Variations in MTF and NPS between CT scanners with two different IR algorithms and detectors

Abstract

The use of iterative reconstruction (IR) in computed tomography (CT) has become a useful tool for improved image quality or for reduced dose in CT examinations. In this study, the image quality of the two different Siemens IR algorithms, sinogram affirmed iterative reconstruction (SAFIRE) and advanced modelled iterative reconstruction (ADMIRE), were evaluated and compared. Differences between the Stellar detector and the conventional detector and similarities between scanners with the same detector and IR algorithm were also examined. The objective image quality parameters modulation transfer function (MTF) and noise power spectrum (NPS) were measured on a Catphan 600 phantom (The Phantom Laboratory Incorporated, NY) for five different Siemens CT scanners. MTF was calculated from the circular edge of the sensitometry targets in Catphan to facilitate measurements at different contrasts and dose levels. The results showed that the image quality was improved by using ADMIRE compared to SAFIRE on the same CT scanner equipped with the Stellar detector for certain specific tasks. The MTF was higher for the three low contrast objects when the sharp reconstruction kernel was applied. The CT scanners equipped with the Stellar detector showed an improved image quality compared to the CT scanners equipped with the conventional detector. Larger differences in MTF and NPS were observed between the detectors than between SAFIRE and ADMIRE.