Reduced exposure using asymmetric cone beam processing for wide area detector cardiac CT |
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Authors: | Arash Bedayat Frank J Rybicki Kanako Kumamaru Sara L Powers Jason Signorelli Michael L Steigner Chloe Steveson Shigeyoshi Soga Kimberly Adams Dimitrios Mitsouras Melvin Clouse Richard T Mather |
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Institution: | 1. Applied Imaging Science Laboratory, Department of Radiology, Brigham and Women??s Hospital and Harvard Medical School, Boston, MA, 02115, USA 3. Toshiba Medical Systems Corporation, 1385 Shimoishigami, Otawara-shi, Tochigi-ken, Japan 4. Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA 2. Toshiba Medical Research Institute, 706 N Deerpath Dr, Vernon Hills, IL, USA
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Abstract: | The purpose of this study was to estimate dose reduction after implementation of asymmetrical cone beam processing using exposure differences measured in a water phantom and a small cohort of clinical coronary CTA patients. Two separate 320?×?0.5?mm detector row scans of a water phantom used identical cardiac acquisition parameters before and after software modifications from symmetric to asymmetric cone beam acquisition and processing. Exposure was measured at the phantom surface with Optically Stimulated Luminescence (OSL) dosimeters at 12 equally spaced angular locations. Mean HU and standard deviation (SD) for both approaches were compared using ROI measurements obtained at the center plus four peripheral locations in the water phantom. To assess image quality, mean HU and standard deviation (SD) for both approaches were compared using ROI measurements obtained at five points within the water phantom. Retrospective evaluation of 64 patients (37 symmetric; 27 asymmetric acquisition) included clinical data, scanning parameters, quantitative plus qualitative image assessment, and estimated radiation dose. In the water phantom, the asymmetric cone beam processing reduces exposure by approximately 20% with no change in image quality. The clinical coronary CTA patient groups had comparable demographics. The estimated dose reduction after implementation of the asymmetric approach was roughly 24% with no significant difference between the symmetric and asymmetric approach with respect to objective measures of image quality or subjective assessment using a four point scale. When compared to a symmetric approach, the decreased exposure, subsequent lower patient radiation dose, and similar image quality from asymmetric cone beam processing supports its routine clinical use. |
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