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—In this article, we developed the novel single-end readout depth-of-interaction (DOI) detector with quadrisected crystals comparable in size to a single photo sensor. The proposed DOI detector consists of 784 gadolinium aluminum gallium garnet (GAGG) crystals, which are arranged in four layers of 14 × 14 arrays coupled with an 8 × 8 multipixel photon counter (MPPC) array. The size of each GAGG crystal is 1.45 × 1.45 × 4.5 mm3. Also, each MPPC has a surface area of 3.0 × 3.0 mm2. One pair of four-layered crystals coupled with a partial optical window is arranged across two MPPCs. Boundaries without the partial optical window are covered with optical reflectors. Light sharing is done between a pair of four-layered crystals optically coupled at one end. Each pair is coupled with paired silicon photomultipliers of different patterns. Crystal identification from each pair is obtained from the output rate of two MPPCs. From 511-keV uniform irradiation, responses of all crystal elements in the four layers can be separated clearly on a 2-D position histogram after applying the Anger calculation. Also, DOI information can be mapped to each cluster on curved lines. The energy resolution for all crystals is 9.1% after event reduction of intercrystal scatter.

添付ファイルを参照, 第81回応用物理学会秋季学術講演会

In a previous study, we developed a 4-layer depth-of-interaction (DOI) detector with 1.5 mm crystals for organ-dedicated PET application. However, the crystal size was not appropriate for submillimeter small animal imaging. The aim of this study was to develop a 4-layer DOI detector with a 1 mm crystal pitch to develop a submillimeter resolution small animal PET scanner. The proposed 4-layer DOI detector consisted of an 8 × 8 LYSO crystal array (1 × 1 × 5 mm3) stacked in 4 layers which yielded a total thickness of 20 mm, an acrylic light guide (13 × 13 × 1 mm3), and a 4×4 SiPM array (S13361-3050NE-04, Hamamatsu Photonics, Japan) with a pixel pitch of 3.2 mm. The DOI information was encoded into a 2D flood histogram by using the combination of an enhanced specular reflector and room temperature vulcanized (RTV) rubber on the side surface of the LYSO crystal. Sixteen SiPM output signals were multiplexed into four positional signals (A, B, C, and D) using a charge division circuit, and then digitized by using CAMAC DAQ. A 22Na point source was used to irradiate 511 keV gamma photons to the LYSO crystal array. The 4-layer DOI information could be encoded into the 2D flood histogram with a crystal identification rate of 89% based on the visual check. The energy resolutions of the 1st, 2nd, 3rd, and 4th layers were 11%, 15%, 13%, and 32%, respectively. In conclusion, we developed a single-ended readout 4-layer DOI detector with a 1 mm LYSO pitch and total thickness of 20 mm. In the future, we plan to improve the crystal identification rate further to 100% by optimizing the reflector material and light guide design. After the optimization of the detector performance, we will develop a prototype small animal PET scanner for submillimeter high-resolution and high-sensitivity preclinical molecular imaging., 2019 IEEE Nuclear Science Symposium and Medical Imaging Conference

Depth of interaction (DOI) encoding positron emission tomography (PET) can visualize the 3D distribution of radiopharmaceuticals in animal with high resolution. The aim of this study is to develop a single-ended readout four-layer DOI PET detector with a 1 mm crystal pitch for high resolution small animal imaging. The proposed four-layer DOI crystal block consists of an 8 × 8 LYSO crystal array (1 × 1 × 5 mm3) stacked in four-layer which yielded a total thickness of 20 mm (Fig.1). The DOI information was encoded into a 2D flood histogram, by using a combination of enhanced specular reflector (ESR) and room temperature vulcanizing (RTV) rubber (Fig. 2(a))[1]. The scintillation light were readout by using a 4 × 4 SiPM array (Hamamatsu, S13361-3050NE-04, Japan) with a pixel pitch of 3.2 mm. The sixteen SiPM output signals were multiplexed into four positional signals (A, B, C, and D) and then digitized by using CAMAC DAQ. A Na-22 point source was used to irradiate 511 keV gamma photon to the LYSO crystal array. Most of the LYSO crystals could be identified in 2D flood histogram except at the corner region (Fig. 2(b)). The energy resolutions of the 1st, 2nd, 3rd, and 4th layers were 11%, 15%, 13%, and 32%, respectively (Fig.2(c)). In conclusion, a single-ended readout four-layer DOI PET detector was developed. In future, a prototype small animal PET scanner will be developed for high resolution and high-sensitivity molecular imaging., 15th Int. SCINT 2019

Depth of interaction (DOI) information can minimize the parallax error at the peripheral field of view of a positron emission tomography (PET). In the previous study, we developed a four-layer DOI PET detector with 1.5 mm crystal pitch. The aim of this study is to develop a four-layer DOI PET detector with 1 mm crystal pitch to improve the spatial resolution. The proposed four-layer DOI PET detector consists of an 8 × 8 LYSO crystal array (1 × 1 × 5 mm3) stacked in four-layer which yielded a total thickness of 20 mm, an acrylic light guide (13 × 13 × 1 mm3), and 4 × 4 SiPM array (Hamamatsu, S13361-3050NE-04, Japan) with a pixel pitch of 3.2 mm. In order to encode the DOI information into 2D flood histogram, a combination of enhanced specular reflector (ESR) and room temperature vulcanizing (RTV) rubber was used (Fig. 1). The sixteen SiPM output signals were multiplexed into four positional signals (A, B, C, and D) using charge division circuit, and the multiplexed signals were digitized using CAMAC DAQ (Fig. 2). A Na-22 point source was used to irradiate 511 keV gamma photon to the LYSO crystal array. The energy resolution was measured to be 30.8% (Fig. 3). All the LYSO crystals could be identified in 2D flood histogram except at the corner region (Fig. 4). In conclusion, a single-ended readout four-layer DOI PET detector with 1.1 mm LYSO crystal pitch was developed. In future, the corner crystal identification will be optimized., 第66回応用物理学会春季学術講演会