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Magnetic resonance imaging of the kidneys: current status.

Magnetic resonance imaging (MRI) differs fundamentally from other imaging techniques, since for the first time one method permits simultaneous assessment of macroscopic changes in the kidneys and evaluation of renal functional derangements. To provide morphological information that may compete with the results of computed tomography (CT) and ultrasonography (US), special techniques like artifact compensation, fast imaging, and fat suppression have to be employed. The additional use of a renally eliminated paramagnetic contrast agent permits assessment of parenchymal perfusion and visualization of the passage of the contrast medium, providing information about renal excretory function. Results and clinical utility of state of the art MRI can be summarized as follows: (a) MR is not a screening method; sensitivity is, however, similar to CT when fat suppression and contrast agents are used. (b) Classification of renal masses is almost restricted to the differentiation of cystic, fat-containing, and solid lesions. (c) Contrast-enhanced MRI helps to assess large retroperitoneal masses and to classify them as intra- or extrarenal. (d) Accurate staging of renal cancers is possible; thus, MRI is a good alternative when CT yields uncertain findings and for patients with known contraindications to the administration of iodinated contrast agents. (e) Contrast-enhanced dynamic MRI studies provide semiquantitative evaluation of global and segmental renal function. (f) MR angiography offers the possibility to evaluate renal arteries and veins.