Performance evaluation of a multi-slice CT system

Our purpose in this study was to characterize the performance of a recently introduced multi-slice CT scanner (LightSpeed OX/i, Version 1.0, General E lectric Medical Systems) in comparison to a single-slice scanner from the s ame manufacturer (HiSpeed CT/i, Version 4.0). To facilitate this comparison , a refined definition of pitch is introduced which accommodates multi-slic e CT systems, yet maintains the existing relationships between pitch, patie nt dose, and image quality. The following performance parameters were asses sed: radiation and slice sensitivity profiles, low-contrast and limiting sp atial resolution, image uniformity and noise, CT number and geometric accur acy, and dose. The multi-slice system was tested in axial (1, 2, or 4 image s per gantry rotation) and HQ (Pitch = 0.75) and HS (Pitch = 1.5) helical m odes. Axial and helical acquisition speed and limiting spatial resolution ( 0.8-s exposure) were improved on the multi-slice system. Slice sensitivity profiles, image noise, CT number accuracy and uniformity, and low-contrast resolution were similar. In some MS-helical modes, helical artifacts and ge ometric distortion were more pronounced with a different appearance. Radiat ion slice profiles and doses were larger on the multi-slice system at all s can widths. For a typical abdomen and pelvis exam, the central and surface body doses for 5-mm helical scans were higher on the multi-slice system by approximately 50%. The increase in surface CTDI values (with respect to the single-slice system) was greatest for the 4 x 1.25-mm detector configurati on (190% for head, 240% for body) and least for the 4 x 5-mm configuration (53% for head, 76% for body). Preliminary testing of version 1.1 software d emonstrated reduced doses on the multi-slice scanner, where the increase in body surface CTDI values (with respect to the single-slice system) was 105 % for the 4 x 1.25-mm detector configuration and 10% for the 4 x 5-mm confi guration. In summary, the axial and MO-helical modes of the multi-slice sys tem provided excellent image quality and a substantial reduction in exam ti me and tube loading, although at varying degrees of increased dose relative to the single-slice scanner. (C) 1999 American Association of Physicists i n Medicine. [S0094-2405(99)03411-2].