量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum and Radiological Science and Technology.
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A whole-body positron emission tomography scanner
must be equipped with many detectors so that they are
often composed of low-cost photomultiplier tubes (PMTs), that
is, large anode-type PMTs. The general detector structure has
a scintillation crystal element array coupled on an array of
the large anode PMTs, and for crystal element identification,
the method is needed to get sufficient spread of scintillation
light for distribution among distant PMT anodes. Besides the
common method of using a light guide, some methods have been
proposed for better element identification performance. In this
paper, we introduce a new method, in which the scintillation
light spread is promoted not only by removing reflectors between
crystal elements but also by restricting light exit to the PMTs
by placing additional reflectors at the bottom of the crystal
element array. Because the additional reflectors are parallel to
the PMT surface, we call them parallel reflectors. We verified
our method with a detector consisting of the 2.45 mm × 5 mm
× 15 mm Lu2xGd2(1−x)SiO5:Ce crystal elements and two dualphotocathode
PMTs. Each photocathode was 8 mm × 18 mm in
size. We set a 9×10 crystal element array on the two PMTs and
tried to identify the elements by the 2×2 PMT signals. Detector
performance was evaluated with 137Cs point sources (662-keV
gamma rays). The results showed that despite a significant
decrease in light output at the boundary of the two PMTs,
the method made crystal element identification possible. We measured
energy resolutions of 13.1% and 17.8% for the elements on
the PMT photocathode area and the PMT boundary, respectively.
Our method is applicable to the depth-of-interaction detector
consisting of multilayer crystal element arrays. By inserting
parallel reflectors between the layers, we would be able to control
the path of scintillation light originating in the upper layer. The
effect was first examined in a basic study with two layers of a 2×5
crystal element array. Then, the array of each layer was increased
to 9×9 for performance evaluation. It was difficult to identify all
162 crystal elements with four PMT signals; however, results suggest
the possibility of scintillation light path control in each layer
separately by the parallel reflectors and the potential for better
performance by more precise adjustment of parallel reflectors.
Improvement of a PET Detector Performance by Setting Reflectors in Parallel With PMT Face
