Enhancement of Time-of-Flight PET Image Reconstruction for Long-lived Positron Emitters Using Information from a Prompt Gamma Ray

摘要

Isotopes such as I-124 emit a prompt gamma photon along with a positron leading to a triple coincidence of a 603 keV photon along with a pair of 511 keV annihilation photons. In conventional PET, this third photon degrades image quality and accuracy by creating multiple and random coincidences. Consequently, such prompt gamma emitting isotopes are not desirable. However, we hypothesize that using time-of-flight measurements from all three photons, the event can be more accurately positioned along the line of response between the two 511 keV photons compared to conventional TOF PET that uses the timing information from only the two 511 keV photons. In this work, we present a formulation for positioning positron-gamma TOF-PET events by employing weighted least squares estimation along with numerical simulation results of the positioning accuracy compared to conventional TOF-PET. Our numerical simulation shows that the detection of the third gamma can improve the event localization in positron-gamma (three photon coincidence) TOF-PET from 1% to 20% compared to conventional coincidence depending on the position of the detected prompt gamma ray relative to the detected annihilation photons.