High-Resolution Depth-Encoding PET Detector Module with Prismatoid Light-Guide Array

Abstract

Depth-encoding detectors with single-ended readout provide a practical, cost-effective approach for constructing high resolution and high sensitivity PET scanners. However, the current iteration of such detectors utilizes a uniform glass light guide to achieve depth-encoding, resulting in non-uniform performance throughout the detector array due to suboptimal intercrystal light sharing. We introduce Prism-PET, a singleended readout PET detector module with a segmented light guide composed of an array of prismatoids that introduces enhanced, deterministic light sharing. Methods: High resolution PET detector modules were fabricated with single-ended readout of polished multicrystal lutetium yttrium orthosilicate (LYSO) scintillator arrays directly coupled 4-to-1 and 9-to-1 to arrays of 3.2 × 3.2 mm 2 silicon photomultiplier pixels. Each scintillator array was coupled at the non-readout side to a light guide (one 4-to-1 module with a uniform glass light guide, one 4-to-1 Prism-PET module and one 9-to-1 Prism-PET module) to introduce intercrystal light sharing, which closely mimics the behavior of dual-ended readout with the additional benefit of improved crystal identification. Flood histogram data was acquired using a 3 MBq Na-22 source to characterize crystal identification and energy resolution. Lead collimation was used to acquire data at specific depths to determine depth-of-interaction (DOI) resolution. Results: The flood histogram measurements showed excellent and uniform crystal separation throughout the Prism-PET modules while the uniform glass light guide module had performance degradation at the edges and corners. A DOI resolution of 5.0 mm full width at half maximum (FWHM) and energy resolution of 13% were obtained in the uniform glass light guide module. By comparison, the 4-to-1 coupled Prism-PET module achieved 2.5 mm FWHM DOI resolution and 9% energy resolution. Conclusions: PET scanners based on our Prism-PET modules with segmented prismatoid light guide arrays can achieve high and uniform spatial resolution (9-to-1 coupling with ~ 1 mm crystals), high sensitivity, good energy and timing resolutions (using polished crystals and after applying DOI-correction), and compact size (depth-encoding eliminates parallax error and permits smaller ring-diameter).

Sub‐2 mm depth of interaction localization in PET detectors with prismatoid light guide arrays and single‐ended readout using convolutional neural networks

“…The method was deployed on a single-ended readout depth-encoding module with a prismatoid light guide array [1][2][3]. We tested our CNN on data from crystals not included in the training dataset to determine the efficacy of our approach in practice.…”

“…We fabricated a depth-encoding single-ended readout PET detector module consisting of a 16 × 16 array of 1.4 × 1.4 × 20 mm 3 fully polished LYSO crystals (X-Lum, Shanghai, China) coupled 4-to-1 to an 8 × 8 array of 3.2 × 3.2 mm 2 silicon photomultiplier (SiPM) readout pixels (Hamamatsu S13361-3050AE-08) on one end and to a prismatoid light guide on the opposite end (Prism-PET, Fig. 1) [1][2][3]. The light guide consists of a segmented array of optically isolated prismatoid mirrors which enhance and confine intercrystal light sharing [2].…”

“…The light guide consists of a segmented array of optically isolated prismatoid mirrors which enhance and confine intercrystal light sharing [2]. All crystals coupled to a single prismatoid light guide are coupled to unique SiPM pixels, thus enhancing the centroiding and depth-encoding signals that result from intercrystal light sharing within the light guide [1,2]. Barium sulfate (BaSO 4 ) was inserted between crystals (0.2 mm thickness), between prismatoids and throughout the top surface of the light guide to ensure optical isolation of each prismatoid [23].…”

“…Barium sulfate (BaSO 4 ) was inserted between crystals (0.2 mm thickness), between prismatoids and throughout the top surface of the light guide to ensure optical isolation of each prismatoid [23]. Additional information on the Prism-PET detector module can be found in the literature [1][2][3].…”

“…Depth of interaction (DOI) readout in PET has been widely researched in efforts to reduce parallax error in order to improve spatial resolution uniformity in PET systems [1][2][3][4][5]. Dual-ended readout is a heavily explored depth-encoding method that provides the best reported DOI estimation results, which are on the order of 1−2 mm full width at half maximum (FWHM) [5][6][7][8].…”