There are numerous advantages of multidetector CT Urography over excretory urography (also known as IV pyelography or IV urography) and ultrasound for the evaluation of the urinary tract. Dedicated CT protocols developed for new high speed scanners can evaluate many clinical indications, including:
- "Stone protocol" for the evaluation of urinary tract calculi
- CT Urography for the evaluation of hematuria
- "Renal mass protocol" for the characterization of a known renal mass
Multidetector CT is fast, requiring less than 15 seconds for image acquisition from the kidneys to the bladder, usually during a single breath-hold. The images have good spatial resolution, essentially no mis-registration due to respiratory movement, and can be reconstructed into two- and three-dimensional views of the abdominal anatomy. It is also possible to detect pathology outside the urinary tract. Iodinated contrast agents are not typically required for the detection of renal stones, thus avoiding the risk of adverse reactions to these agents, but are routinely used in CT urography and the renal mass protocol.
In comparison to CT, film urography offers excellent delineation of the renal collecting system anatomy, but it is inferior to multi detector CT for imaging of the renal parenchyma. Both CT and plain film urography require radiation. Ultrasound is good for imaging the kidney parenchyma and for detecting hydronephrosis. It does not require the iodinated contrast, and avoids radiation.
However, ultrasound is not good for detecting urinary tract calculi, and does not adequately image the renal collecting system or ureters. For these reasons, multidetector CT imaging has become the gold standard for the diagnosis of urinary tract calculi, the investigation of hematuria, and the characterization of renal masses and has largely replaced both excretory urography and ultrasound for these purposes.