Objective: Single kidney contrast media clearance was measured using multiphasic CT in patients without acute renal disorder. The aim of this study was to answer two questions. First, how accurate is CT in measuring contrast media clearance compared with plasma clearance? Second, is the accuracy of CT clearance measurements dependent on the timing of CT scans with respect to the contrast media injection?
Subjects and methods: Fifty adult patients without acute renal disorder were included in this study. Each patient underwent CT for clinical indications. The CT protocol consisted of an unenhanced scan and three contrast-enhanced scans 45, 75, and 105 sec after starting an injection of 120 mL of iopromide using an injection rate of 3 mL/sec. All scans included both kidneys. As a reference, plasma clearance of contrast media was determined as a slope clearance by measuring iodine concentration in eight blood specimens up to 8 hr postinjection.
Results: CT clearance was calculated three times for each patient, including early CT clearance, 45-75 sec postinjection; late CT clearance, 75-105 sec postinjection; and overall CT clearance, 45-105 sec postinjection. An overall CT clearance yielded the best correlation with plasma clearance with a correlation coefficient of r = 0.84 and a regression line of y = 7.5 + 0.94x. The mean difference was -3 mL/min (95% confidence interval, -35 to 29 mL/min).
Conclusion: CT clearance calculated from data acquired with a minimally modified diagnostic abdominal CT protocol was well correlated with the reference method in determining contrast media clearance for patients without acute renal disorders. The presented method can be used to calculate single kidney contrast media clearance in patients receiving contrast-enhanced abdominal CT for clinical indications.