Renal artery stenosis: evaluation with conventional angiography versus gadolinium-enhanced MR angiography

Cortical and medullary oxygenation evaluation of kidneys with renal artery stenosis by BOLD-MRI

Aim

Blood oxygen level–dependent magnetic resonance imaging (BOLD-MRI) can measure deoxyhemoglobin content. This study aims to evaluate the capacity of BOLD-MRI, which is possible to evaluate the oxygenation state of kidneys with renal artery stenosis (RAS).

Materials and methods

We performed BOLD-MRI for 40 patients with RAS and for 30 healthy volunteers. We then performed post-scan processing and analysis of manually drawn regions of interest to determine R2* values (relaxation rates) for the renal cortex and medulla. We compared R2* values in patients with RAS with those in the control group, and also compared these values for subgroups with varying degrees of stenosis.

Results

Medulla R2* values were higher than cortex R2* values in the control group. There was no significant difference in R2* values for different segments (upper, middle, lower) of the kidneys. Both cortex and medulla R2* values in patients with RAS were significantly higher than corresponding R2* values in the control group (P < 0.05), and BOLD-MRI was more sensitive to changes in the R2* values in the medulla than in the cortex. Among different subgroups in the RAS group, the medulla R2* values were significantly higher in kidneys with severe stenosis than in those with no obvious obstruction, mild stenosis, or moderate stenosis (P < 0.05).

Conclusion

BOLD-MRI is an effective, noninvasive method for evaluating kidney oxygenation, which is important for proper treatment in RAS. It is sufficiently sensitive for detecting medulla ischemia and anoxia of the kidneys.

An augmented patient-specific approach to administration of contrast agent for CT renal angiography

Purpose

This hybrid retrospective and prospective study performed on 200 consecutive patients undergoing renal CTA, investigates the opacification of renal vasculature, radiation dose, and reader confidence.

Materials and Methods

100 patients were assigned retrospectively to protocol A and the other 100 were allocated prospectively to protocol B. Both protocols implemented a contrast material and saline flow rate of 4.5 mL/sec. Protocol A utilized a 100 mL of low-osmolar nonionic IV contrast material (Ioversol 350 mg I/mL) while protocol B employed a patient-tailored contrast media formula using iso-osmolar non-ionic (Iodixanol 320 mg I/mL).

Results

Arterial opacification in the abdominal aorta and in the bilateral main proximal renal arteries demonstrated no statistical significance (p>0.05). Only the main distal renal artery of the left kidney in protocol B was statistically significant (p<0.046). In the venous circulation, the IVC demonstrated a significant reduction in opacification in protocol B (59.39 HU ± 19.39) compared to A (87.74 HU ± 34.06) (p<0.001). Mean CNR for protocol A (22.68 HU ± 13.72) was significantly higher than that of protocol B (14.75 HU ± 5.76 p< 0.0001). Effective dose was significantly reduced in protocol B (2.46 ± 0.74 mSv) compared to A (3.07 ± 0.68 mSv) (p<0.001). Mean contrast media volume was reduced in protocol B (44.56 ± 14.32 mL) with lower iodine concentration. ROC analysis demonstrated significantly higher area under the ROC curve for protocol B (p< 0.0001), with inter-reader agreement increasing from moderate to excellent in renal arterial visualization.

Conclusion

Employing a patient-tailored contrast media injection protocol shows a significant refinement in the visualization of renal vasculature and reader confidence during renal CTA.

Multimodality imaging of fibromuscular dysplasia

OBJECTIVE

Fibromuscular dysplasia (FMD) is an uncommon non-inflammatory and non-atherosclerotic cause of arterial disease that may result in stenosis, tortuosity, aneurysm, or dissection. The clinical presentation depends on the vascular bed involved and ranges from asymptomatic to multisystem disease and end organ ischemia. The purpose of this article is to review the role of imaging in patients with FMD with an emphasis on renal FMD. The relevant epidemiology, histopathology, imaging techniques, and interpretation of images will be discussed.

CONCLUSION

Renal artery FMD requires a high index of suspicion for accurate and prompt diagnosis and implementation of appropriate therapy. The treatment will vary based on clinical presentation and distribution of involvement. Noninvasive imaging with duplex ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI) are reasonable alternatives for the depiction of FMD in comparison to catheter-directed angiography (CA). Patients with FMD are often treated by multispecialty practice including the interventional radiologist.

Contrast medium administration and image acquisition parameters in renal CT angiography: what radiologists need to know

Over the last decade, exponential advances in computed tomography (CT) technology have resulted in improved spatial and temporal resolution. Faster image acquisition enabled renal CT angiography to become a viable and effective noninvasive alternative in diagnosing renal vascular pathologies. However, with these advances, new challenges in contrast media administration have emerged. Poor synchronization between scanner and contrast media administration have reduced the consistency in image quality with poor spatial and contrast resolution. Comprehensive understanding of contrast media dynamics is essential in the design and implementation of contrast administration and image acquisition protocols. This review includes an overview of the parameters affecting renal artery opacification and current protocol strategies to achieve optimal image quality during renal CT angiography with iodinated contrast media, with current safety issues highlighted.

Ultrasound diagnostics of renal artery stenosis: Stenosis criteria, CEUS and recurrent in-stent stenosis

Background and purpose

As a non-invasive, side effect-free and cost-effective method, ultrasonography represents the method of choice for the diagnosis of renal artery stenosis. Four different criteria in total, including two direct criteria in peak systolic velocity (PSV) and renal aortic ratio (RAR) and two indirect criteria in resistance index (RI) and acceleration time (AT) for the measurement of relevant renal artery stenosis are described, each demonstrating highly variable accuracy in studies. Furthermore, there is controversy over the degree beyond which stenosis becomes therapeutically relevant and which ultrasound PSV is diagnostically relevant in terms of stenosis grading.

Material and methods

This article gives a critical review based on a selective literature search on measurement methodology and the validity of ultrasound in renal artery stenosis. A critical evaluation of methods and a presentation of measurement principles to establish the most precise measurement method possible compared with the gold standard angiography, as well as an evaluation of the importance of computed tomography angiography (CTA) and magnetic resonance angiography (MRA).

Results and conclusions

The PSV provides high sensitivity and specificity as a direct measurement method in stenosis detection and grading. Most studies found sensitivities and specificities of 85–90 % for > 50 % stenosis at a PSV > 180–200 cm/s in ROC curve analysis. Other methods, such as the ratio of the PSV in the aorta to the PSV in the renal artery (RAR) or indirect criteria, such as side to side differences in RI (dRI) or AT can be additionally used to improve accuracy. Contrast-enhanced ultrasound improves accuracy by means of echo contrast enhancement. Although in the past only high-grade stenosis was considered relevant for treatment, a drop in pressure of > 20 mmHg in > 50 % stenosis (PSV 180 cm/s) is classified as relevant for increased renin secretion. Stenosis in fibromuscular dysplasia can be reliably graded according to the continuity equation. Although the available studies on the grading of in-stent restenosis are the subject of controversy, there is a tendency to assume higher cut-off values for PSV and RAR. Whilst MRA and CTA demonstrate an accuracy of > 90 %, this is at the cost of possible side effects for patients, particularly in the case of pre-existing renal parenchymal damage.

Additional online material

This article includes two additional video sequences on visualizing renal artery stenosis. This supplemental material can be found under: dx.doi.org/10.1007/s00772-015-0060-3

The Role of Sonography in Renal Artery Stenosis Evaluation and Stent Placement

A literature review has been conducted to demonstrate the role of duplex sonography in evaluating renal artery stenosis (RAS) as a screening method for patients prior to percutaneous transluminal renal artery stent (PTRAS) placement. The review also evaluates the role of ultrasound surveillance following PTRAS and establishes the overall influence of ultrasound on defining stent efficacy for managing hemodynamically significant renovascular disease. Recent studies have narrowed criteria for intervention through duplex sonographic assessment of RAS to better predict patient benefit and response to stent placement. Studies using sonographic parameters evaluating patients for renal artery stenosis, criteria-dependent stent placement, and postintervention follow-up have shown improved patient response, helping ensure effective and appropriate care in RAS management.

Renal artery stenosis evaluation in chronic kidney disease patients: nonenhanced time-spatial labeling inversion-pulse three-dimensional MR angiography with regulated breathing versus DSA

PURPOSE

To evaluate the diagnostic performance of nonenhanced magnetic resonance (MR) angiographic flow-in technique with three-dimensional balanced steady-state free precession (SSFP) (flow-in balanced SSFP), compared with digital subtraction angiography (DSA) as reference standard, for assessment of renal artery stenosis (RAS) in chronic kidney disease (CKD) patients.

MATERIALS AND METHODS

Institutional review board approval and written informed consent were obtained for this prospective HIPAA-compliant study. Twenty-three patients, 13 men (mean age, 67.6 years ± 8.1 [standard deviation]; age range, 58-86 years) and 10 women (mean age 73.1 years ± 12.4; age range, 49-89 years), were evaluated with flow-in balanced SSFP and DSA. Coronal and axial flow-in balanced SSFP images were obtained with 1.5-T system, with regulated breathing (recorded voice instruction). The quality of flow-in balanced SSFP images was visually evaluated; the degree of stenosis was compared between flow-in balanced SSFP source images and DSA images by using the Wilcoxon signed-rank test. Correlation between images from both modalities was calculated as the Spearman rank-order correlation coefficient; bias was examined with Bland-Altman plots.

RESULTS

Diagnostic images were obtained in all patients. Flow-in balanced SSFP image quality was good in 87% (20 of 23) and moderate in 13% (three of 23) of patients. Forty-five renal arteries were included in the statistical analysis. Of 36 stenoses detected with flow-in balanced SSFP, 28 were relevant (degree of stenosis, ≥ 50%). The stenosis measurements of flow-in balanced SSFP were highly correlated (ρ = 0.91, P < .001) with those of DSA. The Bland-Altman plot showed a slight overestimation of the degree of stenosis (mean bias, 2.33% ± 11.95). The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of flow-in balanced SSFP relative to DSA for the diagnosis of a stenosis of 50% or greater were 93% (26 of 28), 88% (15 of 17), 93% (26 of 28), 88% (15 of 17), and 91% (41 of 45), respectively.

CONCLUSION

Flow-in balanced SSFP with regulated breathing is an appropriate nonenhanced MR angiographic technique for RAS assessment in CKD patients.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101422/-/DC1.

Imaging modalities for renal artery stenosis in suspected renovascular hypertension: prospective intraindividual comparison of color Doppler US, CT angiography, GD-enhanced MR angiography, and digital substraction angiography

The aim of the study was to evaluate the diagnostic accuracy of Color Doppler US, CT Angiography (CTA), and GD-enhanced MR Angiography (MRA) compared with digital subtraction angiography (DSA) for the detection of renal artery stenosis in patients with clinically suspected renovascular hypertension. Fifty-eight patients with suspected renovascular hypertension were enrolled in the study. All patients underwent Color Doppler US, CTA and GD-enhanced MRA. DSA was the gold standard method for the number of renal arteries, existence and degree of stenosis, or evidence of fibromuscular dysplasia. DSA depicted 132 renal arteries, 16 stenoses, and 4 arteries with fibromuscular dysplasia. Color Doppler US failed to detect 1 main and 14 polar arteries. CTA depicted all main renal arteries and 7/16 polar arteries, but failed to detect stenosis in two accessory vessels. Likewise, MRA did not detect stenotic accessory renal arteries, depicted 9/16 polar renal arteries, but missed two main renal arteries. All methods depicted the four main renal arteries with fibromuscular dysplasia. The overall sensitivity, specificity, and positive and negative predictive accuracy were 75%, 89.6%, 60% and 94.6%, respectively, for color Doppler US; 94%, 93%, 71%, and 99%, respectively, for CTA; and 90%, 94.1%, 75%, and 98%, respectively, for GD-enhanced MRA. CTA and GD-enhanced MRA have comparable and satisfactory results with respect to the negative predictive accuracy of the suspected renal artery stenosis. The concept of an imaging algorithm including US as screening test when appropriate and CTA or MRA as the second step-procedure is suggested. Therefore, DSA may be reserved for cases with major discrepancies or therapeutic interventions.

Renal artery stenosis evaluation: diagnostic performance of gadobenate dimeglumine-enhanced MR angiography--comparison with DSA

PURPOSE

To prospectively determine diagnostic performance and safety of contrast material-enhanced (CE) magnetic resonance (MR) angiography with 0.1 mmol per kilogram of body weight gadobenate dimeglumine for depiction of significant steno-occlusive disease (> or =51% stenosis) of renal arteries, with digital subtraction angiography (DSA) as reference standard.

MATERIALS AND METHODS

This multicenter study was approved by local institutional review boards; all patients provided written informed consent. Patient enrollment and examination at centers in the United States complied with HIPAA. Two hundred ninety-three patients (154 men, 139 women; mean age, 61.0 years) with severe hypertension (82.2%), progressive renal failure (11.3%), and suspected renal artery stenosis (6.5%) underwent CE MR angiography with three-dimensional spoiled gradient-echo sequences after administration of 0.1 mmol/kg gadobenate dimeglumine at 2 mL/sec. Anteroposterior and oblique DSA was performed in 268 (91.5%) patients. Three independent blinded reviewers evaluated CE MR angiographic images. Sensitivity, specificity, and accuracy of CE MR angiography for detection of significant steno-occlusive disease (> or =51% vessel lumen narrowing) were determined at segment (main renal artery) and patient levels. Positive and negative predictive values and positive and negative likelihood ratios were determined. Interobserver agreement was analyzed with generalized kappa statistics. A safety evaluation (clinical examination, electrocardiogram, blood and urine analysis, monitoring for adverse events) was performed.

RESULTS

Of 268 patients, 178 who were evaluated with MR angiography and DSA had significant steno-occlusive disease of renal arteries at DSA. Sensitivity, specificity, and accuracy of CE MR angiography for detection of 51% or greater stenosis or occlusion were 60.1%-84.1%, 89.4%-94.7%, and 80.4%-86.9%, respectively, at segment level. Similar values were obtained for predictive values and for patient-level analyses. Few CE MR angiographic examinations (1.9%-2.8%) were technically inadequate. Interobserver agreement for detection of significant steno-occlusive disease was good (79.9% agreement; kappa = 0.69). No safety concerns were noted.

CONCLUSION

CE MR angiography performed with 0.1 mmol/kg gadobenate dimeglumine, compared with DSA, is safe and provides good sensitivity, specificity, and accuracy for detection of significant renal artery steno-occlusive disease.

Chronic intestinal ischaemia: diagnosis

Chronic intestinal ischaemia is a relatively rare but very important clinical entity, which is caused by a reduction in the splanchnic blood flow, most often because of atherosclerosis. Intestinal angina is postprandial abdominal pain developing when the genuine and collateral vessels no longer are able to accommodate the postprandial increasing demand from the gastrointestinal tract and the liver. In addition, the clinical picture very often includes sitophobia and weight loss. In daily clinical practice, conventional angiography is considered as the gold standard, but ultra sonography, computerized tomography and magnetic resonance angiography are gaining momentum when investigating for chronic intestinal ischaemia. These methods depend on imaging of the stenotic vessels not taking into consideration the possibility of sufficient splanchnic perfusion in spite of severely stenotic or occluded vessels. Only a few papers address the physiological consequence of stenotic or occluded vessels - the lack of postprandial increase in splanchnic blood flow.

Multidetector-Row CT Angiography Diagnostic Sensitivity in Evaluation of Renal Artery Stenosis

PURPOSE

The aim of this study was to assess the image quality and interobserver agreement of various multidetector-row computed tomographic angiography postprocessing techniques in the diagnosis of renal artery stenosis (RAS).

MATERIALS AND METHODS

We studied 36 patients (21 men and 15 women; mean age, 49 years) who underwent computed tomography angiography to assess renal arteries for suspected RAS. Patients were analyzed by using a multidetector-row computed tomography. Computer tomographic scans were obtained after intravenous bolus administration of 110 to 140 mL of nonionic contrast material using a 4- to 6-mL/s flow rate. We assessed every patient by using axial scans, multiplanar reconstruction (MPR), maximum intensity projection (MIP), and volume rendering (VR) techniques. For each patient and for each reconstruction method, the image quality of the main renal artery was scored as 0 for bad-quality, 1 for poor-quality, 2 for good-quality, and 3 for excellent-quality images. Two radiologists reviewed computed tomographic images independently. We calculated interobserver agreement and kappa value. We correlated the stenosis degree observed by the 2 readers with the type of reconstruction used.

RESULTS

Overall number of renal arteries studied was 72, and we detected 24 RAS. Quality images obtained an overall (averaged between the 2 observers) value of 133 of 216, 163 of 216, and 145 of 216 for MPR, MIP, and VR, respectively. Our data underlined a statistical difference between MPR images and VR images (P < 0.001). Moreover, we noticed that the images classified as excellent were obtained from a vessel with 350 Hounsfield units or higher. Kappa value was good in MIP and VR methods evaluation but poor with the use of MPR.

CONCLUSIONS

Reformatting techniques usually provided a high visual impact, and in our study, MIP and VR showed the best diagnostic interobserver agreement in quality and reproducibility of stenosis degree.

Navigator-Gated MR Angiography of the Renal Arteries: A Potential Screening Tool for Renal Artery Stenosis

OBJECTIVE

The purpose of our study was to determine how well unenhanced navigator-gated steady-state free precession (Nav SSFP) MR angiography (MRA) performs as a screening test for the detection of renal artery stenosis.

SUBJECTS AND METHODS

Forty patients referred to rule out renal artery stenosis were imaged using an optimized Nav SSFP MRA sequence before conventional contrast-enhanced MRA (CE-MRA). Two radiologists evaluated Nav SSFP for maximum stenosis measurement, and comparison was made with CE-MRA results.

RESULTS

Fifteen of the 40 patients had greater than 50% renal artery stenosis as determined on CE-MRA. Sensitivity for detecting renal artery stenosis with Nav SSFP was 100%; specificity, 84%; negative predictive value, 100%; and positive predictive value, 79%. The average mean stenosis difference between Nav SSFP and CE-MRA was 10% +/- 9%.

CONCLUSION

Sensitivity and negative predictive value for the detection of renal artery stenosis using Nav SSFP were perfect, with an acceptable specificity of 84%. This suggests Nav SSFP is a promising technique for simple unenhanced screening for the detection of renal artery stenosis.

Efficacy and safety of gadodiamide (Gd-DTPA-BMA) in renal 3D-magnetic resonance angiography (MRA): a phase II study

PURPOSE

To determine the most efficacious dose of gadodiamide for three-dimensional (3D) contrast-enhanced (CE) magnetic resonance angiography (MRA) of the renal arteries on a patient level based on the sensitivity in detecting the main hemodynamically relevant (> or =50% or occlusion) renal artery stenosis (RAS) using intra-arterial digital subtraction angiography (IA DSA) as the gold standard.

MATERIALS AND METHODS

This prospective, randomized, double-blind, parallel-group, multicenter study included 273 patients referred to IA DSA for suspected RAS. Patients underwent 3D CE MRA after injection of 0.01, 0.05, 0.1, or 0.2mmol/kg of body weight gadodiamide (0.5mmol/ml). The images were assessed for location and degree of RAS by independent blinded readers (MRA: three readers, IA DSA: one reader). Hypothesis testing for a significant trend in sensitivity across dose groups was based on the one-sided Cochran-Armitage style trend test for each independent MRA reader.

RESULTS

The lowest dose group (0.01mmol/kg) proved non-efficacious in detecting hemodynamically relevant (i.e., > or =50% or occlusion) RAS. A statistically significant dose trend (p<0.001) was shown for each of the three independent readers. Depending on reader, the sensitivity obtained with 0.05, 0.1, and 0.2mmol/kg was 63.9-86.1%, 75.8-91.4% and 80.6-90.6%, the specificity was 66.7-73.9%, 59.3-75.0%, and 59.3-75.0% and accuracy was 67.8-78.9%, 75.4-77.4%, and 76.3-81.0%, for the three dose groups, respectively. There were eight non-severe adverse events (AEs). Three serious AEs occurring in one patient were judged not related to gadodiamide by the on-site investigator.

CONCLUSION

A significant dose trend between the four doses examined was observed. The lowest dose (0.01mmol/kg) differed significantly from those of the other three doses. Based on the analysis of the primary and secondary endpoints, 0.1mmol/kg gadodiamide appears to be the most suitable dose in diagnosing hemodynamically relevant RAS. The present study also demonstrated gadodiamide to be safe and well tolerated.

A multicenter, site-independent, blinded study to compare the diagnostic accuracy of contrast-enhanced magnetic resonance angiography using 1.0M gadobutrol (Gadovist™) to intraarterial digital subtraction angiography in body arteries

PURPOSE

Prospective evaluation of diagnostic accuracy of single field-of-view contrast-enhanced MR Angiography (ceMRA) with 1.0M gadobutrol compared to intraarterial DSA in body arteries.

MATERIALS AND METHODS

In an European multicenter study 179 patients underwent ceMRA and DSA. For each indication five prospectively defined vessel segments were evaluated by local investigators onsite and by three site-independent blinded readers (BR) independently.

RESULTS

The agreement between ceMRA and DSA diagnosis was statistically significant in the onsite (96.6%) and blinded reader (86.6-90.2%) evaluation. Sensitivity, specificity, accuracy, positive (PPV) and negative predictive values (NPV) for detection of relevant stenosis (>50%) were calculated for the right and left internal carotid arteries, and common and external iliac arteries: Sensitivity was 95-98% (onsite) and 76-96% (BR), specificity 94-96% (onsite) and 86-94% (BR), accuracy 96% (onsite) and 87-93% (BR), NPV 98-99% (onsite) and 84-98% (BR), and PPV 79-93% (onsite) and 44-91% (BR), respectively.

CONCLUSION

CeMRA of body arteries using 1.0M gadobutrol provides diagnostic information comparable to intraarterial DSA.

Gadobenate dimeglumine-enhanced MR angiography: Diagnostic performance of four doses for detection and grading of carotid, renal, and aorto-iliac stenoses compared to digital subtraction angiography

PURPOSE

To determine the diagnostic performance of contrast-enhanced MR angiography (CE-MRA) with four doses of gadobenate dimeglumine for detection of significant steno-occlusive disease of the carotid, renal, and pelvic vasculature.

MATERIALS AND METHODS

Eighty-four patients with suspected disease of the renal (n = 16), pelvic (n = 41), or carotid (n = 27) arteries underwent CE-MRA (3D-spoiled gradient-echo sequences) at 1.5T. CE-MRA was performed with gadobenate dimeglumine at 0.025, 0.05, 0.1, or 0.2 mmol/kg (23, 24, 19, and 18 patients, respectively) administered at 2 mL/sec. Accuracy, sensitivity, specificity, and positive and negative predictive values (PPV and NPV, respectively) for detection of significant disease (>50% stenosis or occlusion for renal/pelvic arteries; >70% stenosis or occlusion for carotid arteries) was determined by three fully blinded, independent radiologists using conventional digital subtraction angiography (DSA) as reference standard. All comparisons were tested statistically (ANOVA, chi-square, and Mantel-Haenszel tests as appropriate) and reader agreement (kappa) was assessed.

RESULTS

Values for accuracy, sensitivity, specificity, PPV, and NPV on CE-MRA were consistently higher for 0.1 mmol/kg gadobenate dimeglumine (accuracy = 95.2-97.3%, sensitivity = 84.2% (all readers), specificity = 96.9-99.2%, PPV = 80.0-94.1%, NPV = 97.6-97.7%). The greater accuracy of the 0.1 mmol/kg dose was significant (P < 0.01, all readers) compared to all other dose groups. Agreement between the three readers was good for all dose groups (kappa >/=0.58), with the highest percent agreement (85.7%) noted for the 0.1 mmol/kg dose.

CONCLUSION

Significantly better diagnostic performance on CE-MRA of the renal, pelvic, and carotid arteries is achieved with a gadobenate dimeglumine dose of 0.1 mmol/kg bodyweight.

Steady-state free precession MRA of the renal arteries: Breath-hold and navigator-gated techniques vs. CE-MRA

PURPOSE

To explore the use of breath-hold and navigator-gated noncontrast Steady State Free Precession (SSFP) MR angiography (MRA) protocols for the evaluation of renal artery stenosis (RAS).

MATERIALS AND METHODS

Twenty patients referred to rule out RAS were imaged using two breath-hold and one navigator-gated SSFP MRA sequences. All patients underwent contrast-enhanced MRA (CE-MRA). Two radiologists evaluated all sequences both qualitatively (blur, artifacts, reader confidence) and quantitatively (maximum stenosis). Using CE-MRA as truth, a receiver operating characteristics (ROC) curve was generated and a statistical analysis of navigator-gated SSFP (Nav SSFP) was performed.

RESULTS

Seven patients had >50% renal artery stenosis by CE-MRA. Nav SSFP performed significantly better than either breath-hold SSFP technique in terms of blur, artifacts, and reader confidence. Using a 50% threshold for stenosis, sensitivity for detecting RAS was 100%, with a specificity of 85% and a negative predictive value of 100%. The average mean stenosis difference between Nav SSFP and CE-MRA was 9 +/- 9%.

CONCLUSION

Nav SSFP outperformed breath-hold SSFP in measures of image quality and reader confidence. Sensitivity and negative predictive value for detecting RAS with Nav SSFP was perfect, with an acceptable specificity of 85%. This suggests further study is warranted to evaluate Nav SSFP as a noncontrast screening technique for renal artery stenosis.

Fibromuscular Dysplasia of the Main Renal Arteries: Comparison of Contrast-enhanced MR Angiography with Digital Subtraction Angiography

PURPOSE

To retrospectively evaluate the sensitivity and specificity of contrast material-enhanced magnetic resonance (MR) angiography by using digital subtraction angiography as the reference standard in patients with hypertension and renal artery fibromuscular dysplasia (FMD).

MATERIALS AND METHODS

Institutional review board approval was obtained, with waiver of informed consent. The results of renal contrast-enhanced MR angiography were retrospectively analyzed in 25 patients with hypertension (24 women, one man; mean age, 48 years +/- 19 [standard deviation]; age range, 18-72 years) who had FMD diagnosed on the basis of clinical and angiographic features. All examinations were performed at 1.5 T. Results were analyzed by two readers, and a third reader established a consensus in case of discrepancy. Sensitivity, specificity, and 95% confidence intervals (CIs) were calculated for FMD and for each possible type of FMD lesion ("string of pearls" appearance, stenosis, and aneurysm). A linear-weighted kappa statistic was calculated to determine agreement between digital subtraction angiography and contrast-enhanced MR angiography for the diagnosis of FMD and to determine inter- and intraobserver agreement regarding FMD diagnosis.

RESULTS

Fifty main renal arteries were analyzed, 35 of which demonstrated abnormal arteriographic features of FMD (stenosis, 22 arteries; string of pearls, 21 arteries; and aneurysm, four arteries). The sensitivity and specificity of contrast-enhanced MR angiography for the diagnosis of FMD were 97% (95% CI: 83%, 100%) and 93% (95% CI: 66%, 100%), respectively. Sensitivity was 68% (95% CI: 83%, 100%), 95% (95% CI: 74%, 100%), and 100% (95% CI: 40%, 100%) for the diagnosis of stenosis, string of pearls, and aneurysm, respectively. Linear-weighted kappa statistics for inter- and intraobserver agreement regarding FMD diagnosis were 0.63 and 0.92, respectively.

CONCLUSION

In patients with renal FMD, contrast-enhanced MR angiography can reliably facilitate diagnosis by demonstrating characteristic lesions.

Utilizing SENSE to reduce scan duration in high-resolution contrast-enhanced renal MR angiography

PURPOSE

To evaluate the use of sensitivity encoding (SENSE) to reduce scan time and decrease detrimental artifacts arising from motion and bolus profile effects during contrast-enhanced MR angiography (CE-MRA) of the renal arteries (RAs).

MATERIALS AND METHODS

A direct comparison of conventional and SENSE (acceleration factor 2) CE-MRA protocols was performed on 20 patients. Each patient underwent both scans. Both protocols achieved the same resolution, but the SENSE protocol was 50% faster and utilized a faster injection than the conventional scan. Three radiologists graded the images for image quality, artifact levels, and reader confidence.

RESULTS

While the signal-to-noise ratio (SNR) decreased (26+/-5 vs. 30+/-10; P=0.04) with the SENSE protocol, the image-quality scores for four identified segments of the RAs increased or were unchanged. The largest improvements in image quality occurred in the more distal segments of the RAs. Parenchymal ringing (P=0.005) and RA blurring (P=0.006) were significantly reduced, and there was a trend toward improvement of RA ringing despite the increased injection rate.

CONCLUSION

The faster SENSE scan maintained nearly the same SNR (due to faster injection of Gd-chelate), reduced artifact levels, and improved image quality ratings for the distal renal vessels.

Functional magnetic resonance imaging in renal artery stenosis

Renal artery stenosis (RAS) is the leading cause of secondary hypertension. Magnetic resonance (MR) imaging and in particular MR angiography have evolved into important diagnostic tools for the detection and grading of RAS due to the lack of ionizing radiation and nephrotoxic contrast agent. This review describes state-of-the-art MR angiographic techniques and introduces the reader to current concepts of RAS grading with MR angiography. We compare MR angiography with conventional angiography and intravascular ultrasound as a standard of reference. The technical basis of functional imaging techniques such as arterial spin labeling perfusion measurements, contrast-enhanced perfusion measurements, and MR flow measurements are explained. Their value for the grading and detection of RAS and for the differentiation of renovascular from renal parenchymal disease is discussed. An overview about imaging during and after interventional therapy of RAS and an introduction to the current understanding of prediction of successful interventional therapy finishes this review.

Update of renal imaging

Significant technical improvements have allowed the use of radiological techniques to play a growing role in the imaging of renal diseases. Noninvasive ultrasound methods (ie, sonography and Doppler) are now positioned as first-line methods for the evaluation of renovascular diseases. Multidetector computed tomography is able to provide high spatial resolution images of the kidneys and renal arterial vessels. Magnetic resonance imaging, which provides higher signal-to-noise ratio and higher spatial and/or temporal resolution, can display both morphological information about renal parenchyma and vessels and functional data, including perfusion, filtration, diffusion, or oxygenation. In renovascular diseases, these techniques have the potential to drive new strategies, including Doppler sonography as a first-line method, followed by computed tomography angiography or magnetic resonance angiography, depending mainly on renal function. Imaging of parenchymal renal diseases is developing toward more quantitative (volumetric and functional measurements) and more specific (through in vivo cell targeting) acquisitions for obtaining the adequate information on tissue characteristics relevant either for diagnosis or for prognosis or treatment follow-up.

Renal blood flow measurements with use of phase-contrast magnetic resonance imaging: normal values and reproducibility

PURPOSE

To assess the validity and the direct, short-term, and long-term reproducibility of renal blood flow (RBF) measurements with phase-contrast (PC) magnetic resonance (MR) imaging.

MATERIALS AND METHODS

In 20 healthy volunteers, RBF measurements were repeated with and without repositioning. Internal validity was assessed by comparing the total RBF with the difference in aortic flow above and below the renal arteries. In 19 healthy volunteers, RBF measurements were performed at two different occasions. In 40 healthy volunteers, RBF measurements were performed to assess normal values as a function of age. Analyses were performed according to Bland and Altman.

RESULTS

The technical success rate ranged from 78% to 85%. Total RBF and the difference in aortic flow rates showed good agreement (Pearson correlation coefficient, 0.72; P = .002). Directly repeated measurements had a mean difference of 54 mL/min in total RBF with a coefficient of variation (CV) of 17%. For repeated measurements with repositioning, the mean difference in total RBF was 74 mL/min (CV, 23%). Repeated measurements on different occasions showed a CV of 20%. The mean total RBF of the 40 healthy volunteers was 838 mL/min +/- 244 (SD).

CONCLUSIONS

RBF measurement with PC MR has a success rate greater than 75%. The demonstrated internal reliability of this method and fair reproducibility of the flow parameters is crucial for further studies of the renal artery with MR imaging.

Contrast-enhanced MR angiography and digital subtraction angiography in living renal donors: diagnostic agreement, impact on decision making, and costs

OBJECTIVE

The objective of our study was to evaluate the diagnostic agreement, the impact on decision making, and the costs of contrast-enhanced MR angiography and digital subtraction angiography in the workup of living renal donors.

CONCLUSION

Contrast-enhanced MR angiography for the preoperative evaluation of renal donors is superior to digital subtraction angiography in revealing vascular anomalies and depicting parenchymal abnormalities and is less costly; furthermore, it does not lead to preoperative decisions that differ from those based on digital subtraction angiography. If contrast-enhanced MR angiography does not provide sufficient information to make a confident decision, an additional digital subtraction angiography examination should be performed.

High-Spatial-Resolution MR Angiography of Renal Arteries with Integrated Parallel Acquisitions: Comparison with Digital Subtraction Angiography and US

PURPOSE

To retrospectively compare three-dimensional gadolinium-enhanced magnetic resonance (MR) angiography, performed with an integrated parallel acquisition technique for high isotropic spatial resolution, with selective digital subtraction angiography (DSA) and intravascular ultrasonography (US) for accuracy of diameter and area measurements in renal artery stenosis.

MATERIALS AND METHODS

The study was approved by the institutional review board, and consent was obtained from all patients. Forty-five patients (17 women, 28 men; mean age, 62.2 years) were evaluated for suspected renal artery stenosis. Three-dimensional gadolinium-enhanced MR angiograms were acquired with isotropic spatial resolution of 0.8 x 0.8 x 0.9 mm in 23-second breath-hold with an integrated parallel acquisition technique. In-plane diameter of stenosis was measured along vessel axis, and perpendicular diameter and area of stenosis were assessed in cross sections orthogonal to vessel axis, on multiplanar reformations. Interobserver agreement between two radiologists in measurements of in-plane and perpendicular diameters of stenosis and perpendicular area of stenosis was assessed with mean percentage of difference. In a subset of patients, degree of stenosis at MR angiography was compared with that at DSA (n = 20) and intravascular US (n = 11) by using Bland-Altman plots and correlation analyses.

RESULTS

Mean percentage of difference in stenosis measurement was reduced from 39.3% +/- 78.4 (standard deviation) with use of in-plane views to 12.6% +/- 9.5 with use of cross-sectional views (P < .05). Interobserver agreement for stenosis grading based on perpendicular area of stenosis was significantly better than that for stenosis grading based on in-plane diameter of stenosis (mean percentage of difference, 15.2% +/- 24.2 vs 54.9% +/- 186.9; P < .001). Measurements of perpendicular area of stenosis on MR angiograms correlated well with those on intravascular US images (r(2) = 0.90).

CONCLUSION

Evaluation of cross-sectional images reconstructed from high-spatial-resolution three-dimensional gadolinium-enhanced MR renal angiographic data increases the accuracy of the technique and decreases interobserver variability.

The limitations of magnetic resonance angiography in the diagnosis of renal artery stenosis: Comparative analysis with conventional arteriography

PURPOSE

Gadolinium-enhanced magnetic resonance angiography (MRA) is commonly used as a screening modality for the detection of renal artery stenosis. However, evidence supporting its utility in clinical practice is lacking; few rigorous studies have compared MRA with contrast arteriography (CA). After making anecdotal clinical observations that MRA sometimes overestimated the degree of renal artery stenosis, we decided to determine the interobserver variability, sensitivity, specificity, and diagnostic accuracy of MRA compared with CA.

METHODS

From September 1999 to April 2003, we evaluated 68 renal arteries in 34 patients with clinically suspected renal artery stenosis using both MRA and CA. All studies were independently reviewed by four blinded observers. Renal arteries were categorized by MRA as normal, <50%, and >50% stenosis/occlusion. The sensitivity, specificity, and accuracy of MRA detection of renal artery stenosis were compared to CA as the gold standard. Interobserver variability (kappa) was also calculated.

RESULTS

MRA demonstrated 87% sensitivity, 69% specificity, 85% accuracy, 95% negative predictive value, and 51% positive predictive value for the diagnosis of renal artery stenosis. Interobserver agreement was moderate for MRA (kappa = 0.53) and good for CA (kappa = 0.76). In 21 arteries (31%), MRA was falsely positive.

CONCLUSIONS

In patients with a high clinical suspicion of renal artery stenosis, MRA is 87% sensitive in the detection of >50% stenosis. However, MRA is relatively nonspecific compared with CA and results in significant overestimation of renal artery stenosis in nearly one third of patients. To reduce unnecessary CA, clinicians should consider supplemental studies.

Contrast-enhanced MR Angiography of the renal arteries: blinded multicenter crossover comparison of gadobenate dimeglumine and gadopentetate dimeglumine

PURPOSE

To prospectively and intraindividually compare 0.1 mmol/kg gadobenate dimeglumine with 0.2 mmol/kg gadopentetate dimeglumine for contrast material-enhanced magnetic resonance (MR) angiography of the renal arteries.

MATERIALS AND METHODS

Institutional review board approval was granted by each of three participating centers. The study accorded with international standards for good clinical practice and Declaration of Helsinki and subsequent amendments. Patients gave written informed consent before enrollment. Patients (n = 34) underwent two MR angiographic examinations more than 48 hours but less than 12 days apart. Gadobenate dimeglumine followed by gadopentetate dimeglumine was administered in 18 patients; the order of administration was reversed in 16 patients. A 1.5-T MR imager was used with a phase-encoded three-dimensional spoiled breath-hold pulse sequence. Two blinded independent readers qualitatively assessed randomized subtracted maximum intensity projection images. A three-point scale for diagnostic quality (0, poor; 1a or 1p, moderate; and 2a or 2p, adequate [a and p refer, respectively, to absence and presence of vascular lesions]) was used to score each of nine segments of the abdominal aorta and both renal arteries (possible overall score, 18). Quantitative assessment (vessel signal-to-noise ratio [SNR], vessel-muscle contrast-to-noise ratio [CNR]) of source images was performed for regions of interest in supra-, juxta-, and infrarenal aorta segments and psoas muscle. Data were tested with analysis of variance for two-period crossover design. Interreader agreement was evaluated with Cohen kappa statistics.

RESULTS

No difference in mean image quality between the two contrast agents was observed; scores for gadobenate dimeglumine and gadopentetate dimeglumine were 15.15 and 15.23 for reader 1 and 16.77 and 17.01 for reader 2. The order of contrast material administration likewise produced no quality differences: readers 1 and 2 reported scores of 14.4 +/- 4.2 (standard deviation) and 16.7 +/- 2.3, respectively, when gadobenate dimeglumine was given first, and 15.2 +/- 1.8 and 16.6 +/- 1.6, respectively, when gadopentetate dimeglumine was given first. Results of quantitative evaluation showed increasing SNR and CNR with gadobenate dimeglumine in segments at progressively lower levels of the aorta, but increases in SNR and CNR at the infrarenal aorta (48.3 vs 40.6 and 44.2 vs 36.4, respectively) were not significant (P = .05 for both).

CONCLUSION

Gadobenate dimeglumine at a dose of 0.1 mmol/kg is comparable to gadopentetate dimeglumine at 0.2 mmol/kg for contrast-enhanced renal MR angiography.

Renal MR angiography

The high accuracy of renal MR angiography makes it well suited for diagnosing renal vascular disease. A comprehensive examination includes three-dimensional gadolinium MR angiography to assess lumenal anatomy and functional techniques to assess the hemodynamic significance of any stenosis identified. Postprocessing is critical to provide reformations, maximum intensity projections, and optional volume-rendered images to display arteries in an angiographic format for optimal demonstration of any vascular lesions. It is important to review source images to avoid missing pathologic findings. As MR imaging continues to develop, the renal MR angiography examination will likely expand to include extensive functional information about creatinine clearance, flow, and response to pharmacologic agents as well as spectroscopy, diffusion, perfusion, phase contrast, and other techniques.

Gadopentetate dimeglumine-enhanced three-dimensional MR-angiography: dosing, safety, and efficacy

Noninvasiveness, inherent three-dimensionality allowing reformations in any desired plane, and safe contrast agents, coupled with high diagnostic accuracy have driven the rise in popularity of contrast-enhanced MR angiography (CE-MRA) within the medical community. Reflecting its dominant market share as a paramagnetic contrast agent, gadopentetate dimeglumine (Gd-DTPA) has been used for the majority of clinically-performed MRA exams. Over the period January 1994 to February 2002, a total of 172 original studies describing the use of gadolinium-enhanced MRA in more than three human subjects were identified. Of these, 117 described the use of Gd-DTPA as the contrast agent for MRA. A total of 4046 subjects who received Gd-DTPA for MRA are described in these studies. Analysis of these data demonstrate Gd-DTPA to be a safe contrast agent for MRA when applied in a dose ranging from 0.1 to 0.3 mmol/kg of bodyweight. The documented clinical results show Gd-DTPA to be efficacious in the assessment of the arterial system. The effectiveness of Gd-DTPA-enhanced MRA extends beyond the detection, localization, and characterization of arterial disease, and encompasses choice and planning of appropriate therapy, as well as evaluation of therapeutic effectiveness.

Magnetic resonance angiography for preoperative evaluation of potential kidney donors1

BACKGROUND

Careful evaluation of the renovascular anatomy for living kidney donors is essential to optimize donor and recipient outcomes. Arteriography has been the standard for delineating the renovascular anatomy. However, this procedure is invasive. Magnetic resonance angiography (MRA) is an attractive, noninvasive alternative. The aim of this study was to evaluate the accuracy of MRA in potential living kidney donors.

METHODS

A retrospective comparison of the preoperative MRA results with the intraoperative anatomy was performed in 189 living kidney donors.

RESULTS

MRA interpretations correctly identified the vascular anatomy of the donor kidneys in 173 donors (91.5%). In the remaining 16 patients (8.5%), the MRA interpretation was inaccurate. In 10 patients, the MRA reported fewer arteries than the number encountered during the donor operation, whereas in six patients MRA reported more arteries than what found during operation. In seven patients, MRA supplied additional important anatomical information, including kidney size disparity, the presence of nephrolithiasis, the presence of a renal cyst, and renal artery stenosis. All kidneys were successfully transplanted. The misinterpretation of the MRA did not adversely affect the recipient outcome.

CONCLUSION

The noninvasive MRA evaluation of donor renovascular anatomy is an acceptable substitute for traditional angiography.

MR techniques for renal imaging

This article describes the principles, attributes, and pitfalls of the many MR imaging approaches available for assessment of renal-related disorders. Tables 1 and 2 summarize the specific approach and rationale.

Renal MR angiography: current debates and developments in imaging of renal artery stenosis

Because of its safety and robustness with reproducible image quality, three-dimensional gadolinium-enhanced magnetic resonance angiography (3D-Gd-MRA) has been widely established as a diagnostic tool for screening and grading of renal artery stenosis. Accuracy and superiority over other noninvasive imaging procedures was again demonstrated in two recent meta-analyses. However, ambiguous results on the accuracy of this technique have been reported recently, again questioning the sole role of this modality for diagnostic assessment of the renal arteries. The main deficiencies of the technique are limited spatial resolution, high interobserver variability, limited anatomic coverage, as well as inability to assess the stenosis site after stent placement. In addition, a high level of competition has been introduced by techniques such as 16 detector multislice computed tomography, which generates superb image quality, with broad anatomic coverage and high spatial resolution, with minimal technical complexity. Lastly, aggressive search for renal artery stenosis by angiographic techniques in patients with hypertension is of debate, since only a limited percentage of these patients benefit from interventions. In this article, a comprehensive approach to high-resolution 3D-Gd-MRA, using parallel imaging in combination with cardiac-gated, phase-contrast flow measurements, is reviewed. This review is based on various studies and articles that address many of the problems of 3D-Gd-MRA. By making use of maximum spatial resolution and additional functional data, MRI permits accurate detection and grading of renal artery stenosis in most cases, with acceptable interobserver variability.

Atherosclerotic ischemic renal disease. Diagnosis and prevalence in an hypertensive and/or uremic elderly population

BACKGROUND

Atherosclerotic ischemic renal disease is a frequent cause of end-stage renal failure leading to dialysis among the elderly; Its prevalence is inferred from autopsy or retrospective arteriographic studies. This study has been conducted on 269 subjects over 50 with hypertension and/or CRF, unrelated to other known causes of renal disease.

METHODS

All 269 patients were studied either by color-flow duplex sonography (n = 238) or by renal scintigraphy (n = 224), and 199 of the 269 patients were evaluated using both of these techniques. 40 patients, found to have renal artery stenosis (RAS), were subjected to 3D-contrast enhancement Magnetic Resonance Angiography (MRA) and/or Selective Angiography (SA). An additional 23 cases, negative both to scintigraphy and to ultrasound study, underwent renal angiography (MRA and/or SA).

RESULTS

Color-duplex sonography, carried out in 238 patients, revealed 49 cases of RAS. MR or SA was carried out in 35 of these 49 patients, and confirmed the diagnosis in 33. Color-duplex sonography showed a PPV value of 94.3% and NPV of 87.0% while renal scintigraphy, carried out in 224 patients, had a PPV of 72.2% and a NPV of 29.4%. Patients with RAS showed a higher degree of renal insufficiency compared to non stenotic patients while there were no differences in proteinuria. RAS, based on color-duplex sonography studies, was present in 11% of patients in the age group 50-59, 18% in the 60-69 and 23% at age 70 and above.

CONCLUSIONS

A relatively large percentage of the elderly population with renal insufficiency and/or hypertension is affected by RAS and is at risk of developing end-stage renal failure. Color-duplex ultrasonography is a valid routine method of investigation of population at risk for renal artery stenosis.

Renal arteries: navigator-gated balanced fast field-echo projection MR angiography with aortic spin labeling: initial experience

A cardiac-triggered free-breathing three-dimensional balanced fast field-echo projection magnetic resonance (MR) angiographic sequence with a two-dimensional pencil-beam aortic labeling pulse was developed for the renal arteries. For data acquisition during free breathing in eight healthy adults and seven consecutive patients with renal artery disease, real-time navigator technology was implemented. This technique allows high-spatial-resolution and high-contrast renal MR angiography and visualization of renal artery stenosis without exogenous contrast agent or breath hold. Initial promising results warrant larger clinical studies.

Time-resolved contrast-enhanced magnetic resonance angiography of the carotid arteries: diagnostic accuracy and inter-observer variability compared with selective catheter angiography

RATIONALE AND OBJECTIVES

To assess the diagnostic accuracy and interobserver variability of contrast-enhanced magnetic resonance angiography (CE-MRA) in a time-resolved technique compared with digital subtraction angiography (x-ray DSA) in patients with suspected stenoses of the internal carotid artery.

MATERIALS AND METHODS

A total of 43 patients were enrolled in this prospective study. All patients underwent selective x-ray DSA involving a total of 84 carotid arteries. CE-MRA was performed in a time-resolved technique with a fast gradient-echo sequence on a 1.5 T MR scanner: TR 3.8 milliseconds, TE 1.49 milliseconds. Four consecutive measurements, each a duration of 10 seconds, were performed with omission of measuring bolus transit time. Four independent radiologists scored the degree of stenosis. The interobserver variability was calculated for CE-MRA and x-ray DSA.

RESULTS

In the 43 cases, at least one MRA measurement showed arterial contrast without venous degradation. Compared with x-ray DSA the mean sensitivity and specificity for grading stenosis > or = 70% were 98% and 86%, respectively. The interobserver agreement was substantial with no significant difference between CE-MRA (kappa value 0.794) and x-ray DSA (kappa value 0.786).

CONCLUSIONS

The short acquisition time of a fast CE-MRA sequence allows a selective visualization of the internal carotid arteries without degradation from venous enhancement. It is a reliable method with a good interobserver agreement.

Value of MR angiography before percutaneous transluminal renal artery angioplasty and stent placement

PURPOSE

To determine the benefit of preprocedural three-dimensional gadolinium (Gd)-enhanced magnetic resonance (MR) angiography before percutaneous transluminal renal artery angioplasty and stent placement (PTRA/S) in terms of procedural success, iodinated contrast material load, and procedure duration.

MATERIALS AND METHODS

Over an 18-month period, 39 patients underwent attempted percutaneous renal angioplasty with or without stent placement. A total of 48 renal arteries were treated (40 cases of atherosclerosis, one of stent restenosis, five of fibromuscular dysplasia, and two of transplant stenosis). Preprocedural Gd-enhanced MR angiography was available in 16 procedures (41%). Procedural outcome, complications, iodinated contrast material load, number of diagnostic angiographic runs, and total procedure duration were each compared between two subgroups: patients who had preprocedural Gd-enhanced MR angiography ("prior MR angiography group") and those who did not ("no MR angiography" group).

RESULTS

All procedures were technically successful. The two groups were equivalent in terms of age and disease pattern. However, technical complexity of the procedure was judged to be high in five of 16 procedures in the prior MR angiography group compared to three of 23 procedures in the no MR angiography group (P =.16). Bilateral or dual interventions were performed in six of 16 procedures in the prior MR angiography group compared to three of 23 in the no MR angiography group (P =.075). Iodinated contrast material load was significantly lower in the prior MR angiography group than in the no MR angiography group (68.7 mL +/- 28.4 vs 119.1 mL +/- 49.2 mL;P <.0008). The number of diagnostic angiographic runs before interventions were also significantly lower in the prior MR angiography group (1.2 +/- 0.4 vs 2.6 +/- 0.7; P <.0001). Overall procedure duration was comparable between the two groups (91.9 +/- 47.8 vs 112.2 +/- 49.4;P =.2).

CONCLUSION

Preprocedural planning with use of Gd-enhanced MR angiography significantly reduces the iodinated contrast material requirement during percutaneous renal artery interventions. It can also significantly shorten procedure duration.

MR angiography of the renal arteries

During, the past decade. MRA has evolved from an cxperimental technique into the modality of choice for the noninvasive evaluation of renovascular disease. The recent widespread application of MRA for these indications has been driven primarily by the advent of 3D contrast-enhanced MRA. which provides a fast, reliable technique for imaging large vascular territories and generates images, after postprocessing, similar in appearance to digital subtraction angiography. The cross-sectional volumetric nature of contrast-enhanced MRA affords some advantages over conventional catheter angiography. Although 3D contrast-enhanced MRA forms the backbone of vascular MR studies, several adjunctive sequences are employed to maximize the diagnostic yield of the examination. For example. flow-dependant imaging is used to complement the morphologic images of contrast-enhanced MRA by providing hemodynamic information. As such, MRA is unique among noninvasive imaging modalities in that it offers a comprehensive evaluation of anatomy and function. The availability and reliability of MRA extend renal artery screening to a wider spectrum of patients. Current applications of renal MRA range from detection of renal artery stenosis to evaluation for renal transplant donors.

Thin-section multidetector CT angiography of renal artery stents

OBJECTIVE

This study was undertaken as a pilot investigation to compare multidetector CT angiography with conventional catheter angiography for the visualization of the renal artery lumen after renal artery stent placement.

SUBJECTS AND METHODS

CT angiography was performed within 24-48 hr of renal artery stent placement in 15 patients. Two patients had bilateral stents, resulting in a total of 17 stents. CT angiography was performed using a multidetector scanner and a bolus of IV contrast material with the scanning delay determined by a small-volume timing bolus. A volumetric data set was acquired through the stented arteries in the axial plane using a 4.0 x 1.25 mm detector configuration and a pitch of 3:1. The stent lumen diameter, as measured on direct CT angiography and curved multiplanar reformations in both the axial and coronal planes, was compared with that measured on catheter angiography.

RESULTS

The lumina of all 17 stents were well visualized and patent on both CT angiography and catheter angiography. Anatomic definition, including stent position and wall apposition in the renal artery, correlated well with catheter angiography. The diameter of the renal artery stent lumen measured on catheter angiography (mean, 5.9 +/- 1.3 mm) was greater than that on CT angiography (mean stent lumen diameter for direct axial plane was 4.6 +/- 1.0 mm, for curved multiplanar reformations in the axial plane was 4.3 +/- 1.0 mm, and for curved multiplanar reformations in the coronal plane was 4.4 +/- 1.0 mm) in 14 (82%) of 17 stents.

CONCLUSION

CT angiography produced interpretable multiplanar images of the renal artery, even with a metallic stent in place, and was adequate for determining stent patency. Compared with catheter angiography, the intrastent luminal diameter was underestimated in most patients who underwent CT angiography.

Morphologic and functional magnetic resonance imaging of renal artery stenosis: a multireader tricenter study

The effect of combined morphologic and functional magnetic resonance (MR) imaging on the interobserver and intermodality variability for the grading of renal artery stenosis is assessed. In a randomized, blinded tricenter analysis, seven readers evaluated 43 renal arteries on x-ray digital subtraction angiography (DSA), 3D-Gadolinium MR angiography (3D-Gd-MRA), cine phase-contrast flow measurement (PC-flow), and a combined analysis of the last two. Interobserver variability was assessed for the grading of renal artery stenosis as well as regional vessel visibility. Intermodality variability for stenosis grading was analyzed in cases in which the readers agreed on the degree of stenosis in DSA. DSA had a substantial interobserver variability for the grading of stenosis (mean kappa kappa 0.64). 3D-Gd-MRA revealed a slightly improved interobserver variability but incorrectly graded 6 of 34 stenoses on a two-point scale (<50%, > or =50%). The combined approach of 3D-Gd-MRA and PC-flow revealed the best (P = 0.0003) interobserver variability (median kappa = 0.75) and almost perfect intermodality agreement with DSA (97% of cases). These findings were confirmed in a prospective analysis of 97 renal arteries. The vessel visibility of the renal artery ostium was significantly better in 3D-Gd-MRA than in DSA, whereas the visibility of the hilar and intrarenal vessels was significantly worse (P = 0.0001). A combined morphologic and functional MR examination significantly reduces interobserver variability and offers reliable and reproducible grading of renal artery stenosis based on stenosis morphology and hemodynamic changes. It can be considered a safe and noninvasive alternative for diagnostic DSA in cases that do not require assessment of intrarenal vessels.

Multiphase magnetic resonance angiography of the abdominal and pelvic arteries: results of a bicenter multireader analysis

RATIONALE AND OBJECTIVES

The objective is to assess the diagnostic accuracy and interobserver variability of multiphase 3D gadolinium-enhanced magnetic resonance angiography (3D-Gd-MRA) for assessment of abdominal and pelvic vascular disease.

METHODS

In 41 patients from two different institutions multiphase 3D-Gd-MRA of the aorta and pelvis was performed using an identical scanning protocol. In a single breath-hold three to four consecutive phases were acquired. Stenoses in the renal arteries, and aorta and pelvic arteries were independently evaluated by three readers and compared with digital subtraction angiography. Interobserver variability was compared by means of a kappa statistic.

RESULTS

Accuracy for stenosis grading consistently ranged between 80% and 90% for all three readers in all vessel segments studied. Good interobserver agreement was found with kappa values exceeding 0.75. Vessel segments with delayed fill-in could be reliably detected on the multiple successive MRA phases. Overall, MRA was rated slightly superior to Digital Subtraction Angiography in terms of interobserver variability, diagnostic confidence and image quality.

CONCLUSIONS

Multiphase MRA is a highly robust technique with reproducible accuracy for different observers and different institutions. It can therefore be recommended for screening of atherosclerotic abdominal and pelvic disease.

Gadolinium-enhanced 3D MR angiography of renal artery stenosis: a pilot comparison of maximum intensity projection, multiplanar reformatting, and 3D volume-rendering postprocessing algorithms

RATIONALE AND OBJECTIVES

The authors compared diagnostic accuracy of maximum intensity projection (MIP), multiplanar reformatting (MPR), and three-dimensional (3D) volume rendering (VR) in the evaluation of gadolinium-enhanced 3D magnetic resonance (MR) angiography of the renal arteries. They hypothesized that VR is as accurate as or more accurate than MIP and MPR at depicting renal artery stenosis.

MATERIALS AND METHODS

The study group comprised 28 consecutive patients who underwent gadolinium-enhanced 3D MR angiography of the renal arteries. Studies were postprocessed to display images in MIP, MPR, and VR formats. Digital subtraction angiography (DSA), when performed (nine of 28 patients), was the standard for comparison. For each main renal artery, an estimate of percentage stenosis was made for any stenoses detected by three independent radiologists. For calculation of sensitivity, specificity, and accuracy, MR angiographic stenosis estimates were categorized as mild (0%-39%), moderate (40%-69%), or severe (> or = 70%). DSA stenosis estimates of 70% or greater were considered hemodynamically significant.

RESULTS

Analysis of variance demonstrated MIP estimates of stenosis were statistically greater than VR estimates in two readers and greater than MPR estimates in all readers for all patients. MIP images also showed the largest mean difference from DSA stenosis estimates for all three readers. For both VR and MPR, mean differences between MR angiographic stenoses estimates and DSA estimates reached significance for only one reader, whereas, for MIP versus DSA, mean differences reached significance for all three readers. Although not statistically significant compared with DSA, accuracies of VR (87%) and MPR (89%) were greater than that of MIP (81%).

CONCLUSION

In this pilot study, MIP was the least accurate of the three image display algorithms tested. VR and MPR yielded similar values for each method of comparison.

MR renography with low-dose gadopentetate dimeglumine: feasibility

PURPOSE

To develop a low-dose magnetic resonance (MR) renographic method performed with and without an angiotensin converting enzyme (ACE) inhibitor and in conjunction with gadolinium-enhanced MR angiography in patients with suspected renovascular disease.

MATERIALS AND METHODS

Thirty-two patients underwent MR renography (turbo fast low-angle shot sequence: repetition time, 5 msec; echo time, 2.3 msec; flip angle, 15 degrees; one coronal image acquired every 2 seconds for 4 minutes) following intravenous injection of 2 mL of gadopentetate dimeglumine, which was repeated following intravenous injection of an ACE inhibitor. Contrast material-enhanced MR angiography was also performed. On the basis of renographic findings, renal cortex and renal medulla enhancement curves and normalized enhancement ratios were analyzed.

RESULTS

The cortex and medulla showed an early transient period of enhancement within 20 seconds (vascular phase). During 1-2 minutes, a second, gradual increase in medullary enhancement, reflecting transit of filtered contrast material, was observed that was significantly greater in patients with a serum creatinine level less than 2 mg/dL (177 micromol/L) than in those with a level of 2 mg/dL or greater (P < .01). After injection of the ACE inhibitor, patients with elevated creatinine levels showed low renal medullary enhancement regardless of the presence of renal artery stenosis (RAS). However, in patients with creatinine less than 2 mg/dL, medullary enhancement ratios after injection of the ACE inhibitor were consistently lower in patients with RAS of 50% or greater than in those without stenosis (P = .02 to .08).

CONCLUSION

Low-dose MR renography can be performed in the clinical setting before and after injection of an ACE inhibitor, and its potential use for evaluating decreased renal function as a consequence of RAS is promising.

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.

Incidence of adrenal masses in patients referred for renal artery stenosis screening MR

RATIONALE AND OBJECTIVES

Prior work has shown the efficacy of magnetic resonance (MR) in renal artery stenosis evaluation. The increasing role of renal artery stenosis in the differential diagnostic evaluation of hypertension raises the question of whether MR should be used as a screening modality. This project evaluated the additional potential benefits of MR by determining the incidence of adrenal masses in this selected population.

METHODS

A 2-year retrospective study analysis of patients who failed to respond to antihypertensive medical management and were referred for renal MR for hypertension amassed 77 subjects ranging in age from 18 to 88 years. A masked analysis for adrenal masses was performed on this data set. Magnetic resonance techniques included T2-weighted turbo spin-echo (repetition time [TR] 2000-4000 ms, echo time [TE] 80-100 ms, turbo factor 2-16), T1-weighted spin-echo (TR 200-500 ms, TE 10-30 ms), gradient-echo time-of-flight (TR 26 ms, TE 6.9 ms, 40 degrees flip angle, 2 excitations), and dynamic gadopentetate dimeglumine-enhanced MR angiography (three-dimensional gradient recalled echo, TR 10 ms, TE 3 ms, 40 degrees flip angle, 1 excitation).

RESULTS

Thirty-three patients had renal artery disease, 44 had normal renal arteries, and 7 had adrenal masses. Forty-three percent of patients who underwent renal MR had disease of the renal arteries detected, and 9% of patients referred for MR had adrenal masses that would have been missed with scintigraphy and/or angiography, of which 57% were responsible for hypertension.

CONCLUSIONS

The ability to evaluate renal artery and adrenal anatomy globally can be useful, as exemplified in the current series, and the adrenals should be examined carefully in any renal MR in a hypertensive patient.

Interobserver variability in the evaluation of chronic mesenteric ischemia with gadolinium-enhanced MR angiography

RATIONALE AND OBJECTIVES

The purpose of this study was to assess interobserver variability in the interpretation of gadolinium-enhanced magnetic resonance (MR) angiograms of splanchnic vessels in patients suspected of having chronic mesenteric ischemia (CMI).

MATERIALS AND METHODS

Two readers blinded to the initial interpretation retrospectively reviewed gadolinium-enhanced MR angiograms obtained for suspected CMI in 26 patients (20 women and six men; age range, 23-77 years; mean age, 61 years) who also underwent conventional angiography. Each reader graded the degree of stenosis based on the percentage diameter reduction of the celiac artery (CA), superior mesenteric artery (SMA), and inferior mesenteric artery (IMA) by using a five-point ordinal scale: 0, no stenosis: 1, mild stenosis (<50%); 2, moderate stenosis (50%-75%); 3, severe stenosis (>75%); 4, occluded artery. Using the conventional angiogram as a reference standard, authors determined sensitivity and specificity for each observer, assigning two thresholds (grades 2 and 3) as significant stenoses. A kappa statistic (kappa) measured interobserver agreement.

RESULTS

With grade 2 stenosis used as a threshold, cumulative accuracies for detecting significant stenosis were 0.95 (95% confidence interval, 0.86-0.99) for reader A and 0.97 (0.88-1.0) for reader B. Interobserver agreement for grading proximal splanchnic stenosis was 0.90 for CA, 0.92 for SMA, and 0.48 for IMA.

CONCLUSION

Gadolinium-enhanced MR angiography is reproducibly accurate for detection of proximal splanchnic artery stenosis, with good to excellent interobserver agreement.