25 March 2008 A comparison of three CT voltage optimization strategies
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Abstract
We evaluated three strategies for optimizing the x-ray tube voltage in chest CT examinations: (1) keeping patient dose constant and maximizing contrast to noise ratios (CNR); (2) keeping CNR constant and minimizing patient effective dose (E); (3) maximizing CNR2/E. Lung and soft tissue Hounsfield unit values, together with the corresponding image noise, were measured in a Rando phantom at x-ray tube voltages between 80 and 140 kV. A CT dosimetry software package (ImPACT) was used to compute effective doses as a function of CT x-ray tube voltage for adult patients undergoing chest CT examinations. CNR and patient dose in chest CT examinations both increase with increasing x-ray tube voltage at a fixed mAs. All optimization strategies provided similar qualitative results, which showed the best imaging performance was achieved at the lowest x-ray tube voltage (80 kV). Optimization using constant CNR or effective dose is preferred since these methods provide explicit choices of optimal kV/mAs combinations, as well as quantitative data on how changing kV would modify CNR and/or patient dose. The CNR2/Dose figure of merit does not offer explicit choices of kV/mAs for performing CT examinations, and changes in FOM value are more difficult to relate to changes in imaging performance or patient dose.
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Kent M. Ogden, Walter Huda, Mohammad R. Khorasani, Ernest M. Scalzetti, "A comparison of three CT voltage optimization strategies", Proc. SPIE 6913, Medical Imaging 2008: Physics of Medical Imaging, 691351 (25 March 2008); doi: 10.1117/12.773305; https://doi.org/10.1117/12.773305
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