Performance assessment of pixelated LaBr3 detector modules for time-of-flight PET

Our recent measurements with pixelated LaBr3 Anger-logic detectors for use in time-of-flight (TOF) PET have demonstrated excellent energy resolution (5.1% at 511 keV) and coincidence time resolution (313 ps full width at half maximum, FWHM) with small prototype configurations [1]. A full size detector module suitable for a whole-body 3D PET scanner has been constructed based on the prototype designs and consists of 1620 4 x 4 x 30 mm(3) LaBr3 crystals. We have utilized simulations to guide experimental measurements with the goal of optimizing energy and time resolution in evaluating triggering configurations and pulse shaping needed in a full system. Experimental measurements with the detector module indicate energy and time resolution consistent with our earlier prototypes when measured at low count rate. At very high count rate the energy, time and spatial resolution degrade due to pulse pileup. While it is possible to reduce pulse pileup by using smaller photomultiplier tubes (i.e., 39 mm instead of 50 mm diameter), we are trying to limit the total number of PMTs needed for a full-scale PET scanner with a large axial field-of-view. Therefore, we have designed and tested a pulse shaping circuit to improve the detector response and performance at high count rate. Simulations of a complete LaBr3 scanner indicate significant improvements in noise equivalent count rate (NEC) and spatial resolution can be achieved using pulse shaping.