Reproduction of response functions of a multi-pixel-type energy-resolved photon counting detector while taking into consideration interaction of X-rays, charge sharing and energy resolution

摘要

Energy-resolved photon counting detectors (ERPCD) are currently being developed for medical application. It is hoped that these detectors can be used for deriving precise material information. When used for that purpose, many researchers are concerned with the necessity to consider the response of ERPCD for analysis of measured spectra. To solve this issue, we plan to apply a correction for incomplete energy signals using the application of software. For establishing a correction procedure, we should know the response of ERPCD in terms of interactions between detector materials (Cd, Zn and Te), charge sharing effect, and energy resolution. First, to derive the ideal response of the ERPCD "R₁", Monte-Carlo simulation was carried out. In the simulated R₁, characteristic X-ray peaks of Cd and Te were clearly observed; these peaks are produced in multi-pixel-type detectors. Second, taking into consideration the charge sharing effect and energy resolution, response function "R₂" was determined; constant-component-type charge sharing function and energy dependent Gaussian function were assumed based on published articles. Then comparing the experimental spectra (50 and 80 kV) measured with our test-model detector, parameters for R2 were determined. As a result, we can reproduce X-ray spectra measured with a multi-pixel-type ERPCD; typical parameters for R₂ are peak efficiency 25% and energy resolution 8% at 80 keV. Next, using the X-ray spectra folded with R₁×R₂, ratios of full-energy peaks in the spectra were analyzed. X-ray attenuation of aluminum having a thickness of 1 cm was calculated for dental radiography application. In our application for material identification, attenuation coefficient μt should be determined from the measured spectra. When a tube voltage of 80 kV was applied, obtained μt for 50-80 keV is in good agreement with the theoretical values. Based on the present research, the results of response function experiments will be applied to our material identification method which was developed using ideal X-ray spectra.