Original Research

Contrast Enhanced MR Angiography With ParallelImaging in the Early Period After RenalTransplantation

Hubert Gufler, MD,1,2* Wolfgang Weimer, MD,3 Kathleen Neu, MD,3 Sabine Wagner, MD,1

and Wigbert Stephan Rau, MD2

Purpose: To evaluate renal allograft vessels in the earlyperiod after kidney transplantation with three-dimensional(3D) contrast-enhanced MR angiography (3D CE MRA) us-ing a parallel imaging technique.

Materials and Methods: Sixty-three consecutive patientswere examined with 3D CE MRA and integrated SENSEtechnique (Sensitivity Encoding) 2 to 21 days after renaltransplantation. MR angiography studies were analyzed forthe presence of arterial stenosis. The degree of renal trans-plant artery stenosis was graded qualitatively as �50% �mild, 50–70% � moderate, 70–99% � severe, and occlu-sion. Four patients (6.3%) with moderate (n � 1) or severe(n � 3) arterial stenoses on CE MRA underwent selectiveintra-arterial digital subtraction angiography. In two pa-tients, selective intravenous digital subtraction angiogra-phy (DSA) was performed.

Results: Twenty-seven (42.9%) of the 63 patients had nor-mal CE MR angiograms, 29 (46%) showed mild, 3 patients(4.8%) moderate, and 4 patients (6.3%) severe stenoses ofthe donor artery. In three patients, the severe stenosis ofthe graft artery was confirmed by surgery or intra-arterialDSA. One patient with suspicion of severe arterial stenosison MRA had moderate vessel narrowing on DSA. Twelvemonths after kidney transplantation, serum creatinine lev-els were not significantly different in patients with mild andmoderate stenoses from those without (P � 0.19) but sig-nificantly different from those with severe stenoses (P �0.05).

Conclusion: The incidence of mild and moderate vesselnarrowing at the arterial anastomosis is unexpectedly highin the early period after kidney transplantation and is mostlikely due to surgery-related tissue edema.

Key Words: magnetic resonance angiography; parallel im-aging; renal transplantationJ. Magn. Reson. Imaging 2009;29:909–916.© 2009 Wiley-Liss, Inc.

THE PREVALENCE OF arterial hypertension after renaltransplantation ranges from 74% to 86% (1). Trans-plant renal artery stenosis accounts for approximately1 to 5% of cases of posttransplant hypertension andapproximately 75% of all posttransplant vascular com-plications (2). The incidence of transplant artery steno-sis varies, depending on the definition and diagnosticmethod used, from 1% to 23% (3).

Digital subtraction angiography (DSA) is the acceptedthough not a perfect reference test for the assessment ofstenoses in transplant vessels (4–6). However, it is in-vasive, associated with radiation exposure and with therisk of nephrotoxicity due to the use of ioninated con-trast agent, particularly in patients with impaired renalfunction. Therefore, noninvasive imaging modalities areused first-line to detect and locate vascular complica-tions after renal transplantation.

Color coded Doppler ultrasonography provides infor-mation about the perfusion in the transplanted kidney,it is relatively inexpensive, not invasive, and can beperformed at bedside while the patient is still in theintensive care unit. However, the method is stronglyoperator dependent and does not allow for a reliableexclusion of transplant artery stenosis in a part of pa-tients with high-peak systolic velocities at the anasto-mosis, in vessel kinking, and in pronounced loop (7).The reported cutoff values for relevant arterial stenosisvary in a wide range between 180 cm/s and 300 cm/sand seem not to be discriminative in the immediatepostoperative phase (8–10). High peak systolic veloci-ties at the anastomosis of the renal transplant arteryare particularly common in the early postoperative pe-riod.

Three-dimensional (3D) contrast-enhanced MR an-giography (CE MRA) is an accepted technique for exam-ination of the abdominal aorta, the renal arteries, andthe renal transplant arteries with the advantages of notbeing invasive and not using ionizing radiation (11,12).

1Department of Diagnostic and Interventional Radiology, UniversityClinic of Rostock, Rostock, Germany.2Department of Diagnostic Radiology, University of Giessen, Giessen,Germany.3Medical Clinic II, University of Giessen, Giessen, Germany.*Address reprint requests to: H.G., Department of Diagnostic and In-terventional Radiology, University Clinic of Rostock, Ernst Heyde-mannstrasse 6, D-18055 Rostock, Germany. E-mail: hgufler@gmx.deReceived June 21, 2008; Accepted January 6, 2009.DOI 10.1002/jmri.21726Published online in Wiley InterScience (www.interscience.wiley.com).

JOURNAL OF MAGNETIC RESONANCE IMAGING 29:909–916 (2009)

© 2009 Wiley-Liss, Inc. 909

A meta-analysis study demonstrated that computed to-mographic angiography (sensitivity, 96–100; specific-ity, 95–99) and 3D CE MRA (88–100; 75–100) per-formed significantly better than ultrasonography (17–100; 76–98), captopril renal scintigraphy (57–94; 44–98), and captopril test (15–68; 76–93) in detecting renalartery stenosis (13). In a multicenter study, however,the reported sensitivity for 3D CE MRA in the detectionand grading of renal artery stenosis was only 62% andthe specificity 84% (14). These poor results may beattributed to the non-uniform MR systems and to partlyout of date software equipment used in the studies withfield strengths of 1 or 1.5 Tesla (T), range of pixel sizesfrom 1 � 1.3 � 2.2 mm to 1 � 1.9 � 3 mm, andacquisition times from 25 to 30 s. With the integrationof advanced parallel acquisition techniques, the acqui-sition time can be reduced substantially, alternativelythe spatial resolution or the number of slices can beincreased at a constant acquisition time (15–17). Byincreasing the acquisition matrix from 208 to 416 andkeeping the scan time constant, Born et al achieved asignificant improvement in imaging quality of the ab-dominal arteries using the SENSE technique withbreath hold 3D CE MRA on a 1.5T system (18).

The purpose of our study was to evaluate the renalallograft vessels in the early period after kidney trans-plantation using a fast contrast-enhanced 3D MR an-giography acquisition and a parallel imaging technique.

MATERIALS AND METHODS

Patients

Between February 2003 and May 2005, 63 consecutivepatients of a single transplant center participated inthis study. The age of the patients (26 women and 37men) ranged from 15 to 71 years (median age � 47.1years). MRI of the pelvis and CE MRA were offered to allpatients after renal transplantation to exclude surgery-related complications and graft artery stenosis. Twopatients refused, one of them because of claustropho-bia, the remaining patients (or their parents) gave in-formed consent. All but two patients, who were exam-ined on the second postoperative day because ofdeterioration of renal function, underwent MR imaging10 to 21 days after transplantation. Color Doppler ul-trasonography was performed within 2 h after trans-plantation; 1 week after transplantation; before dis-charge from hospital; and 3, 6, and 12 months aftertransplantation or closer if creatinine levels gave sus-picion of impaired renal function. Graft function, in-cluding serum creatinine levels, was assessed accord-ing to the European best practice guidelines for renaltransplantation (19).

Imaging Technique

MR angiography was performed on a 1.5T Philips Gy-roscan Intera (Philips Medical Systems, Best, The Neth-erlands) with high power gradients (maximum ampli-tude � 60 mT, slew rate � 150 mT/m/s) using aparallel imaging technique (Sensitivity encoding,SENSE). For signal reception, a four-element phased-array surface coil was used covering the entire pelvis.

The coil sensitivity profiles required for the sensitivityencoding image reconstruction were derived from a sep-arate calibration scan that preceded parallel imaging.Axial 2D T1-weighted spoiled gradient-echo (repetitiontime/echo time [TR/TE] � 120/4.6 ms; flip angle � 80°;matrix � 256 � 256; field of view [FOV] � 320–400;acceleration � 1.5, in the anterior–posterior phase-en-coding direction; acquisition time � 15–21 s; slicethickness � 7 mm) and T2-weighted turbo spin-echobreath hold sequences (TR/TE � 2500/100 ms; echotrain length � 53; matrix � 256 � 256; FOV � 320–400; slice thickness � 6 mm; acquisition time � 12 s)were obtained to examine the renal parenchyma, theperirenal region and the pelvis. Additionally, a respira-tory triggered 2D steady-state free precession (SSFP)sequence (TR/TE � 4.2/2.1 ms; flip angle � 90°; ma-trix � 192 � 192; FOV � 320–400; slice thickness � 5;acceleration � 1.5, in the anterior–posterior phase-en-coding direction) in at least the axial plane was used tovisualize the vascular structures (Fig. 1a,b). SSFPscans served as reference images for planning the 3DCE MRA. For this purpose, a three-point mode wasused, which allows investigators to span a plane in anydesired spatial orientation. We set these points at thearterial anastomosis, in the center of the graft, and inthe proximal ipsilateral common iliac artery that theentire kidney and the graft artery were covered by theacquisition slap. A breath-hold 3D spoiled gradient-echo sequence was used for MR angiography (TR/TE �4.3 ms/1.5 ms; flip angle � 35°; interpolated slicethickness, 1.0–1.2 mm; matrix, 432 � 512; FOV �280–380 cm; centric phase-encode ordering scheme,which fills in the central k-space lines first; accelera-tion � 2, in the anterior–posterior direction; acquisitiontime � 19–23 s; Fig. 1c). 0.1 mmol/kg body weight ofGd-DTPA (Magnevist, Schering, Germany) at 2.5 mL/swere administered intravenously by power injector. Thebolus of contrast medium was traced with real-timeMR-imaging (BolusTrak) in the coronal plane that cov-ered the abdomen and the pelvis. The 3D GRE MRangiographic sequence was started when the bolus ofthe contrast medium reached the iliac artery. After CEMRA, the axial 2D T1-weighted gradient echo sequencewas repeated. Contrast-enhanced MR-urography wasfinally carried out 4–5 min after gadolinium adminis-tration using the same pulse sequence as for 3D GREMRA but changing the slice thickness to 2–2.5 mm toinclude the whole kidney and the bladder into the slab(Fig. 1d).

In four patients with moderate (n � 1) or severe (n �3) arterial stenoses on CE MRA, selective arterial DSAwas performed. These patients had deterioration of re-nal function and/or sudden onset or worsening of pre-existing arterial hypertension, which are establishedcriteria for severe transplant artery stenosis in the ab-sence of graft rejection, ureteric obstruction, and infec-tion (1). Selective intravenous DSA was carried out intwo patients after anticoagulation therapy for venousthrombosis initially diagnosed by CE MRA. Three pa-tients with mild and one patient with moderate arterialstenosis received follow-up MRA 1 year after renaltransplantation (Fig. 2).

910 Gufler et al.

Image Analysis

All MRA examinations were transferred to a postpro-cessing workstation (EasyVision 5.1, Philips, Best, TheNetherlands). Two radiologists with 6 (H.G.) and 3 years(K.N.) of experience in reading MR angiograms, inter-preted the 3D MRA images immediately after data ac-quisition. Both were blinded to the ultrasonographicfindings. 3D multiplanar reformations were createdfrom the 3D MRA data set along the axis of the graftartery, and if needed, perpendicular to the course of thevessel. Maximum intensity projections (MIPs) from theentire slab and thin MIPs with a maximum of 5 mmwere created by the reader. The degree of renal trans-plant artery stenosis was graded qualitatively as de-scribed by Huber et al as follows: �50% � mild, 50–70% � moderate, 70–99% � severe, and occlusion

compared with a normal segment distal to the stenosis(4). When clear grading of the stenosis was not possiblequalitatively, particularly near the limits of the catego-ries, additional quantitative analysis was done (10 pa-tients). Measurements of the diameters at the stenosissite and in a normal vessel segment distal to the steno-sis site were performed manually. The percentage ofdiameter stenosis was calculated according to theNorth American Symptomatic Carotid EndarterectomyTrial definition (20).

Statistical Analysis

The serum creatinine levels at 0, 3, 6, and 12 monthsafter renal transplantation were determined in thesame laboratory using the same method. These results

Figure 1. a–d: Imaging protocol. a: 2D-SSFP sequence axial image with respiratory triggering to visualize vascular structuresfor planning 3D CE MRA. Arterial anastomosis with left common iliac artery (black arrow). b: Coronal 2D-SSFP sequenceshowing anastomosis of the graft vein (white arrows) with the iliac vein (white star). c: MIP reformatted 3D CE MRA depicts thenormal transplant artery anastomosis (solid arrow), open arrow indicating internal iliac artery. d: MIP reformatted 3D CE MRurogram demonstrates normal renal pelvis and ureter (contrast agent in iliac vessel, black star).

Parallel Imaging MRA of Renal Transplant 911

were compared for patients with and without anasto-motic stenoses using the two-sample two-tailed Stu-dent t-test. A P value of less than 0.05 was considered toindicate a statistically significant difference.

RESULTS

The findings on CE MRA and MRI are summarized inTable 1. In 27 (42.9%) of 63 patients, MRA showednormal renal transplant arteries without stenosis of thegraft artery. Mild vessel narrowing (�50%) at the iliactransplant artery anastomosis was found in 29 (46%)patients. Four patients (6.3%) had severe stenoses(�70%) of the donor artery. Three (4.8%) patientsshowed a moderate narrowing (50–70%) of the lumen ofthe graft artery. Blood pressure had not deterioratedsince transplantation in these three patients and theserum creatinine concentration decreased gradually in-dicating normal graft function. Therefore, no interven-tional therapy was performed. The follow-up colorDoppler ultrasonographic examinations were unre-markable in these patients.

In one of the four patients with severe stenosis on CEMRA, vessel narrowing was downgraded to moderate onDSA (performed 3 days after CE MRA); therefore, nointerventional treatment was performed. A follow-upMRA 1 year later showed only mild stenosis.

In the second patient, a severe stenosis at the anas-tomosis was diagnosed by CE MRA on the 11th postop-erative day. On the 30th day an intra-arterial DSA wasperformed because serum creatinine levels (2.1 mg/dL)and blood pressure remained elevated, and color Dopp-ler ultrasonography was suspicious for severe arterialstenosis. On DSA, the stenosis was graded moderate,therefore, no balloon angioplasty was performed. As theblood pressure deteriorated further, a second intra-arterial DSA was carried out 1 year after transplanta-tion. The stenosis at the anastomosis was then esti-mated to be severe (Fig. 3). Percutaneous balloonangioplasty and stent placement were technically suc-cessful.

The third patient had a severe stenosis of the graftartery 1 cm distally to the vascular anastomosis on CEMRA, but perfusion of the transplant was normal atsurgery. As renal function deteriorated further, a sec-ond CE MRA was performed the following day confirm-ing the findings of the initial CE MRA (Fig. 4). Digitalangiography then proved the diagnosis of severe steno-sis of the transplant artery due to intimal lacerations. Astent graft was placed successfully. Serum creatininelevels dropped from 4 mg/dL before intervention to 3.2mg/dL, 2.3 mg/dL, and 2.1 mg/dL 3, 6, and 12 monthsafter transplantation.

Figure 2. a,b: At 15 days afterrenal transplantation. a: MIP of3D CE MRA shows moderatestenosis (long arrow). Open ar-row indicates graft vein andanastomosis with the iliac vein.b: MIP of 3D CE MRA 12months later demonstratesmild narrowing at the anasto-mosis.

Table 1List of Diagnoses at CE-MR Angiography and MR Imaging*

Anatomical features on MRI* No. Pathologic findings on MRI No.

Normal anastomosis 27 Graft arterial stenosisSite of Anastomosis Mild and moderate 32

Iliac bifurcation 54 Severe 4External iliac artery 9 Seroma of the abdominal wall 35

Complex graft vessel anatomy Perirenal seroma 511 supplementary artery 3 Venous thrombosis 22 supplementary arteries 2 Mild venous compression 13 supplementary arteries 1 Parenchymal infarcts 4

*Confirmed at surgery.

912 Gufler et al.

The fourth patient showed an elongated transplantartery with severe narrowing of the vessel lumen nearthe anastomosis on MRA. At surgery, arterial thrombo-sis was found caused by intimal damage. After throm-bectomy, reanastomosis of the graft artery was per-formed. The patient had an episode of acute transplantrejection during follow-up. Serum creatinine levels de-creased from 5.2 mg/dL before surgery to 4.3 mg/dL,3.8 mg/dL, and 4.0 mg/dL, 3, 6, and 12 months aftertransplantation.

Two patients (3.2%) had thrombosis of the transplantvein. In one patient, partial thrombosis of the donorvein was diagnosed on CE MRA. After 2 days on anti-coagulation therapy, selective intravenous DSA showedno thrombi. A second patient developed graft veinthrombosis 6 weeks after transplantation, diagnosed by

CE MRA. After systemic anticoagulation, the thrombihad resolved. The patient developed chronic transplantrejection later on.

There were no statistically significant differences ofserum creatinine levels between patients with mild andmoderate stenoses and those without 12 months afterkidney transplantation (P � 0.19). However, a signifi-cant difference was found between the patients withmild to moderate stenosis and patients with severe ste-nosis (Table 2).

DISCUSSION

Research regarding MR angiography in the early post-transplantation period, defined as the first 4 weeksafter renal transplantation, is limited in the literature

Figure 3. a–c: A 26-year-old man on the 11th day after renal transplantation showing persistent arterial hypertension. a: MIPof 3D CE MRA shows severe stenosis at the anastomotic level (arrow). b: On intra-arterial DSA, the stenosis (white arrow) wasestimated of moderate grade. As hypertension accelerated, intra-arterial DSA was repeated 12 months later, confirming severestenosis of the graft artery. c: Percutaneous balloon angioplasty and stenting (black arrow) was performed.

Figure 4. a,b: A 48-year-oldpatient on the 10th day afterrenal transplantation, with ar-terial hypertension and ele-vated creatinine serum levels.a: MIP of the CE MRA showssevere stenosis (arrow) of thegraft artery 1 cm distal to theanastomosis. b: Intra-arterialDSA confirms severe stenosisdue to an intimal flap. Treat-ment consisted in placing astent graft.

Parallel Imaging MRA of Renal Transplant 913

(21). Our study shows that vessel narrowing at thearterial anastomosis is a common finding on CE MRA inthe early period after renal transplantation (Fig. 5). Wefound mild stenosis at the anastomosis in 46.7% of allgrafts and a moderate arterial stenosis in three patients(4.8%). Serum creatinine and blood pressure measure-ments, however, were unremarkable in these patients.This high incidence of anastomotic narrowing has notbeen reported so far. We assume that tissue swelling(due to tissue damaging during harvesting and sutur-ing) at the vascular anastomosis is the most probableunderlying pathologic process for this imaging finding.This hypothesis is corroborated first, by observationsobtained with color Doppler ultrasonography showinghigh peak velocities at the vascular anastomosis in thefirst weeks after transplantation (7). Second, we found areduction of the grade of stenosis on follow-up MR an-giography in four patients 1 year after transplantation.

Graft arterial stenosis can occur at any time afterrenal transplantation, but it is reported as a complica-tion mainly of the later post transplantation period,presenting with newly developed or progressive hyper-tension, deterioration of renal function, or both (22).

Arterial stenoses after renal transplantation may belocated at the anastomotic site due to vessel perfusioninjury, faulty suture technique, or reaction to suturematerial, or distally to the anastomosis due to rejection,turbulent flow from kidney malposition, arterial twist-ing, kinking, and compression (23–26). Excessive trac-tion of the graft artery during the harvesting, cannula-tion for transplant perfusion, or a surgical clamp maycause endothelial injury, intimal tears, and vasculardissection. Beecroft et al found that primary treatmentof transplant artery stenosis with percutaneous balloonangioplasty with or without stent placement has goodintermediate-term patency and is associated with sig-nificant early improvement in blood pressure and cre-atinine level (27). Early detection and management ofarterial dissection is mandatory because renal arterythrombosis may be the consequence, leading to graftloss.

Severe graft artery stenosis may also occur in theearly postoperative phase (21). In this period, arterialstenosis must be differentiated from acute rejection,venous thrombosis, ureteric obstruction, and infection;all can cause worsening of renal function. We foundthis complication in 2 of 63 patients (3.2%) examined 2days after renal transplantation. Both severe stenoseswere caused by transplant artery lacerations. One ofthe patients had a proximal intimal flap, which led toarterial thrombosis, confirmed by surgery.

A crucial issue is how to manage moderate stenosesdetected by angiography (MRA, DSA) in the early periodafter renal transplantation. On the basis of our study,we suggest to perform clinical follow-up in these casesunless blood pressure profiles, laboratory data, andcolor Doppler ultrasonographic findings sustain the di-agnosis of severe stenosis.

Renal vein thrombosis is seen in 0.3 to 4% of patientsin the first week after transplantation (28,29). Risk fac-tors for graft venous thrombosis are vessel compressionby a lymphocele or a hematoma, hypercoagulability,hypovolemia, and technical problems at surgery. Therewere two patients with graft vein thrombosis (3.2%) inour series. In one patient, this complication did not

Table 2Serum Creatinine Levels Before MR Imaging; 3, 6, and 12 Months After Kidney Transplantation, Separated for Patients WithAnastomotic Stenosis and Those Without*

Months after kidney transplantation

0 3 6 12Pts without stenosis (n�27); mean creatinine levels 1.95 1.66 1.55 1.66SD 1.18 0.38 0.32 0.41Pts with stenosis (n�29); mean creatinine levels 1.73 2.16 1.88 1.97SD 0.53 0.74 0.54 0.56Level of significance, P 0.50 0.04† 0.09 0.14

*Creatinine levels, means, SD, and p values of patients without anastomotic stenoses and patients with mild and moderate stenoses.†Indicates statistically significant difference (two-tailed Student t-test).

Figure 5. MIP of 3D CE MRA. A 66-year-old women with alarge perfusion defect (arrows) of the lower third of the renalgraft due to occlusion of an accessory artery. Mild stenosis ofthe main graft artery is also seen (open arrow).

914 Gufler et al.

occur in the early postoperative period but developed 6weeks after transplantation.

There are limitations of our study. Only four patientsobtained intra-arterial angiography for comparison,therefore, no sensitivity or specificity values for 3D CEMRA could be calculated. Second, the evaluation of thegraft stenoses in most cases was performed qualita-tively. Measuring the vessel area perpendicular to thecourse of the graft artery may have yielded more accu-rate results for 3D CE MRA (12). Third, a further con-straint of this study is that we did not compare MR-based stenosis detection with and without parallelimaging to confirm that increased image quality leadsto a more accurate grading of transplant artery steno-ses. Last, our MR scanner software allowed a maximumparallel imaging factor of 2. Michaely et al have shownthat MRA using an iPAT (integrated parallel imagingtechnique) factor of 3 is feasible with almost isotropicsubmillimeter resolution (0.9 � 0.8 � 1.0 mm) (17).Shorter scan times and higher spatial resolution led toa significant better depiction of segmental and subseg-mental arteries. We speculate that accuracy of stenosisgrading would have been more precise if these technol-ogies were applied.

It has been recently reported that a serious adversereaction called nephrogenic systemic fibrosis (NSF) mayoccur after exposure to gadolinium-based contrastagents in patients with end-stage renal disease, glomer-ular filtration rates below 30 ml/min, acute renal dys-function due to the hepatorenal syndrome or in theperioperative liver transplantation period (30–32). Thispotential complication makes it advisable to administergadolinium-based contrast agents only after careful as-sessment of the risks and benefits of a planned MRexamination in patients after kidney transplantation.At the time of our study, it was not known that gado-linium-based contrast agents are potentially harmful inpatients with severely restricted renal function. Two ofour patients would then have been excluded from thestudy. We are not aware of any cases of nephrogenicsystemic fibrosis in our study group after havingchecked the medical reports of the follow-up examina-tions.

In conclusion, our study shows that mild to moderatevessel narrowing at the arterial anastomosis area is acommon finding in the early period after kidney trans-plantation. This high incidence has not been reportedso far. Conventional intra-arterial angiography can berestricted to patients with elevated blood pressure, im-pairment of renal function in conjunction with incon-clusive color Doppler ultrasonographic findings whoshow severe stenosis on CE-MR angiography.

REFERENCES

1. Campistol JM, Romero R, Paul J, Guitierrez-Dalmau A. Epidemiol-ogy of arterial hypertension in renal transplant patients: changesover the last decade. Nephrol Dial Transplant 2004;19(Suppl 3):62–66.

2. Bruno S, Remuzzi G, Ruggenenti. Transplant renal artery stenosis.J Am Soc Nephrol 2004;15:134–141.

3. Fervenza FC, Lafayette RA, Alfrey EJ, Petersen J. Renal arterystenosis in kidney transplants. Am J Kidney Dis 1998;31:142–148.

4. Huber A, Heuck A, Scheidler J, et al. Contrast-enhanced MR an-giography in patients after kidney transplantation. Eur Radiol2001;11:2488–2495.

5. Loubeyre P, Cahen R, Crozel F, et al. Transplant renal artery ste-nosis: evaluation of diagnosis with magnetic resonance angiogra-phy compared with color duplex sonography and arteriography.Transplantation 1996;62:446–450.

6. Krumme B, Pisarski P, Blum U, Kirste G, Schollmeyer P. Unusualcause of early graft dysfunction after kidney transplantation. Am JNephrol 1998;18:237–239.

7. Thalhammer C, Aschwander M, Mayr M, Koller M, Steiger J, JaegerKA. Duplex sonography after living donor kidney transplantation:new insights in the early postoperative phase. Ultraschall Med2006;27:141–145.

8. Li J, Ji Z, Cai S, Jiang Y, Dai Q, Zhang J. Evaluation of severetransplant renal artery stenosis with doppler sonography. J ClinUltrasound 2005;33:261–269.

9. Lockhart ME, Wells CG, Morgan DE, Fineber NS, Robbin ML. Re-versed diastolic flow in the renal transplant: perioperative implica-tions versus transplants older than 1 month. AJR Am J Roentgenol2008;190:650–655.

10. Patell U, Khaw KK, Hughes NC. Doppler ultrasound for detection ofrenal transplant artery stenosis - threshold peak systolic velocityneeds to be higher in a low-risk of surveillance population. ClinRadiol 2003;58:772–777.

11. Werder R, Nanz D, Lutz AM, et al. Assessment of the abdominalaorta and its visceral branches by contrast-enhanced dynamicvolumetric hepatic parallel magnetic resonance imaging: feasibil-ity, reliability and accuracy. Eur Radiol 2007;17:541–551.

12. Schoenberg SO, Rieger J, Weber CH, et al. High-spatial-resolutionMR angiography of renal arteries with integrated parallel acquisi-tions: comparison with digital subtraction angiography and US.Radiology 2005;235:687–698.

13. Vasbinder GB, Nelemans PJ, Kessels AG, Kroon AA, de Leeuw PW,van Engelshoven JM. Diagnostic tests for renal artery stenosis inpatients suspected of having endovascular hypertension: a meta-analysis. Ann Intern Med 2001;135:401–411.

14. Vassbinder GBC, Nelemans PJ, Kessels AG, et al. Renal ArteryDiagnostic Imaging (RADISH) Study Group. Accuracy of computedtomographic angiography and magnetic angiography for diagnos-ing renal artery stenosis. Ann Intern Med 2004;141:674–682.

15. Pruessmann KP, Weiger M, Scheidegger MB, Boesiger P. SENSE:sensitivity encoding for fast MRI. Magn Reson Med 1999;42:952–962.

16. Wilson GJ, Eubank WB, Vasbinder GB, et al. Utilizing SENSE toreduce scan duration in high-resolution contrast-enhanced renalMR angiography. J Magn Reson Imaging 2006;24:873–879.

17. Michaely HJ, Herrmann KA, Kramer H, et al. High resolution renalMRA: comparison of image and vessel depiction with different par-allel imaging acceleration factors. J Magn Reson Imaging 2006;24:95–100.

18. Born M, Willinek WA, Gieseke J, von Falkenhausen M, Schild H,Kuhl CK. Sensitivity encoding (SENSE) for contrast-enhanced 3DMR angiography of the abdominal arteries. J Magn Reson Imaging2005;22:559–565.

19. European best practice guidelines for renal transplantation (Part1). Nephrol Dial Transplant 2000;15(Suppl 7):67–69.

20. North American Symptomatic Carotid Endarterectomy Trial Col-laboration: beneficial effect of carotid endarterectomy in symptom-atic patients with high-grade carotid stenosis. N Engl J Med 1991;325:445–453.

21. Takahashi M, Humke U, Girndt M, Kramann B, Uder M. Earlyposttransplantation renal allograft perfusion failure due to dissec-tion: diagnosis and interventional treatment. AJR Am J Roentgenol2003;180:759–763.

22. Amante AJ, Kahan BD. Technical complications of renal transplan-tation. Surg Clin North Am 1994;74:1117–1131.

23. Halimi JM, Al-Najjar A, Buchler M, et al. Transplant renal arterystenosis: potential role of ischemia/reperfusion injury and long-term outcome following angioplasty. J Urol 1999;161:28–32.

24. Patel NH, Jindal RM, Wilkin T, et al. Renal arterial stenosis in renalallografts: retrospective study of predisposing factors and outcomeafter percutaneous transluminal angioplasty. Radiology 2001;219:663–667.

25. Wong W, Fynn SP, Higgins RM, et al. Transplant renal arterystenosis in 77 patients: does it have an immunological cause?Transplantation 1996;61:215–219.

Parallel Imaging MRA of Renal Transplant 915

26. Pouria S, State OI, Wong W, Hendry BM. CMV infection is associ-ated with transplant renal artery stenosis. Q J Med 1998;91:185–189.

27. Beecroft JR, Rajan DK, Clark TW, Robinette M, Stavropoulos SW.Transplant renal artery stenosis: outcome after percutaneous in-tervention. J Vasc Interv Radiol 2004;15:1407–1413.

28. Akbar SA, Jafri SZ, Amendola MA, Madrazo BL, Salem R, Bis KG.Complications after renal transplantation. Radiographics 2005;25:1335–1356.

29. Giustacchini P, Pisanti F, Citterio F, De Gaetano AM, CastagnetoM, Nanni G. Renal vein thrombosis after renal transplantation:

an important cause of graft loss. Transplant Proc 2002;34:2126–2127.

30. Marckmann P, Skov L, Rossen K, Heaf JG, Thomsen HS. Nephro-genic systemic fibrosis: suspected etiological role of gadodiamideused for contrast-enhanced magnetic resonance imaging. J Am SocNephrol 2006;17:2359–2362.

31. Lin SP, Brown JJ. MR contrast agents: physical and pharmacologicbasics. J Magn Reson Imaging 2007;25:884–899.

32. Cohan RH, Ellis JH, Hussain HK, et al. Nephrogenic systemicfibrosis: report of 29 patients. AJR Am J Roentgenol 2008;190:736–741.

916 Gufler et al.