Energy-resolving photon counting detectors (ERPCDs) used for medical X-ray diagnosis have the potential to extract quantitative information concerning various organs. Previously, we proposed an analysis procedure to determine the effective atomic number (Zeff), but parameter optimization is required. The purpose of this study is to develop an imaging simulator and to derive optimal imaging conditions. First, we created an imaging simulator taking into consideration the following three elements: (1) X-ray attenuation in objects, (2) detector response of cadmium zinc telluride (CZT), and (3) statistical fluctuation. Second, virtual phantoms consisting of soft tissue (Zeff=6.5) and bone (Zeff=13) with mass thicknesses (ρt) of 0.1 to 80g/cm2 were made, and the Zeff images were generated under various imaging conditions related to tube voltages (60 to 120kV) and energy bin settings (10keV intervals). Then, the optimal imaging condition was derived from the accuracy analysis of Zeff images. Furthermore, a demonstration of clinical quantitative images was performed by using digital phantom which was created from voxel data of the CT image of human body phantom. The optimized imaging conditions were a tube voltage of 120kV with energy bin settings of 20–30–50–120keV. The applicable thickness ranges (achieving differences of +/- 1.0 from theoretical Zeffvalues) for Zeff=13 and 6.5 were ρt=0.8 to 10g/cm2 and 2 to 20g/cm2, respectively. Using the above imaging conditions, we succeeded in generating accurate quantitative images of the pelvic region.
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