PURPOSE To compare image quality on computed tomographic (CT) images acquired with adaptive statistical iterative reconstruction (ASIR) and novel model-based iterative reconstruction (MBIR) techniques in the context of oncological surveillance using ultra-low dose scanning parameters. METHOD AND MATERIALS 30 patients scheduled for standard of care CT chest/abdomen/pelvis were scanned using ASIR reconstruction and in addition were scanned at 2 pre-selected ultra-low dose scans (using noise index of 60 and 70) with images reconstructed using MBIR. Objective and subjective image qualities were compared. Effective doses for each scans were recorded. Quantitative data such as objective image noise and mean attenuation were analyzed by comparing standard deviations, 95% confidence interval and calculating percentage difference. Mean image noise values and attenuation values were compared between different reconstruction algorithms using ANOVA. The interobserver variation and percentage agreement between the two radiologists for each of the assessed subjective image quality and lesion assessment parameters were estimated by using weighted k-statistics. Kruskal-Wallis rank sum test was used to test for equality of median scores among all subjective parameters RESULTS Objective image analysis supports significant noise reduction with low dose scans using MBIR technique (p<0.05). There was no significant change in the mean CT numbers between different reconstructions (p>0.05). There was no significant difference between subjective image quality of ultra-low dose MBIR scan compared with standard dose scan using ASIR (p>0.05). Dose recorded were substantially lower for low dose MBIR protocol (up to 75% reduction compared with ASIR). Average effective doses were 8.5mSv, 3.8mSv and 2.4mSv for standard scan NI33, NI60 and NI70 respectively. CONCLUSION MBIR shows superior reduction in noise and improved image quality and most importantly substantial dose reduction can be achieved by increasing the noise index parameters as tested in this study. This is a preliminary study, and part of a much larger study of which the results will be available in full at the RSNA 2012. CLINICAL RELEVANCE/APPLICATION To combat against increase use of CT and concerns associated with radiation, MBIR offers another tool in the radiology armoury offering substantial dose reduction without affecting image quality.
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