The potential of scintillator-based photon counting detectors: evaluation using Monte Carlo simulations.

Direct conversion photon counting detectors (PCDs) using CdTe, CZT, or Si for the sensor material are being investigated and manufactured. Indirect conversion, scintillator-based PCDs have historically thought to be too slow for the high flux requirements of diagnostic CT. Recent scintillators investigated for e.g. PET applications are very fast and inspire us to rethink this paradigm. We evaluate the potential of a LaBr₃:Ce PCD using Monte Carlo simulations. We compared a CdTe PCD and a LaBr₃:Ce PCD, assuming a pixel density of 9 pixels/mm² in each case and a surrounding 2D anti-scatter grid. A 1×1 mm² area was illuminated by flat field X-rays and the lower bound on the noise for varying contrast types and material decomposition scenarios was calculated. For conventional imaging without material decomposition, the LaBr₃:Ce PCD performed worse than CdTe because of the need to wrap pixels in reflector, which reduces geometric efficiency. For water-bone material decomposition, the two PCDs performed similarly with our assumptions on pulse shape and PCD geometry. For three-material decomposition with a K-edge imaging agent, LaBr₃:Ce reduced variance by about 35% because of the elimination of charge sharing that is present in CdTe. These results motivate further exploration of scintillator-based PCDs as an alternative to direct conversion PCDs, especially with future K-edge imaging agents.