Autonomous Timing Calibration for Time-of-Flight PET

Timing calibration is critical to achieve the best possible timing resolution. In this work, we present an autonomous timing calibration for 3D TOF PET by explicitly using intrinsic TOF data consistency. First, we derive generalized consistency equations in native coordinates for 3D TOF PET scanners with arbitrary transverse geometry, including polygonal PET scanners with modular detectors as a special case. In native coordinates, the two degrees of entangled redundancy and rich structure of 3D TOF data are explicitly elicited and exploited by the two TOF consistency equations. We then develop an autonomous timing calibration as an application of the TOF data consistency equations. Timing offsets can be computed by solving the two linear timing offset equations involving two TOF moments–the zeroth and first TOF moments. Currently, timing calibration is usually obtained from a specialized data acquisition with known tracer distribution, e.g., a cylinder phantom, or an annulus phantom. The proposed autonomous timing calibration can be applied to data acquired with an arbitrary tracer distribution, which eliminates the need for a specialized data acquisition. To evaluate the method, we perform GATE simulations of a generic 3D TOF PET scanner with a NEMA phantom, and timing offsets were embedded into the list-format data event-by-event. We then deposit the list-format event into two TOF moments, and the timing offsets were accurately computed using a Landweber algorithm. Next generation TOF PET scanners have significantly improved timing resolution using silicon photomultiplier (SiPM) based detectors, which may require frequent timing calibration and close monitoring in performance compared to photomultiplier-tube based detectors. The proposed autonomous timing calibrations allows the residual timing offsets be corrected automatically using clinical data sets whenever computing resources are available.