@misc{oai:repo.qst.go.jp:00065375,
 author = {稲玉, 直子 and 平野, 祥之 and 錦戸, 文彦 and 新田, 宗孝 and 山谷, 泰賀 and 稲玉 直子 and 平野 祥之 and 錦戸 文彦 and 新田 宗孝 and 山谷 泰賀},
 month = {Nov},
 note = {To achieve high spatial resolution in all 3 dimensions on a PET detector, we have developed the DOI detector named X’tal cube. Structure of the X’tal cube is shown in Figure 1a). Since a multi-pixel photon counters (MPPC) is small enough not to interfere with radiations, the X’tal cube has MPPCs on all six sides of a scintillation crystal block. The crystal block are then segmented into cubes by only optical discontinuity so that scintillation light originating in a segment spreads to all 3 dimensions and is detected by the MPPCs at all six surfaces of the crystal block. Figure 1b) is the 3 dimensional (3D) position histogram obtained by the irradiation of 511 keV gamma-rays from 22Na sources to an X’tal cube [1]. The X’tal cube was consisted of a LYSO crystal block segmented 3-dimensionally into an 18 × 18 × 18 array of 1 mm × 1 mm × 1 mm cubes by laser processing [2]. The histogram represents the results of an Anger-type calculation using all MPPC signals for all events and crystal segment responses are formed by the results in it. Figure 1c) shows a 2D position histogram for a central segment layer extracted from the histogram in Figure 1b). It shows clear discrimination of most 18 × 18 responses but some corner responses and that indicates capability of the X’tal cube for 1 mm spatial resolution in all 3 dimensions. We found in further study that optimization in the Anger-type calculation improves the segment identification performance as shown in Figure 1d) which represents the same responses as Figure 1c).    
\n 
Figure 1. a) Structure of the X’tal cube. b) 3D position histogram obtained by the X’tal cube including a crystal block segmented into cubes 1 mm on each side. c) 2D position histogram corresponding to the 5th-layer of the X’tal cube. d) The same 2D position histogram as c) but with optimized Anger-type calculation.
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 As the next step, we tried 2-sides readout on the X’tal cube for a compact shape to gain packing fraction of a PET system [3]. We confirmed so far that segment identification was possible by only 2-sides readout, the top and bottom surfaces of the crystal block, for the LYSO crystal block segmented into a 6 × 6 × 6 array of 3 mm × 3 mm × 3 mm cubes by laser processing. Figure 2a) is the 3D position histogram obtained by the irradiation of 511 keV gamma-rays to the X’tal cube. Figure 2b) is a 2D position histogram extracted from Figure 2a) and responses in it are corresponding to 6 × 6 segments in a central layer of the crystal block. These figures prove enough segment identification performance.  
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Figure 2. a) 3D position histogram obtained by the X’tal cube including a crystal block segmented into cubes 3 mm on each side. b) 2D position histogram corresponding to the 3rd-layer of the X’tal cube.
\nFor energy performance, we obtained comparable energy resolution between a central segment and an outer segment for both the X’tal cubes mentioned above. The next study will be the measurement of time resolution, which much depends on the data acquisition system., PIPA2013 運営スタッフ兼発表者},
 title = {X'tal cube: 3-dimensional position sensitive PET detector},
 year = {2013}
}