What is the current role of CT urography and MR urography in the evaluation of the urinary tract?

Technologic advances in both computed tomography (CT) and magnetic resonance (MR) imaging have resulted in the ability to image the urinary tract in ways that surpass the prior mainstay of urinary tract imaging, the intravenous urogram. In adults, for most, if not all, historical indications for intravenous urography, CT urography or MR urography is now the preferred examination. Although a variety of techniques for both examinations have been described, each test provides more diagnostic information than does intravenous urography. With the introduction of multidetector technology, CT urography, to date, has emerged as the initial heir apparent to intravenous urography; many years of experience have now clearly demonstrated that CT is the test of choice for many urologic problems, including urolithiasis, renal masses, urinary tract infection, trauma, and obstructive uropathy. CT urography provides a detailed anatomic depiction of each of the major portions of the urinary tract--the kidneys, intrarenal collecting systems, ureters, and bladder--and thus allows patients with hematuria to be evaluated comprehensively. MR urography can be used also to evaluate the urinary tract and has the advantage of not using ionizing radiation and the potential to provide more functional information than CT. However, MR urography is less established and less reliably results in diagnostic image quality relative to CT urography. Although both tests can be used to evaluate the urinary tract, several issues remain and include reaching a consensus on the optimal protocols and appropriate utilization in an era of cost containment and heightened concerns about radiation exposure.