Mean randoms estimation from list mode data

A method comprising:

• acquiring list mode data describing true coincidences and delay coincidences detected by a positron emission tomography scanner during a scan of an object;
• determining a plurality of time periods of the scan based on a distance moved by a bed supporting the object during each of the plurality of time periods;
• for each crystal of the positron emission tomography scanner, determine, from the list mode data, a number of delay coincidences which include the crystal for each of the plurality of time periods of the scan;
• for each crystal, determining a singles rate associated with each time period based on the number of delay coincidences determined for all of the plurality of crystals for the time period;
• for each time period, determining estimated mean randoms for each of a plurality of pairs of the crystals based on the singles rate associated with the time period for each crystal of the crystal pair, where estimated mean randoms determined for a pair of the crystals for a first time period are different from estimated mean randoms determined for the pair of the crystals for a second time period;
• for each of the plurality of pairs of crystals, determining a composite estimated mean randoms based on the estimated mean randoms determined for the crystal pair for each time period;
• and
• reconstructing an image of the object based on the composite estimated mean randoms for each of the plurality of pairs of crystals and the detected true coincidences.

A non-transitory computer-readable medium storing processor-executable process steps which when executed by a processing unit of a computing system, cause the computing system to:

• acquire list mode data describing true coincidences and delay coincidences detected by a positron emission tomography scanner during a scan of an object;
• determine a plurality of time periods of the scan based on a distance moved by a bed supporting the object during each of the plurality of time periods;
• for each crystal of the positron emission tomography scanner, determine, from the list mode data, delay coincidences which include the crystal for each of the plurality of time periods;
• for each crystal, determine a singles rate associated with each time period based on the number of delay coincidences determined for all of the plurality of crystals for the time period;
• for each time period, determine estimated mean randoms for each of a plurality of pairs of the crystals based on the singles rate associated with the time period for each crystal of the crystal pair, where estimated mean randoms determined for a pair of the crystals for a first time period are different from estimated mean randoms determined for the pair of the crystals for a second time period;
• for each of the plurality of pairs of crystals, determine a composite estimated mean randoms based on the estimated mean randoms determined for the crystal pair for each time period;
• and
• reconstruct an image of the object based on the composite estimated mean randoms for each of the plurality of pairs of crystals and the detected true coincidences.