Demonstration of renal tubular flow by selective angiographic computed tomography

A high-speed computed tomography scanner was used to study the bulk flow of a small bolus of nonionic contrast medium through the renal tubules of five dogs. A 0.5-mL bolus of iohexol 300 (150 mg iodine) was injected rapidly into the renal artery, and transverse images of the kidney were obtained at 15-second intervals over 300 seconds. The mean attenuation values measured in regions of interest in the papilla and the cortex were displayed as a function of time. Curves from the papillary regions of interest showed two peaks, the first corresponding to the 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 terminal collecting tubules. The cortical regions of interest showed the cortical return peak, which corresponded to the passage of the bolus through the distal convoluted tubules. The peaks generated by this method can be used to measure the transit times of the bolus from the glomeruli to the loops of Henle in the papilla, from the loops of Henle to the distal convoluted tubules, and from the distal convoluted tubules to the distal collecting tubules. The mean total transit time in dehydrated dogs was 169 seconds. The method is compared with contrast-enhanced magnetic resonance imaging (with gadolinium diethylenetriaminepentaacetic acid), which has been used by other researchers for the same purpose.