Development of a z-axis tilting technique using a chest phantom to reduce radiation exposure during computed tomography coronary angiography.

Abstract

Japan has the highest estimated exposure frequency of diagnostic X-rays in the world. Furthermore, the volumetric computed tomography dose index (CTDIvol) and dose length product (DLP) of computed tomography coronary angiography are relatively high in Japanese diagnostic reference levels, and it is important to reduce both dose indices. This study proposed a new exposure reduction technique, the vanishing liver position (VLP), where the body is tilted to the right in the z-axis. The VLP advantages include reduction in the scanning range and overlap between the heart and the liver. Three different electrocardiogram protocols were employed, and changes in the tube current in the z-axis were measured during each protocol. Additionally, changes in the radiation exposure caused by z-axis tilting were evaluated. Our results indicate that this technique reduced CTDIvol and DLP by 6.2 and 8.9%, respectively, at most, indicating that this technique can reduce radiation exposure.