Design of Layered CdZnTe Sensor for X-ray Absorptiometry via Monte Carlo N-Particle Simulations

We report on the possibility that a new dual-energy X-ray absorptiometry can potentially be designed by Monte Carlo N-Particle (MCNP) simulations to determine the optimal conditions for the thickness of double-layered CdZnTe detector layers and the X-ray tube voltages. The optimal thicknesses of the front and the rear CdZnTe in a detector and an intermediate filter have been determined from transmitted X-ray spectra. In addition, the performance has been tested with a virtual phantom composed of bone and soft tissue. Two types of CdZnTe detectors, one with a single and the other with a 2x2 square array, were simulated with a pencil-type beam of X-rays having spectra generated using the SRS 78 program for 80, 90, 100, 110, and 120 kV. According to the analysis of the relative detection efficiency for X-ray photons for both CdZnTe detectors, the optimum detector-layer thicknesses were found to be 0.5 mm and 3 mm for the front and the rear CdZnTe detectors, respectively, at 120 kV. The X-ray spectra collected from the front and the rear CdZnTe detectors show considerable variability depending upon the locations the beam passes through; the center of a phantom, the boundary between bone and soft tissue, and a soft-tissue-only region. From these results-based MCNP simulations, we suggest that a new bone mineral densitometry sensor based on this double-layered CdZnTe detector has a very promising configuration.