TH-C-I-611-07: Quantum Efficiency of An MCP Detector: Monte Carlo Calculation

Abstract

Purpose: To calculate quantum efficiency (QE) of the microchannel plate (MCP) detector at different x‐ray tube voltages using Monte Carlo method.Method and Materials:Monte Carlo calculation of the QE was performed using GEANT4. The MCPs with channel diameters of 2–25 μm and lead contents of 50%, 38%, 20%, 8% and 0% were considered. QE calculations were performed using GEANT4 for monochromatic photons at 200 energy points in the 0–200 keV range with 1 keV steps. QE of MCP was calculated for 35, 45, 90, and 120 kVp photon beams from tungsten target x‐ray tube, passed through corresponding soft tissue equivalent filters. QE for polychromatic photon beams were calculated by weighting the monochromatic QE with the photon energy distribution of the filtered x‐ray spectra. Results: The QE for 35 kVp beam was 83% and 86% for MCPs with 2 μm channel diameter and 50% lead content, and 5 μm channel MCP with no lead in the material, respectively. Efficiency was decreased to 51% at 35 kVp for MCP with 50% lead content and 5 μm channel diameter. The efficiencies for 45 kVp photon beams were 68% and 76% for MCPs with 50% lead and no lead, respectively, and 5 μm channel diameter. QE was increased at 45 kVp to 91% for 2 μm channel MCP with 50% lead. The QE of the 90 kVp and 120 kVp beams were in the 81–92% ranges except the lead free MCP, for which it was decreased to 20–30%. Conclusion:Monte Carlo calculations of the quantum efficiency of the edge on MCP detector shown that the smaller the MCP channel diameter, the higher the QE. Commercially available MCPs with 5–6 μm channel diameters can provide sufficiently high quantum efficiency for medical x‐ray imaging applications.