Count rate and dynamic range of an X-ray imaging system with MCP detector

Abstract

X-ray imaging system with edge-on MCP detector has recently been evaluated for potential application in medical imaging. Although this system has been able to provide good quality images, its clinical implementation is limited by its low count rate. The system count rate was limited by a delay line position encoding electronics, which processes the events serially. The count rate of the MCP was also limited because of high gain required for delay line electronics. In this work, the count rate and dynamic range of the system was evaluated. The count rate limitation due to readout electronics and MCP was measured separately. Pulse counting and charge integrating modes of the MCP detector was used. Photon beams for these measurements were generated using an X-ray tube at 50 and 90 kVp peak potentials with 41 and 75 keV average photon energies, respectively. The electronics dead time was measured to be 20% at 200 kHz total system count rate. In addition, 15–30% of the photon signals were not detected by delay line electronics due to exponential pulse height distribution of the MCP signals. The exponential pulse height distribution of the MCP was due to the edge on illumination mode of the MCP and the high energy X-ray photon beam. Image artifacts due to dead time and signal loss were evaluated. Multichannel ASIC readout electronics was considered as a potential solution to the count rate and dynamic range problem. It was shown that the edge-on MCP detector can operate in pulse counting mode at low gains of 10 4–10 5 e/photon required for ASIC electronics. It was also shown that at this low gain, the MCP count rate can be increased up to 1.33×10 6 count/s/pixel, for 100 μm detector pixels, which is appropriate for clinical X-ray imaging.