A 1.5 mm BGO PET detector with DOI measurement

Abstract

To achieve a PET system that simultaneously offers high sensitivity, high spatial resolution, improved signal to noise ratio (SNR), and depth of interaction (DOI) measurement, we propose and implement a high DOI resolution PET detector based on a 1.5 × 1.5 × 20 mm³ BGO crystal array. In addition, we introduce a vertical line-source irradiation DOI calibration method, which enables simultaneous calibration of all detectors in the system and greatly simplifies the overall workflow. The proposed detector incorporates a 10 × 8 array of BGO crystals (1.5 × 1.5 × 20 mm³) coupled to a 5 × 4 MPPC array. A 6 mm high light-sharing window (LSW) is placed between crystals to enhance the depth dependent light transport, thereby enabling effective DOI estimation even for low light yield BGO. DOI conversion functions were established using both mechanical collimation experiments and the proposed vertical line-source irradiation at the system center.
Using mechanical collimation, we obtained an average DOI resolution of 4.4 mm (FWHM) and a mean absolute error (MAE) of 2.2 mm at depths of 4, 8, 12, and 16 mm. With the vertical line-source irradiation method, the measured DOI resolution was 4.9 mm (FWHM) with an MAE of 3.1 mm. Imaging experiments using a Derenzo phantom demonstrated that DOI correction noticeably improved image sharpness and contrast. For the 1.1 mm rod structures, the valley to peak ratio (VPR) decreased from 60.7% (uncorrected) to 36.5% (mechanical collimation calibration) and 37.7% (vertical line-source irradiation calibration), confirming substantial enhancement in spatial resolution. The proposed BGO detector and DOI calibration approach collectively provide high DOI performance, high sensitivity, and efficient calibration, offering a practical pathway toward the development of next generation high resolution and high sensitivity BGO based PET systems.