Attenuation changes of the normal and ischemic canine kidney. Dynamic CT scanning after intravenous contrast medium bolus.

The potential of CT scanning to explore total and regional renal blood flow was evaluated in a dog model with unilateral renal artery stenosis (n = 7, reduction of renal blood flow: 32-75% of base line flow). Attenuation versus time curves were generated for the renal cortex and medulla, as well as for the aorta and renal vein. A fast CT scanner was used which allowed for up to 24 scans/minute at the same level (slice thickness: 10 mm). A total of 10 ml contrast medium was injected into a peripheral vein for each scan series taken. During baseline conditions, the curve of the renal cortex and medulla demonstrated 2 peaks. The first peak was mainly related to early vascular enhancement, whereas the second peak corresponded mainly to the appearance of contrast medium in the distal convolutes and collecting ducts. Ischemia of the kidney resulted in a reduction of the first peak and a flattening of the leading edge slope. Transport of contrast medium through the extravascular compartments of the kidney was delayed during ischemia. Relative renal blood flow was obtained from the CT data by dividing peak enhancement by rise-time as assessed from the cortical curve. All measurements were related to baseline flow and validated by flow measurements using radioactive labeled microspheres (n = 5). Correlation was found to be r = 0.97.