A timing calibration device for performing timing calibration of a positron emission tomography (PET) imaging device , the timing calibration device comprising: a radioactive source comprising a positron-emitting radioisotope having a decay path including emission of two oppositely directed 511 keV gamma rays and at least one cascade gamma ray at a cascade gamma ray energy different from 511 keV; an electronic processor operatively connected to receive a timestamped radiation detection event data set acquired from the radioactive source by the PET imaging device; and a non-transitory storage medium storing instructions readable and executable by the electronic processor to perform a timing calibration method including: processing the timestamped radiation detection event data set using energy window filtering and time window filtering to generate a coincidence data set , the coincidence data set including coincident event pairs consisting of two coincident 511 keV events, and the coincidence data set further including at least one of coincident event pairs consisting of one coincident 511 keV event and one coincident cascade event at the cascade gamma ray energy, or coincident triplets consisting of two coincident 511 keV events and one coincident cascade event at the cascade gamma ray energy; and generating a timing calibration for the PET imaging device comprising offset times for PET detectors of the PET imaging device using the coincidence data set. a radioactive source comprising a positron-emitting radioisotope having a decay path including emission of two oppositely directed 511 keV gamma rays and at least one cascade gamma ray at a cascade gamma ray energy different from 511 keV; an electronic processor operatively connected to receive a timestamped radiation detection event data set acquired from the radioactive source by the PET imaging device; and a non-transitory storage medium storing instructions readable and executable by the electronic processor to perform a timing calibration method including: processing the timestamped radiation detection event data set using energy window filtering and time window filtering to generate a coincidence data set , the coincidence data set including coincident event pairs consisting of two coincident 511 keV events, and the coincidence data set further including at least one of coincident event pairs consisting of one coincident 511 keV event and one coincident cascade event at the cascade gamma ray energy, or coincident triplets consisting of two coincident 511 keV events and one coincident cascade event at the cascade gamma ray energy; and generating a timing calibration for the PET imaging device comprising offset times for PET detectors of the PET imaging device using the coincidence data set. processing the timestamped radiation detection event data set using energy window filtering and time window filtering to generate a coincidence data set , the coincidence data set including coincident event pairs consisting of two coincident 511 keV events, and the coincidence data set further including at least one of coincident event pairs consisting of one coincident 511 keV event and one coincident cascade event at the cascade gamma ray energy, or coincident triplets consisting of two coincident 511 keV events and one coincident cascade event at the cascade gamma ray energy; and generating a timing calibration for the PET imaging device comprising offset times for PET detectors of the PET imaging device using the coincidence data set. <EOS>