CTA, however, has the drawback of potential postcontrast acute kidney injury and radiation exposure in addition to insensitivity to mild RAS [38]. A noncontrast CT of the abdomen and pelvis may be helpful in patients with suspected hemorrhage or in the evaluation for nephrolithiasis in the transplant kidney. It also may be useful to define the extent of a peri- transplant fluid collection or in patients who cannot receive intravenous contrast. Magnetic Resonance Imaging and Magnetic Resonance Angiography MRI is being increasingly used as a second-line imaging modality for the evaluation of kidney transplants. Like a CT with and without contrast, an MRI with and without contrast may aid in characterization of renal masses and perinephric fluid collections. Although the risk of nephrotoxicity following gadolinium chelate contrast administration remains controversial [39], there is increased risk for NSF in this patient population that often has compromised renal function [34,40]. Fortunately, nonenhanced MRI pulse sequences may provide useful information in patients that have contrast contraindications and serve as an alternative to CT. Unfortunately, MRA suffers from a few pitfalls that may lead to a false diagnosis of stenosis or an overestimation of a stenosis. These include artifacts caused by metallic surgical clips near the transplant artery that result in signal loss near the artery, giving the false impression of stenosis. Venous contamination due to inaccurate timing of the arterial bolus is another artifact that can affect the accuracy of diagnosis. Careful evaluation of the source images and multiplanar reformats will help solve these problems [45]. In addition to depicting areas of stenosis in the main renal artery, MRA is able to depict areas of infarction within the kidney, which are seen as areas of heterogeneous T1 and T2 signal intensity and as focal areas of nonenhancement on the postcontrast images.
Renal Transplant Dysfunction. CTA, however, has the drawback of potential postcontrast acute kidney injury and radiation exposure in addition to insensitivity to mild RAS [38]. A noncontrast CT of the abdomen and pelvis may be helpful in patients with suspected hemorrhage or in the evaluation for nephrolithiasis in the transplant kidney. It also may be useful to define the extent of a peri- transplant fluid collection or in patients who cannot receive intravenous contrast. Magnetic Resonance Imaging and Magnetic Resonance Angiography MRI is being increasingly used as a second-line imaging modality for the evaluation of kidney transplants. Like a CT with and without contrast, an MRI with and without contrast may aid in characterization of renal masses and perinephric fluid collections. Although the risk of nephrotoxicity following gadolinium chelate contrast administration remains controversial [39], there is increased risk for NSF in this patient population that often has compromised renal function [34,40]. Fortunately, nonenhanced MRI pulse sequences may provide useful information in patients that have contrast contraindications and serve as an alternative to CT. Unfortunately, MRA suffers from a few pitfalls that may lead to a false diagnosis of stenosis or an overestimation of a stenosis. These include artifacts caused by metallic surgical clips near the transplant artery that result in signal loss near the artery, giving the false impression of stenosis. Venous contamination due to inaccurate timing of the arterial bolus is another artifact that can affect the accuracy of diagnosis. Careful evaluation of the source images and multiplanar reformats will help solve these problems [45]. In addition to depicting areas of stenosis in the main renal artery, MRA is able to depict areas of infarction within the kidney, which are seen as areas of heterogeneous T1 and T2 signal intensity and as focal areas of nonenhancement on the postcontrast images.