  In this study we evaluated the task-based image quality of a low contrast
clinical task for the abdomen protocol (e.g., pancreatic tumour) of three
different CT vendors, exploiting three model-based iterative reconstruction
(MBIR) levels. We used three CT systems equipped with a full, partial, advanced
MBIR algorithms. Acquisitions were performed on a phantom at three dose levels.
Acquisitions were reconstructed with a standard kernel, using filtered back
projection algorithm (FBP) and three levels of the MBIR. The noise power
spectrum (NPS), the normalized one (nNPS) and the task-based transfer function
(TTF) were computed following the method proposed by the American Association
of Physicists in Medicine task group report-233 (AAPM TG-233). Detectability
index (d') of a small lesion (small feature; 100 HU and 5-mm diameter) was
calculated using non-prewhitening with eye-filter model observer (NPWE).The
nNPS, NPS and TTF changed differently depending on CT system. Higher values of
d' were obtained with advanced-MBIR, followed by full-MBIR and
partial-MBIR.Task-based image quality was assessed for three CT scanners of
different vendors, considering a clinical question. Detectability can be a tool
for protocol optimisation and dose reduction since the same dose levels on
different scanners correspond to different d' values.
