Evaluation of a TOF-PET detector design that achieves ≤ 100 ps coincidence time resolution

Abstract

Positron emission tomography (PET) detectors for clinical systems employ scintillation crystal element that are typically $\ge 20$ mm length and 3–5 mm in width optically coupled on their narrow end to a photosensor. The aspect ratio of this traditional crystal element configuration yields low light collection efficiency of scintillation photons and significant, interaction depth-dependent scintillation light transit time jitter from the 511 keV photon interaction position to the exit interface of the crystal. Alternatively, coupling the photosensor on the long side of the crystal elements results in near-complete light collection efficiency and low scintillation photon transit time jitter. In this new scintillation light readout configuration, the achievable coincidence time resolution (CTR) with 3x3x20 mm $^{\mathbf {3\, }}$ LGSO:Ce(0.025 mol%) crystals coupled to a row of SensLJ SiPMs, multiplexed to a single timing channel, is $102 \pm 2$ ps FWHM using simple leading edge time pickoff. This is in contrast to a CTR of $137 \pm 2$ ps FWHM that is achieved when the same crystals are coupled to a single 3x3 mm $^{\mathbf {2\, }}$ SiPM in the standard ”end coupled” configuration. In this work, we present an experimental investigation into the achievable timing performance using this side readout configuration. Altogether, the side readout configuration offers an immediate solution for 100 ps clinical PET detectors and mitigates factors affecting ongoing efforts to achieve sub-100 ps FWHM CTR.