Position reconstruction in detectors based on continuous crystals coupled to silicon photomultiplier arrays

Sensitivity represents one of the major limitations for high resolution systems used in emission imaging for nuclear medicine. Currently, detectors are based on pixelated scintillators to detect ionizing radiation. There is a recent growing interest in continuous scintillators due to their increased sensitivity by eliminating insensitive areas in the detector crystals and reduced cost. To use such crystal an accurate position estimation algorithm is required to determine the location where photons interact, as opposed to pixelated scintillators, where the position is given by the crystal where the interaction took place. Additionally, including the depth where the photon interacted (DoI) inside the scintillator in the reconstruction algorithm, can be used to mitigate parallax effects. In this work we investigate the feasibility of using an existing analytical position estimation method applied to two different detectors designed to be used in two different imaging modalities: Positron Emission Tomography (PET) and Compton imaging. An LYSO crystal coupled to a 8×8 SiPM array, as one of the detector heads for the PET prototype, and a LaBr₃ crystal coupled to a 4×4 SiPM array, as part of a Compton telescope comprised of several stacked detectors, is used for each application. Results show that submillimetric resolution is measured with both detectors in most of the studied positions, near the centre and close to the edges, in Monte Carlo simulations and experimentally. The measured FWHM for the PET detector is 0.6 mm while the FWHM measured for the detector used in the Compton camera is ~0.7 mm. DoI measurements were taken only in simulations of the PET detector, where submillimetric bias was achieved and ~1.6 mm FWHM was measured.