Performance evaluation of near-real time angular tube current modulation in X-ray computed tomography using real-time dosimeter: a phantom study

In X-ray computed tomography (CT), angular tube current modulation (TCM) minimizes the unnecessary travel of X-rays in the anteroposterior direction. This study aimed to evaluate the performance of near-real time angular TCM in a CT scanner using a real-time dosimeter when different-sized elliptical phantoms were scanned. Air kerma and air kerma rate profiles of small and large elliptical phantoms were measured using a solid-state detector with a fixed tube current (FTC) and TCM with the same volume CT dose index (6.20 mGy for the small phantom and 12.32 mGy for the large phantom) displayed on the CT console. Image noises were evaluated by measuring the standard deviation of CT numbers in specific regions in the phantoms. The air kerma at the central and upper and lower peripheral holes were decreased with TCM, whereas air kerma at left and right peripheral holes were increased. With both phantom sizes, the air kerma rate profiles stabilized when TCM was used after the first two cycles. The standard deviations of CT numbers in images of the small phantom were 10.7 ± 1.3 and 10.3 ± 1.2 Hounsfield units (HU) with the FTC and TCM, respectively, and those of the large phantom were 20.6 ± 2.0 and 19.6 ± 1.7 HU, respectively. Therefore, angular TCM can adjust the tube current during each tube rotation according to the phantom’s angular attenuation profile and can decrease the image noises. It can also decrease the variance of air kerma within the in-plane direction.