QUANTITATIVE EVALUATION OF THORAX CT IMAGE QUALITY: PRELIMINARY RESULTS—A NEW APPROACH TO OLD PROBLEMS

The optimization of dose in Computed Tomography is a topic of ongoing research, including the search for objective image-quality metrics, especially in the clinical setting. This study evaluated the ability of new image-quality metrics to discriminate between Low-Dose and Diagnostic chest CT protocols in the same patients. Thirty clinical examinations corresponding to 15 patients were analyzed (one study per protocol for each patient). The metrics considered were the clinical contrast-to-noise ratio (CNRc) and its mean value (CNRca), as well as the clinical spatial resolution expressed as the full width at half maximum (FWHMc) and its mean value per image (FWHMca), estimated from the edge-spread function of relevant anatomical structures. Size-specific dose estimates (SSDE) were 8.8 ± 1.5 mGy for the Low-Dose protocol and 13.5 ± 2.9 mGy for the Diagnostic protocol. CNRc and FWHMca exhibited statistically significant differences between protocols: FWHMca ranged from 1.40–1.97 mm in Low-Dose scans versus 0.9–1.2 mm in Diagnostic scans. These results confirm that CNRc, FWHMc and, in particular, FWHMca can quantitatively characterize clinical image quality, although larger-scale studies are needed to consolidate these observations.