Signal analysis for improved timing resolution with scintillation detectors for TOF PET imaging

Clinical TOF PET systems offer significantly degraded timing performance in comparison to that measured with small crystal geometries of the same scintillators. The usage of long, narrow crystal geometries is a major contributor to the degradation in system timing performance. We explore the effect of increased pixel length on timing performance of LaBr₃[Ce], CeBr₃ and LYSO detectors. Using fast signal digitization we characterize the response of the detector to 511keV photons interacting at different depths. Systematic shift in time pickoff with interaction depth is shown to degrade the timing performance of long crystals. Collected light, signal shape and signal arrival time are shown to correlate with interaction depth. The depth dependence of detector response shows strong dependence on surface treatment, with finer surface treatment corresponding to reduced depth sensitivity. The correlated dependencies of time pickoff, energy and signal shape offer a method for recovering timing information lost due to interaction depth dispersion. An energy-based correction to the time pickoff is shown to improve detector timing resolution. The improvement in timing performance of thick detectors with single sided readout demonstrates the benefit of inclusion of additional signal information attainable by fast signal digitization.