(Radiographics. 2001;21:1505-1517.)
© RSNA, 2001
Renal Transplant Evaluation with MR Angiography and MR Imaging1
Mark D. Hohenwalter, MD,
Christopher J. Skowlund, MD,
Scott J. Erickson, MD,
Sundaram Hariharan, MD,
William S. Rilling, MD,
Martin R. Crain, MD and
Peter Drescher, MD
1 From the Departments of Radiology (M.D.H., C.J.S., S.J.E., W.S.R., M.R.C., P.D.) and Medicine (S.H.), Medical College of Wisconsin, 9200 W Wisconsin Ave, Milwaukee, WI 53226. Presented as an education exhibit at the 2000 RSNA scientific assembly. Received April 17, 2001; revision requested May 21 and received June 18; accepted June 18. Address correspondence to M.D.H. (e-mail: mhohen@mcw.edu).
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Abstract
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Magnetic resonance (MR) angiography is a widely used, noninvasive tool for evaluating the aorta and its branches. It is particularly useful in renal transplant recipients because it provides anatomic detail of the transplant artery without nephrotoxic effects. Volume rendering is underutilized in MR angiography, but this technique affords high-quality three-dimensional MR angiograms, especially in cases of tortuous or complex vascular anatomy. An imaging protocol was developed that includes gadolinium-enhanced MR angiography of the transplant renal artery with volume rendering and multiplanar reformation postprocessing techniques. Axial T2-weighted and contrast material–enhanced T1-weighted MR images are also obtained to examine the renal parenchyma itself and to evaluate for hydronephrosis or peritransplant fluid collections. This imaging protocol allows rapid global assessment of the renal transplant arterial system, renal parenchyma, and peritransplant region. It can also help detect or exclude many of the various causes of renal transplant dysfunction (eg, stenosis or occlusion of a transplant vessel, peritransplant fluid collections, ureteral obstruction). Conventional angiography can thus be avoided in patients with normal findings and reserved for those with MR angiographic evidence of stenosis.
Index Terms: Kidney, MR, 81.1214, 81.12142 • Kidney, transplantation, 81.455 • Renal angiography, 81.12142, 961.12942 • Renal arteries, MR, 81.1214, 81.12142, 961.12942 • Renal arteries, stenosis or obstruction, 961.7173
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Introduction
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Renal transplantation is a common surgical procedure, with approximately 11,000 procedures performed annually in the United States (1). Causes of graft dysfunction can be categorized as vascular, parenchymal, or extrinsic. Vascular causes include stenosis or occlusion of the transplant artery or vein. Parenchymal causes include acute tubular necrosis, rejection, and medication toxicity. Peritransplant fluid collections and ureteral obstruction are examples of extrinsic causes of graft dysfunction.
Accurate imaging assessment of the transplanted kidney is critical for implementing effective treatment. Ultrasonography (US) is usually performed initially for detection of peritransplant fluid collections and hydronephrosis. It is also useful for assessing transplant arterial and venous patency and determining Doppler indices. However, US is operator dependent, and the main transplant artery is often incompletely visualized.
Intra-arterial digital subtraction angiography is the standard of reference for evaluating the transplant artery; however, it is invasive, and iodinated contrast material is potentially nephrotoxic. This is particularly relevant because dysfunctional transplanted kidneys typically have compromised renal function.
Several studies have demonstrated the usefulness of magnetic resonance (MR) angiography in the evaluation of the transplant renal artery (2–5). Most of these studies use MR angiography with maximum intensity projection (MIP) and multiplanar volume reformation (MPVR) techniques. Other studies have shown the usefulness of MR imaging in the evaluation of the transplanted kidney and peritransplant region (6,7).
In this article, we describe our imaging protocol and the appearance of normal transplanted kidneys and transplant arteries at MR imaging and MR angiography. We also discuss and illustrate selected related abnormalities, including arterial kinking, transplant artery stenosis, fibromuscular dysplasia, infarction, lymphocele, hydronephrosis, renal masses and cysts, and complex vascular anatomy. In addition, we demonstrate the use of volume-rendered postprocessing techniques with MR angiography.
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Imaging Protocol
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A total of 18 patients with renal transplants have undergone MR imaging evaluation at our institution in the past 2 years. The patients ranged from 21 to 82 years of age, and the interval between transplantation and MR imaging ranged from 3 months to 14 years. All MR imaging was performed on a 1.5-T Horizon LX or CV MR scanner (GE Medical Systems, Milwaukee, Wis) with a phased-array torso coil (Medical Advances, Milwaukee, Wis).
The patients are given oxygen via a nasal cannula to aid in breath holding, and a peripheral intravenous line is connected to a power injector (Medred, Indianola, Pa) for the contrast material–enhanced portion of the examination. Total time for the examination is 30 minutes or less.
T2-weighted MR Imaging
After a sagittal or coronal T1-weighted localizing sequence is performed, axial fat-suppressed fast spin-echo T2-weighted MR images are obtained through the transplanted kidney. Parameters for this sequence are as follows: repetition time, 3,400–6,700 msec; echo time, 98 msec; bandwidth, 16 kHz; field of view, 32–38 cm x 22–38 cm; section thickness, 7 or 8 mm with an intersection gap of 2 mm; matrix, 256 x 224; and two signals acquired. Total imaging time is 3.5–6 minutes. More recently, a breath-hold single-shot fast spin-echo T2-weighted MR imaging sequence has been performed to decrease imaging time.
MR Angiography
A timing bolus is used to determine the time to peak arterial enhancement. Following the intravenous injection of 2 mL of gadolinium-based contrast material, 20 sequential axial fast spoiled gradient-echo MR images are obtained at one location at the level of the distal aorta. Representative parameters are as follows: flip angle, 20°; repetition time, 17 msec; echo time, 1.9 msec; bandwidth, 15.6 kHz; field of view, 30 cm; section thickness, 15 mm; matrix, 256 x 128; and one signal acquired. Each scan takes 2.3 seconds for a total imaging time of 47 seconds. Time to peak aortic enhancement can be determined by multiplying the sequential number of the image with the highest aortic signal intensity by 2.3 seconds. Injection-to-scan delay is then determined with the following equation: Injection-to-scan delay = time to aortic peak + (injection time/2) - (scan time/2).
The diagnostic MR angiography sequence is a coronal three-dimensional (3D) time-of-flight fast multiplanar spoiled gradient-echo breath-hold sequence performed with the following parameters: flip angle, 45°; repetition time, 6.1–6.4 msec; echo time, 1.3–1.5 msec; bandwidth, 31.2 kHz; field of view, 24–30 cm; section thickness, 2.0–3.0 mm; matrix, 256 x 128–192 cm; and one signal acquired. Total imaging time is 24–40 seconds. The field of view is made as small as possible so that phase wrap does not extend into the renal transplant hilum. The interval between sections is one-half the section thickness due to the use of a zero-fill interpolation function (ZIP x 2). Thus, the effective section thickness is 1–1.5 mm. The number of phase-encoding steps is usually 128 but can be increased to 160 or even 192 if the patient is able to suspend respiration long enough. If the patient is very ill or unable to suspend respiration, the use of one-half signal acquired will still result in diagnostic images. An unenhanced test run of the MR angiographic sequence is performed to ensure an adequate coverage area and field of view.
Gadolinium-enhanced T1-weighted MR Imaging
Following acquisition of the source MR angiograms, an axial gadolinium-enhanced fat-suppressed fast multiplanar spoiled gradient-echo T1-weighted sequence is performed through the transplanted kidney. Typical parameters are as follows: repetition time, 165–210 msec; echo time, 4.2 msec; bandwidth, 31.2 kHz; field of view, 30–38 cm x 22.5–38 cm; section thickness, 10 mm with no intersection gap; matrix, 256 x 160; and one signal acquired. Total imaging time is 22–35 seconds.
Postprocessing
The source MR angiograms are transferred to an Advantage Windows workstation with software version 3.1 (GE Medical Systems, Milwaukee, Wis). Postprocessing includes reformatting with MIP, MPVR, and volume rendering techniques. The MIP images represent a summated depiction of the volumetric data set but use only the pixel with the highest signal intensity along a given ray. The MPVR images are sections of variable thickness displayed with MIP technique. The volume-rendered images include the entire volumetric data set, producing a 3D likeness that can be rotated and displayed in any projection. The volume-rendering software includes algorithms or transfer functions that make use of properties such as opacity and brightness to depict the voxel values (8). With computed tomographic (CT) angiography, the values are in Hounsfield units, whereas with MR angiography, the values relate to signal intensity. The images can be further refined with window width and level adjustment as well as colorization.
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Normal Imaging Appearance of Transplanted Kidneys
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Transplanted kidneys are preferentially placed extraperitoneally in the right iliac fossa. The donor artery is usually anastomosed to the ipsilateral external or common iliac artery, and the ureter is anastomosed to the bladder. Drawings illustrating a normal transplanted kidney and selected renal transplant abnormalities are shown in Figure 1.
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Figure 1a. (a) Drawing illustrates a normal transplanted kidney with vascular and ureteric anastomoses. (b) Drawing illustrates selected posttransplantation abnormalities, including arterial stenosis, infarction, a peritransplant fluid collection, and hydronephrosis.
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Figure 1b. (a) Drawing illustrates a normal transplanted kidney with vascular and ureteric anastomoses. (b) Drawing illustrates selected posttransplantation abnormalities, including arterial stenosis, infarction, a peritransplant fluid collection, and hydronephrosis.
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T2-weighted MR Imaging
On axial fat-suppressed fast spin-echo T2-weighted MR images, the transplanted kidney is hyperintense with respect to the relatively hypointense surrounding structures (Fig 2). This allows easy identification of peritransplant fluid collections, intraparenchymal cysts or masses, and hydronephrosis.
MR Angiography
Coronal dynamic arterial-phase 3D time-of-flight source MR angiograms are shown in Figure 3. These images demonstrate arterial-phase enhancement of the aorta and of the iliac and transplant renal arteries. In addition, the renal parenchyma is depicted in the corticomedullary phase, which is useful in identifying perfusion defects. MIP reformatting provides a summated global depiction of the aortoiliac system, transplanted kidney, and transplant artery (Fig 4). MPVR images can be constructed in planes that best demonstrate the main and segmental renal arteries (Fig 5). An MPVR image can also be used to estimate the size of the transplanted kidney (Fig 5d).
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Figure 3a. (a) Coronal arterial-phase 3D time-of-flight source MR angiogram demonstrates the aorta. (b) Source MR angiogram demonstrates the main transplant renal artery. The transplanted kidney is shown in the corticomedullary phase.
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Figure 3b. (a) Coronal arterial-phase 3D time-of-flight source MR angiogram demonstrates the aorta. (b) Source MR angiogram demonstrates the main transplant renal artery. The transplanted kidney is shown in the corticomedullary phase.
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Figure 5a. (a-c) MPVR images show the normal aortoiliac system (a), main renal artery anastomosis (b), and segmental transplant renal arteries (c). (d) MPVR image demonstrates usefulness of the reformatted image for estimating transplanted kidney size.
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Figure 5b. (a-c) MPVR images show the normal aortoiliac system (a), main renal artery anastomosis (b), and segmental transplant renal arteries (c). (d) MPVR image demonstrates usefulness of the reformatted image for estimating transplanted kidney size.
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Figure 5c. (a-c) MPVR images show the normal aortoiliac system (a), main renal artery anastomosis (b), and segmental transplant renal arteries (c). (d) MPVR image demonstrates usefulness of the reformatted image for estimating transplanted kidney size.
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Figure 5d. (a-c) MPVR images show the normal aortoiliac system (a), main renal artery anastomosis (b), and segmental transplant renal arteries (c). (d) MPVR image demonstrates usefulness of the reformatted image for estimating transplanted kidney size.
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In addition, volume rendering is an excellent 3D reformatting technique because it displays the entire arterial-phase volume data set. The images can be displayed in any projection to best delineate vessel relationships (Fig 6). Images obtained with two different volume-rendering software programs are shown in Figure 7a and Figure 7b. Thresholding can be adjusted so that the renal parenchyma can be removed from the image to highlight the segmental arteries (Fig 7c).
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Figure 6a. Volume-rendered MR angiograms obtained from the same data set but displayed with different magnification and rotation demonstrate a normal transplant artery anastomosis (b) and normal segmental vessels (a).
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Figure 6b. Volume-rendered MR angiograms obtained from the same data set but displayed with different magnification and rotation demonstrate a normal transplant artery anastomosis (b) and normal segmental vessels (a).
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Figure 7a. (a, b) Volume-rendered images obtained with different preset algorithms depict normal transplant anatomy. (c) Volume-rendered image demonstrates the usefulness of thresholding to "remove" the renal parenchyma and highlight the segmental arteries.
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Figure 7b. (a, b) Volume-rendered images obtained with different preset algorithms depict normal transplant anatomy. (c) Volume-rendered image demonstrates the usefulness of thresholding to "remove" the renal parenchyma and highlight the segmental arteries.
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Figure 7c. (a, b) Volume-rendered images obtained with different preset algorithms depict normal transplant anatomy. (c) Volume-rendered image demonstrates the usefulness of thresholding to "remove" the renal parenchyma and highlight the segmental arteries.
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Volume rendering is commonly used in the construction and display of 3D models for CT angiography. To our knowledge, however, its use in conjunction with MR angiography has not been widely reported. As the images demonstrate, it affords high-quality 3D MR angiograms and is relatively easy to use. Postprocessing of an MR angiogram by an experienced technologist or radiologist takes only about 15 minutes.
Contrast–enhanced MR Imaging
Axial contrast-enhanced fat-suppressed T1-weighted MR images are obtained at the end of the MR angiography study (Fig 8). These images are useful in demonstrating perfusion defects, masses, peritransplant fluid collections, and hydronephrosis.
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Transplant Abnormalities
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Arterial Kinking
MR angiography is an excellent noninvasive method for visualizing the main renal artery. If the transplant donor artery is excessively long, it can become kinked, resulting in turbulent blood flow (Fig 9) (9). If the corresponding reduction in renal transplant blood flow is significant, surgical revision is usually necessary. The artery can also kink at the anastomosis, resulting in narrowing (9).
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Figure 9a. Main transplant renal artery kinking in a 64-year-old woman with kidney dysfunction. The patient had undergone renal transplantation 4 years earlier. MPVR (a) and volume-rendered (b, c) images demonstrate an apparent kink in the midportion of the transplant renal artery (arrow).
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Figure 9b. Main transplant renal artery kinking in a 64-year-old woman with kidney dysfunction. The patient had undergone renal transplantation 4 years earlier. MPVR (a) and volume-rendered (b, c) images demonstrate an apparent kink in the midportion of the transplant renal artery (arrow).
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Figure 9c. Main transplant renal artery kinking in a 64-year-old woman with kidney dysfunction. The patient had undergone renal transplantation 4 years earlier. MPVR (a) and volume-rendered (b, c) images demonstrate an apparent kink in the midportion of the transplant renal artery (arrow).
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Transplant Artery Stenosis
Transplant renal artery stenosis has been reported to occur in 1%–12% of patients, but the prevalence may be as high as 25% (10). Causes include atherosclerotic disease in the donor or recipient arteries, surgical trauma to the vessels, improper or inadequate suture technique, and immunologic phenomena (9,10). Arterial stenosis can occur any time after transplantation and may be suspected when there is abrupt onset of hypertension or unexplained impairment of renal function (9). The stenosis can occur in the native iliac artery, at the anastomosis, or in the donor renal artery. Noninvasive methods of evaluating for stenosis without iodinated contrast material include US, captopril radionuclide imaging, and MR angiography (Fig 10). In cases of suspected transplant renal artery stenosis, MR imaging can be used as a screening study, with angiography reserved for selected patients who may be amenable to angioplasty. If the main renal artery has a normal MR imaging appearance, unnecessary angiography can be avoided.
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Figure 10a. Segmental artery stenosis in an 82-year-old man with an elevated serum creatinine level. The patient had undergone transplantation 4 months earlier. MPVR (a) and volume-rendered (b) images demonstrate a segmental transplant renal artery stenosis (arrow). This finding was not believed to be clinically significant because the patient presented with renal dysfunction rather than hypertension.
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Figure 10b. Segmental artery stenosis in an 82-year-old man with an elevated serum creatinine level. The patient had undergone transplantation 4 months earlier. MPVR (a) and volume-rendered (b) images demonstrate a segmental transplant renal artery stenosis (arrow). This finding was not believed to be clinically significant because the patient presented with renal dysfunction rather than hypertension.
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Fibromuscular Dysplasia
Although rare, the development of fibromuscular dysplasia in a donor transplant renal artery has been reported (Fig 11) (11).
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Figure 11a. Fibromuscular dysplasia in a 46-year-old man who had undergone transplantation 4 years earlier. The patient underwent MR angiography because of an elevated serum creatinine level and hypertension. (a, b) MPVR (a) and volume-rendered (b) images demonstrate the proximal transplant artery, which has an irregular beaded appearance, a finding that suggests fibromuscular dysplasia. (c) CO2 angiogram demonstrates corresponding vessel irregularity; however, there was no significant pressure gradient to warrant angioplasty. The patient subsequently underwent transplant biopsy, which demonstrated rejection.
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Figure 11b. Fibromuscular dysplasia in a 46-year-old man who had undergone transplantation 4 years earlier. The patient underwent MR angiography because of an elevated serum creatinine level and hypertension. (a, b) MPVR (a) and volume-rendered (b) images demonstrate the proximal transplant artery, which has an irregular beaded appearance, a finding that suggests fibromuscular dysplasia. (c) CO2 angiogram demonstrates corresponding vessel irregularity; however, there was no significant pressure gradient to warrant angioplasty. The patient subsequently underwent transplant biopsy, which demonstrated rejection.
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Figure 11c. Fibromuscular dysplasia in a 46-year-old man who had undergone transplantation 4 years earlier. The patient underwent MR angiography because of an elevated serum creatinine level and hypertension. (a, b) MPVR (a) and volume-rendered (b) images demonstrate the proximal transplant artery, which has an irregular beaded appearance, a finding that suggests fibromuscular dysplasia. (c) CO2 angiogram demonstrates corresponding vessel irregularity; however, there was no significant pressure gradient to warrant angioplasty. The patient subsequently underwent transplant biopsy, which demonstrated rejection.
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Infarction
Source MR angiograms and axial contrast-enhanced T1-weighted images are useful for evaluating the renal parenchyma. Renal transplant infarcts manifest as wedge-shaped areas of decreased parenchymal enhancement. Early infarction can be the result of preservation damage to the donor kidney or arterial complications related to surgery (12). Later infarction can be caused by embolic phenomena. A study by Cosio et al (12) also suggests an association of infarction with cytomegalovirus infection and acute rejection (Fig 12).
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Figure 12. Transplanted kidney infarction in a 71-year-old man who presented with renal dysfunction and hypertension. The patient had undergone transplantation 4 months earlier. Source MR angiogram demonstrates multiple peripheral wedge-shaped perfusion defects representing multifocal infarcts (arrow). Subsequent MR angiograms (not shown) demonstrated that the renal artery was widely patent. The cause of the infarcts was not determined.
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Lymphocele
Peritransplant fluid collections usually represent lymphoceles, hematomas, urinomas, or abscesses. Axial T2-weighted MR images clearly depict fluid collections with increased signal intensity (Fig 13). If large enough, the collections can result in mass effect on the renal parenchyma, collecting system, or vascular supply, resulting in dysfunction. Treatment options for symptomatic collections include percutaneous drainage and surgery.
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Figure 13. Lymphocele in a 72-year-old woman who presented with transplant dysfunction. The patient had undergone renal transplantation 11 years earlier. Axial T2-weighted MR image demonstrates a peritransplant fluid collection with homogeneous hyperintensity (arrow). These findings are consistent with an incidental lymphocele that did not result in significant parenchymal, vascular, or ureteral compression.
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Hydronephrosis
Causes of hydronephrosis (eg, anastomotic stricture) can often result in dysfunction. Stenosis of the transplant ureter has been reported in 2%–10% of transplants, with causes including surgical technical factors and ureteral fibrosis secondary to ischemia (13). Mild hydronephrosis may not be clinically significant (Fig 14). In cases of significant hydronephrosis, treatment options include surgical reconstruction. In cases of short-segment distal ureteral strictures, urologic balloon dilation with stent placement is an option (13).
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Figure 14. Mild hydronephrosis in a 46-year-old man who presented with hypertension and an elevated serum creatinine level. The patient had undergone renal transplantation 7 months earlier. Axial T2-weighted MR image demonstrates mild prominence of the transplanted kidney collecting system.
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Renal Masses and Cysts
Renal transplant recipients can develop solid masses or cysts in the transplanted kidney. MR imaging is useful for differentiating between solid and cystic lesions (Fig 15). Posttransplantation lymphoproliferative disorder is a lymphoma-like condition associated with the Epstein-Barr virus and is present in approximately 1% of solid organ transplant recipients (14). A major risk factor is degree of immunosuppression (14). Ali et al (6) described five cases of posttransplantation lymphoproliferative disorder affecting a transplanted kidney, manifesting as either a hilar mass or intraparenchymal mass. In their study, the lesions were hypointense at both T1- and T2-weighted MR imaging and demonstrated minimal enhancement (6).
Complex Vascular Anatomy
Figure 16 clearly demonstrates the usefulness of noninvasive MR angiography with volume-rendered reconstruction in cases of complex vascular anatomy.
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Figure 16a. Complex vascular anatomy in a 31-year-old woman. The patient had undergone renal transplantation 9 years earlier and placement of a venous patch graft due to renal artery stenosis 4 years after transplantation. Anteroposterior (a) and oblique (b) volume-rendered MR angiograms demonstrate clear patency of the patch graft between the external iliac artery and the main transplant renal artery (arrow), thereby illustrating the usefulness of being able to view MR angiograms in any 3D projection.
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Figure 16b. Complex vascular anatomy in a 31-year-old woman. The patient had undergone renal transplantation 9 years earlier and placement of a venous patch graft due to renal artery stenosis 4 years after transplantation. Anteroposterior (a) and oblique (b) volume-rendered MR angiograms demonstrate clear patency of the patch graft between the external iliac artery and the main transplant renal artery (arrow), thereby illustrating the usefulness of being able to view MR angiograms in any 3D projection.
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Clip Artifact
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A potential common pitfall with MR angiography is metallic artifact from vascular clips in the surgical bed (Figs 17, 18). This potential pitfall can be avoided by recognizing its characteristic MR imaging appearance and correlating the imaging findings with those at prior CT or conventional radiography.
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Figure 17a. Surgical clip artifact in a 28-year-old man who presented with hypertension. The patient had undergone renal transplantation 3 years earlier. (a, b) Source MR angiogram (a) and MPVR image (b) demonstrate an apparent metallic clip artifact in the distal external iliac artery, just proximal to the transplant artery anastomosis (arrow). (c) Volume-rendered image shows a small corresponding irregularity in the vessel (arrowhead). (d) CO2 angiogram helps confirm that the irregularity was caused by a clip artifact (arrowhead).
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Figure 17b. Surgical clip artifact in a 28-year-old man who presented with hypertension. The patient had undergone renal transplantation 3 years earlier. (a, b) Source MR angiogram (a) and MPVR image (b) demonstrate an apparent metallic clip artifact in the distal external iliac artery, just proximal to the transplant artery anastomosis (arrow). (c) Volume-rendered image shows a small corresponding irregularity in the vessel (arrowhead). (d) CO2 angiogram helps confirm that the irregularity was caused by a clip artifact (arrowhead).
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Figure 17c. Surgical clip artifact in a 28-year-old man who presented with hypertension. The patient had undergone renal transplantation 3 years earlier. (a, b) Source MR angiogram (a) and MPVR image (b) demonstrate an apparent metallic clip artifact in the distal external iliac artery, just proximal to the transplant artery anastomosis (arrow). (c) Volume-rendered image shows a small corresponding irregularity in the vessel (arrowhead). (d) CO2 angiogram helps confirm that the irregularity was caused by a clip artifact (arrowhead).
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Figure 17d. Surgical clip artifact in a 28-year-old man who presented with hypertension. The patient had undergone renal transplantation 3 years earlier. (a, b) Source MR angiogram (a) and MPVR image (b) demonstrate an apparent metallic clip artifact in the distal external iliac artery, just proximal to the transplant artery anastomosis (arrow). (c) Volume-rendered image shows a small corresponding irregularity in the vessel (arrowhead). (d) CO2 angiogram helps confirm that the irregularity was caused by a clip artifact (arrowhead).
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Figure 18a. Surgical clip artifact mimicking stenosis in a 56-year-old man who presented with renal dysfunction and hypertension. The patient had undergone renal transplantation 9 years earlier. (a) MPVR MR angiogram demonstrates an area of apparent narrowing in the main renal artery (arrow). (b) Subsequent contrast-enhanced MR angiogram demonstrates a widely patent main renal artery with a clip at the site of the MR imaging pseudostenosis (arrowhead).
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Figure 18b. Surgical clip artifact mimicking stenosis in a 56-year-old man who presented with renal dysfunction and hypertension. The patient had undergone renal transplantation 9 years earlier. (a) MPVR MR angiogram demonstrates an area of apparent narrowing in the main renal artery (arrow). (b) Subsequent contrast-enhanced MR angiogram demonstrates a widely patent main renal artery with a clip at the site of the MR imaging pseudostenosis (arrowhead).
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Conclusions
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Volume rendering is an underutilized technique with MR angiography but affords high-quality 3D angiographic images, especially in cases of tortuous or complex vascular anatomy. The MR imaging protocol presented in this article includes volume rendering and allows rapid global assessment of the renal transplant arterial system, renal parenchyma, and peritransplant region. This protocol can help detect or exclude many of the various causes of transplant dysfunction. Invasive angiography can be avoided in patients with normal findings, instead being reserved for patients with MR angiographic evidence of stenosis. Angiography can then help determine the hemodynamic significance of a stenosis and help select patients for intervention.
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Acknowledgments
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The authors thank Jackie Lane of Medical Center Graphics, along with Mary Thielke and Annie Roy, for their help in image preparation, Robert Fenn for the original artwork, and Sue Liberski for secretarial assistance.
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Footnotes
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Abbreviations: MIP = maximum intensity projection,
MPVR = multiplanar volume reformation,
3D = three-dimensional
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References
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Abstract
Introduction
