MEASUREMENT OF RENAL PERFUSION AND BLOOD-FLOW WITH FAST COMPUTED-TOMOGRAPHY

Fast computed tomography (CT) is one of the few methods available to m easure cortical and medullary renal blood flow (RBF) directly. Because these measurements are complicated by passage of the contrast medium into extravascular compartments, we used the residual opacity followin g the vascular blush as an index to account for extravascular iohexol. Kidneys of anesthetized dogs were examined in situ by fast CT followi ng intra-aortic injections of iohexol. Perfusion was analyzed during a control period and three subsequent periods in which RBF was reduced by 10%, 30%, and 50%. Cortical microvascular distribution volume chang ed from 19.7 +/- 2.8% to 19.8 +/- 1.7%, 15.3 +/- 1.2%, and 9.9 +/- 1.7 %, respectively, without significant alterations in cortical mean tran sit time. Microvascular distribution volume was divided by mean transi t time to determine tissue perfusion. Cortical perfusion changed from 3.8 +/- 0.7 to 3.9 +/- 0.6, 3.1 +/- 0.5, and 2.2 +/- 0.5 mL.min(-1).mL tissue(-1). Total cortical blood flow (cortical perfusion multiplied by cortical volume) decreased from 164 +/- 32 to 159 +/- 31, 117 +/- 2 0, and 86 +/- 22 mL/min, respectively. Medullary microvascular distrib ution volume, mean transit time, perfusion, and total blood flow remai ned unchanged. Fast CT-determined total RBFs (cortex plus medulla) wer e similar to simultaneous electromagnetic flow measurements. These res ults indicate that renal regional perfusion is more dependent on the m icrovascular distribution volume than mean transit time and that varia tions in renal tissue perfusion with reduction of RBF are more apparen t in the cortex than in the medulla.