DEMONSTRATION OF RENAL TUBULAR FLOW BY SELECTIVE ANGIOGRAPHIC COMPUTED-TOMOGRAPHY

A high-speed computed tomography scanner was used to study the bulk fl ow of a small bolus of nonionic contrast medium through the renal tubu les of five dogs. A 0.5-mL bolus of iohexol 300 (150 mg iodine) was in jected rapidly into the renal artery, and transverse images of the kid ney were obtained at 15-second intervals over 300 seconds. The mean at tenuation values measured in regions of interest in the papilla and th e cortex were displayed as a function of time. Curves from the papilla ry regions of interest showed two peaks, the first corresponding to th e passage of the bolus through the loops of Henle that extend into the papilla and the second to the passage of the bolus through the termin al collecting tubules. The cortical regions of interest showed the cor tical return peak, which corresponded to the passage of the bolus thro ugh the distal convoluted tubules. The peaks generated by this method can be used to measure the transit times of the bolus from the glomeru li to the loops of Henle in the papilla, from the loops of Henle to th e distal convoluted tubules, and from the distal convoluted tubules to the distal collecting tubules. The mean total transit time in dehydra ted dogs was 169 seconds. The method is compared with contrast-enhance d magnetic resonance imaging (with gadolinium diethylenetriaminepenta- acetic acid), which has been used by other researchers for the same pu rpose.