DigiPET: sub-millimeter spatial resolution small-animal PET imaging using thin monolithic scintillators

Abstract

A new preclinical PET system based on dSiPMs, called DigiPET, is presented. The system is based on thin monolithic scintillation crystals and exhibits superior spatial resolution at low-cost compared to systems based on pixelated crystals. Current dedicated small-rodent PET scanners have a spatial resolution in the order of 1 mm. Most of them have a large footprint, requiring considerable laboratory space. For rodent brain imaging, a PET scanner with sub-millimeter resolution is desired. To achieve this, crystals with a pixel pitch down to 0.5 mm have been used. However, fine pixels are difficult to produce and will render systems expensive. In this work, we present the first results with a high-resolution preclinical PET scanner based on thin monolithic scintillators and a large solid angle. The design is dedicated to rat-brain imaging and therefore has a very compact geometry. Four detectors were placed in a square arrangement with a distance of 34.5 mm between two opposing detector modules, defining a field of view (FOV) of 32 × 32 × 32 mm(3). Each detector consists of a thin monolithic LYSO crystal of 32 × 32 × 2 mm(3) optically coupled to a digital silicon photomultiplier (dSiPM). Event positioning within each detector was obtained using the maximum likelihood estimation (MLE) method. To evaluate the system performance, we measured the energy resolution, coincidence resolving time (CRT), sensitivity and spatial resolution. The image quality was evaluated by acquiring a hot-rod phantom filled with (18)F-FDG and a rat head one hour after an (18)F-FDG injection. The MLE yielded an average intrinsic spatial resolution on the detector of 0.54 mm FWHM. We obtained a CRT of 680 ps and an energy resolution of 18% FWHM at 511 keV. The sensitivity and spatial resolution obtained at the center of the FOV were 6.0 cps kBq(-1) and 0.7 mm, respectively. In the reconstructed images of the hot-rod phantom, hot rods down to 0.7 mm can be discriminated. In conclusion, a compact PET scanner was built using dSiPM technology and thin monolithic LYSO crystals. Excellent spatial resolution and acceptable sensitivity were demonstrated. Promising results were also obtained in a hot-rod phantom and in rat-brain imaging.

Preclinical positron emission tomography scanner based on a monolithic annulus of scintillator: initial design study

“…8. Peak sensitivity (at the center of the scanner) is predicted to be 10.1%, which compares well with the peak sensitivities of scanners utilizing arrays of discrete detector elements (1.19% to 6.72% 37 ), and with those utilizing monolithic scintillator-based detectors (0.3% to 9% 36,40,41 ). Enhanced detection sensitivity increases the flexibility and capabilities available to researchers.…”

“…36,40,41 In these systems, detection sensitivity is improved by eliminating the nonscintillating regions between adjacent detector elements present in pixelated detectors. These regions can represent nontrivial fractions of the area of a detector, especially when very small elements are used.…”

Side readout of long scintillation crystal elements with digital SiPM for TOF‐DOI PET

“…On the other hand, there are numerous detector designs in research systems aimed at optimizing one or more of the aforementioned characteristics. For example, utilizing semiconductor detector like cadmium zinc telluride (CZT) that can achieve excellent spatial and energy resolutions; 4 detector configurations that provides depth-of-interaction (DOI) information; 5 detectors utilizing monolithic scintillator that provides good spatial resolution and manufacturability; [6][7][8][9] and nonconventional radiation detectors such as resistive plate chamber (RPC)-PET with superior spatial information, 10 etc. Among the various possible detector types for PET, scintillation crystal based detectors are by far the most prevalent due to established technologies and trade-off of the characteristics mentioned above.…”

A Promising Future: Comparable Imaging Capability of MRI-Compatible Silicon Photomultiplier and Conventional Photosensor Preclinical PET Systems

“…Comparison was facilitated by the fact that the two systems share nearly identical scintillation crystal geometry. Dark noise problems can be minimized if each SiPM matrix element has an individual signal-processing channel (4,10,11), but this solution would need a tremendous number of electronic channels. To reduce the number of channels, a special readout arrangement was developed in row-column manner for the SiPM matrix.…”

“…The considerably lower noise of SiPMs than of avalanche photodiodes and the high gain (;10 6 ) are additional features making this technology promising for PET photodetectors in high magnetic fields. Some approaches to the inclusion of SiPM in a full-ring PET detector system have already been introduced (4,10,11). At the University of Debrecen, we recently developed a preclinical PET system, the MiniPET-3, based on the gantry parameters of the MiniPET-2 (12) with lutetium-yttrium oxyorthosilicate crystal detectors.…”