Parameter Selection for Convex Optimization Time Calibration for a 2-Panel PET System.

Coincidence timing calibration is fundamental to PET imaging. The electronics, cable lengths, and detector physics such as charge drift and depth dependence add to the measured time differences in coincidence sorting - increasing random rate, decreasing true rate, and degrading system performance. This work investigates the parameter selection for convex optimization (Ordinary Least Squares) for timing calibration. We test the correlation between commonly selected parameters and the experimentally measured coincidence time difference. Additionally, we test 127 nested models of a parameterized regression equation to identify the those which optimize MSE, BIC, and FWHM, respectively. In each of these models, the FWHM performance improved ~53%, though the value shifted from ~ 304 to 160 ns - far from ~ 10 ns FWHM CZT can achieve. The results point to the lack of a necessary parameter, such as trigger threshold level or temperature, or data which is too variable for the OLS optimization.