The impact of time-of-flight timing resolution using clinical FDG patient data

The goal of the work was to understand the impact on clinical measures of timing resolution for time-of-flight (TOF) fully-3D iterative reconstruction. We compared TOF impact to that from use of a PET detector response model. Sixteen FDG-avid features in 13 whole-body FDG studies acquired on a TOF-capable PET/CT system were used. A NEMA image quality phantom was also studied for comparison and reconstruction timing kernel investigation. Image reconstruction settings for the patient data were typical of clinical use for each combination of reconstruction settings (TOF/PSF). The timing in the acquired PET coincidence data (550ps) was broadened to two degraded timing resolutions of 750ps and 950ps. In the resulting images, contrast was calculated as the ratio of FDG-avid feature standard uptake value (SUV_max) to liver SUV_mean, The contrast was calculated for each feature and compared across reconstruction parameters (TOF/PSF) and with use of TOF at the three timing resolutions. Results: The average increase in feature contrast using TOF (vs. non-TOF) was 13% and 15% without and with PSF. The average increase in feature contrast using PSF (vs. no PSF) was 18% and 20% without and with TOF. When timing resolution of the patient data was degraded from 550 to 750 and 950ps, the average feature contrast fell 1.2% and 0.0% with no PSF and 4.9% and 7.6% with PSF. These trends agreed well with results found using the phantom. Functional fits to the data are suggestive of the magnitude of potential contrast gain with improvement in system timing resolution and use of PSF. Conclusion: Both TOF and PSF improve contrast as measured in the FDG-avid features. Including PSF together with TOF appears to further improve the feature contrast as the system timing resolution improves.