and real-time visualization. Ultrasound contrast is also non-nephrotoxic and non-hepatotoxic, allowing evaluation of patients with renal insufficiency. This article reviews the use of CEUS for the guidance and follow-up of thermal ablative procedures of renal masses.