Accuracy of volume measurement using helical CT

Our goal was to determine the accuracy of volume estimation using helical CT. Helical CT scans were conducted with regularly and irregularly shaped polyvinylchloride bags containing saline of varying volumes immersed in peanut oil during various rates of movement of 0, 10, 15, and 20 cycles/min, using a motorized platform, designed to simulate respiratory motion. Ten cancer patients were scanned with CT to determine optimum upper and lower Hounsfield unit thresholds. The volumes of two human livers and kidneys were also measured in vitro under the same conditions. For all conditions, the accuracy and bias of volume estimation for saline bags ranged from 95.0 to 99.2 and -3.46 to 4.04%, respectively, and the accuracy and bias for the estimation of liver and kidney volumes were 95.6 and 3.12%, respectively. This study shows that helical CT is a highly accurate technique for estimating volume, even in the presence of simulated respiratory motion.