Sub-3 mm, near-200 ps TOF/DOI-PET imaging with monolithic scintillator detectors in a 70 cm diameter tomographic setup

Abstract

Recently, a monolithic scintillator detector for time-of-flight (TOF)/depth-of-interaction (DOI) positron emission tomography (PET) was developed. It has a detector spatial resolution of ~1.7 mm full-width-at-half-maximum (FWHM), a coincidence resolving time (CRT) of ~215 ps FWHM, and ~4.7 mm FWHM DOI resolution. Here, we demonstrate, for the first time, the imaging performance of this detector in a 70 cm diameter PET geometry. We built a tomographic setup representative of a whole-body clinical scanner, comprising two coaxially rotating arms, each carrying a detector module, and a central, rotating phantom table. The fully automated setup sequentially acquires all possible lines of response (LORs) of a complete detector ring, using a step-and-shoot acquisition approach. The modules contained 2 × 2 detectors, each detector consisting of a 32 mm × 32 mm × 22 mm LYSO crystal and a digital silicon photomultiplier (dSiPM) array. The system spatial resolution was assessed using a Na-22 point source at different radial distances in the field-of-view (FOV). Using 2D filtered back projection (2D FBP, non-TOF), tangential and radial spatial resolutions of ~2.9 mm FWHM were obtained at the center of the FOV. The use of DOI information resulted in almost uniform spatial resolution throughout the FOV up to a radial distance of 25 cm, where the radial and tangential resolution are ~3.3 mm FWHM and ~4.7 mm FWHM, respectively, whereas without DOI the resolution deteriorates to ~9 mm FWHM. Additional measurements were performed with a Na-22 filled Derenzo-like phantom at different locations within the FOV. Images reconstructed with a TOF maximum-likelihood expectation-maximization (TOF ML-EM) algorithm show that the system is able to clearly resolve 3 mm diameter hot rods up to 25 cm radial distance. The excellent and uniform spatial resolution, combined with an energy resolution of 10.2% FWHM and a CRT of ~212 ps FWHM, indicates a great potential for monolithic scintillators as practical high-performance detectors in TOF/DOI-PET systems.

Shared-photodetector readout to improve the sensitivity of positron emission tomography

“…However, the readout electronics and position estimation algorithms are more complicated and require very careful calibration compared to PET detectors based on scintillator arrays, which typically use simple center of gravity algorithms to estimate the gamma photon interaction position (Joung et al 2002, Wang et al 2011 and Du et al 2016). Furthermore, the resolution obtained from PET detectors based on thick monolithic scintillators are not in general as good as these obtained from PET detectors based on scintillator arrays (Borghi et al 2018 and Du et al 2018).…”

Sensors for Positron Emission Tomography Applications

“…The relevant signal conditioning and processing printed circuit board (PCB) is placed beneath the tile. Measurements and prototypes of PET based on the DPC series have been widely investigated by many research groups in recent years [135,136,137,138,139,140,141,142,143,144].…”

“…The spatial resolution in the system level was ~2.9 mm at the center of the FoV by employing a 2D FBP method. By using the DOI information, the system had an almost uniform distribution of spatial resolution from the center of the FoV up to a radial distance of 25 cm, where the radial spatial resolution was measured to be ~3.3 mm FWHM and the tangential spatial resolution was ~4.7 mm FWHM [143]. Table 5 shows a summary of the application of the DPC series to different types of PET detectors and Table 6 summarizes some applications of DPC dSiPMs for PET systems.…”

A Novel DOI Positioning Algorithm for Monolithic Scintillator Crystals in PET Based on Gradient Tree Boosting

“…Digital Object Identifier 10.1109/TRPMS.2018.2884320 the brain or female breast [4]- [6]. Recently, the advantages of DOI information have also been experimentally validated for a clinical case with a 70 cm diameter tomographic setup [7]. Furthermore, DOI is expected to also improve the performance of long-axial field-of-view PET systems (Total Body PET) [8].…”