Incorporation of time-of-flight information in PET list-mode reconstruction using a projector with accurate detector PSF modeling

In list-mode PET reconstruction the projector is an operator that computes on-the-fly the spatial detector response related to a specific line-of-response (LOR). In the literature, many projectors with PSF modeling have been proposed with different levels of accuracy. A recently proposed projector based on the random sampling of the intrinsic detector response function was shown to accurately model all detector effects including geometry and crystal scatter. Recent PET scanners have the capability to measure the difference in the time arrival of the annihilation gamma photon pairs, also called time-of-flight (TOF). Many studies have shown the benefits, in terms of image quality, from the use of the TOF within the reconstruction process. In this study we evaluate the impact of including TOF information within a projector that includes a full modeling of the detector response. A comparative study with non-TOF image reconstruction using a projector with no (Siddon) and a less accurate (Gaussian) detector PSF modeling was also included in this study. All reconstruction algorithms were implemented on multi-GPUs. Results have shown that combining both TOF and PSF allows a double benefit on the reconstructed images. Contrast recovery was improved by nearly a factor of two, and overall execution times including TOF information were reduced by half compared to corresponding non-TOF reconstructions.