Abstract
Purpose: To quantify image quality differences between the average of n low‐dose images and a single high‐dose image of equivalent effective dose. Method and Materials: An electron density phantom (CIRS) was scanned on a 16‐slice CT scanner 25 times each at 12, 24, 48, 72, and 144 mAs (130 kVp, 5 mm slices, standard‐body filter). Low‐mAs scans were averaged to simulate 25 realizations of 9 high‐mAs scans: 24mAs=2×12mAs, 48mAs=2×24mAs=4×12mAs, 72mAs=3×24mAs=6×12mAs, 144mAs=2×72mAs=3×48mAs=6×24mAs=12×12mAs. Mean and standard deviation (SD) were calculated for 18 ROIs over a range of materials (−790 to 235 HU) on matched pairs of simulated and acquired images. The Welch's t‐test was used to evaluate differences in mean and SD between images. Similar experiments were performed on a Catphan® and anthropomorphic‐body phantom (ATOM, CIRS). Catphan images were visually scored for spatial and low‐contrast resolution. Profiles through selected ATOM images from the head, shoulder, and thorax were compared. Results: For every simulation, the average (range) difference in mean CT number between simulated and acquired images over all ROIs was <1 HU (−0.1±0.4 to 0.7±1.1 HU); no statistically significant difference was observed for any one material (p⩾0.27). For every simulation, the average (range) relative difference in SD over all ROIs was ⩽4% (−4.0% ±4.9% to 3.6%±3.1%); no statistically significant difference was observed for any one material (p⩾0.56). Spatial resolution of simulated images was ± 1 lp/cm of acquired images and low‐contrast resolution was ± 1 disc at all contrast levels. ATOM images profiles showed excellent agreement in all slices. Conclusion: Image quality of the average of n low‐mAs CT images is equivalent to a high‐mAs (nxlow‐mAs) image for the dose range studied; suggesting prospective CT dose‐reduction studies may be feasible using multiple low‐dose CT image acquisitions in place of the single high‐dose diagnostic scan.
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