Performance evaluation of a multi-slice CT system

Abstract

Our purpose in this study was to characterize the performance of a recently introduced multi‐slice CT scanner (LightSpeed QX/i, Version 1.0, General Electric Medical Systems) in comparison to a single‐slice scanner from the same manufacturer (HiSpeed CT/i, Version 4.0). To facilitate this comparison, a refined definition of pitch is introduced which accommodates multi‐slice CT systems, yet maintains the existing relationships between pitch, patient dose, and image quality. The following performance parameters were assessed: radiation and slice sensitivity profiles, low‐contrast and limiting spatial resolution, image uniformity and noise, CT number and geometric accuracy, and dose. The multi‐slice system was tested in axial (1, 2, or 4 images per gantry rotation) and HQ (Pitch = 0.75) and HS (Pitch = 1.5) helical modes. 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 HS‐helical modes, helical artifacts and geometric distortion were more pronounced with a different appearance. Radiation slice profiles and doses were larger on the multi‐slice system at all scan 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 detector configuration (190% for head, 240% for body) and least for the configuration (53% for head, 76% for body). Preliminary testing of version 1.1 software demonstrated 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 4×1.25‐mm detector configuration and 10% for the 4×5‐mm configuration. In summary, the axial and HQ‐helical modes of the multi‐slice system provided excellent image quality and a substantial reduction in exam time and tube loading, although at varying degrees of increased dose relative to the single‐slice scanner.