High-Spatial-Resolution 3D Balanced Turbo Field-Echo Technique for MR Angiography of the Renal Arteries: Initial Experience 1

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1 Kenneth L. Coenegrachts, MD Romhild M. Hoogeveen, PhD Johan A. Vaninbroukx, MD Hilde T. Bosmans, PhD Didier J. Bielen, MD Geert Maleux, MD Frederik Maes, PhD Pascal Hamaekers Raymond H. Oyen, MD, PhD Guy J. Marchal, MD, PhD Index terms: Magnetic resonance (MR), threedimensional, Magnetic resonance (MR), vascular studies, Renal arteries, stenosis or obstruction, , Published online before print /radiol Radiology 2004; 231: Abbreviations: DSA digital subtraction angiography MIP maximum intensity projection 3D three-dimensional 1 From the Department of Radiology (K.L.C., J.A.V., H.T.B., D.J.B., G.M., P.H., R.H.O., G.J.M.) and Laboratory of Medical Imaging Research (F.M.), University Hospitals Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium; and Philips Medical Systems, Best, the Netherlands (R.M.H.). Received January 11, 2003; revision requested March 24; final revision received August 4; accepted September 29. Address correspondence to K.L.C. ( kcoenegrachts74@yahoo.com). Author contributions: Guarantors of integrity of entire study, K.L.C., H.T.B., R.H.O., G.J.M.; study concepts and design, K.L.C., H.T.B., R.H.O., G.J.M.; literature research, K.L.C., H.T.B.; clinical studies, K.L.C., J.A.V., G.M., P.H.; data acquisition, K.L.C., P.H.; data analysis/interpretation, K.L.C., R.M.H., H.T.B., D.J.B., G.M.; statistical analysis, K.L.C., F.M.; manuscript preparation, K.L.C., H.T.B.; manuscript definition of intellectual content, K.L.C., H.T.B., R.H.O., G.J.M.; manuscript editing, K.L.C., H.T.B.; manuscript revision/review, J.A.V., R.H.O., G.J.M.; manuscript final version approval, H.T.B., G.J.M. RSNA, 2004 High-Spatial-Resolution 3D Balanced Turbo Field-Echo Technique for MR Angiography of the Renal Arteries: Initial Experience 1 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, 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 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, 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 was for grading of stenoses and 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. RSNA, 2004 The current state-of-the-art magnetic resonance (MR) angiographic technique for renal artery imaging involves the application of a fast gradient-echo sequence during intravenous injection of a T1 contrast agent. Several studies in which contrast-enhanced MR angiography was compared with digital subtraction angiography (DSA) have established the value of contrast-enhanced MR angiography (1 7). Some authors have concluded that contrast-enhanced MR angiography can be used to screen for renovascular disease (8). Compared with contrast-enhanced MR techniques, flow-based MR techniques such as time-of-flight or phase-contrast imaging have never been used successfully for this purpose. One of the main problems has been insufficient vessel to soft-tissue signal intensity contrast relative to the saturation of the signal of inflowing blood. In addition, relatively long acquisition times made image acquisition during a single breath hold impossible with flow-based techniques. Image blurring was the result. In practice, only the proximal centimeters of the main renal arteries could be successfully visualized (9,10). 237

2 There are several clinical situations in which the use of a contrast agent for MR angiography compromises the quality of other investigations performed during the same MR imaging session. A typical example is the work-up of a patient prior to renal surgery: A single imaging session that includes the acquisition both of a renal perfusion study and of contrast-enhanced MR angiographic images is not optimal for either one or the other of these measurements. The relative invasiveness and cost of the intravenous contrast agent used at MR angiography limit the potential of this technique for large-scale screening. The balanced turbo field-echo MR angiographic technique is based on a gradient-echo sequence in which the gradients are fully balanced without spoiling of the transverse magnetization. The result is a steady-state signal that is nearly independent of the actual repetition time. The signal-to-noise ratio is relatively high even without the use of a contrast agent (11). The short repetition time allows imaging during a single breath hold. High spatial resolution is achieved with the small voxel sizes and dedicated k-space schemes. Because of the specific characteristics of the balanced turbo field-echo technique on the one hand and the relatively high T2/T1 ratio of the blood on the other hand (11,12), blood vessels maintain a hyperintense signal over a longer distance than with conventional time-of-flight techniques. The purpose of our study was to compare a multislab balanced turbo fieldecho MR angiographic technique, without the use of a contrast agent, with DSA for imaging of the renal arteries. MATERIALS AND METHODS Patients Twenty-five patients (eight women and 17 men aged years; mean age of women, 75.6 years 5.8 [SD]; mean age of men, 70.6 years 15.5) who were suspected of having renal artery stenosis and were scheduled for abdominal DSA were randomly selected for additional examination of the renal arteries with balanced turbo field-echo MR angiography. There were no statistically significant differences between the age distributions by sex. Written informed consent was obtained for all patients. Our institutional ethics committee approved our study. MR Imaging Technique All MR examinations were performed with a 1.5-T MR imager (Intera; Philips Medical Systems, Best, the Netherlands). The maximum gradient strength was 30 mt/m. The minimum time taken to reach this gradient amplitude was 200 sec. All examinations were performed with a phased-array body coil. A balanced fast field-echo sequence was applied in the coronal plane for localization of the origin of the main renal arteries and in the sagittal plane for localization of the origin of the superior mesenteric artery. A balanced turbo fieldecho sequence then was applied with the following parameters: repetition time msec/echo time msec, 6.9/3.45; flip angle, 80. The water-fat shift was 0.4 pixel (bandwidth, Hz/pixel). The number of shots was 39. The matrix was reconstructed to a matrix. A field of view of 300 mm and a rectangular field of view of 35% (reduction to 35% in the number of phase encodings) were used. The imaging percentage was 100%. Reconstructed voxel dimensions were mm. Water-selective excitation was performed for fat suppression. Phase wrapping was eliminated in the anteroposterior direction with activation of fold-over suppression (number of signals acquired, two) and caudocephalad with 5% section oversampling. Three saturation pulses were applied prior to each balanced turbo field-echo shot to provide venous signal suppression (Fig 1). Two saturation slabs covered the hilum of each kidney. A third saturation slab was positioned parallel and caudal to the three-dimensional (3D) imaging volume at a distance of 10 mm to provide suppression of signal from the inferior vena cava. The acquisition time per 3D slab was 21 seconds. Breath holding was performed at end expiration. The acquisition protocol consisted of two measurements: a single-slab acquisition at the level of the main renal arteries, and a multislab acquisition (multiple overlapping thin-slab acquisitions, or MOTSA) that covered the arterial anatomy from the origin of the superior mesenteric artery to the aortic bifurcation. Total imaging time was less than 10 minutes per patient. After acquisition of the 3D MR angiographic data, maximum intensity projection (MIP) images in different planes were obtained at the main console of the MR imaging unit by using the standard tools. Conventional angiography was preceded by sterile preparation of the groin with a 70% alcohol solution containing 0.5% chlorhexidine. Angiography was performed with local anesthesia by using a 1% xylocaine solution (Astra Zeneca, Brussels, Belgium). Prior to puncture of the femoral artery, a small cutaneous incision was made with a no. 11 surgical blade (Swann-Morton, Sheffield, England) held flat. Either a single arterial wall puncture or the Seldinger technique was used with a needle-styletted 18- gauge intravenous catheter (SurFlash; Terumo, Louvain, Belgium). After introduction of a inch, 150-cm, angledtip hydrophilic guide wire (Kayak; Boston Scientific Medi-Tech, Natick, Mass), a 5-F, 150-cm-long sheath (Radiofocus Introducer II; Terumo) was inserted, along which a calibrated pigtail catheter (Royal Flush; Cook, Winston-Salem, NC) was advanced to the estimated level of the ostium of the renal arteries. An anteroposterior view and two oblique projections at an angle of approximately 45 were obtained during the injection of 30 ml of iobitridol (Xenetix 300; Codali Guerbet, Brussels, Belgium), a nonionic contrast agent containing 300 mg of iodine per milliliter, at a rate of 15 ml per second by using an injector (Mark V Plus; Medrad, Indianola, Pa). Angiography was performed with a C-arm system (Integris 3000; Philips Medical Systems). MR angiography and DSA were performed within 1 week of each other, with MR angiography preceding DSA in all cases. Image Evaluation All images were evaluated independently by three vascular radiologists (J.A.V., D.J.B., G.M., with 6, 16, and 11 years of experience, respectively, in the interpretion of MR angiography and DSA studies). All MR images were stored on optical disk and reviewed at a picture archiving and communication system workstation (Agfa, Antwerp, Belgium). In a first session, the balanced turbo field-echo images were evaluated. To prevent bias, the images from the different patients were presented in random order. The DSA images were evaluated in a second session 2 weeks after the first session. In cases of disagreement among the three evaluating radiologists, a final evaluation was performed by consensus in a third evaluation session. A third evaluation session was performed for images from one patient. Images were evaluated for depiction of the entire main renal artery to the point of its branching into the segmental arteries at the level of the renal hilum. Detection of stenosis at the level of the main renal arteries was recorded. Ostial loca- 238 Radiology April 2004 Coenegrachts et al

3 Figure 1. Coronal (left), transverse (upper right), and sagittal (lower right) images from balanced fast field-echo MR imaging show the positioning of the 3D acquisition volume at the level of the main renal arteries, the two saturation slabs over the hila of both kidneys, and the third saturation slab parallel and caudal to the acquisition volume at a distance of 10 mm. tion of stenosis was defined as location within 5 mm of the origin of the main renal artery; nonostial location was defined as location more than 5 mm from the origin of the main renal artery. Detected stenoses were classified in four groups according to grade (ie, percentage of reduction in luminal diameter): less than 50%, 50% 80%, more than 80%, and occlusion. All detected stenoses were measured with calipers on the images. Images also were evaluated for depiction of accessory renal arteries. In addition, the source images and MIP images obtained with balanced turbo field-echo MR angiography were assessed for artifacts. Motion artifacts were evaluated as absent, present without degradation of diagnostic quality, or present with degradation of diagnostic quality. Saturation of the venous signal and overlapping hyperintensities in the surrounding tissues were assessed as either absent or present. Statistical Analysis For statistical analysis, each stenosis grade was assigned an ordinal score. Absence of stenosis was assigned a score of 0, stenosis of less than 50% was assigned a score of 1, stenosis of 50% 80% was assigned a score of 2, stenosis of more than 80% was assigned a score of 3, and occlusion was assigned a score of 4. Sensitivity, specificity, negative predictive value, and positive predictive value of as a diagnostic test for renal artery stenosis were calculated for all main renal arteries evaluated for stenosis. Receiver operating characteristic analysis was performed for evaluation of all main renal arteries for hemodynamically significant stenosis. DSA was the method of reference. Because stenoses of more than 80% were considered hemodynamically significant, grades 0 2 were regarded as negative test results for renal artery stenosis and grades 3 and 4 were regarded as positive test results for renal artery stenosis. The Cohen analysis was used to test for agreement between balanced turbo fieldecho MR angiography and DSA with respect to grade of stenosis and with respect to the presence or absence of hemodynamically significant stenosis. RESULTS DSA depicted 50 main renal arteries in 25 patients. Eleven stenotic lesions, six with ostial locations and five with nonostial locations, were detected. In another patient, a string-of-beads pattern compatible with fibromuscular dysplasia was detected on the right side. The results of stenosis grading with DSA and with balanced turbo field-echo MR angiography are shown in the Table for 46 of 50 main renal arteries. The Table does not include grading results from one patient who was uncooperative and in whom the main renal arteries, which appeared normal on DSA images, could not be evaluated with balanced turbo field-echo imaging. In addition, results from the patient with fibromuscular dysplasia are not shown in the Table. Eleven accessory renal arteries one in each patient with detected stenosis were depicted with DSA. Balanced turbo field-echo MR angiography successfully depicted 46 of 50 main renal arteries at least to the point of their branching into the segmental arteries (Fig 2). Two main renal arteries were not depicted because the patient was uncooperative during MR angiography. In the remaining two main renal arteries, the part of the main artery that was distal to a high-grade stenosis could not be visualized until the branching point. All 11 stenotic lesions were detected and accurately localized with the balanced turbo field-echo technique, which Volume 231 Number 1 MR Angiography of Renal Arteries 239

4 Comparison of Grading with Both Balanced Turbo Field-Echo MR Angiography and DSA in 46 Main Renal Arteries Grade at Balanced Turbo Field-Echo MR Angiography No 50% also correctly depicted the abnormalities in the patient with fibromuscular dysplasia (Fig 3). This patient was not evaluated further for stenosis grading. The results of stenosis grading with versus DSA are shown in the Table. With balanced turbo field-echo imaging, seven of 11 stenotic lesions were correctly graded (Fig 4); there was disagreement, however, in the grading of four stenotic lesions. Results with the balanced turbo field-echo technique were the same as those with DSA in 42 of the 46 main renal arteries evaluated for stenosis, including all 35 main renal arteries with no stenosis, three with stenosis of less than 50%, and four with stenosis of more than 80%. The results of stenosis grading with differed from those with DSA in four main renal arteries with stenotic lesions (the same four of 11 mentioned in the preceding paragraph). Although the results of stenosis grading with the balanced turbo field-echo technique were wrong in these four arteries, the grading error in three of the arteries would have had no influence on patient work-up (Table). The results of stenosis grading and the diagnostic work-up based only on were wrong in one main renal artery. In the assessment of all 46 main renal arteries for the presence of significant stenosis, had a sensitivity, specificity, negative predictive value, and positive predictive value of four of four (100%), 41 of 42 (98%), 41 of 41 (100%), and four of five (80%), respectively. The area under the receiver operating characteristic curve was (standard error, 0.039; 95% CI: 0.901, 0.994). With respect to the presence or absence of significant stenosis, the value was (95% CI: 0.639, 1.115). With respect to grade of stenosis, the value was (95% CI: 0.578, 0.986). Balanced turbo field-echo Grade at DSA 50% 80% MR angiography also depicted 10 of 11 accessory renal arteries (Fig 5). In 22 of 25 patients, there was no visible motion degradation of the source images. On images from two patients, motion degradation was present, but the images were considered diagnostically useful. One study was nondiagnostic because of motion degradation. In all but one patient, there was complete saturation of the venous signal. On the other hand, the MIP images were mostly of poor quality due to overlapping hyperintensities from surrounding tissues. DISCUSSION 80% Occlusion No stenosis % stenosis % 80% stenosis % stenosis Occlusion Balanced turbo field-echo imaging belongs to the same category as the earlierintroduced time-of-flight techniques. Because of the specific features of the balanced turbo field-echo technique and the relatively high T2/T1 ratio of the blood, blood vessels show hyperintense signal over a longer distance with balanced turbo field-echo imaging than with conventional time-of-flight techniques. The application of water-selective excitation is crucial to obtain good fat suppression. The unique property of balanced turbo field-echo techniques the splitting of the train of radiofrequency pulses into several trains of balanced turbo field-echo pulses (balanced turbo field-echo shots) is crucial for venous signal suppression. With the proposed use of saturation pulses, the balanced turbo field-echo technique allows robust saturation of the signal coming from blood in the renal veins and the inferior vena cava. Acquisition of volumes in the transverse plane is preferred to maximize the inflow effect, as in time-of-flight studies in the brain, in which multiple overlapping thin slabs are routinely acquired if the whole brain must be imaged (13). The shortest possible repetition time and echo time are used: A short echo time is Figure 2. (a) Source image from balanced turbo field-echo (6.9/3.45; flip angle, 80 ) MR angiography shows two normal main renal arteries at the level of their branching into the segmental and intrarenal arteries. (b) Corresponding coronal MIP image and (c) coronal image from DSA show the main renal arteries (arrows). A fluid accumulation in the bile duct (arrowhead) degrades the MIP image. Figure 3. (a) Source image from balanced turbo field-echo (6.9/3.45; flip angle, 80 ) MR angiography and coronal image from DSA show a string-of-beads pattern (arrow) indicative of fibromuscular dysplasia in the distal right main renal artery. used to minimize flow-induced dephasing, and a short repetition time guarantees an acceptable acquisition time. 240 Radiology April 2004 Coenegrachts et al

5 Figure 4. (a) Source image and corresponding (b) coronal MIP image from balanced turbo field-echo (6.9/3.45; flip angle, 80 ) MR angiography and (c) coronal image from DSA show a stenotic lesion (arrow) in the ostium of the left main renal artery. Theoretically, the extent of the segment of the renal arteries visualized with the balanced turbo field-echo technique still partly depends on the inflow saturation effect. The amount of saturation is much smaller with the balanced turbo field-echo technique than with time-offlight methods because of intrinsic preservation of the transverse magnetization. Saturation is not problematic for evaluation of the main renal arteries in either young or old patients on source images acquired with the balanced turbo fieldecho technique, compared with the previously used flow-based techniques (time-of-flight and phase-contrast imaging). This finding is remarkable because only the first few proximal centimeters of the main renal arteries could be visualized with these earlier techniques on a routine basis (9,10). The correct grading of stenoses has always been a challenge with MR angiography. Time-of-flight techniques tend to lead to overestimation of stenosis because of signal dispersion in turbulent flow. This situation is aggravated in phase-contrast imaging. Contrast-enhanced MR angiography is less sensitive to this effect because the echo time is extremely short. In a recent study, Saloner et al (14) found that even with contrast-enhanced MR angiography, grading of stenoses might be incorrect. A true reference standard may be intraoperative measurement. Ex vivo validation can be based on casts made from specimens, as proposed by Saloner et al (14). Specimens were not available to us, however, because most of the patients in our study did not undergo renal artery surgery. DSA was chosen as the reference standard. This study shows that it is feasible to correctly grade stenotic lesions of different severity with the balanced turbo field-echo technique, although there is a tendency to overestimate stenoses with this technique, compared with DSA. This can be explained by a dephasing effect at the level of stenosis that is similar to known effects in time-of-flight and phase-contrast techniques. In the balanced turbo field-echo sequence, echo time is as short as possible to minimize its sensitivity to dephasing effects. There is no clear explanation for the underestimation of one stenosis with balanced turbo field-echo MR angiography. In four of 50 main renal arteries in this study, imaging with the balanced turbo field-echo technique was suboptimal. In two main renal arteries, depiction was poor because the patient was uncooperative. In two main renal arteries, the part of the main renal artery distal to a highgrade stenosis could not be visualized until the point of branching into the segmental arteries. A dephasing effect at the level of these stenoses and a loss of sufficient inflow could explain the loss of signal in the main renal artery distal to the stenosis. In such cases, use of the balanced turbo field-echo technique for initial evaluation may result in a need for additional angiographic examinations that would have been obviated by use of contrast-enhanced MR angiography. evaluation with the balanced turbo field-echo sequence resulted in neither false-positive nor false-negative findings. This fact is important for the comparison of this technique with previously used flow-based techniques (time-of-flight and phase-contrast imaging), because many false-positive results in the past were caused by flow artifacts (9,15,16). The combination of a good inflow effect and a good T2/T1 ratio of the blood can explain these findings. A benefit of the balanced turbo fieldecho sequence is the acquisition speed and the ability to perform imaging during breath holding. The advantages of imaging during breath holding are obvious and include the reduction or avoidance of motion artifacts. The spatial resolution of images acquired with this technique is acceptable overall but may have to be further improved for more accurate assessment of stenoses. The one patient with fibromuscular dysplasia is not a sufficiently large sample from which to draw conclusions concerning the ability of balanced turbo field-echo MR angiography to depict fibromuscular dysplasia. More patients with proved fibromuscular dysplasia at DSA will have to be evaluated with balanced turbo field-echo MR angiography for comparison in future studies. The quality of the MIP images was mostly insufficient because of overlapping hyperintensities from fluid in the intestines, bile in the distal extrahepatic ducts, or fluid in a prominent ureter. In this regard, the source images from balanced turbo field-echo MR angiography are far more important for diagnosis and stenosis grading than are MIP images. More advanced visualization techniques should be used in future MR angiographic examinations with balanced turbo field-echo techniques. The high sensitivity and negative predictive value of balanced turbo field-echo MR angiography for the evaluation of hemodynamically significant main renal artery stenoses suggest that this method may have prospects for use in the screening and selection of patients for interventional DSA of the renal arteries. With respect to grading of stenosis, the value reveals substantial agreement. With respect to depicting the presence of significant stenosis, the value reveals almost perfect agreement. The main limitation of this study is the restricted number of cases. Further clinical studies are needed to confirm these preliminary results. Technical optimizations are needed to improve the quality of the MIP images and the grading of stenoses. A reduction of echo time may further reduce the dephasing effect at the level of stenoses. A further reduction of the acquisition time with, for instance, parallel imaging or more powerful slew Volume 231 Number 1 MR Angiography of Renal Arteries 241

6 Figure 5. (a, b) Source images and (c) corresponding oblique transverse MIP image from balanced turbo field-echo (6.9/3.45; flip angle, 80 ) MR angiography show an accessory right renal artery (arrows). These images exemplify the high spatial resolution achievable with the balanced turbo field-echo technique. (d) Coronal image from DSA confirms the presence and location of the accessory artery (arrows). rates will probably allow improvement of the results in uncooperative patients. The use of a navigator-gated technique might also help to improve image quality in uncooperative patients. An improvement of spatial resolution will probably be of benefit in the evaluation of fibromuscular dysplasia and of stenotic lesions. In conclusion, the balanced turbo fieldecho technique in most cases enabled accurate visualization of the main renal arteries to the point of their branching into the segmental arteries without the use of an intravenous contrast agent. Correlation with DSA was good in the grading of main renal artery stenoses and in the depiction of accessory renal arteries. The balanced turbo field-echo technique presented holds promise for accurate differentiation between normal arteries and arteries with atherosclerotic disease. References 1. Schoenberg SO, Bock M, Knopp MV, et al. Renal arteries: optimization of three-dimensional gadolinium-enhanced MR angiography with bolus-timing-independent fast multiphase acquisition in a single breath hold. Radiology 1999; 211: Masunaga H, Takehara Y, Isoda H, et al. Assessment of gadolinium-enhanced time-resolved three-dimensional MR angiography for evaluating renal artery stenosis. AJR Am J Roentgenol 2001; 176: Van Hoe L, De Jaegere T, Bosmans H, et al. Breath-hold contrast-enhanced three-dimensional MR angiography of the abdomen: time-resolved imaging versus single-phase imaging. Radiology 2000; 214: Maki JH, Chenevert TL, Prince MR. Contrastenhanced MR angiography. Abdom Imaging 1998; 23: Hany TF, Debatin JF, Leung DA, Pfammatter T. Evaluation of the aortoiliac and renal arteries: comparison of breath-hold, contrast-enhanced, three-dimensional MR angiography with conventional catheter angiography. Radiology 1997; 204: Schoenberg SO, Knopp MV, Bock M, Prince MR, Allenberg JR. Combined morphologic and functional assessment of renal artery stenosis using gadolinium enhanced magnetic resonance imaging. Nephrol Dial Transplant 1998; 13: Schoenberg SO, Essig M, Bock M, Hawighorst H, Sharafuddin M, Knopp MV. Comprehensive MR evaluation of renovascular disease in five breath holds. J Magn Reson Imaging 1999; 10: Dong Q, Schoenberg SO, Carlos RC, et al. Diagnosis of renal vascular disease with MR angiography. RadioGraphics 1999; 19: Loubeyre P, Revel D, Garcia P, et al. Screening patients for renal artery stenosis: value of three-dimensional time-of-flight MR angiography. AJR Am J Roentgenol 1994; 162: Duda SH, Schick F, Teufl F, et al. Phase-contrast MR angiography for detection of arteriosclerotic renal artery stenosis. Acta Radiol 1997; 38: Hoogeveen RM, Vasbinder B. High-resolution 3D breath-hold inflow balanced-ffe of the renal arteries (abstr). In: Proceedings of the Tenth Meeting of the International Society for Magnetic Resonance in Medicine. Berkeley, Calif: International Society for Magnetic Resonance in Medicine, 2002; Scheffler K, Heid O, Hennig J. Magnetization preparation during the steady state: fat-saturated 3D TrueFISP. Magn Reson Med 2001; 45: Davis WL, Warnock SH, Harnsberger HR, Parker DL, Chen CX. Intracranial MRA: single volume vs. multiple thin slab 3D time-offlight acquisition. J Comput Assist Tomogr 1993; 17: Saloner D, Ong K, Rapp JH, and the ACSCEPT investigators. Overestimation of carotid stenosis on contrast-enhanced MRA (abstr). In: Proceedings of the Tenth Meeting of the International Society for Magnetic Resonance in Medicine. Berkeley, Calif: International Society for Magnetic Resonance in Medicine, 2002; Lewin JS. Time-of-flight magnetic resonance angiography of the aorta and renal arteries. Invest Radiol 1992; 27(suppl):S84 S Loubeyre P, Cahen R, Grozel F, et al. Transplant renal artery stenosis: evaluation of diagnosis with magnetic resonance angiography compared with color duplex sonography and arteriography. Transplantation 1996; 62: Radiology April 2004 Coenegrachts et al