Design of a lanthanum bromide detector for time-of-flight 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 positron emission tomography (PET) scanner based on time-of-flight (TOF). We have utilized theoretical simulations and experimental measurements to investigate the design and performance of pixelated 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 mm×4 mm × 30 mm geometry. Measured energy resolutions (at 511 keV) of 4.1% for a single crystal and an average of 5.1% for an array of 100 crystals have been achieved with our best samples. 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 photomultiplier tubes (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% cerium-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 (4 mm × 4 mm × 30 mm) coupled directly to a PMT was measured to be 275 ps full-width at half-maximum (FWHM). With an array of 100 crystals coupled to a light guide and seven PMT cluster an average time resolution of 290 ps FWHM was obtained by summing the signals from the PMT cluster. Ultimately, two 5.0% Ce-doped LaBr₃ Anger-logic detectors placed in coincidence yielded a time resolution of 313 ps FWHM.