A system and method are provided for determining the onset of gamma interactions for positron emission tomography (PET) imaging more accurately than with existing techniques. The timing of a sequence of primary trigger events is obtained and used to determine a weighted combination, which mixes the timing information from the various primary trigger events to compute an overall event trigger timing with improved time resolution. Numerical simulations demonstrate that the invention improves time resolution by approximately 10% over state-of-the-art methods. This improved time resolution directly benefits the imaging performance of the PET scanner, especially in time-of-flight (TOF) mode, where a high time resolution directly translates to a reduction in image noise at the same dose—or, alternatively, a reduction of dose to the patient or scan time for the same image quality.