Pilot Studies With BGO Scintillators Coupled to Low-Noise, Large-Area, SiPM Arrays

Abstract

Despite the fact that timing capabilities for devices based on BGO are limited when compared with LYSO or LSO based systems, the cost of BGO is considerably lower and could thus, be an option for devices with high scintillator volumes (as in the case of nuclear medicine scanners), but also in smaller dedicated imagers. Recently, many studies have been carried out in order to determine the potential capabilities of BGO for PET and SPECT applications, where BGO scintillator crystals have been coupled to SiPM photosensor devices. However, so far these studies have only been done on small-size BGO samples. In this work, we have studied three different BGO size configurations, coupled to a 12 × 12 low-noise SiPM array. Each SiPM has an active area of 3 × 3 mm 2 with a pixel pitch of 4.2 mm. A special charge division network providing information for each row and column output of the SiPM array has been used. The first tested BGO configuration has 2.5 mm crystal pixel pitch and 10 mm thickness, while the second makes use of smaller 1.5 mm pixels with 1.67 mm pitch but only 3 mm thick. The third evaluated configuration provided limited photon depth of interaction (DOI) information by using two staggered layers of BGO pixels also with 2.5 mm pitch and with a total thickness of 20 mm. Performances of these configurations in terms of spatial and energy resolutions have been determined. Energy resolution as good as 14.2% was obtained. Our results indicate that single layer crystal arrays with pixel values as low as 1.5 mm or two staggered layers with 2.5 mm pitch are well suited for PET applications, such as low-cost and high performance dedicated PET systems or large systems.

Highly improved operation of monolithic BGO-PET blocks

“…The main motivation of this work is a new opportunity to build PET systems requiring large volume of scintillators at a moderate cost. We have recently showed the possibility of a dual-layer BGO block using crystal arrays [4]. Here, we have also demonstrated the possibility of using monolithic blocks achieving almost 5 mm FWHM in DOI resolution.…”

“…Each row and column signal was charge integrated with a time gate of 600 ns (see figure 1 right for a signal example). We have already shown that this value is optimal for our data acquisition system [3,4]. This row-column readout approach makes it possible to characterize the scintillation X-Y light projections.…”

“…Initial studies carried out by our team have shown BGO based detector imaging capabilities high enough to resolve crystal arrays of 30 × 30 elements with 1.67 mm pitch (6 mm height) and energy resolutions as good as 12% [3]. In a prior study using larger pixels of 2 mm, it was also shown the system capability to provide photon depth of interaction (DOI) information using two staggered crystal arrays (10 mm + 10 mm total thickness) with an energy resolution in the 16% range [4].…”

Performance evaluation of dual-ended readout PET detectors based on BGO arrays with different reflector arrangements

“…They were improved to 27%-30% with the DOI correction. The energy resolution in this study is worse than the energy resolutions of other BGO detectors with similar pitch (Zhang et al 2002, Gu et al 2013, González et al 2016, mainly due to the fact that the BGO elements used here that have unpolished lateral surfaces and Toray reflectors which provide good DOI resolution, however, reduce the number of scintillation photons reaching the SiPMs and shift the 511 keV photopeak as a function of depth (figure 10 (right)).…”