Investigation of spatial resolution improvement by use of a mouth-insert detector in the helmet PET scanner

Abstract

The dominant factor limiting the intrinsic spatial resolution of a positron emission tomography (PET) system is the size of the crystal elements in the detector. To increase sensitivity and achieve high spatial resolution, it is essential to use advanced depth-of-interaction (DOI) detectors and arrange them close to the subject. The DOI detectors help maintain high spatial resolution by mitigating the parallax error caused by the thickness of the scintillator near the peripheral regions of the field-of-view. As an optimal geometry for a brain PET scanner, with high sensitivity and spatial resolution, we proposed and developed the helmet-chin PET scanner using 54 four-layered DOI detectors consisting of a 16 × 16 × 4 array of GSOZ scintillator crystals with dimensions of 2.8 × 2.8 × 7.5 mm. All the detectors used in the helmet-chin PET scanner had the same spatial resolution. In this study, we conducted a feasibility study of a new add-on detector arrangement for the helmet PET scanner by replacing the chin detector with a segmented crystal cube, having high spatial resolution in all directions, which can be placed inside the mouth. The crystal cube (which we have named the mouth-insert detector) has an array of 20 × 20 × 20 LYSO crystal segments with dimensions of 1 × 1 × 1 mm. Thus, the scanner is formed by the combination of the helmet and mouth-insert detectors, and is referred to as the helmet-mouth-insert PET scanner. The results show that the helmet-mouth-insert PET scanner has comparable sensitivity and improved spatial resolution near the center of the hemisphere, compared to the helmet-chin PET scanner.

Simulation study on sensitivity performance of a helmet-shaped brain PET scanner based on the Plug&Imaging detector design

“…A FDG point source was instead used for a prototype composed of LYSO crystals [31] and the sensitivity measured in the central position of the scanner axis fits in the interval 7-8.5%. Similarly, also the sensitivity measured using a simulated FDG point source for a GSO crystal-based helmet [32] reaches a value between 7-8.5%. In both previous cases the achieved sensitivity at the FOV centre is lower than the one we see in the FOV centre of our helmet.…”

“…Further helmet prototypes, described in [30][31][32], with a similar design were simulated. Using a hemispherical phantom full of a FDG-distributed solution, the proposed helmet-chin PET, composed of GSO crystal scintillators, shows 1.5 times higher total sensitivity than a classic cylindrical scanner made out the same number and type of crystals [30].…”

Performance Simulation of an Ultrahigh Resolution Brain PET Scanner Using 1.2-mm Pixel Detectors

“…An image resolution of 3 mm was reported at the center of the field-of-view [2]. Another interesting concept is the Helmet PET [3]–[5], which was designed to improve the sensitivity for human brain imaging using a compact hemisphere and detectors add-on. The Helmet PET has a spatial resolution of 3 mm and can achieve 2.6 times higher sensitivity for the brain region with less than 14 the number of detectors compared to standard whole-body scanners.…”

Characterization of Dedicated PET Equipment with Non-Conventional Geometry

“…The reconstruction process is complex, requiring synchronization of the probe position relative to the external PET detectors. Referring to the brain, a novel design has been simulated and constructed that combines a semi-spherical PET structure with detectors at the chin area, see Figure 13 right [70] [71]. With this novel PET configuration, authors are able to obtain a sensitivity close to 10% at the FOV center, and a spatial resolution of 2 mm.…”