Experimental investigation of the potential of LaBr ₃ :Ce, LYSO:Ce, and YAP:Ce for scintillator-based x-ray photon-counting detectors

<i>Objective.</i>We investigate scintillation detectors with silicon photomultipliers (SiPMs) as alternatives to direct-conversion detectors based on CdTe/Cd_1-<i>x</i>Zn<i>_x</i>Te (CZT) for x-ray photon-counting imaging. Here, we measure counting and spectral performance of three scintillators and compare the results with performances reported in literature for CdTe/CZT detectors for diagnostic photon-counting computed tomography (PCCT).<i>Approach.</i>We built 1 × 1 mm²single-pixel detectors by coupling readily available LYSO:Ce, YAP:Ce, and LaBr₃:Ce scintillators to ultrafast SiPMs. Pulse processing was optimized for rate capability rather than energy resolution. We exposed the detectors to three radioisotopes to determine energy response proportionality and energy resolution. Using an x-ray tube, we measured x-ray spectra and count rate curves, i.e. output count rate (OCR) versus input count rate (ICR).<i>Main results.</i>The energy resolutions of the LYSO:Ce and YAP:Ce detectors exceed 30% full-width-at-half-maximum (FWHM) at 60 keV, with YAP:Ce showing a more proportional response. For a 30 keV count-detection threshold, the maximum OCR of the YAP:Ce detector is 5.4 Mcps pixel^-1for paralyzable-like counting, while the OCR approaches 12.5 Mcps pixel^-1for nonparalyzable-like counting. The LYSO:Ce detector reaches 4.5 Mcps pixel^-1and 10 Mcps pixel^-1, respectively, and the LaBr₃:Ce detector 10.4 Mcps pixel^-1and 22 Mcps pixel^-1. Thereby, the rate capability of the LaBr₃:Ce detector is almost 80% of that reported for two CdTe/CZT detectors for diagnostic PCCT. Moreover, the LaBr₃:Ce detector has high proportionality and an energy resolution of about 20% FWHM at 60 keV, which is comparable to at least one CdTe detector for diagnostic PCCT. The x-ray tube spectra measured using the scintillation detectors show reasonable agreement with incident spectra.<i>Significance.</i>This work indicates that LaBr₃:Ce-based detectors may become an alternative to direct-conversion detectors for diagnostic PCCT, whereas LYSO:Ce- and YAP:Ce-based detectors appear better suited for applications with lower ICR, e.g. cone-beam PCCT in radiotherapy. Ways to further improve x-ray photon-counting scintillation detectors are also discussed.