Z-axis high-contrast resolution for multi- vs. single-slice CT

Abstract

One aspect of image quality that should be considered when migrating scan protocols from single-slice helical CT (SSCT) to multi-slice CT (MSCT) is z-axis high-contrast resolution. The aim of this study was to compare z-axis high-contrast resolution of MSCT with that of a similarly designed SSCT for various combinations of slice thickness and pitch. A point response phantom was used to acquire slice sensitivity profiles (SSPs) and calculate z-axis resolution (10% of MTF). Additionally, a resolution pattern phantom was used to subjectively evaluate limiting z-axis resolution. Both analytical and subjective results revealed that the SSCT had higher z-axis resolution than the MSCT for nominal 5 mm slice thickness (at comparable pitches). However, for nominal 10 mm slice thickness the MSCT demonstrated z-axis resolution that was comparable or superior to SSCT. Additionally, notable differences in the shape of the SSP for axial scans were observed on the MSCT unit due to the presence of detector septa. Several conclusions can be drawn from these results including: (1) z-axis resolution is not necessarily 'better' for MSCT and should be evaluated prior to transferring scan protocols from single- to multi-slice CT, and (2) a simple acrylic plate resolution phantom may be used to quickly and effectively evaluate z-axis resolution.