Enhancing timing performance of heterostructures with double-sided readout

Heterostructured scintillators offer a promising solution to balance the sensitivity and timing in TOF-PET detectors. These scintillators utilize alternating layers of materials with complementary properties to optimize performance. However, the layering compromises time resolution due to light transport issues. This study explores double-sided readout -- enabling improved light collection and Depth-of-Interaction (DOI) information retrieval -- to mitigate this effect and enhance the timing capabilities of heterostructures. The time resolution and DOI performances of 3x3x20 mm 3 BGO&EJ232 heterostructures were assessed in a single- and double-sided readout (SSR and DSR, respectively) configuration using high-frequency electronics. Selective analysis of photopeak events yielded a DOI resolution of 6.4x0.04mm. Notably, the Coincidence Time Resolution (CTR) improved from 262±8 ps (SSR) to 174±6 ps (DSR) when measured in coincidence with a fast reference detector. Additionally, symmetrical configuration of two identical heterostructures in coincidence was tested, yielding in DSR a CTR of 254±8 ps for all photopeak events and 107±5 ps for the fastest events. By using high-frequency double-sided readout, we could measure DOI resolution and improve the time resolution of heterostructures of up to 40%. The DOI information resulted intrinsically captured in the average between the timestamps of the two SiPMs, without requiring any further correction.