Speaker
Description
Introduction: High-resolution depth-of-interaction (DOI) and coincidence time resolution (CTR) are critical factors for improving the performance of next-generation Time-of-Flight (TOF) PET scanners. While dual-side readout (DSR) configurations provide DOI information, the precise estimation of the interaction time remains a challenge due to optical transport delays and the stochastic nature of photon detection. This work presents a timing method based on maximum likelihood estimation (MLE) specifically designed for DSR detectors to optimize coincidence timing resolution.
Methods: The study includes Monte Carlo simulations, including scintillation and Cherenkov light production, and experimental measurements using 4x4x20 mm3 LYSO and BGO crystals coupled to Broadcom NUV-MT SiPMs on both ends. The MLE algorithm utilizes reference probability density functions (PDFs) that characterize the optical transport and SiPM response at different DOI layers. For the experimental data, these PDFs were acquired using a Na-22 point source and coincidence measurements with a 4x4x5 mm3 LYSO crystal. The timing reconstruction process first performs a DOI estimation for each crystal and subsequently estimates the interaction time.The CTR performance was evaluated using two identical DSR detectors by processing four timestamps per event using MLE algorithm and compared against single-side readout (front-only and back-only) and the numerical average of both SiPMs of each crystal.
Results: The CTR FWHM (FWTM) values, in ps, for LYSO simulations were 281.7 (517.0) for back SiPM, 265.2 (524.5) for front SiPM, 155.7 (291.0) for numerical average, and 152.7 (291.6) for MLE. For BGO simulations, values were 267.0 (811.6) for back SiPM, 228.6 (697.9) for front SiPM, 124.5 (621.7) for numerical average, and 119.4 (286.8) for MLE. Experimental LYSO measurements yielded 159.3 (541.2) for back SiPM, 143.8 (678.8) for front SiPM, 137.7 (435.5) for numerical average, and 143.9 (520.9) for MLE. Experimental BGO values were 1332.5 (3457.9) for back SiPM, 1325.5 (3211.5) for front SiPM, 1220.4 (2963.8) for numerical average, and 944.2 (2050.5) for MLE.
Conclusion: The integration of MLE with DSR detectors improves timing estimation by incorporating the statistical information of both scintillation and Cherenkov photons. This approach compensates for the degradation caused by DOI effects and optical transport delays. The results demonstrate that while the difference of averages improves the FWHM, the MLE method is necessary to effectively constrain the temporal distribution. This is particularly evident in BGO crystals, where the MLE utilizes the fast Cherenkov photon contribution to narrow the timing peak and suppress the broad temporal tails characteristic of BGO scintillation. These findings indicate that MLE is an effective tool for achieving high-resolution coincidence timing in TOF-PET systems utilizing long scintillation crystals. Current experimental results are limited by the low sampling rate of the acquisition system. Further refinements using higher-speed electronics are currently underway to minimize this instrumental jitter.
| Track | FTMI |
|---|---|
| Presentation type | Oral |