Time-Of-Flight PET Image Reconstruction with Complex Timing Kernels: The Case of BGO Cherenkov Photons

Time-of-Flight (TOF) reconstruction in Positron Emission Tomographic (PET) scanners uses a single kernel to reconstruct all events. However, recently developed detectors combining prompt emission and typical scintillation signal produce output events with different timing spreads. One such detectors technology is based on BGO crystals with Cherenkov photons. Thanks to fast silicon photo-multipliers sensitive in the near-ultraviolet and high-frequency electronic readout, the faint Cherenkov signal produced by the interaction of 511 keV gamma photons can be detected as faster pulse rise times. We present initial results from a Monte Carlo simulation and image reconstruction platform for detectors with multiple timing resolutions in this work. Simulated timing spreads show excellent agreement with the experimental measurements. In addition, the reconstruction software can reconstruct images using listmode and projection data. In terms of contrast recovery, the proposed multi-kernel model with BGO-Cherenkov detectors presents a similar recovery as a typical Gaussian model with LYSO detectors and timing resolution 213 ps. To the best of our knowledge, the use of multiple complex TOF kernels in image reconstruction has not been investigated in the past. However, further optimisations are needed in order to obtain the best possible results.