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SummaryTo evaluate the usefulness of hybrid iterative reconstruction (iDose) for quantification of calcium content in the coronary artery on 64-detector computed tomography (CT), an anthropomorphic cardiac CT phantom containing cylinders with known calcium content was scanned at tube current-time products of 15, 20, 25, and 50 mAs using 64-detector CT. The images obtained at 15, 20, 25, and 50 mAs were reconstructed using filtered back projection (FBP), and those at 15, 20, and 25 mAs were also reconstructed using iDose. Then the volume and mass of the calcium content in the cylinders were calculated and compared with the true values. The Agatston score was also evaluated. The Agatston score and mass of calcium obtained at 50 mAs using FBP were 656.92 and 159.91 mg, respectively. In contrast, those obtained at 25 mAs using iDose were 641.91 and 159.05 mg, respectively. No significant differences were found in the calcium measurements obtained using FBP and iDose. In addition, the Agatston score and mass of calcium obtained at 15 mAs and 20 mAs using iDose were not significantly different from those obtained at 25 mAs with iDose. By using iDose, accurate quantification of calcium in the coronary artery can be achieved at 15 mAs using 64-detector CT. The radiation dose can be significantly reduced in coronary artery calcium scoring without impairing the detection and quantification of coronary calcification.

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Real-time radiation dose management is important because staff members working in interventional radiology may be exposed to relatively high doses of primary and scattered radiation from the body of a patient. In this study, we investigated the dependence of energy and dose rate of the commercially available semiconductor detector named Pocket Geiger (POKEGA) for personal monitoring in diagnostic X-rays. In the energy-dependence study, a suitable metal filter and the threshold level were examined for energy compensation using a Monte Carlo calculation code. Moreover, the energy dependence of the POKEGA with an optimal metal filter was compared with that of commercially available active personal dosimeters (APDs). With an aluminum filter, the difference of the ratio of the absorbed dose of silicon to that of air was ±7% for a tube voltage of 70-110 kV and a cutoff energy of 23 keV in the calculation. The energy response of the APDs, except the PDM-122B-SHC and the POKEGA, met the required JIS standard from 50 to 110 kV. In the dose rate-dependence study, a high linearity was observed up to 2.2 mGy h using the POKEGA with an aluminum filter.