Which phase of CT urography provides information about parenchymal enhancement?

• A. Nephrographic phase.
• B. Non-contrast phase.
• C. Excretory phase.
• D. Arterial phase.

Answer: (A)

Parenchymal enhancement is best evaluated during the nephrographic phase, when the contrast has equilibrated within the renal cortex and medulla and the entire renal parenchyma becomes uniformly enhanced. This timing—roughly 80–100 seconds after contrast injection—highlights differences in tissue density across the parenchyma, making it easier to detect and characterize lesions, inflammation, or scar tissue.

The arterial phase, by contrast, emphasizes renal arteries and cortical perfusion in a more vascular pattern rather than overall parenchymal texture. The excretory phase focuses on the collecting system and urinary tract as contrast begins to fill the calyces, pelvis, and ureters. The non-contrast phase lacks enhancement entirely, so it doesn’t reveal parenchymal enhancement patterns.