Development of a novel depth of interaction PET detector using highly multiplexed G‐APD cross‐strip encoding

Abstract

Purpose: The aim of this study was to develop a prototype PET detector module for a combined small animal positron emission tomography and magnetic resonance imaging (PET/MRI) system. The most important factor for small animal imaging applications is the detection sensitivity of the PET camera, which can be optimized by utilizing longer scintillation crystals. At the same time, small animal PET systems must yield a high spatial resolution. The measured object is very close to the PET detector because the bore diameter of a high field animal MR scanner is limited. When used in combination with long scintillation crystals, these small-bore PET systems generate parallax errors that ultimately lead to a decreased spatial resolution. Thus, we developed a depth of interaction (DoI) encoding PET detector module that has a uniform spatial resolution across the whole field of view (FOV), high detection sensitivity, compactness, and insensitivity to magnetic fields. Methods: The approach was based on Geiger mode avalanche photodiode (G-APD) detectors with cross-strip encoding. The number of readout channels was reduced by a factor of 36 for the chosen block elements. Two 12 × 2 G-APD strip arrays (25 μm cells) were placed perpendicular on each face of a 12 × 12 lutetium oxyorthosilicate crystal block with a crystal size of 1.55 × 1.55 × 20 mm. The strip arrays were multiplexed into two channels and used to calculate the x, y coordinates for each array and the deposited energy. The DoI was measured in step sizes of 1.8 mm by a collimated 18 F source. The coincident resolved time (CRT) was analyzed at all DoI positions by acquiring the waveform for each event and applying a digital leading edge discriminator. Results: All 144 crystals were well resolved in the crystal flood map. The average full width half maximum (FWHM) energy resolution of the detector was 12.8% ± 1.5% with a FWHM CRT of 1.14 ± 0.02 ns. The average FWHM DoI resolution over 12 crystals was 2.90 ± 0.15 mm. Conclusions: The novel DoI PET detector, which is based on strip G-APD arrays, yielded a DoI resolution of 2.9 mm and excellent timing and energy resolution. Its high multiplexing factor reduces the number of electronic channels. Thus, this cross-strip approach enables low-cost, high-performance PET detectors for dedicated small animal PET and PET/MRI and potentially clinical PET/MRI systems.

A new method for depth of interaction determination in PET detectors

“…The DOI resolution achieved is in fact comparable to what has been reported by exploiting the light sharing through triangular teeth shaped reflectors separating the individual scintillators (Ito et al 2013), while it is consistently better as compared to solutions adopting light sharing through an ESR reflector (Yang et al 2009) or light sharing among multiple layers of crystals arranged in offsetted positions (Ito et al 2010). Better DOI resolution has been found for double side G-APD cross-strip readout (Kolb et al 2014), but with worse timing resolution. Phosphor coated scintillators also show better DOI resolution (Berg et al 2016), but at the same time perform worse in terms of both energy and timing resolution.…”

“…Various DOI encoding techniques have been proposed in literature in order to overcome this issue. Some examples include, among the others, independent readout of multiple layers of crystals (Levin 2002), pulse-shape discrimination schemes Daube-Witherspoon 1987, Wiener et al 2013), detectors with light sharing DOI encoding (Miyaoka et al 1998, Liu et al 2001, Yang et al 2009, Ito et al 2010, double side readout methods (Bugalho et al 2009), phosphor coated scintillators (Berg et al 2016) and double side G-APD cross-strip readout (Kolb et al 2014).…”

Quantitative Rodent Brain Receptor Imaging

“…Furthermore, resolving the exact position of the γ-photons within the crystals allows an increased sampling rate within the FOV. This improvement leads to an increase in spatial resolution and helps to keep it constant over the entire FOV [28]. Thus, the depth-ofinteraction resolution addresses the parallax error and enables the use of long crystals in a high-resolution PET system, which increases the sensitivity [28].…”

Development of depth encoding small animal PET detectors using dual‐ended readout of pixelated scintillator arrays with SiPMs

“…Clinic whole body PET scanners and preclinical PET scanners were already built with SiPM based detectors . But so far only a few studies were done on dual‐ended readout PET detector development with SiPMs and all of those studies used crystal size of 1.5 mm or bigger . The focus of this work is to develop high resolution, high efficient and high DOI resolution small animal PET detectors using dual‐ended readout of pixelated LYSO arrays optically coupled with SiPM arrays.…”