Ability of a phase shift US contrast agent to improve imaging of the main renal arteries

Effectiveness of contrast-enhanced duplex ultrasound for detecting renal artery stenosis: A systematic review

PURPOSE

Contrast-enhanced duplex ultrasound (CEUS) might be a useful tool to diagnosing renal artery stenosis (RAS). We amalgamated and reviewed the evidence assessing the diagnostic accuracy of CEUS on detecting RAS compared to angiography.

METHODS

This preregistered systematic review included studies that compared the presence of RAS via CEUS with angiography. Sources were searched in November 2022 and included Scopus, EMBASE, MEDLINE, CINAHL, and Academic Search Premier (n = 1717). The Quality Assessment of Diagnostic Studies 2 tool assessed study quality. Results are presented narratively.

RESULTS

The studies included (n = 11) had a total of 447 unique participants (193 females) and average age of 56 ± 9 years. Five of eleven studies investigated CEUS using SonoVue contrast agent and reported an average accuracy (91% ± 2%), sensitivity (91% ± 3%), specificity (90% ± 5%), negative predictive value (86% ± 6%), and positive predictive value (94% ± 1%) with all values >80%. The accuracy of CEUS using other types of contrast agent (n = 6), including Levovsit (n = 3/6), Definity (n = 1/6), perfienapent emulsion (n = 1/6), and perfluorocarbon-exposed sonicated dextrose albumin (n = 1/6) was mixed. These studies detected an average accuracy of 91 ± 11% (n = 2/3% > 80%), sensitivity of 98% ± 4%, (n = 3/3% > 80%), and specificity of 86% ± 10% (n = 2/3% > 80%). Included studies had generally low risk of bias and applicability concerns except for unclear flow and timing (n = 7/11) and applicability of patient selection (n = 4/11).

CONCLUSION

Despite being limited by the heterogeneity of included studies, our review indicates a high overall diagnostic accuracy for CEUS to detect RAS compared to angiography, with the largest evidence-base for SonoVue contrast. Radiologists and hospital decision makers should consider CEUS as an acceptable alternative to angiography.

Predictors of diagnostic success with renal artery duplex ultrasonography

BACKGROUND

Renal artery duplex ultrasonography (RA-DUS) is commonly used for the evaluation and follow-up of renal artery atherosclerotic disease. In a complete study, renal artery flow is evaluated from the vessel origin to the intraparenchymal branches. The quality of RA-DUS is in part technologist-dependent, but many factors may affect the ability to complete a diagnostic examination. This study evaluated the clinical and technical factors that predict the ability to obtain a complete RA-DUS examination.

METHODS

A prospective evaluation of all patients undergoing RA-DUS between July 2008 and February 2009 was performed. Factors such as patient age, gender, body mass index, technologists' years of experience, patient care setting (inpatient vs. outpatient), bedside examination, smoking before the examination, fasting status, and recent abdominal surgery were all recorded. Multivariate logistic regression analysis was performed. A p value of ≤ 0.05 was considered significant.

RESULTS

During the study period, 250 patients underwent RA-DUS (mean age: 59.9 ± 17.8 years, 57% [143] female). A total of 87 (35%) examinations were incomplete. This included nondiagnostic examinations which did not exhibit any segment of the renal artery. Factors that were associated with an incomplete examination included technologists' years of experience (OR = 0.92, p = 0.042), bedside examination (OR = 4.17, p = 0.016), and recent abdominal surgery (OR = 3.45, p = 0.047). Body mass index, fasting status, and smoking before the examination did not affect the ability to obtain a complete study.

CONCLUSIONS

One-third of the RA-DUS studies were classified as incomplete by the strict criteria used in this prospective study. An experienced ultrasound technologist is more likely to obtain a complete RA-DUS examination. Recent abdominal surgery and bedside examinations were predictive of a limited examination as well. Vascular laboratories should consider these factors when scheduling examinations so as to obtain complete RA-DUS studies, as well as improve the cost-effectiveness of resource utilization.

[Doppler US of the urinary system and renal vessels in normal and pathologic conditions]

The interest of Doppler ultrasound (US) in urinary tract investigation has dramatically increased during the past 10 years. It can provide useful diagnostic informations in pedicular and intrarenal vascular disorders, some medical nephropathies, in the assessment of renal tumors and urinary tract disorders including urolithiasis, acute obstruction and ureteral reflux. Recent technical improvements including the development of US contrast agents (microbubbles) have contributed to increase the diagnostic accuracy of the technique.

The contrast-enhanced Doppler ultrasound with perfluorocarbon exposed sonicated albumin does not improve the diagnosis of renal artery stenosis compared with angiography

There are no studies investigating the effect of the contrast infusion on the sensitivity and specificity of the main Doppler criteria of renal artery stenosis (RAS). Our aim was to evaluate the accuracy of these Doppler criteria prior to and following the intravenous administration of perfluorocarbon exposed sonicated albumin (PESDA) in patients suspected of having RAS. Thirty consecutive hypertensive patients (13 males, mean age of 57 +/- 10 years) suspected of having RAS by clinical clues, were submitted to ultrasonography (US) of renal arteries before and after enhancement using continuous infusion of PESDA. All patients underwent angiography, and haemodynamically significant RAS was considered when >or=50%. At angiography, it was detected RAS >or=50% in 18 patients, 5 with bilateral stenosis. After contrast, the examination time was slightly reduced by approximately 20%. In non-enhanced US the sensitivity was better when based on resistance index (82.9%) while the specificity was better when based on renal aortic ratio (89.2%). The predictive positive value was stable for all indexes (74.0%-88.0%) while negative predictive value was low (44%-51%). The specificity and positive predictive value based on renal aortic ratio increased after PESDA injection respectively, from 89 to 97.3% and from 88 to 95%. In hypertensives suspected to have RAS the sensitivity and specificity of Duplex US is dependent of the criterion evaluated. Enhancement with continuous infusion of PESDA improves only the specificity based on renal aortic ratio but do not modify the sensitivity of any index.

Renal imaging with ultrasound contrast: current status

The application of UCAs to the kidney is still in its infancy; however, there are several areas of great promise. UCAs may replace CT in complex renal cyst evaluation and follow-up, eliminating the need for costly CT scans with their attendant potential contrast nephrotoxicity. This approach may decrease patient and physician uncertainty and improve diagnostic confidence. The use of UCAs is likely to be clinically useful in the evaluation of the indeterminate small renal mass on CT or MR imaging. Another probable useful application will be in renal artery stenosis. Routine application of UCAs may increase the percentage of diagnostic examinations, increase diagnostic confidence, and decrease examination times. It also will likely become the first line of evaluation in pyelonephritis, and be useful in immediate assessment of residual tumor after radiofrequency ablation. Of course, substantial additional work needs to be performed in large groups of patients to prove this currently optimistic outlook.

Evaluation of the patients with renovascular hypertension after percutaneous revascularization by Doppler ultrasonography

OBJECTIVE

Evaluation of the effectiveness of percutaneous revascularization is based primarily on clinical criteria, and laboratory findings rather than direct investigation of luminal width. The purpose of this study was to evaluate the success of endovascular revascularization with serial Doppler ultrasound (US) examinations.

METHODS AND MATERIAL

19 patients (14 were atherosclerotic, five were with fibromuscular dysplasia) with suspected renovascular hypertension treated by percutaneous revascularization were included in a prospective study. Patients had 23 renal artery stenoses reducing the diameter by more than 50%. Doppler US examinations were performed before intervention, and 1 day, 3 and 6 months after intervention.

RESULTS

Initial revascularization was technically successful in 21 of 23 stenoses (91.3%) (18 PTRA, three stent placement). Hypertension was cured in five atherosclerotic and in five fibromuscular dysplasia (FMD) patients, and improved in four atherosclerotic patients. Residual stenosis was determined in six patients and the others were evaluated as normal by initial postprocedure Doppler US. As based on Doppler US, restenosis (>60%-narrowing) was depicted in four of six (66.6%) renal arteries with residual stenosis, and one of 15 (6.6%) normal renal arteries at 1 year. This difference in restenosis rates (residual stenosis vs. normal) was significant (P<0.05).

CONCLUSION

Positive predictor for recurrence was a residual renal artery stenosis documented by Doppler US 1 day after percutaneous revascularization in atherosclerotic cases.

Sonography in renovascular hypertension

OBJECTIVE

To familiarize practitioners with different sonographic manifestations of renal artery compromise and the sonographic techniques for renal artery imaging.

METHODS

Approximately 1500 examinations evaluating for renal artery disease are performed in our vascular laboratory every year. Most of the patients have the symptoms of hypertension (possibly related to renovascular etiology) and renal insufficiency. From our cumulative experience, the optimal scanning techniques are defined for each renal artery, for extrarenal versus intrarenal vascular evaluation, and for patients with different body habitus. We have also tabulated our technical success rate. Cases with sonographic evidence of renal artery compromise are identified. The validity, sensitivity, and specificity of different parameters are examined.

RESULTS

We achieve an approximately 75% to 80% success rate in obtaining technically adequate studies. We have not found the tardus-parvus waveform evaluation to be as valuable as direct interrogation of the renal artery.

CONCLUSIONS

Duplex/color Doppler sonography serves a vital role in the diagnosis of renal artery stenosis and occlusion; it has an excellent correlation with contrast-enhanced angiography. It is also used for intraoperative or postrevascularization surveillance to show evidence of recurring stenosis, thrombosis, and other complications.

Detection of renal artery stenosis: prospective comparison of captopril-enhanced Doppler sonography, captopril-enhanced scintigraphy, and MR angiography

OBJECTIVE

The objective of our study was to compare the value of captopril-enhanced Doppler sonography, captopril-enhanced renal scintigraphy, and gadolinium-enhanced MR angiography for detecting renal artery stenosis.

SUBJECTS AND METHODS

Forty-one patients with suspected renovascular hypertension were prospectively examined with captopril-enhanced Doppler sonography, captopril-enhanced renal scintigraphy, gadolinium-enhanced MR angiography, and catheter angiography. The sensitivity and specificity of each technique for detecting renal artery stenosis measuring 50% or greater and 70% or greater were compared using the McNemar test. Positive and negative predictive values were estimated for populations with 5% and 30% prevalence of renal artery stenosis. Kappa values for interobserver agreement were assessed for both gadolinium-enhanced MR angiography and catheter angiography.

RESULTS

For detecting renal artery stenosis measuring 50% or greater, the sensitivity of gadolinium-enhanced MR angiography (96.6%) was greater than that of captopril-enhanced Doppler sonography (69%, p = 0.005) and captopril-enhanced renal scintigraphy (41.4%, p = 0.001). No significant difference in specificity was observed among modalities. For renal artery stenosis measuring 50% or greater, positive and negative predictive values were respectively 62% and 86% for captopril-enhanced Doppler sonography, 49% and 76% for captopril-enhanced renal scintigraphy, and 53% and 98% for gadolinium-enhanced MR angiography. Interobserver agreement was high for both gadolinium-enhanced MR angiography (kappa = 0.829) and catheter angiography (kappa = 0.729).

CONCLUSION

Gadolinium-enhanced MR angiography is the most accurate noninvasive modality for detecting renal artery stenosis greater than or equal to 50%. The use of captopril-enhanced Doppler sonography in combination with gadolinium-enhanced MR angiography for identifying renal artery stenosis needs to be evaluated with a cost-effectiveness analysis.

Ultrasound contrast harmonic imaging of abdominal organs

Ultrasound contrast agents consist of microbubbles, which are the most effective acoustic backscatters. The interaction between the insonating ultrasound beam and the microbubbles is very complex and basic understanding of their behavior under various sound fields has been fundamental to the development of improved methods of visualizing and displaying the contrast agents. Although echo enhancers have been under development for a long time, their clinical applications have been limited to enhancing the Doppler signals in difficult cases. However, recent advances in harmonic imaging and the development of new tissue-specific contrast agents stand to broaden the scope of ultrasound diagnostic potential beyond simply rescuing failed Doppler examinations. This article reviews the current and potential applications of ultrasound contrast harmonic imaging in the abdomen.

Sonographic contrast agents in vascular imaging

The use of ultrasound contrast agents for peripheral vascular imaging has not been adapted widely worldwide and remains experimental in the United States. Nevertheless, there is considerable interest in contrast agents, because they potentially might offer substantial benefits for peripheral vascular imaging. This article reviews the status of ultrasound contrast agents. It includes a thorough discussion of the types of agents that are available or are under development and an assessment of the desirable properties of an ideal contrast agent. The interaction of these agents with ultrasound is considered next, including consideration of the advantages of harmonic imaging with contrast. Finally, the potential clinical benefits of contrast, as revealed by the authors experience and published data, are reviewed for a variety of cerebral, peripheral, and abdominal vascular applications. These include the carotid arteries, transcranial Doppler, extremity arteries and veins, the renal arteries, and hepatic vessels.

Imaging of renovascular hypertension: respective values of renal scintigraphy, renal Doppler US, and MR angiography

Renovascular hypertension affects 15%-30% of patients who have clinical criteria suggestive of renovascular disease. Noninvasive screening is crucial for patient selection prior to conventional angiography and renal revascularization. Renal scintigraphy has been reported to be sensitive for detection of renovascular hypertension, but some of its limitations (eg, in the setting of bilateral renal artery stenosis and renal failure) should be considered. Doppler ultrasonography (US) allows direct evaluation of the renal arteries as well as transrenal Doppler waveform analysis, but it remains operator dependent. Gadolinium-enhanced magnetic resonance (MR) angiography is becoming an excellent alternative to conventional angiography. The main limiting factors of this technique are inadequate visualization of segmental and accessory renal arteries as well as a tendency toward overestimation of stenoses. Given the high cost and low availability of MR angiography, scintigraphy and Doppler US should be considered the primary studies in screening for renovascular hypertension. MR angiography could be reserved for patients with inconclusive scintigraphic and Doppler US results, patients with high clinical suspicion of renovascular hypertension, and patients with a contraindication to conventional angiography.

Renal arteries in patients at risk of renal arterial stenosis: multicenter evaluation of the echo-enhancer SH U 508A at color and spectral Doppler US. Levovist Renal Artery Stenosis Study Group

PURPOSE

To assess SH U 508A in the diagnosis of suspected renal arterial stenosis by means of ultrasonography (US) and to confirm the safety of SH U 508A in a clinical setting.

MATERIALS AND METHODS

A randomized crossover study was performed in 198 patients from 14 European centers who were referred for renal arterial angiography because they were suspected of having renal arterial stenosis. All patients underwent nonenhanced and SH U 508A-enhanced Doppler US of the renal arteries. Doppler criteria included measurement of renal arterial peak systolic velocity (threshold, 1.4-2.0 m/sec) in all centers and renoaortic ratio (threshold, 3.0-3.5) in nine.

RESULTS

The number of examinations with successful results increased following enhanced Doppler US examination--160 (83.8%) compared with 122 (63.9%) with nonenhanced Doppler US (P = .001), including patients with obesity or renal dysfunction. Renal arterial stenosis (> or =50%) was detected at angiography in 72 patients. Results at enhanced Doppler US were in agreement with results at angiography more often than with results at nonenhanced Doppler US in the diagnosis or exclusion of renal arterial stenosis (P = .001). For patients examined with nonenhanced and enhanced Doppler US, sensitivity (80.0% and 83.7%, respectively) and specificity (80.8% and 83.6%, respectively) remained unchanged. There were no clinically important adverse events following use of SH U 508A.

CONCLUSION

In patients suspected of having renal arterial stenosis, SH U 508A increased the number of diagnostic renal arterial Doppler studies.

Duplex ultrasonography in assessing restenosis of renal artery stents

PURPOSE

To determine the accuracy and optimal threshold values of duplex ultrasonography (US) in assessing restenosis of renal artery stents.

METHODS

Twenty-four consecutive patients with 33 renal arteries that had previously been treated with placement of a Palmaz stent underwent duplex US prior to intraarterial digital subtraction angiography (DSA), which was the reference standard. Diagnostic accuracy of in-stent peak systolic velocity (PSV) and reno-aortic ratio (RAR = PSV renal stent/PSV aorta) in detecting > 50% in-stent restenosis were evaluated by the receiver operating characteristic curve. Sensitivity and specificity were determined using the optimal threshold values, and using published threshold values: RAR > 3.5 and in-stent PSV > 180 cm/sec.

RESULTS

Six examinations were technically inadequate. Nine stents had residual or restenosis > 50% at DSA. The two duplex parameters were equally accurate since areas under the curves were similar (0.943). With optimal threshold values of 226 cm/sec for PSV and 2.7 for RAR, sensitivities and specificities were 100% and 90%, and 100% and 84%, respectively. Using the published duplex criteria resulted in sensitivities and specificities of 100% and 74% for PSV, and 50% and 89% for RAR.

CONCLUSION

Duplex US is a sensitive modality for detecting in-stent restenosis if laboratory-specific threshold values are used.

Contrast-Enhanced Doppler Ultrasound of Renal Artery Stenosis: Prologue to a Promising Future

Over the past few years, there has been extensive research for a reliable, noninvasive, and nonionizing imaging method to screen for renal artery stenosis (RAS). Doppler ultrasound (US) is one of many modalities that have been evaluated for the detection of RAS. The lack of standardization in examination protocols and diagnostic criteria, as well as the wide differences in reported accuracy among different laboratories, however, have prevented universal acceptance of this technique as a reliable screening test for RAS. Recently, the introduction of US contrast agents has substantially expanded the potentials of color Doppler US. The use of microbubble echo enhancers in combination with harmonic Doppler imaging has been shown to improve diagnostic confidence by improving the operator's ability to visualize the renal arteries, and to significantly reduce the number of equivocal examinations. In addition, contrast-enhanced harmonic Doppler US can currently provide objective functional assessment of RAS through analysis of time-intensity renal enhancement curve. State-of-the-art contrast-enhanced Doppler US seems to have the potential to become a useful screening test for patients at risk from renovascular hypertension and a tool for follow-up of patients who undergo revascularization procedures.

Effect of US contrast agents on spectral velocities: in vitro evaluation

PURPOSE

To evaluate the effect of ultrasonographic (US) contrast agents on measurements of peak velocity with spectral Doppler US in stenotic and nonstenotic flow states.

MATERIALS AND METHODS

Nonpulsatile flow was established in a flow phantom with 0%, 50%, 75%, and 90% stenoses. SH U 508A, perflenapent emulsion, and perfluorohexane emulsion were the contrast agents evaluated. Before and after administration of each contrast agent, two peak velocity measurements obtained proximal to, at the site of, and distal to the stenosis in each vessel model were averaged. The percentage difference in peak velocity after contrast agent administration was calculated for each site interrogated. The mean, SD, and coefficient of variation of the percentage difference in peak velocity were calculated.

RESULTS

Percentage differences in peak velocity after contrast agent administration at different sample volume sites were not significantly different irrespective of the degree of stenosis or the contrast agent evaluated.

CONCLUSION

The contrast agents evaluated do not produce a statistically significant increase in peak velocity. If this result is corroborated in clinical practice, contrast agents can be used without reevaluating existing Doppler US thresholds for stenosis.

Imaging and stenting for renal artery stenosis

Renal artery stenosis is a potentially correctable cause of hypertension and renal failure, using endoluminal or, less commonly, surgical techniques. A number of imaging techniques can be used to diagnose renal artery stenosis, all with similar accuracy.

Contrast-enhanced magnetic resonance angiography of the renal arteries. Original investigation

RATIONALE AND OBJECTIVES

The authors determine the value of contrast-enhanced, three-dimensional (3D) magnetic resonance angiography (MRA) in the assessment of the renal arteries in comparison with conventional arteriography (CA).

METHODS

One hundred three patients (71 m, 32 f) were evaluated with both CA and 3D MRA. The 3D MRA data set consisted of 44 contiguous sections, acquired in apnea (23-28 seconds) using the following parameters: TR/TE 3.9/1.5 milliseconds, flip angle 40 degrees to 50 degrees, 3/4 k-space acquisition. A bolus of 0.3 mmol/kg BW gadolinium-DTPA was administered intravenously, using an automated injector. A test bolus method was used for timing of the bolus relative to the beginning of the data acquisition. Intra-arterial CA was used as the standard of reference in all patients. Separate interpretations of the CA and MRA results were made by two different pairs of radiologists, who were each blinded to the results of the other exam.

RESULTS

In all, 31 of 33 accessory renal arteries were correctly identified. All 205 main renal arteries were seen with MRA. Of 65 significant stenoses identified on CA, 61 were correctly identified and graded by MRA. Sensitivity and specificity values for the assessment of significant renal arterial lesions were 93% and 90%, respectively.

CONCLUSIONS

Breath-hold, contrast-enhanced 3D MRA allows for the reliable assessment of renal arterial morphology and pathologic states.