Depth‐of‐interaction positron emission tomography detector with 45° tilted silicon photomultipliers using dual‐ended signal readout

Abstract

Background: Small-animal positron emission tomography (PET) systems are widely used in molecular imaging research and drug development. There is also growing interest in organ-dedicated clinical PET systems. In these smalldiameter PET systems, the measurement of the depth-of -interaction (DOI) of annihilation photons in scintillation crystals allows for the correction of parallax error in PET system, leading to an improvement on the spatial resolution uniformity. The DOI information is also useful for improving the timing resolution of PET system as it enables the correction of DOI-dependent time walk in the arrival time difference measurement of annihilation photon pairs. The dual-ended readout scheme is one of the most widely investigated DOI measurement methods, which collects visible photons using a pair of photosensors located at both ends of the scintillation crystal. Although the dual-ended readout allows for simple and accurate DOI estimation, it requires twice the number of photosensors compared to the single-ended readout scheme. Purpose: To effectively reduce the number of photosensors in a dual-ended readout scheme, we propose a novel PET detector configuration that employs 45 • tilted and sparsely arranged silicon photomultipliers (SiPMs). In this configuration, the angle between the scintillation crystal and SiPM is 45 • . Therefore, and thus, the diagonal of the scintillation crystal matches one of the lateral sides of the SiPM. Accordingly, it allows for the use of SiPM device larger than the scintillation crystal, thereby improving light collection efficiency with a higher fill factor and reducing SiPM quantity. In addition, all scintillation crystals can achieve more uniform performance than other dual-ended readout methods with a sparse SiPM arrangement because 50% of the scintillation crystal cross section is commonly in contact with the SiPM. Methods: To demonstrate the feasibility of our proposed concept, we implemented a PET detector that employs a 4 × 4 LSO block with a single crystal dimension of 3.03 × 3.03 × 20 mm 3 and a 45 • tilted SiPM array. The 45 • tilted SiPM array consists of 2 × 3 SiPM elements at the top ("Top SiPM") and 3 × 2 SiPM elements at the bottom ("Bottom SiPM"). Each crystal element of the 4 × 4 LSO block is optically coupled with each quarter section of the Top SiPM and Bottom SiPM pair. To characterize the performance of the PET detector, the energy, DOI, and timing resolution were measured for Minjee Seo and Haewook Park contributed equally to this work.

Scalable, Time-of-Flight and Depth-of-Interaction Detector Units for High-Resolution PET Systems

“…In parallel to advances in timing performance, a multitude of concepts to encode the DOI of a γ-photon has been developed [20], [31] throughout the past decades, evoking many patents [32]- [35]. For example, concepts considered multi-layered scintillator or detector matrices [36]- [39] and different reflector geometries in one-to-one coupled matrices [40]- [42] or other light-sharing concepts [14], [43].…”