[Show abstract][Hide abstract] ABSTRACT: A crystal-based timing calibration method is implemented and investigated on a GE PET scanner. This method first calculates block-level adjustments using a commercially available algorithm, and then, based on the calculated block-level adjustments, derives the crystal-level adjustments needed within each block. Concurrently with the time difference acquisition for block-pair adjustment, the time differences are also accumulated for all the crystals within each block. The crystal averages are calculated from the accumulated crystal time differences and represent the time differences among these crystals. The crystal-based adjustments are set to correct for both block time differences and crystal variations. A method to minimize the discrepancy in averaged correction for a block before and after discretization of the desired crystal adjustments is proposed. The performance of this crystal-based timing adjustment method is also presented.