Time-resolved contrast-enhanced MR angiography of renal artery stenosis: diagnostic accuracy and interobserver variability

OBJECTIVE: The purpose of this study was to evaluate diagnostic accuracy and interobserver variability of time-resolved three-dimensional gadolinium-enhanced MR angiography in the detection of renal artery stenosis in comparison with intraarterial digital subtraction angiography as the standard of reference. SUBJECTS AND METHODS: Forty consecutive patients (age range, 25-81 years; mean, 62.9 +/- 11.9 years) with suspected renal artery stenosis underwent intraarterial digital subtraction angiography and gadolinium-enhanced MR angiography, performed on a 1.5-T system with fast low-angle shot three-dimensional imaging (3.8/1.49 [TR/TE], 25 degrees flip angle, 10-sec acquisition time, and 1.5-mm partition thickness). Three time-resolved phases were obtained in a single breath-hold. Digital subtraction angiography and gadolinium-enhanced MR angiography were evaluated by four observers who studied 80 main renal arteries and 19 accessory vessels to evaluate the degree of stenosis. A stenosis reducing the intraarterial diameter by more than 50% was regarded as hemodynamically significant. Interobserver variability was calculated. RESULTS: Only one gadolinium-enhanced MR angiography study was not of diagnostic quality, as a result of failure of the power injector. All main branches were of diagnostic quality in 38 (97.4%) of the remaining 39 gadolinium-enhanced MR angiography studies. Seventeen (89.5%) of 19 accessory renal arteries were depicted with gadolinium-enhanced MR angiography. The overall sensitivity for significant stenoses was 92.9%. The overall specificity was 83.4%, and the overall accuracy was 85.9%. Interobserver variability of gadolinium-enhanced MR angiography exceeded that of digital subtraction angiography. CONCLUSION: Time-resolved three-dimensional gadolinium-enhanced MR angiography is a useful noninvasive method of screening suspected renal artery stenosis because of its easy application, short examination time, and high sensitivity despite of its higher interobserver variability.     

Diagnostic accuracy of time-resolved 2D projection MR angiography for symptomatic infrapopliteal arterial occlusive disease

OBJECTIVE: Our objective was to evaluate the diagnostic accuracy of time-resolved 2D projection MR angiography in detecting calf and pedal artery occlusive disease. MATERIALS AND METHODS: Time-resolved MR angiography of calf and pedal arteries was performed on 59 symptomatic legs of 52 patients using the head coil and bolus injections of 6 mL of gadolinium contrast medium. Selective X-ray digital subtraction angiography was performed within 30 days after MR angiography. Calf and pedal arteries were divided into 10 segments. X-ray digital subtraction angiography and MR angiography images were retrospectively interpreted by three expert observers, who graded segments as having no significant stenosis, significant stenosis (> 50%), or occlusion. The accuracy of MR angiography interpretations was compared with the accuracy of consensus X-ray digital subtraction angiography interpretations as the standard of reference. Arterial segments with discrepant grading on X-ray digital subtraction angiography and MR angiography were reviewed again to determine the reasons for disagreement. RESULTS: Arterial phase MR angiography images free of venous contamination were obtained in every case. The agreement between MR angiography and X-ray digital subtraction angiography in depicting infrapopliteal arterial disease was fair to good (kappa = 0.44-0.92). Overall sensitivity and specificity were 83% and 87%, respectively, for detecting significant stenosis of calf and pedal arteries and 86% and 93%, respectively, for detecting occlusions. Accuracy was higher in the larger vessels-for example, calf (84%) compared with foot (71%). In 21% (22/105) of the segments graded differently on MR angiography than on X-ray digital subtraction angiography, it was believed that MR angiography was more likely to be correct than X-ray digital subtraction angiography because of visualization of late-filling arteries on MR angiography that did not opacify on X-ray digital subtraction angiography. CONCLUSION: Time-resolved 2D projection MR angiography accurately evaluates calf and pedal arteries without degradation from venous contamination.     

Accessory renal arteries are not related to hypertension risk: a review of MR angiography data

OBJECTIVE: It has been hypothesized that accessory renal arteries are related to the risk of hypertension. Our goal was to determine the prevalence of accessory renal arteries in hypertensive patients using MR angiography and to assess the relationship between accessory renal arteries and hypertension risk. MATERIALS AND METHODS: From 1996 to 2002, 185 hypertensive patients underwent MR angiography of the renal arteries at our institution for assessment of renal artery stenosis. MR angiograms were obtained using a 1.5-T magnet, IV gadolinium, and 3D gradient-echo sequences. Interpretations of the MR angiograms were retrospectively reviewed. RESULTS: Of 185 hypertensive patients, 45 (24%) showed accessory renal arteries. Of these 45 patients, nine (20%) showed renal artery stenosis and 36 (80%) showed no significant stenosis. Of the 140 patients with a single renal artery, 42 (30%) showed renal artery stenosis and 98 (70%) showed no stenosis. The odds ratio of renal artery stenosis in the accessory renal artery group versus the single renal artery group was 0.58 (95% confidence interval, 0.26-1.3%), which is not statistically significant at a power of 0.85 (chi(2) = 1.705; p = 1.0). CONCLUSION: We found no statistically significant difference in the prevalence of renal artery stenosis between patients with accessory renal arteries and those without accessory renal arteries. Assuming that the presence of two separate causes of hypertension in the same patient would be unlikely, this finding implies that accessory renal arteries are a vascular anomaly and not a direct cause of hypertension. The findings are potentially relevant in refuting the theory of accessory renal arteries as an anatomically treatable cause of hypertension.     

Comparison of intraarterial and IV gadolinium-enhanced MR angiography with digital subtraction angiography for the detection of renal artery stenosis in pigs.

OBJECTIVE: Catheter-based intraarterial injections of gadolinium are useful during MR imaging-guided endovascular procedures to generate rapid vascular road maps. Using an animal model of renal artery stenosis, we tested the hypothesis that intraarterial gadolinium-enhanced MR angiography is as accurate as IV gadolinium-enhanced MR angiography and digital subtraction angiography (DSA). We also tested the hypothesis that intraarterial MR angiography uses less gadolinium than IV MR angiography. MATERIALS AND METHODS: We induced bilateral renal artery stenosis in five pigs. All pigs underwent comparative imaging with DSA, IV MR angiography, and aortic catheter-directed intraarterial MR angiography. For IV and intraarterial MR angiography, we used the same three-dimensional acquisition. We assessed differences in quantitative stenosis measurements among DSA, IV MR angiography, and intraarterial MR angiography using the Wilcoxon's signed rank test. RESULTS: Mean stenosis measurements (+/-SD) were as follows: DSA, 58% +/- 12%; IV MR angiography, 63% +/- 9.3%; and intraarterial MR angiography, 64% +/- 11%. There were no statistically significant differences in accuracy between DSA and IV MR angiography (p = 0.06), DSA and intraarterial MR angiography (p = 0.16), or IV and intraarterial MR angiography (p = 0.70). Intraarterial MR angiography used a mean gadolinium dose of 5.6 mL, compared with 9 mL for IV MR angiography. CONCLUSION: In swine, IV and intraarterial MR angiography have a similar accuracy for detecting renal artery stenosis. Intraarterial MR angiography uses smaller doses of injected gadolinium.     

Evaluation of dynamic gadolinium-enhanced breath-hold MR angiography in the diagnosis of renal artery stenosis.

OBJECTIVE: The aim of our study was to evaluate a three-dimensional gadolinium-enhanced breath-hold MR angiography sequence using standard MR gradients in detecting renal artery stenosis. SUBJECTS AND METHODS: Forty-two patients referred for angiography for suspected renal artery stenosis underwent both conventional digital subtraction angiography (DSA) and MR angiography. MR angiography was performed on a 1.5-T scanner with standard gradients. A fast multiplanar spoiled gradient-echo sequence was used with the following parameters: TR/TE, 10.3/1.9; flip angle, 45 degrees; field of view, 36 x 32 cm; matrix size, 256 x 128; one excitation; volume thickness, 70 mm; and partitions, 28. Gadolinium was administered IV as a dynamic bolus of 30-40 ml. Conventional and MR angiographic images were interpreted by two radiologists in consensus. RESULTS: DSA revealed 87 renal arteries, of which 79 were in 35 patients with native kidneys and eight arteries were in seven patients with transplanted kidneys. Gadolinium-enhanced MR angiography showed 85 (98%) of 87 renal arteries. Seventeen patients had 20 significant (>50% stenosis) renal artery stenoses and five patients had five occluded renal arteries revealed by DSA. MR angiography revealed 85 renal arteries (98%), 20 stenoses (100%), and five occlusions (100%). Gadolinium-enhanced MR angiography led to one false-positive interpretation for renal artery stenosis and no false-negative interpretations. Thus, the sensitivity, specificity, and accuracy of MR angiography for renal artery stenosis were 100%, 98%, and 99%, respectively. CONCLUSION: The MR angiography pulse sequence we used was an effective and reliable technique for the diagnosis of renal artery stenosis. The sequence can be performed on widely available MR equipment that does not require fast gradient hardware.     

High-spatial-resolution 3D balanced turbo field-echo technique for MR angiography of the renal arteries: initial experience

PURPOSE: To compare a multislab balanced turbo field-echo magnetic resonance (MR) angiographic technique, without the use of a contrast agent, with digital subtraction angiography (DSA) for imaging of the renal arteries. MATERIALS AND METHODS: Twenty-five randomly selected patients (eight women and 17 men; age range, 27-88 years; mean age, 72 years) suspected of having renal artery stenosis underwent both DSA and balanced turbo field-echo MR angiography. A consensus result was obtained among three radiologists in evaluation of main renal arteries on balanced turbo field-echo images and DSA images. Sensitivity, specificity, and negative and positive predictive values of the balanced turbo field-echo technique were calculated, and receiver operating characteristic analysis was performed for depiction of hemodynamically significant stenosis. Cohen kappa analysis was used to assess agreement between the two imaging methods in grading of stenoses and depiction of significant stenosis. Accessory renal arteries also were evaluated. RESULTS: Fifty main renal arteries and 11 accessory arteries were fully depicted with DSA. DSA depicted 11 stenotic lesions in the main renal arteries. In comparison, balanced turbo field-echo MR angiography enabled visualization of 46 of 50 main renal arteries to their first branching points and depicted 10 of 11 accessory arteries. Sensitivity, specificity, negative predictive value, and positive predictive value of this technique for depiction of significant stenosis were 100% (four of four), 98% (41 of 42), 100% (41 of 41), and 80% (four of five), respectively. The area under the receiver operating characteristic curve was 0.988. kappa was 0.782 for grading of stenoses and 0.877 for depiction of significant stenosis. CONCLUSION: Multislab balanced turbo field-echo imaging has potential as an MR angiography technique for depiction of normal and diseased renal arteries.     

Renal artery stenosis in swine: feasibility of MR assessment of renal function during percutaneous transluminal angioplasty

PURPOSE: To prospectively test--in a swine model of renal artery stenosis (RAS)--the hypothesis that magnetic resonance (MR) imaging can reveal changes in renal function at the time of percutaneous transluminal angioplasty (PTA). MATERIALS AND METHODS: In this animal care and use committee-approved study, high-grade unilateral RAS was surgically induced in six pigs. MR imaging at 3.0 T was used for intraprocedural assessment of the anatomic and physiologic changes induced by x-ray-guided PTA. With use of MR imaging, changes in single-kidney glomerular filtration rate, extraction fraction, and renal blood flow were assessed during PTA. The arterial diameter of stenosis before and after PTA was assessed by using conventional digital subtraction angiography. Mean changes in functional and anatomic parameters were compared by using the Wilcoxon signed rank test (alpha = .05). RESULTS: At digital subtraction angiography, the mean percentage of stenosis was 69% +/- 10 (standard deviation) before PTA and 26% +/- 10 after PTA (P<.03). Mean pre- and post-PTA extraction fraction values were 0.11 +/- 0.03 and 0.19 +/- 0.06, respectively (P<.03). The mean single-kidney glomerular filtration rate before PTA, 19 mL/min +/- 13, increased to 41 mL/min +/- 33 after PTA (P<.03). There was no significant change in mean renal blood flow after PTA (P=.44). CONCLUSION: In swine, MR imaging can reveal changes in renal function after x-ray-guided PTA for unilateral RAS.     

Renal time-resolved MR angiography: quantitative comparison of gadobenate dimeglumine and gadopentetate dimeglumine with different doses

PURPOSE: Results with different doses of gadobenate dimeglumine and gadopentetate dimeglumine were compared at magnetic resonance (MR) angiography of the renal arteries. The signal-to-noise ratio (SNR) was evaluated as a quantitative measure of image quality. MATERIALS AND METHODS: Sixty consecutive patients (age range, 24-81 years; mean age, 65 years) underwent intraarterial digital subtraction angiography (DSA) and contrast material-enhanced time-resolved MR angiography. DSA was the standard of reference. Fifteen patients received gadopentetate dimeglumine at doses of 0.2 or 0.1 mmol per kilogram of body weight. Fifteen patients received gadobenate dimeglumine at doses of 0.05 or 0.1 mmol/kg. The SNR was calculated in the aorta and both main renal arteries. The number and degree of stenoses of the renal arteries and accessory vessels were evaluated by four observers. RESULTS: SNRs with gadobenate dimeglumine at a dose of 0.1 mmol/kg were significantly superior to those with gadopentetate dimeglumine at a dose of 0.1 mmol/kg. Differences were not statistically significant between the SNRs in the other groups. Eleven (85%) of 13 hemodynamically significant renal artery stenoses were detected correctly with MR angiography as were 22 (85%) of 26 accessory renal arteries. CONCLUSION: SNRs with gadobenate dimeglumine were higher than those with gadopentetate dimeglumine, but in most cases the differences in SNRs were not statistically significant.     

Renal arteriography using gadolinium enhanced 3D MR angiography--clinical experience with the technique, its limitations and pitfalls.

Gadolinium enhanced 3D MR angiography (MRA) is becoming a widely accepted technique for imaging the vascular system. We set out to evaluate its accuracy and reliability in visualization of renal arteries in the clinical setting. Gadolinium enhanced MRA was performed in 15 potential live renal donors and 26 patients suspected of having renal artery stenosis who were referred for digital subtraction angiography (DSA). MRA was performed on a 1.5 T MR scanner in a single breath hold. Images from each study were prospectively analysed for demonstration of number of main and accessory renal arteries and degree of renal artery stenosis in a double blind fashion. All the main and accessory arteries were visualized on MRA in the renal donor group, but in one case a branch was not identified owing to breathing artefact. In one case, an extrarenal vascular anomaly was not demonstrated on MRA. In the renal artery stenosis group, sensitivity, specificity and negative predictive values of 96%, 93% and 96% were obtained for clinically significant stenosis (>50%). Gadolinium enhanced MRA proved to be a useful technique in demonstration of renal arterial anatomy and grading of renal artery stenosis. However, we encountered some pitfalls and limitations of the technique during the process. It is important to be aware of these before accepting it as the sole technique in clinical practice.     

Value of image subtraction in 3D gadolinium-enhanced MR angiography of the renal arteries

The objective of this study was to evaluate quantitatively and qualitatively the effect of image subtraction on the image quality of three-dimensional (3D) gadolinium-enhanced MR angiograms of the renal arteries. Breath-hold 3D gadolinium MR angiography (MRA) as well as conventional contrast angiography of the renal arteries was performed on 20 patients with suspected renovascular hypertension. MR angiograms were acquired before and during dynamic infusion of gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA). Contrast-enhanced images were compared with images that had undergone voxel-by-voxel signal intensity subtraction of contrast-enhanced data from precontrast data. One false positive finding for significant renal artery stenosis was recorded with MRA using conventional angiography as the gold standard. Image subtraction did not alter the diagnosis at MRA in any case. The mean contrast-to-noise ratio (CNR) was significantly higher (P < .05) on the subtraction MR angiograms compared to the nonsubtracted MR angiograms. There was no significant difference in the signal-to-noise ratio (SNR). Qualitative analysis revealed a significant improvement in image quality after image subtraction with respect to visualization of the distal renal arteries. In conclusion, image subtraction improves the quality of renal MRA in terms of both CNR and visualization of the distal renal arteries.     

Equilibrium-phase MR angiography of the aortoiliac and renal arteries using a blood pool contrast agent

OBJECTIVE: The purpose of this study was to determine the diagnostic usefulness of a new blood pool contrast agent, NC100150, for assessing the aortoiliac and renal arteries. SUBJECTS AND METHODS: Twenty patients with hemodynamically significant stenosis (> or =50% of luminal diameter) of the iliac or renal arteries or an aortic aneurysm documented by digital subtraction angiography underwent MR angiography at 1.5 T after administration of NC100150. Three-dimensional MR angiographic data sets were collected ill the equilibrium phase. In a prospective analysis, each vascular segment (16 segments per arterial tree) was evaluated. RESULTS: All patients tolerated the NC100150 administration well. Mean contrast-to-noise ratios of the vascular data collected in the equilibrium phase of NC100150 was 3.3+/-15.9. Compared with digital subtraction angiography, the sensitivity and specificity of MR angiography for the renal arteries were 82% and 98%, respectively; for the common iliac arteries, 86% and 97%, respectively; for the external iliac arteries, 80% and 100%, respectively; and for the internal iliac arteries, 71% and 977, respectively. All 83 aneurysmal changes revealed by digital subtraction angiograpy of the aortoiliac arteries were well displayed on the MR angiographic data sets. CONCLUSION: Equilibrium-phase NC 00150-enhanced three-dimensional MR angiography shows high specificity when evaluating the abdominal and pelvic vascular systems, but the attendant venous overlap can limit the assessment of stenosis in renal and pelvic arterial segments.     

MR imaging- versus conventional X-ray fluoroscopy-guided renal angioplasty in swine: prospective randomized comparison

PURPOSE: To test the hypothesis that the technical success rates, complication rates, and procedural times for magnetic resonance (MR) imaging-guided percutaneous transluminal angioplasty (PTA) and conventional (x-ray) fluoroscopy-guided PTA for treatment of renal artery stenosis are similar. MATERIALS AND METHODS: The study was animal care and use committee approved. After surgically inducing bilateral renal artery stenosis in 11 swine, the authors performed baseline digital subtraction angiography. They transferred each animal to a 1.5-T MR imaging unit and randomly decided which artery would be treated with MR-guided PTA. With MR imaging guidance, angioplastic devices were tracked by using active and passive techniques. Vascular depiction was achieved by using catheter-directed MR angiography. Stenotic vessels were dilated by using 5-6-mm-diameter balloon catheters. PTA was then performed in the contralateral artery by using conventional fluoroscopy-guided techniques. With the intention to treat, the authors compared the technical success (residual stenosis < 50%) rates, complication rates, and procedural times for each guidance method. They compared technical successes and complications by using the McNemar test and procedural times by using a paired t test, with P < .05 indicating a significant difference. RESULTS: The authors successfully dilated nine (82%) of 11 renal arteries with MR guidance and all 11 arteries (100%) with conventional fluoroscopic guidance. The difference was not significant (P = .5). Complications occurred in three (27%) arteries with MR guidance and in one (9%) artery with fluoroscopic guidance, with no significant differences (P = .5). The mean MR-guided PTA procedural time was 46 minutes longer than the fluoroscopy-guided PTA procedural time; this difference was significant (P = .01). CONCLUSION: In a small cohort of swine, the authors did not observe a significant difference between MR imaging- and conventional fluoroscopy-guided renal artery PTA in terms of success and complication rates. However, no evidence of similarity between the techniques should be assumed. Procedural times differed significantly.     

MR-guided angioplasty of renal artery stenosis in a pig model: a feasibility study

PURPOSE: To test the hypothesis that magnetic resonance (MR) imaging can guide the percutaneous treatment of renal artery stenosis in a pig model. MATERIALS AND METHODS: Ameroid constrictors were surgically placed around six renal arteries in four pigs. After 30-36 days, all stenoses were documented by conventional x-ray aortograms. MR-guided renal angioplasty was attempted for three stenoses. For these pigs, MR angiography was performed with use of contrast-enhanced three-dimensional (3D) techniques. The authors visualized catheters by filling them with dilute 4% gadolinium and imaging with two-dimensional (2D) and 3D MR fast spoiled gradient recalled echo techniques. Under MR guidance, the authors advanced a selective catheter into the affected renal artery and crossed the stenosis with a nitinol guide wire. Angioplasty was performed with a balloon catheter filled with dilute gadolinium. Stenosis and luminal diameter measurements were compared before and after angioplasty. RESULTS: After ameroid constrictor placement, four significant stenoses, one mild stenosis, and one occlusion developed. Under MR guidance, the authors achieved technical success in performing three of three (100%) attempted dilations. After MR-guided angioplasty, the mean reduction in stenosis was 35% and the mean increase in luminal diameter was 1.6 mm. CONCLUSION: Use of MR guidance for the angioplasty of renal artery stenosis in pigs is feasible.     

MR imaging assessment of changes in renal function with renal artery stent placement in swine

PURPOSE: To prospectively test the hypothesis that magnetic resonance (MR) imaging can detect changes in renal function at the time of renal artery stent placement in a swine model of renal artery stenosis (RAS). MATERIALS AND METHODS: In this animal care and use committee-approved study, hemodynamically significant (>50%) RAS was surgically induced in six pigs. MR imaging was employed for assessment of the anatomic and physiologic changes induced by fluoroscopically guided stent placement. With MR imaging, we assessed changes in renal blood flow (RBF), extraction fraction (EF), and single-kidney glomerular filtration rate (skGFR) during the procedure. Arterial diameter stenosis before and after stent placement was assessed with x-ray digital subtraction angiography (DSA). Mean changes in functional and anatomic parameters were compared with the Wilcoxon matched-pairs test, with an alpha level of 0.05. RESULTS: There was no significant change in mean RBF after stent deployment (P=.44). Mean EF increased from 0.19+/-0.08 before stent placement to 0.31+/-0.17 after stent placement (P=.16). Mean skGFR measurements were 25 mL/min+/-16 before stent placement and 41 mL/min+/-28 after stent placement (P<.05). According to x-ray DSA measurements, mean stenosis measurements were 60%+/-12% before stent placement and 24%+/-16% after stent placement (P<.02). CONCLUSIONS: In swine, MR imaging can detect immediate changes in renal function after radiographically guided stent placement for unilateral RAS. This functional MR technique may have applications in the setting of hybrid MR/x-ray DSA procedure suites.     

Assessment of aortoiliac and renal arteries: MR angiography with parallel acquisition versus conventional MR angiography and digital subtraction angiography

PURPOSE: To prospectively compare the image quality, sensitivity, and specificity of three-dimensional gadolinium-enhanced magnetic resonance (MR) angiography accelerated by parallel acquisition (ie, fast MR angiography) with MR angiography not accelerated by parallel acquisition (ie, conventional MR angiography) for assessment of aortoiliac and renal arteries, with digital subtraction angiography (DSA) as the reference standard. MATERIALS AND METHODS: The study was approved by the institutional review board; informed consent was obtained from all patients. Forty consecutive patients (33 men, seven women; mean age, 63 years) suspected of having aortoiliac and renal arterial stenoses and thus examined with DSA underwent both fast (mean imaging time, 17 seconds) and conventional (mean imaging time, 29 seconds) MR angiography. The arterial tree was divided into segments for image analysis. Two readers independently evaluated all MR angiograms for image quality, presence of arterial stenosis, and renal arterial variants. Image quality, sensitivity, and specificity were analyzed on per-patient and per-segment bases for multiple comparisons (with Bonferroni correction) and for dependencies between segments (with patient as the primary sample unit). Interobserver agreement was evaluated by using kappa statistics. RESULTS: Overall, the image quality with fast MR angiography was significantly better (P=.001) than that with conventional MR angiography. At per-segment analysis, the image quality of fast MR angiograms of the distal renal artery tended to be better than that of conventional MR angiograms of these vessels. Differences in sensitivity for the detection of arterial stenosis between the two MR angiography techniques were not significant for either reader. Interobserver agreement in the detection of variant renal artery anatomy was excellent with both conventional and fast MR angiography (kappa=1.00). CONCLUSION: Fast MR angiography and conventional MR angiography do not differ significantly in terms of arterial stenosis grading or renal arterial variant detection.     

3D MR angiography of renal arteries: comparison of volume rendering and maximum intensity projection algorithms

PURPOSE: To compare volume rendering (VR) and maximum intensity projection (MIP) as postprocessing techniques of magnetic resonance (MR) angiography for detection and quantification of renal artery stenosis. MATERIALS AND METHODS: Twenty-seven patients underwent three-dimensional contrast material-enhanced MR angiography of the renal arteries with a 1.5-T imager. For each renal artery, targeted MIP and VR images were reconstructed in oblique coronal and transverse orientations. For each modality, image generation and evaluation were performed interactively by two independent radiologists blinded to angiographic results. In comparison with digital subtraction angiography (DSA) findings, stenosis quantification and detection by using MIP and VR were evaluated with the use of 50% and 70% cutoff points by using linear regression analysis and 2 x 2 tables. Overall image quality and vascular delineation on MIP and VR images were also compared. RESULTS: All main and accessory renal arteries depicted at DSA were also demonstrated on MIP and VR images. VR performed slightly better than MIP for quantification of stenoses greater than 50% (VR: r(2) = 0.84, P <.001; MIP: r(2) = 0.38, P =.001) and significantly better for severe stenoses (VR: r(2) = 0.83, P <.001; MIP: r(2) = 0.21, P =.1). For detection of stenosis, VR yielded a substantial improvement in positive predictive value (VR: 95% and 90%; MIP: 86% and 68% for stenoses greater than 50% and 70%, respectively). Image quality obtained with VR was not significantly better than that with MIP; however, vascular delineation on VR images was significantly better. CONCLUSION: The VR technique of renal MR angiography enabled more accurate detection and quantification of renal artery stenosis than did MIP, with significantly improved vascular delineation.     

Using gadolinium-enhanced three-dimensional MR angiography to assess arterial inflow stenosis after kidney transplantation

OBJECTIVE: Our objective was to evaluate use of gadolinium-enhanced three-dimensional (3D) MR angiography in the assessment of suspected arterial inflow stenosis after kidney transplantation. SUBJECTS AND METHODS: Twenty-eight consecutive patients receiving kidney transplants (26 single-kidney transplants and two en block transplants) with suspected arterial inflow stenosis were examined with two MR angiography sequences: gadolinium-enhanced 3D fast spoiled gradient-recalled (SPGR) imaging and 3D phase-contrast imaging. Twenty-four of these patients then were examined using the gold standards: either digital subtraction angiography (DSA) (n = 23) or surgery (n = 1). MR angiography and DSA studies were independently and prospectively analyzed for the presence of arterial stenoses (mild [<50%], severe [50-90%], or critical [>90%]) in the iliac, anastomotic, and renal artery segments. Two independent observers retrospectively evaluated the MR angiography sequences for ability to detect or exclude significant (> or = 50%) arterial stenoses. RESULTS: In 22 single-kidney transplants, DSA showed eight significant stenoses in 66 arterial segments. MR angiograms adequately showed 66 of 66 segments (prospective observers) and 64 of 66 segments (each retrospective observer), which were subsequently evaluated. The sensitivity and specificity of MR angiography in revealing significant stenoses were 100% and 98% (prospective analysis), 88% and 98% (retrospective observer 1), and 86% and 100% (retrospective observer 2). Concordance between observers showed kappa values exceeding .85 for all comparisons except the analysis of phase-contrast series (kappa = .62). In one en block transplant, DSA showed that stenosis was greater than 90%, although it had been graded at less than 50% with MR angiography. CONCLUSION: Gadolinium-enhanced 3D MR angiography accurately evaluated arterial inflow in single-kidney transplants.     

Assessment of gadolinium-enhanced time-resolved three-dimensional MR angiography for evaluating renal artery stenosis

OBJECTIVE: The purpose of this study was to assess the image quality of gadolinium-enhanced time-resolved three-dimensional (3D) MR angiography and to evaluate its accuracy in revealing renal artery stenosis. SUBJECTS AND METHODS: Thirty-nine patients underwent MR angiography using an ultrafast 3D Fourier transform spoiled gradient-recalled acquisition in the steady state (TR/TE range, 2.6/0.7--0.8). Five seconds after administration of 15--20 mL gadodiamide hydrate, four or five consecutive data sets with imaging times of 7.0--7.6 sec were acquired during a single breath-hold. A timing examination was not performed. Image quality was assessed using quantitative analysis (signal-to-noise, contrast-to-noise, and venous-to-arterial enhancement ratios) and qualitative analysis (presence of venous overlap, presence of artifacts, and degree of renal arterial enhancement). MR angiography depiction of the renal artery stenosis was evaluated using conventional angiography as the standard of reference. RESULTS: On the best arterial phase, average aortic signal-to-noise ratio (+/-SD) was 74.5 +/- 24.4, aorta-to--inferior vena cava contrast-to-noise ratio was 70.8 +/- 23.4, and inferior vena cava--to-aorta venous-to-arterial enhancement ratio was 0.03 +/- 0.04. No venous overlap was seen in 38 of 39 patients. Substantial enhancement of renal arteries was seen in all patients without any noticeable artifacts. MR angiography correctly depicted the degree of stenosis in 44 of 47 normal arteries, 13 of 16 mildly stenotic arteries, five of five moderately stenotic arteries, three of four severely stenotic arteries, and one of one occluded artery. Sensitivity and specificity for revealing greater than 50% stenosis was 100%. CONCLUSION: Time-resolved 3D MR angiography can provide high-quality arteriograms. Its performance in revealing renal artery stenosis is comparable with that of conventional angiography.     

High-spatial-resolution contrast-enhanced MR angiography of the renal arteries: a prospective comparison with digital subtraction angiography

PURPOSE: To evaluate a high-spatial-resolution three-dimensional (3D) contrast material-enhanced magnetic resonance (MR) angiographic technique for detecting proximal and distal renal arterial stenosis. MATERIALS AND METHODS: Twenty-five patients underwent high-spatial-resolution small-field-of-view (FOV) 3D contrast-enhanced MR angiography of the renal arteries, which was followed several minutes later by more standard, large-FOV 3D contrast-enhanced MR angiography that included the distal aorta and iliac arteries. For both acquisitions, MR fluoroscopic triggering and an elliptic centric view order were used. Two readers evaluated the MR angiograms for grade and hemodynamic significance of renal arterial stenosis, diagnostic quality, and presence of artifacts. MR imaging results for each patient were compared with those of digital subtraction angiograms. RESULTS: The high-spatial-resolution small-FOV technique provided high sensitivity (97%) and specificity (92%) for the detection of renal arterial stenosis, including all four distal stenoses encountered. The portrayal of the segmental renal arteries was adequate for diagnosis in 19 (76%) of 25 patients. In 12% of the patients, impaired depiction of the segmental arteries was linked to motion. CONCLUSION: The combined high-spatial-resolution small-FOV and large-FOV MR angiographic examination provides improved spatial resolution in the region of the renal arteries while maintaining coverage of the abdominal aorta and iliac arteries.     

Accuracy of contrast-enhanced MR angiography in predicting angiographic stenosis of the internal carotid artery: linear regression analysis

BACKGROUND AND PURPOSE: We sought to assess whether contrast-enhanced MR angiography is able to predict the degree of angiographic stenosis of the internal carotid artery within a clinically acceptable margin of error, thereby decreasing the need for angiography. In addition, we sought to assess whether adding ultrasound peak systolic velocity (PSV) as an additional regressor improves the accuracy of prediction. METHODS: A retrospective review of our institution's records for a 4-year period was conducted to identify all patients who had undergone evaluation of their carotid arteries using digital subtraction angiography, contrast-enhanced MR angiography, and ultrasonography. All internal carotid artery stenoses ranging from 10% to 90% at carotid angiography were selected (n = 22). Measurements were then obtained based on the North American Symptomatic Carotid Endarterectomy Trial style by using the digital subtraction angiograms and contrast-enhanced MR angiograms in a blinded fashion. The correlation between digital subtraction angiography data and contrast-enhanced MR angiography data was assessed by conducting linear regression analysis. Multiple regression analysis was then conducted to determine whether the inclusion of ultrasound PSV as an additional regressor increased the accuracy of prediction. RESULTS: The correlation between the degree of stenosis measured by digital subtraction angiography and that measured by contrast-enhanced MR angiography was r = 0.967. The 95% confidence interval for the line of means showed low errors bounds, ranging as low as +/-2.8%. The 95% confidence interval for individual prediction of angiographic stenosis based on a given contrast-enhanced MR angiographic measurement, however, was significantly larger, being no less than +/-13.6%. With the inclusion of PSV, the adjusted correlation was r = 0.965. CONCLUSION: A clear linear relationship exists between digital subtraction angiographic and contrast-enhanced MR angiographic measurements of carotid stenosis. Increasing severity of stenosis as measured by contrast-enhanced MR angiography corresponds to increasing severity at angiography. Although the predictive value of contrast-enhanced MR angiography is excellent in the mean, it is less reliable for predicting the degree of angiographic stenosis in the individual patient, showing rather wide confidence intervals. Furthermore, the inclusion of PSV as an additional regressor does not improve the predictive accuracy beyond that of contrast-enhanced MR angiography alone.