Compton PET: a layered structure PET detector with high performance

Abstract

In most high-resolution PET detector designs, there is an inherent trade-off between spatial resolution and detector efficiency. We have developed and tested a new geometry for the detector module which avoids this trade-off. The module uses a layered structure, in which four crystal slabs are stacked in the depth direction and optically separated by enhanced specular reflector (ESR) film. The scintillation light within each layer is measured by 16 SiPMs located on the four sides of the crystal. Analog signals from all SiPMs (4 × 16) on the four sides of the crystal are digitized individually using a 64-channel TOFPET-2 module. The four-sided readout method reduces the problem of light trapping resulting from total internal reflection when reading out the end(s) of traditional scintillation crystal arrays, thus increasing the light collection efficiency. In this work, we demonstrate the readout of a complete layered detector with 4 layers. The high light collection efficiency results in a FWHM energy resolution of 10.3%, and a FWHM timing resolution of 348 ps. The distribution of scintillation light detected by the SiPMs was used to decode the interaction position of each gamma ray using a trained neural network. A FWHM spatial resolution of 1.1 ± 0.1 mm was achieved. This design allows the detection efficiency of the module to be increased by adding additional crystal slabs along the depth direction. Since the position, energy, and timing are measured for each layer independently, increasing the system sensitivity by adding more layers will not affect the spatial/energy/timing resolution. Furthermore, the layered structure allows partial recovery of position information for events that undergo Compton scatter within the detector.

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

“…Recently, there has been an increased focus in Compton scatter localization in PET modules, which would enable higher sensitivity and the use of scintillator crystals with smaller cross‐sections (since intercrystal Compton scatter is more likely as crystal size decreases) 43,44 . Neural networks have been researched to perform Compton positioning and have been tested with limited success in a variety of PET detectors, including the MINDView brain PET scanner, 45 the Sherbrooke LabPET‐4 preclinical scanner, which uses phoswich scintillators, 46 and a detector module consisting of a monolithic scintillator with an SiPM array on each lateral face 47 . In addition, the framework for performing accurate Compton localization using single‐ended readout depth‐encoding modules was laid out in a recent paper, demonstrating that high DOI resolution is a critical component in determining the primary interaction site 48 .…”

Characterization and Simulation of an Adaptable Fan-Beam Collimator for Fast Calibration of Radiation Detectors for PET

“…An alternative approach is dedicated setups shaping a gamma beam usually consisting of a material with high atomic mass (e.g., tungsten or lead). First, parallel hole collimators with precise drilling of known diameter ranging from 0.5 mm to 1.0 mm were employed for PET detector calibration [9], [24], [25], [27], [31]. The thickness of the shielding material and shape of the parallel hole determine the beam profile.…”

Characterization of a High-Aspect Ratio Detector With Lateral Sides Readout for Compton PET

“…In particular, Li et al [6] developed a prototype detector based on CsI(Tl) with layers of dimensions 27.4 × 27.4 × 3 mm 3 (aspect ratio of 9.1). A similar concept was carried out based on LYSO crystals [7] but with smaller layer dimensions of 13.34 × 13.34 × 2.75 mm 3 (aspect ratio of 4.8).…”

“…We envisaged the use of very high-aspect ratio crystal configurations based on LYSO [8]. We have selected a crystal design with entrance and exit faces of the gamma-ray radiation of conventional dimensions of 51.5 × 51.5 mm 2 and a thickness of only 3 mm, resulting in a high-aspect ratio of 17.2, which is significantly larger than previous experimental works [6], [7]. The dimensions of our detector make them suitable for both whole or total-body PET, but also to organ-dedicated PET systems [9].…”

“…In this work, four different methods to estimate the interaction position based on the center of the gravity algorithm have been implemented and compared in order to assess the most suitable one for this detector configuration and aspect ratio. The center of the gravity algorithm is easier to implement compared to other approaches as suggested in [7] for large aspect ratio designs. Also, a novel calibration method for energy and planar coordinates based on Voronoi diagrams has been successfully implemented.…”