Design of a lanthanum bromide detector for TOF PET

Recent improvements in the growth and packaging of lanthanum bromide (LaBr₃) in addition to its superb intrinsic properties of high light output, excellent energy resolution, and fast decay time, make it a viable detection material for a PET scanner based on time-of-flight (TOF). We have utilized theoretical simulations and experimental measurements to investigate the design and performance of pixilated LaBr₃ Anger-logic detectors suitable for use in a TOF PET scanner. Our results indicate that excellent energy resolution can be obtained from individual as well as multicrystal arrays of LaBr₃ in a 4×4×30 mm³ geometry. Measured energy resolutions (at 511 keV) of 4.3% for a single crystal and an average of 5.31% for an array of 100 crystals have been achieved. Both simulations and experimental measurements of an Anger-logic based detector consisting of the LaBr₃ crystal array coupled to a continuous light guide and seven PMTs, have resulted in the ability to clearly discriminate 511 keV interactions in each crystal. We have measured coincidence time resolutions for both 0.5% and 5.0% Ce-doped LaBr₃ and found that the higher level of Ce-doping yielded superior results with little to no degradation in light output or energy resolution. The time resolution for a single 5.0% Ce-doped LaBr₃ crystal coupled directly to a PMT was measured to be 275 ps. With a 25 crystal array coupled to a light guide and seven PMT cluster an average time resolution of 308 ps was obtained by summing the signals from the PMT cluster. Ultimately, 5.0% and 0.5% Ce-doped LaBr₃ Anger-logic detectors placed in coincidence yielded a time resolution of approximately 505 ps.