CT-urography and MR-urography of the urogenital tract

Abstract

In contrast to intravenous urography (IVU), MR-urography (MRU) and CT-urography (CTU) provide images of both the lumen and surrounding structures of the upper urinary tract. MRU can be based on either static-fluid MRU, including heavily T2-weighted sequences, such as TSE, RARE, HASTE, SSFSE, or trueFISP, or gadolinium-enhanced excretory MRU, applying sequences such as fast T1-weighted 3D-GRE. T2-weighted MRU particularly visualizes the dilated urinary tract, even in non-excreting kidneys. In contrast, T1-weighted MRU reflects excretory renal function. Furosemide (5–10mg) improves uniform distribution of gadolinium in the collecting system and urinary tract and decreases susceptibility artefacts (T2*-effects) in the urine. The advent of multidetector-row computed tomography (MDCT) has markedly improved evaluation of the urinary tract. CTU can be performed with sub-millimeter sections during a single breath-hold. Similar to gadolinium-enhanced excretory MRU, CTU is also an excretory urography technique, which can also be combined with low-dose furosemide or intravenous saline solution for accelerated passage of excreted contrast media. CTU is associated with radiation exposure and potential risk of nephrotoxicity of radiographic contrast media. For broad routine clinical application, there is still a need for dose reduction protocols despite the ongoing technical developments in CTU. Both MRU and CTU techniques, in combination with standard MRI or CT, permit comprehensive examination of the entire urinary tract. Clinical applications include diagnosis of intrinsic and extrinsic tumors, or complex or congenital anomalies affecting the urinary tract, assessment of renal transplants, and chronic urolithiasis.