Optimization of scan delay for multi-phase computed tomography by using bolus tracking in normal canine kidney

This study was performed to optimize scan delays for canine kidney by using a bolus-tracking technique. In six beagle dogs, computed tomography (CT) of the kidney was performed three times in each dog with different scan delays after a bolus-tracking trigger of 100 Hounsfield units (HU) of aortic enhancement. Delays were 5, 20, 35, and 50 sec for the first scan, 10, 25, 40, and 55 sec for the second scan, and 15, 30, 45, and 60 sec for the third scan. The renal artery-to-vein contrast difference peaked at 5 sec, and the renal cortex-to-medulla contrast difference peaked at 10 sec. The renal cortex-to-medulla contrast difference approached zero at a scan delay of 30 sec after the bolus trigger. For the injection protocol used in this study, the optimal scan delay times for renal arterial, corticomedullary, and nephrographic phases were 5, 10, and 30 sec after triggering at 100 HU of aortic enhancement using the bolus-tracking technique. The bolus-tracking technique is useful in multi-phase renal CT study as it compensates for different transit times to the kidney among different animals, requires a small dose of contrast media, and does not require additional patient radiation exposure.