@misc{oai:repo.qst.go.jp:00073061,
 author = {Nitta, Munetaka and Nishikido, Fumihiko and Inadama, Naoko and Tashima, Hideaki and Kawai, Hideaki and Yamaya, Taiga and 新田 宗孝 and 錦戸 文彦 and 稲玉 直子 and 田島 英朗 and 山谷 泰賀},
 month = {Nov},
 note = {We have developed the X’tal cube PET detector which ‘ is composed of 96 multi pixel photon counters (MPPCs) and a (13.1 mm)3 LYSO scintillator segmented into the 17 x 17 x 17 array. Each segment size is (0.77 mm)3. Six 4 x 4 MPPC arrays cover all six surfaces of the LYSO scintillator. The Anger calculation from 96 MPPC signals is used to determine the segment detecting a gamma-ray. We confirmed that the X’tal cube achieved sub-millimeter isotropic spatial resolution. However, we also observed inter crystal scattering (ICS) events as background events. There is a concern that ICS events degrade contrast of PET images for the high spatial resolution PET scanner.
\n We proposed a method to discriminate the ICS events and applied it to the X’tal cube. If the photo absorption event occurs at one segment, the distribution of spread light on each MPPC is the same for every event. On the other hand, even if the result of the Anger calculation is the same as the photo absorption event, the distribution of spread light by the ICS events differs from that of the photo absorption event because scintillation light is generated at different segments. To discriminate the ICS events,  first using a uniform irradiation experiment, we obtained the mean and standard deviation of pulse height peak of each MPPC for the segment to set the threshold for the discrimination of the ICS events. Then for each detected event, each MPPC pulse height was measured and the chi-square value was calculated. If the chi-square value exceeded the threshold, the event was eliminated as an ICS event. Next, to prove that our method can eliminate the ICS events, we obtained the response function by a fan-beam scanning experiment. We compared the results before and after applying our method. At the central part of the X’tal cube, full width half maximum of the ICS distribution in the response function was improved from 4.0 mm to 2.1 mm and over 50% of the ICS events were eliminated., IEEE NSS-MIC2018},
 title = {Elimination of Inter Crystal Scattering Events in the X'tal Cube PET Detector with (0.77 mm)3 Segments},
 year = {2018}
}