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Patients with kidney failure require kidney replacement therapy. While renal transplantation remains the treatment of choice for kidney failure, renal replacement therapy with hemodialysis may be required owing to the limited availability and length of time patients may wait for allografts or for patients ineligible for transplant owing to advanced age or comorbidities. The ideal hemodialysis access should provide complication-free dialysis by creating a direct connection between an artery and vein with adequate blood flow that can be reliably and easily accessed percutaneously several times a week. Surgical arteriovenous fistulas and grafts are commonly created for hemodialysis access, with newer techniques that involve the use of minimally invasive endovascular approaches. The emphasis on proactive planning for the placement, protection, and preservation of the next vascular access before the current one fails has increased the use of US for preoperative mapping and monitoring of complications for potential interventions. Preoperative US of the extremity vasculature helps assess anatomic suitability before vascular access creation, increasing the rates of successful maturation. A US mapping protocol ensures reliable measurements and clear communication of anatomic variants that may alter surgical planning. Postoperative imaging helps assess fistula maturation before cannulation for dialysis and evaluates for early and late complications associated with arteriovenous access. Clinical and US findings can suggest developing stenosis that may progress to thrombosis and loss of access function, which can be treated with percutaneous vascular interventions to preserve access patency. Vascular access steal, aneurysms and pseudoaneurysms, and fluid collections are other complications amenable to US evaluation. © RSNA, 2023 Supplemental material is available for this article. Test Your Knowledge questions for this article are available through the Online Learning Center.

Fatty liver disease has a high and increasing prevalence worldwide, is associated with adverse cardiovascular events and higher long-term medical costs, and may lead to liver-related morbidity and mortality. There is an urgent need for accurate, reproducible, accessible, and noninvasive techniques appropriate for detecting and quantifying liver fat in the general population and for monitoring treatment response in at-risk patients. CT may play a potential role in opportunistic screening, and MRI proton-density fat fraction provides high accuracy for liver fat quantification; however, these imaging modalities may not be suited for widespread screening and surveillance, given the high global prevalence. US, a safe and widely available modality, is well positioned as a screening and surveillance tool. Although well-established qualitative signs of liver fat perform well in moderate and severe steatosis, these signs are less reliable for grading mild steatosis and are likely unreliable for detecting subtle changes over time. New and emerging quantitative biomarkers of liver fat, such as those based on standardized measurements of attenuation, backscatter, and speed of sound, hold promise. Evolving techniques such as multiparametric modeling, radiofrequency envelope analysis, and artificial intelligence-based tools are also on the horizon. The authors discuss the societal impact of fatty liver disease, summarize the current state of liver fat quantification with CT and MRI, and describe past, currently available, and potential future US-based techniques for evaluating liver fat. For each US-based technique, they describe the concept, measurement method, advantages, and limitations. © RSNA, 2023 Online supplemental material is available for this article. Quiz questions for this article are available through the Online Learning Center.

Competing Interests: Conflict of Interest Dr. Robbin Michelle: Philips Medical grant support paid to institution.

Excessive liver fat (steatosis) is now the most common cause of chronic liver disease worldwide and is an independent risk factor for cirrhosis and associated complications. Accurate and clinically useful diagnosis, risk stratification, prognostication, and therapy monitoring require accurate and reliable biomarker measurement at acceptable cost. This article describes a joint effort by the American Institute of Ultrasound in Medicine (AIUM) and the RSNA Quantitative Imaging Biomarkers Alliance (QIBA) to develop standards for clinical and technical validation of quantitative biomarkers for liver steatosis. The AIUM Liver Fat Quantification Task Force provides clinical guidance, while the RSNA QIBA Pulse-Echo Quantitative Ultrasound Biomarker Committee develops methods to measure biomarkers and reduce biomarker variability. In this article, the authors present the clinical need for quantitative imaging biomarkers of liver steatosis, review the current state of various imaging modalities, and describe the technical state of the art for three key liver steatosis pulse-echo quantitative US biomarkers: attenuation coefficient, backscatter coefficient, and speed of sound. Lastly, a perspective on current challenges and recommendations for clinical translation for each biomarker is offered., (© RSNA, 2022.)

Vascular imaging with color and power Doppler is a useful tool in the assessment of various disease processes. Assessment of blood flow, from infarction and ischemia to hyperemia, in organs, neoplasms, and vessels, is used in nearly every US investigation. Recent developments in this area are sensitive to small-vessel low velocity flow without use of intravenous contrast agents, known as microvascular flow imaging (MVFI). MVFI is more sensitive in detection of small vessels than color, power, and spectral Doppler, reducing the need for follow-up contrast-enhanced US (CEUS), CT, and MRI, except when arterial and venous wash-in and washout characteristics would be helpful in diagnosis. Varying clinical applications of MVFI are reviewed in adult and pediatric populations, including its technical underpinnings. MVFI shows promise in assessment of several conditions including benign and malignant lesions in the liver and kidney, acute pathologic abnormalities in the gallbladder and testes, and superficial lymph nodes. Future potential of MVFI in different conditions (eg, endovascular repair) is discussed. Finally, clinical cases in which MVFI correlated and potentially obviated additional CEUS, CT, or MRI are shown., (© RSNA, 2022.)

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.

Importance: National initiatives have emphasized the use of autogenous arteriovenous fistulas (AVFs) for hemodialysis, but their purported benefits have been questioned., Objective: To examine AVF usability, longer-term functional patency, and remedial procedures to facilitate maturation, manage complications, or maintain patency in the Hemodialysis Fistula Maturation (HFM) Study., Design, Setting, and Participants: The HFM Study was a multicenter (n = 7) prospective National Institutes of Health National Institute of Diabetes and Digestive and Kidney Diseases cohort study performed to identify factors associated with AVF maturation. A total of 602 participants were enrolled (dialysis, kidney failure: 380; predialysis, chronic kidney disease [CKD]: 222) with AVF maturation ascertained for 535 (kidney failure, 353; CKD, 182) participants., Interventions: All clinical decisions regarding AVF management were deferred to the individual centers, but remedial interventions were discouraged within 6 weeks of creation., Main Outcomes and Measures: In this case series analysis, the primary outcome was unassisted maturation. Functional patency, freedom from intervention, and participant survival were summarized using Kaplan-Meier analysis., Results: Most participants evaluated (n = 535) were men (372 [69.5%]) and had diabetes (311 [58.1%]); mean (SD) age was 54.6 (13.6) years. Almost two-thirds of the AVFs created (342 of 535 [64%]) were in the upper arm. The AVF maturation rates for the kidney failure vs CKD participants were 29% vs 10% at 3 months, 67% vs 38% at 6 months, and 76% vs 58% at 12 months. Several participants with kidney failure (133 [37.7%]) and CKD (63 [34.6%]) underwent interventions to facilitate maturation or manage complications before maturation. The median time from access creation to maturation was 115 days (interquartile range [IQR], 86-171 days) but differed by initial indication (CKD, 170 days; IQR, 113-269 days; kidney failure, 105 days; IQR, 81-137 days). The functional patency for the AVFs that matured at 1 year was 87% (95% CI, 83.2%-90.2%) and at 2 years, 75% (95% CI, 69.7%-79.7%), and there was no significant difference for those receiving interventions before maturation. Almost half (188 [47.5%]) of the AVFs that matured had further intervention to maintain patency or treat complications., Conclusions and Relevance: The findings of this study suggest that AVF remains an accepted hemodialysis access option, although both its maturation and continued use require a moderate number of interventions to maintain patency and treat the associated complications.

Background: The first endovascular arteriovenous fistula (endoAVF) device (WavelinQ), a novel percutaneous technique of AVF creation, was approved by the Food and Drug Administration in 2018 and has been placed in a small number of United States patients on hemodialysis. It is unknown how often patients with advanced CKD have vascular anatomy suitable for WavelinQ creation. The goal of this study was to determine the proportion of patients with vascular anatomy suitable for WavelinQ creation and to assess patient characteristics associated with such suitability., Methods: All patients referred for vascular access placement at a large academic medical center underwent standardized preoperative sonographic vascular mapping to assess suitability for an AVF. During a 2-year period (March 2019 to March 2021), we assessed the suitability of the vessels for creation of WavelinQ. We then compared the demographic characteristics, comorbidities, and vascular mapping measurements between patients who were or were not suitable for WavelinQ., Results: During the study period, 437 patients underwent vessel mapping. Of these, 51% of patients were eligible for a surgical AVF, and 32% were eligible for a WavelinQ AVF; 63% of those suitable for a surgical AVF were also suitable for a WavelinQ AVF. Patients with a vascular anatomy suitable for WavelinQ were younger (age 55±15 versus 60±14 years, P =0.01) but similar in sex, race, diabetes, hypertension, coronary artery disease, and peripheral artery disease., Conclusions: Among patients with CKD with vascular anatomy suitable for a surgical AVF, 63% are also suitable for a WavelinQ endoAVF. Older patients are less frequently suitable for WavelinQ., Competing Interests: M. Allon reports consultancy agreements with CorMedix and scientific advisor or membership with the Kidney360 Editorial Board as Editor-in-Chief. M.L. Robbin reports research funding from Philips Medical and scientific advisor or membership with the Journal of Ultrasound in Medicine Editorial Board, the Radiology Editorial Board, and the Ultrasound Quarterly Editorial Board. R. Varma reports speakers bureau for Becton, Dickinson and Company. All remaining authors have nothing to disclose., (Copyright © 2022 by the American Society of Nephrology.)

Contrast-enhanced ultrasound has emerged as a useful imaging modality for the evaluation of the transplant kidney. Advantages over traditional imaging modalities such as computed tomography and magnetic resonance imaging include the ability to visualize a lesion's enhancement pattern in real time, the lack of nephrotoxicity, and relatively low cost. Potential uses of contrast-enhanced ultrasound include characterization of solid and cystic transplant renal masses, assessment for pyelonephritis and identification of its complications, and evaluation of transplant complications in immediate and delayed settings. Contrast-enhanced ultrasound will likely play an increasing role for evaluating the transplant kidney, as an accurate diagnosis based on imaging can direct treatment and prevent unnecessary interventions., (© 2020 by the American Institute of Ultrasound in Medicine.)

Thyroid ultrasound with gray-scale and color Doppler is the most helpful imaging modality to differentiate normal thyroid parenchyma from diffuse or nodular thyroid disease by evaluating glandular size, echogenicity, echotexture, margins, and vascularity. The various causes of diffuse thyroid disease often have overlapping sonographic imaging features. Thyroid nodules may be hyperplastic or neoplastic, with most due to benign hyperplastic changes in architecture and benign follicular adenomas; only a small percentage are malignant. A systematic approach to nodule morphology that includes evaluation of composition, echogenicity, margin, shape, and any echogenic foci can guide decision to biopsy or follow nodules., Competing Interests: Disclosure The authors have nothing to disclose., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Background Quantitative blood flow (QBF) measurements that use pulsed-wave US rely on difficult-to-meet conditions. Imaging biomarkers need to be quantitative and user and machine independent. Surrogate markers (eg, resistive index) fail to quantify actual volumetric flow. Standardization is possible, but relies on collaboration between users, manufacturers, and the U.S. Food and Drug Administration. Purpose To evaluate a Quantitative Imaging Biomarkers Alliance-supported, user- and machine-independent US method for quantitatively measuring QBF. Materials and Methods In this prospective study (March 2017 to March 2019), three different clinical US scanners were used to benchmark QBF in a calibrated flow phantom at three different laboratories each. Testing conditions involved changes in flow rate (1-12 mL/sec), imaging depth (2.5-7 cm), color flow gain (0%-100%), and flow past a stenosis. Each condition was performed under constant and pulsatile flow at 60 beats per minute, thus yielding eight distinct testing conditions. QBF was computed from three-dimensional color flow velocity, power, and scan geometry by using Gauss theorem. Statistical analysis was performed between systems and between laboratories. Systems and laboratories were anonymized when reporting results. Results For systems 1, 2, and 3, flow rate for constant and pulsatile flow was measured, respectively, with biases of 3.5% and 24.9%, 3.0% and 2.1%, and -22.1% and -10.9%. Coefficients of variation were 6.9% and 7.7%, 3.3% and 8.2%, and 9.6% and 17.3%, respectively. For changes in imaging depth, biases were 3.7% and 27.2%, -2.0% and -0.9%, and -22.8% and -5.9%, respectively. Respective coefficients of variation were 10.0% and 9.2%, 4.6% and 6.9%, and 10.1% and 11.6%. For changes in color flow gain, biases after filling the lumen with color pixels were 6.3% and 18.5%, 8.5% and 9.0%, and 16.6% and 6.2%, respectively. Respective coefficients of variation were 10.8% and 4.3%, 7.3% and 6.7%, and 6.7% and 5.3%. Poststenotic flow biases were 1.8% and 31.2%, 5.7% and -3.1%, and -18.3% and -18.2%, respectively. Conclusion Interlaboratory bias and variation of US-derived quantitative blood flow indicated its potential to become a clinical biomarker for the blood supply to end organs. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Forsberg in this issue.

Background: Preoperative ultrasound mapping is routinely used to select vessels meeting minimal threshold diameters for surgical arteriovenous fistula (AVF) creation but fails to improve AVF maturation rates. This suggests a need to reassess the preoperative ultrasound criteria used to optimize AVF maturation., Methods: We retrospectively identified 300 catheter-dependent patients on hemodialysis with a new AVF created between 2010 and 2016. We then evaluated the associations of preoperative vascular measurements and hemodynamic factors with unassisted AVF maturation (successful use for dialysis without prior intervention) and overall maturation (successful use with or without prior intervention). Multivariable logistic regression was used to identify preoperative factors associated with unassisted and overall AVF maturation., Results: Unassisted AVF maturation associated with preoperative arterial diameter (adjusted odds ratio [aOR], 1.50 per 1-mm increase; 95% confidence interval [95% CI], 1.23 to 1.83), preoperative systolic BP (aOR, 1.16 per 10-mm Hg increase; 95% CI, 1.05 to 1.28), and left ventricular ejection fraction (aOR, 1.07 per 5% increase; 95% CI, 1.01 to 1.13). Overall AVF maturation associated with preoperative arterial diameter (aOR, 1.36 per 1-mm increase; 95% CI, 1.10 to 1.66) and preoperative systolic BP (aOR, 1.17; 95% CI, 1.06 to 1.30). Using receiver operating curves, the combination of preoperative arterial diameter, systolic BP, and left ventricular ejection fraction was fairly predictive of unassisted maturation (area under the curve, 0.69). Patient age, sex, race, diabetes, vascular disease, obesity, and AVF location were not associated with maturation., Conclusions: Preoperative arterial diameter may be an under-recognized predictor of AVF maturation. Further study evaluating the effect of preoperative arterial diameter and other hemodynamic factors on AVF maturation is needed., (Copyright © 2020 by the American Society of Nephrology.)

Background: The utility of early postoperative ultrasound measurements in predicting arteriovenous fistula (AVF) clinical maturation is uncertain., Methods: We investigated the relationships of ultrasound parameters with AVF clinical maturation in newly created AVF, measured at 1 day and 2 and 6 weeks, in 602 participants of a multicenter, observational cohort study. A backward elimination algorithm identified ultrasound measurements that independently predicted unassisted and overall AVF maturation. Candidate variables included AVF blood flow, diameter, and depth, upper arm arterial diameter, presence of stenosis, presence of accessory veins, seven case-mix factors (age, sex, black race, AVF location, diabetes, dialysis status, and body mass index), and clinical center. We evaluated the accuracy of the resulting models for clinical prediction., Results: At each ultrasound measurement time, AVF blood flow, diameter, and depth each predicted in a statistically significant manner both unassisted and overall clinical maturation. Moreover, neither the remaining ultrasound parameters nor case-mix factors were associated with clinical AVF maturation after accounting for blood flow, diameter, and depth, although maturation probabilities differed among clinical centers before and after accounting for these parameters. The crossvalidated area under the receiver operating characteristic curve for models constructed using these three ultrasound parameters was 0.69, 0.74, and 0.79 at 1 day and 2 and 6 weeks, respectively, for unassisted AVF clinical maturation and 0.69, 0.71, and 0.76, respectively, for overall AVF maturation., Conclusions: AVF blood flow, diameter, and depth moderately predicted unassisted and overall AVF clinical maturation. The other factors considered did not further improve AVF maturation prediction., (Copyright © 2018 by the American Society of Nephrology.)

Background and Objectives: Postoperative ultrasound is commonly used to assess arteriovenous fistula (AVF) maturation for hemodialysis, but its utility for predicting unassisted AVF maturation or primary AVF patency for hemodialysis has not been well defined. This study assessed the predictive value of postoperative AVF ultrasound measurements for these clinical AVF outcomes., Design, Setting, Participants, & Measurements: We queried a prospective vascular access database to identify 246 patients on catheter-dependent hemodialysis who underwent AVF creation between 2010 and 2016 and obtained a postoperative ultrasound within 90 days. Multivariable logistic regression was used to evaluate the association of clinical characteristics and postoperative ultrasound measurements with unassisted AVF maturation. A receiver operating characteristic curve estimated the predictive value of these factors for unassisted AVF maturation. Finally, multivariable survival analysis was used to identify factors associated with primary AVF patency in patients with unassisted AVF maturation., Results: Unassisted AVF maturation occurred in 121 out of 246 patients (49%), assisted maturation in 55 patients (22%), and failure to mature in 70 patients (28%). Using multivariable logistic regression, unassisted AVF maturation was associated with AVF blood flow (odds ratio [OR], 1.30; 95% confidence interval [95% CI], 1.18 to 1.45 per 100 ml/min increase; P <0.001), forearm location (OR, 0.37; 95% CI, 0.08 to 1.78; P =0.21), presence of stenosis (OR, 0.45; 95% CI, 0.23 to 0.88; P =0.02); AVF depth (OR, 0.88; 95% CI, 0.77 to 1.00 per 1 mm increase; P =0.05), and AVF location interaction with depth (OR, 0.50; 95% CI, 0.28 to 0.84; P =0.02). The area under the receiver operating characteristic curve, using all these factors, was 0.84 (95% CI, 0.79 to 0.89; P <0.001). Primary AVF patency in patients with unassisted maturation was associated only with AVF diameter (hazard ratio, 0.84; 95% CI, 0.76 to 0.94 per 1 mm increase; P =0.002)., Conclusions: Unassisted AVF maturation is predicted by AVF blood flow, location, depth, and stenosis. AVF patency after unassisted maturation is predicted only by the postoperative AVF diameter., (Copyright © 2018 by the American Society of Nephrology.)

Background: Half of surgically created arteriovenous fistulas (AVFs) require additional intervention to effectively support hemodialysis. Postoperative care and complications may affect clinical maturation., Study Design: Hemodialysis Fistula Maturation (HFM) Study, a 7-center prospective cohort study., Setting & Participants: 491 patients with single-stage AVFs who had neither thrombosis nor AVF intervention before a 6-week postoperative ultrasonographic examination and who required maintenance hemodialysis., Predictors: Postoperative care processes and complications., Outcomes: Attempted cannulation, successful cannulation, and unassisted and overall clinical maturation as defined by the HFM Study criteria., Results: AVF cannulation was attempted in 443 of 491 (90.2%) participants and was eventually successful in 430 of these 443 (97.1%) participants. 263 of these 430 (61.2%) reached unassisted and 118 (27.4%) reached assisted AVF maturation (overall maturation, 381/430 [88.6%]). Attempted cannulation was less likely in patients of surgeons with policies for routine 2-week versus later-than-2-week first postoperative visits (OR, 0.21; 95% CI, 0.06-0.70), routine second postoperative follow-up visits (OR, 0.39; 95% CI, 0.15-0.97), and a routine clinical postoperative ultrasound (OR, 0.28; 95% CI, 0.14-0.55). Attempted cannulation was also less likely among patients undergoing procedures to assist maturation (OR, 0.51; 95% CI, 0.27-0.98). Unassisted maturation was more likely for patients treated in facilities with access coordinators (OR, 1.91; 95% CI, 1.17-3.12), but less likely after precannulation nonstudy ultrasounds (OR per ultrasound, 0.42 [95% CI, 0.26-0.68]) and initial unsuccessful cannulation attempts (OR per each additional attempt, 0.90 [95% CI, 0.83-0.98]). Overall maturation was less likely with infiltration before successful cannulation (OR, 0.44; 95% CI, 0.22-0.89). Among participants receiving maintenance hemodialysis before AVF surgery, unassisted and overall maturation were less likely with longer intervals from surgery to initial cannulation (ORs for each additional month of 0.81 [95% CI, 0.76-0.88] and 0.93 [95% CI, 0.89-0.98], respectively) and from initial to successful cannulation (ORs for each additional week of 0.87 [95% CI, 0.81-0.94] and 0.88 [95% CI, 0.83-0.94], respectively)., Limitations: Surgeons' management policies were assessed only by questionnaire at study onset. Most participants received upper-arm AVFs, planned 2-stage AVFs were excluded, and maturation time windows were imposed. Some care processes may have been missed and the observational design limits causal attribution., Conclusions: Multiple processes of care and complications are associated with AVF maturation outcomes., (Copyright © 2017 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.)

Liver lesions are often incidentally detected on ultrasound examination and may be incompletely characterized, requiring further imaging. Contrast-enhanced ultrasound (CEUS) was recently approved by the Food and Drug Administration in the United States for liver lesion characterization. CEUS has the ability to characterize focal liver lesions and has been shown to be superior to color Doppler and power Doppler ultrasound in the detection of tumor vascularity. Differentiating benign from malignant liver lesions is essential to characterizing liver lesions. The CEUS imaging characteristics of benign liver lesions are reviewed, including hepatic cysts, hemangiomas, focal fat, focal nodular hyperplasia, hepatocellular adenomas, abscesses, and traumatic lesions.

Computed tomography (CT) and magnetic resonance imaging (MRI) are two of the workhorse modalities of abdominopelvic radiology. However, these modalities are not without patient- and technique-specific limitations that may prevent a timely and accurate diagnosis. Contrast-enhanced ultrasound (CEUS) is an effective, rapid, and cost-effective imaging modality with expanding clinical utility in the United States. In this pictorial essay, we provide a case-based discussion demonstrating the practical advantages of CEUS in evaluating a variety of pathologies in which CT or MRI was precluded or insufficient. Through these advantages, CEUS can serve a complementary role with CT and MRI in comprehensive abdominopelvic radiology.

Purpose To assess the performance of computer-aided diagnosis (CAD) systems and to determine the dominant ultrasonographic (US) features when classifying benign versus malignant focal liver lesions (FLLs) by using contrast material-enhanced US cine clips. Materials and Methods One hundred six US data sets in all subjects enrolled by three centers from a multicenter trial that included 54 malignant, 51 benign, and one indeterminate FLL were retrospectively analyzed. The 105 benign or malignant lesions were confirmed at histologic examination, contrast-enhanced computed tomography (CT), dynamic contrast-enhanced magnetic resonance (MR) imaging, and/or 6 or more months of clinical follow-up. Data sets included 3-minute cine clips that were automatically corrected for in-plane motion and automatically filtered out frames acquired off plane. B-mode and contrast-specific features were automatically extracted on a pixel-by-pixel basis and analyzed by using an artificial neural network (ANN) and a support vector machine (SVM). Areas under the receiver operating characteristic curve (AUCs) for CAD were compared with those for one experienced and one inexperienced blinded reader. A third observer graded cine quality to assess its effects on CAD performance. Results CAD, the inexperienced observer, and the experienced observer were able to analyze 95, 100, and 102 cine clips, respectively. The AUCs for the SVM, ANN, and experienced and inexperienced observers were 0.883 (95% confidence interval [CI]: 0.793, 0.940), 0.829 (95% CI: 0.724, 0.901), 0.843 (95% CI: 0.756, 0.903), and 0.702 (95% CI: 0.586, 0.782), respectively; only the difference between SVM and the inexperienced observer was statistically significant. Accuracy improved from 71.3% (67 of 94; 95% CI: 60.6%, 79.8%) to 87.7% (57 of 65; 95% CI: 78.5%, 93.8%) and from 80.9% (76 of 94; 95% CI: 72.3%, 88.3%) to 90.3% (65 of 72; 95% CI: 80.6%, 95.8%) when CAD was in agreement with the inexperienced reader and when it was in agreement with the experienced reader, respectively. B-mode heterogeneity and contrast material washout were the most discriminating features selected by CAD for all iterations. CAD selected time-based time-intensity curve (TIC) features 99.0% (207 of 209) of the time to classify FLLs, versus 1.0% (two of 209) of the time for intensity-based features. None of the 15 video-quality criteria had a statistically significant effect on CAD accuracy-all P values were greater than the Holm-Sidak α-level correction for multiple comparisons. Conclusion CAD systems classified benign and malignant FLLs with an accuracy similar to that of an expert reader. CAD improved the accuracy of both readers. Time-based features of TIC were more discriminating than intensity-based features. © RSNA, 2017 Online supplemental material is available for this article.

Introduction: Arteriovenous fistulas (AVF) frequently fail to mature. Postoperative ultrasounds provide objective measurements to predict unassisted AVF use for hemodialysis (unassisted use) and guide interventions to salvage nonmaturing AVFs. The optimal ultrasound criteria to assess AVF maturation are uncertain. We analyzed data from a multicenter, randomized, controlled, clinical trial to compare 2 published ultrasound maturation criteria used to predict unassisted AVF use for hemodialysis., Methods: We retrospectively analyzed prospective data on 105 patients undergoing new AVF creation, who underwent standardized postoperative ultrasounds at 6 and 12 weeks to measure AVF diameter and blood flow. Unassisted AVF use was defined as successful cannulation for ≥90 days without requiring prior surgical or percutaneous interventions. Two ultrasound criteria were assessed: (i) National Kidney Foundation (NKF) Kidney Disease Outcome Quality Initiative criteria: AVF outflow vein lumen diameter ≥6 mm and blood flow ≥600 mL/min; and (ii) University of Alabama at Birmingham (UAB) criteria: AVF outflow vein lumen diameter ≥4 mm and blood flow ≥500 mL/min. Performance characteristics were calculated for both criteria., Results: Compared to the NKF criteria, the UAB criteria had a higher sensitivity (89 vs.68%), but a lower specificity (42 vs. 70%) for unassisted AVF use. For radiocephalic AVFs, the UAB criteria had higher sensitivity (86 vs. 46%) and lower specificity (58 vs. 83%). For brachiocephalic AVFs, both UAB and NKF had high sensitivity (90 and 80%) but low specificity (21 and 53%), respectively., Conclusions: Using the UAB ultrasound criteria would minimize unnecessary early interventions in AVFs likely to mature without an intervention, but would delay interventions in AVFs that are unlikely to mature. The UAB criteria may be preferred in patients receiving a radiocephalic AVF.

Intimal hyperplasia and stenosis are often cited as causes of arteriovenous fistula maturation failure, but definitive evidence is lacking. We examined the associations among preexisting venous intimal hyperplasia, fistula venous stenosis after creation, and clinical maturation failure. The Hemodialysis Fistula Maturation Study prospectively observed 602 men and women through arteriovenous fistula creation surgery and their postoperative course. A segment of the vein used to create the fistula was collected intraoperatively for histomorphometric examination. On ultrasounds performed 1 day and 2 and 6 weeks after fistula creation, we assessed fistula venous stenosis using pre-specified criteria on the basis of ratios of luminal diameters and peak blood flow velocities at certain locations along the vessel. We determined fistula clinical maturation using criteria for usability during dialysis. Preexisting venous intimal hyperplasia, expressed per 10% increase in a hyperplasia index (range of 0%-100%), modestly associated with lower fistula blood flow rate (relative change, -2.5%; 95% confidence interval [95% CI], -4.6% to -0.4%; P =0.02) at 6 weeks but did not significantly associate with stenosis (odds ratio [OR], 1.07; 95% CI, 1.00 to 1.16; P =0.07) at 6 weeks or failure to mature clinically without procedural assistance (OR, 1.07; 95% CI, 0.99 to 1.15; P =0.07). Fistula venous stenosis at 6 weeks associated with maturation failure (OR, 1.98; 95% CI, 1.25 to 3.12; P =0.004) after controlling for case mix factors, dialysis status, and fistula location. These findings suggest that postoperative fistula venous stenosis associates with fistula maturation failure. Preoperative venous hyperplasia may associate with maturation failure but if so, only modestly., (Copyright © 2017 by the American Society of Nephrology.)

Objectives: To determine the utility of contrast-enhanced ultrasound (US) for characterizing renal lesions that were indeterminate on prior imaging., Methods: This Institutional Review Board-approved retrospective diagnostic accuracy study evaluated all patients who underwent renal contrast-enhanced US examinations from 2006 to 2015 at our tertiary care hospital. We compared the number of lesions definitively characterized by contrast-enhanced US with the indeterminate lesions by prior imaging. The accuracy of contrast-enhanced US was compared with the final diagnosis by histologic examination and follow-up (mean, 3.63 years). Accuracy and agreement estimates were compared with the exact binomial distribution to assess statistical significance., Results: A total of 134 lesions were evaluated with contrast-enhanced US, and 106 were indeterminate by preceding computed tomography, magnetic resonance imaging, or US. Only the largest lesion per patient was included in analysis. A total of 95.7% (90 of 94) of the previously indeterminate lesions were successfully classified with contrast-enhanced US. The sensitivity was 100% (20 of 20; 95% confidence interval [CI], 83%-100%; P < .0001); specificity was 85.7% (18 of 21; 95% CI, 62%-97%; P = .0026); positive predictive value was 87.0% (20 of 23; 95% CI, 66%-97%; P = .0005); negative predictive value was 100% (18 of 18; 95% CI, 81%-100%; P < .001); and accuracy was 90.2% (37 of 41; 95% CI, 80%-98%; P < .0001)., Conclusions: Contrast-enhanced US has a high likelihood of definitively classifying a renal lesion that is indeterminate by computed tomography, magnetic resonance imaging, or conventional US., (© 2017 by the American Institute of Ultrasound in Medicine.)

Arteriovenous fistulas (AVFs) and arteriovenous grafts (AVGs) are the vascular accesses of choice for long-term hemodialysis. Strategies to establish and maintain functioning AVFs and AVGs are essential. In addition to clinical evaluation, ultrasound plays a critical role in the evaluation and maintenance of AVFs and AVGs. AVFs have a high rate of failure to mature which can be reliably diagnosed with ultrasound. Treatable etiologies of the failure to mature can often be diagnosed with ultrasound. Causes of secondary AVG failure can also be diagnosed with ultrasound and treated. AVGs have a relatively short functional life expectancy due to a high rate of AVG thrombosis. Ultrasound is a safe, noninvasive way to diagnose vascular stenosis in both AVFs and AVGs prior to thrombosis, potentially saving the access. Routine surveillance ultrasound of asymptomatic AVFs and AVGs is controversial with conflicting studies on its benefit. Routine surveillance ultrasound of AVFs and AVGs is not common practice., (© 2017 Wiley Periodicals, Inc.)

Arteriovenous fistula (AVF) maturation failure is the primary cause of dialysis vascular access dysfunction. To evaluate whether preoperative vascular functional properties predict postoperative AVF measurements, patients enrolled in the Hemodialysis Fistula Maturation Study underwent up to five preoperative vascular function tests (VFTs): flow-mediated dilation (FMD), nitroglycerin-mediated dilation (NMD), carotid-femoral pulse wave velocity, carotid-radial pulse wave velocity, and venous occlusion plethysmography. We used mixed effects multiple regression analyses to relate each preoperative VFT to ultrasound measurements of AVF blood flow rate and venous diameter at 1 day, 2 weeks, and 6 weeks after AVF placement. After controlling for AVF location, preoperative ultrasound measurements, and demographic factors (age, sex, race, and dialysis status), greater NMD associated with greater 6-week AVF blood flow rate and AVF diameter (per absolute 10% difference in NMD: change in blood flow rate =14.0%; 95% confidence interval [95% CI], 3.7% to 25.3%; P<0.01; change in diameter =0.45 mm; 95% CI, 0.25 to 0.65 mm; P<0.001). Greater FMD also associated with greater increases in 6-week AVF blood flow rate and AVF diameter (per absolute 10% difference in FMD: change in blood flow rate =11.6%; 95% CI, 0.6% to 23.9%; P=0.04; change in diameter =0.31 mm; 95% CI, 0.05 to 0.57 mm; P=0.02). None of the remaining VFT parameters exhibited consistent statistically significant relationships with both postoperative AVF blood flow rate and diameter. In conclusion, preoperative NMD and FMD positively associated with changes in 6-week AVF blood flow rate and diameter, suggesting that native functional arterial properties affect AVF development., (Copyright © 2016 by the American Society of Nephrology.)

The use of microbubble contrast greatly enhances the ability of ultrasound to delineate structures and therefore aid in diagnosis. Ultrasound microbubble contrast agents are composed of low-solubility gas encapsulated in a biomaterial shell. These agents use the physics of ultrasound imaging to effectively identify and characterize focal hepatic and renal lesions. Not only can contrast agents be used to evaluate multiple phases of lesion contrast enhancement, but ultrasound also allows for real-time study of enhancement patterns. The short half-life and intravascular location of the microbubbles allows for multiple, sequential administrations of contrast to observe enhancement of lesions in different sites. Furthermore, the ability to perform imaging without ionizing radiation and the lack of nephrotoxicity make contrast-enhanced ultrasound an ideal evaluation method for patients who need serial surveillance or in whom imaging options are severely limited because of renal insufficiency. These techniques are widely used in many countries for diagnostic radiological purposes; however, the lack of both Food and Drug Administration approval and reimbursement for noncardiac hospital-based imaging has delayed widespread use in the United States. Despite these limitations, continued research and innovations in ultrasound contrast make it essential to have a working knowledge of the typical enhancement patterns of frequently seen hepatic and renal lesions as these techniques offer an alternative option for contrast imaging.

Purpose: To assess the anatomic development of native arteriovenous fistula (AVF) during the first 6 weeks after creation by using ultrasonographic (US) measurements in a multicenter hemodialysis fistula maturation study., Materials and Methods: Each institutional review board approved the prospective study protocol, and written informed consent was obtained. Six hundred and two participants (180 women and 422 men, 459 with upper-arm AVF and 143 with forearm AVF) from seven clinical centers underwent preoperative artery and vein US mapping. AVF draining vein diameter and blood flow rate were assessed postoperatively after 1 day, 2 weeks, and 6 weeks. Relationships among US measurements were summarized after using multiple imputation for missing measurements., Results: In 55% of forearm AVFs (68 of 124) and 83% of upper-arm AVFs (341 of 411) in surviving patients without thrombosis or AVF intervention prior to 6 weeks, at least 50% of their 6-week blood flow rate measurement was achieved at 1 day. Among surviving patients without thrombosis or AVF intervention prior to week 2, 70% with upper-arm AVFs (302 of 433) and 77% with forearm AVFs (99 of 128) maintained at least 85% of their week 2 flow rate at week 6. Mean AVF diameters of at least 0.40 cm were seen in 85% (389 of 459), 91% (419 of 459), and 87% (401 of 459) of upper-arm AVFs and in 40% (58 of 143), 73% (104 of 143), and 77% (110 of 143) of forearm AVFs at 1 day, 2 weeks, and 6 weeks, respectively. One-day and 2-week AVF flow rates and diameters were used to predict 6-week levels, with 2-week prediction of 6-week measures more accurate than those of 1 day (flow rates, R(2) = 0.47 and 0.61, respectively; diameters, R(2) = 0.49 and 0.82, respectively)., Conclusion: AVF blood flow rate at 1 day is usually more than 50% of the 6-week blood flow rate. Two-week measurements are more predictive of 6-week diameter and blood flow than those of 1 day. US measurements at 2 weeks may be of value in the early identification of fistulas that are unlikely to develop optimally., ((©) RSNA, 2015 Online supplemental material is available for this article.)

Objective: For ultrasound, a wide variation is often observed among the number and sequence of images acquired for a particular examination type. Scanner-based protocols are preset pathways in the ultrasound machine that guide a sonographer through the required study images. These protocols can streamline image acquisition by improving consistency and efficiency of ultrasound examinations. This study evaluated whether implementation of scanner-based protocol-driven ultrasound improves efficiency by decreasing the scanning duration and number of images acquired., Materials and Methods: Retrospective evaluation of 437 carotid Doppler examinations, 395 complete abdominal ultrasound examinations with Doppler imaging, and 413 bilateral lower extremity venous Doppler examinations for deep venous thrombosis (DVT) performed by five sonographers before and after implementation of scanner-based protocol-driven ultrasound was performed. The scanning duration and number of images acquired for each study were recorded. Statistical analysis compared the scanning duration and number of images acquired before and after implementation of protocol-driven ultrasound. A p value of < 0.05 was considered significant., Results: A significant decrease in scanning duration occurred for both carotid Doppler ultrasound examinations (decrease by 12.4% [2.7 minutes], p < 0.0001) and complete abdominal ultrasound examinations with Doppler imaging (decrease by 7.5% [2.0 minutes], p = 0.0054) after implementation of protocol-driven ultrasound. The decrease in scanning duration was not significant for lower extremity DVT Doppler examinations (p = 0.4192). In addition, there was a significant decrease in the overall number of images obtained for all three types of studies., Conclusion: Scanner-based protocol-driven ultrasound is an effective method that streamlines image acquisition and significantly improves efficiency in an ultrasound department while ensuring consistency and adherence to accreditation guidelines.

Objectives: The purpose of this study was to determine whether preoperative sonographic evaluation of vascular diameters and calcification identifies patients at risk for immediate technical failure of thigh hemodialysis grafts., Methods: A retrospective analysis of 143 chronic hemodialysis patients who underwent thigh graft placement was performed. All patients underwent preoperative sonography to assess arterial and venous waveforms and vascular diameters. The degree of arterial calcification was assessed retrospectively. Patient characteristics and graft outcomes were examined. Statistical analyses were performed, with P< .05 considered clinically significant., Results: Sonography identified no or mild arterial calcification in 113 of 143 patients (79%) and moderate to severe calcification in 30 of 143 patients (21%). Primary surgical technical failure occurred in 23% of patients (7 of 30) with moderate to severe calcification, compared to 3.5% (4 of 113) of those with no or mild calcification (hazard ratio, 6.59; 95% confidence interval, 2.06-21.05; P = .002). Cumulative graft survival (time to permanent failure) was shorter in patients with moderate to severe arterial calcification (3-year graft survival, 37% versus 56%; hazard ratio, 2.32; 95% confidence interval, 1.48-6.69; P= .003) but was not significantly associated with venous (P= .82) or arterial (P = .43) diameters., Conclusions: Preoperative sonographic assessment of thigh vessel diameters and calcification can identify patients who may be at risk for immediate technical graft failure and decreased cumulative graft survival. The use of sonography as a screening examination may improve preoperative assessment and surgical planning of hemodialysis thigh grafts., (© 2015 by the American Institute of Ultrasound in Medicine.)

Background: Arteriovenous fistulas (AVFs) often fail to mature, but the mechanism of AVF nonmaturation is poorly understood. Arterial microcalcification is common in patients with chronic kidney disease (CKD) and may limit vascular dilatation, thereby contributing to early postoperative juxta-anastomotic AVF stenosis and impaired AVF maturation. This study evaluated whether preexisting arterial microcalcification adversely affects AVF outcomes., Study Design: Prospective study., Setting & Participants: 127 patients with CKD undergoing AVF surgery at a large academic medical center., Predictors: Preexisting arterial microcalcification (≥1% of media area) assessed independently by von Kossa stains of arterial specimens obtained during AVF surgery and by preoperative ultrasound., Outcomes: Juxta-anastomotic AVF stenosis (ascertained by ultrasound obtained 4-6 weeks postoperatively), AVF nonmaturation (inability to cannulate with 2 needles with dialysis blood flow ≥ 300mL/min for ≥6 sessions in 1 month within 6 months of AVF creation), and duration of primary unassisted AVF survival after successful use (time to first intervention)., Results: Arterial microcalcification was present by histologic evaluation in 40% of patients undergoing AVF surgery. The frequency of a postoperative juxta-anastomotic AVF stenosis was similar in patients with or without preexisting arterial microcalcification (32% vs 42%; OR, 0.65; 95% CI, 0.28-1.52; P=0.3). AVF nonmaturation was observed in 29%, 33%, 33%, and 33% of patients with <1%, 1% to 4.9%, 5% to 9.9%, and ≥10% arterial microcalcification, respectively (P=0.9). Sonographic arterial microcalcification was found in 39% of patients and was associated with histologic calcification (P=0.001), but did not predict AVF nonmaturation. Finally, among AVFs that matured, unassisted AVF maturation (time to first intervention) was similar for patients with and without preexisting arterial microcalcification (HR, 0.64; 95% CI, 0.35-1.21; P=0.2)., Limitations: Single-center study., Conclusions: Arterial microcalcification is common in patients with advanced CKD, but does not explain postoperative AVF stenosis, AVF nonmaturation, or AVF failure after successful cannulation., (Copyright © 2015 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.)