Urinary obstruction.

Radiologic imaging is commonly used in the diagnosis, classification, and follow-up of renal obstruction. Precise definitions of the elements of urinary obstruction are critical. This article examines the physiology of renal obstruction and the use of such imaging tests as excretory urogram, retrograde pyelography, antegrade pyelography, Whitaker test, ultrasound, CT scan, MR imaging, and radionuclide renography.