TOF Offset Monitoring and Correction of PET System Based on NEMA NEC Data

A method to monitor and correct crystal-level Time-of-Flight (TOF) offset error of Positron Emission Tomography system based on NEMA NEC phantom data is studied, which improves the accuracy of the TOF resolution measurement and reduces the dependence on time correction experiment. The method calculates the TOF offset error of each crystal with the time difference error of all true coincidence events, which are decided by removing scatter and random events following the TOF resolution test in NEMA NU2-2018. The time difference due to the physical position of line source is corrected. The centroid of the statistical distribution of the time difference error represents the residual error of TOF offset of each crystal, which acts as a criterion of time correction status of the crystal. For poorly corrected crystals, the TOF offset could be corrected by adding the residual part. To improve the stability of the correction performance, an iterative process is applied. This method is applied to both experiment and simulation NEC phantom data of uMI Panorama PET/CT system, where the poorly corrected crystal modules are successfully located and corrected, and the TOF resolution performance recovers after the corrections.