Speaker
Description
Introduction: Monolithic scintillators represent a cost-effective alternative to pixelated detector designs in the development of time-of-flight (TOF) PET scanners. However, achieving optimal coincidence time resolution (CTR) in monolithic blocks is limited by the variance in photon arrival times and the complex optical transport across the detector volume. This work evaluates a timing reconstruction method based on maximum likelihood estimation (MLE) using the PETsys TOFPET2 ASIC, which provides individual timestamps for each SiPM channel in the array.
Methods: We evaluated a 32x32x10 mm³ LYSO monolithic crystal wrapped with white reflector coupled using optical grease to an 8x8 Broadcom NUV-MT SiPM array with a 4 mm pitch. The signals were processed using the PETsys TOFPET2 Evaluation Kit. To implement the MLE algorithm, reference probability density functions (PDFs) of the optical transport were derived using a coincidence setup with a Na-22 point source and a 3x3x4 mm³ LYSO pixel as a timing reference to perform a gamma beam scan. The MLE estimator was compared against conventional timing methods, including skew-only and combined skew and time-walk corrections. Additionally, the performance was compared against the numerical average of a varying number of SiPM timestamps and energy-weighted average methods.
Results: The CTR performance was characterized for all evaluated methods. The CTR FWHM obtained using the skew-only correction was 505 ps. The numerical average of N-SiPMs yielded 466 ps (N=2), 534 ps (N=3), 716 ps (N=4), and 1079 ps (N=5), while the energy-weighted average reached 452 ps (N=2), 470 ps (N=3), 548 (N=4), and 688 ps (N=5). The MLE-based timing method achieved a CTR FWHM of 423 ps.
Conclusion: The implementation of an MLE-based timing estimator with the PETsys TOFPET2 ASIC improves the coincidence time resolution of monolithic LYSO detectors. By modeling the optical response through experimental PDFs, the MLE method compensates for the timing degradation inherent in non-segmented crystals. These results demonstrate that the application of statistical estimators to individual SiPM timestamps can align the timing performance of monolithic scintillators with that of more complex pixelated geometries, supporting the use of monolithic designs in high-sensitivity TOF-PET systems.
| Track | FTMI |
|---|---|
| Presentation type | Oral |