Depth of interaction in monolithic scintillators for positron emission tomography

The parallax error introduced by incorrectly assigning the lines-of-response defined by the annihilation photon pairs, limits the attainable spatial resolution in positron emission imaging. Knowledge of the exact position of interaction (x, y, z) inside the scintillation crystal, including the depth of interaction z of the 511 keV photons, reduces this error. In this work, the depth of interaction (DOI) was determined in two different scintillator materials: EJ-232 plastic and LYSO scintillation crystals. These were coupled to an 8×8 silicon photomultiplier (SiPM) array. An analysis of the light distributions produced inside the crystals enabled the determination of the DOI position, allowing the correction for parallax errors. This method is expected to be used in a Positron Emission Mammography (PEM) prototype under development.