@misc{oai:repo.qst.go.jp:00070278,
 author = {Shiraishi, Takahiro and Yoshikawa, Kyosan and Tanimoto, Katsuyuki and Kuroiwa, Toshitaka and Ishii, Noriyuki and Yoshida, Eiji and Yamaya, Taiga and Murayama, Hideo and Ohashi, Seiya and Toubaru, Sachiko and Mizoe, Junetsu and Kamada, Tadashi and Watanabe, Kazuhiro and 白石 貴博 and 吉川 京燦 and 谷本 克之 and 黒岩 俊隆 and 石井 徳幸 and 吉田 英治 and 山谷 泰賀 and 村山 秀雄 and 大橋 靖也 and 桃原 幸子 and 溝江 純悦 and 鎌田 正 and 渡邊 和洋},
 month = {Oct},
 note = {[Purpose]Detectingthe distribution of positron emitter generated by nuclear fragmentationreaction in carbon ion beam therapy (auto-activation) applied at Heavy IonMedical Accelerator in Chiba (HIMAC) by means of positron emission tomography(PET) is novel method for therapy quality assurance especially assessingirradiated area. In clinical auto-activation PET settings, we have experienceda significant difference of image quality between LSO-based PET system andBGO-based PET system. Therefore, we planned and performed some phantomexperiments to compare PET scanner performance to image infinitesimalradioactivity. [Methods]Four different PET scanners were used; EXACT HR+,Biograph 16 HiRez (CTI-Siemens), SET-3000 GX/T (Shimadzu corp.) and jPET D4which provides four-layer-depth-of-interaction (DOI) measurement. The crystaldetector materials of each PET scanner were as follows: BGO, LSO, GSO and GSOwith DOI, respectively. A phantom was filled with 18F solution, and scannedevery 6hr until its radioactivity was decayed to the level of the infinitesimalradioactivity generated in clinical auto-activation PET settings. After CT scanor transmission scan for attenuation correction, emission scan was acquired for40min in 3D mode. The emission images were reconstructed by either FBP or OSEM.Reconstructed images were evaluated by visually.[Result]Image quality of thephantom became worse according to the decay of 18F. In particular, imagequality degraded severely when scanned with LSO-based PET system compared tothe others. GSO-based PET system improved the image of infinitesimal radioactivitybetter compared to that of BGO-PET system, because sensitivity of GSO-based PETsystem was 2-fold-higher than BGO-based PET system. Additionally, jPET D4 whichwas one of GSO-based PET system performed best in image quality for 18F phantomstudy due to high sensitivity derived from DOI measurement. The randomcoincidence events of LSO-based PET system were 1M counts when itsradioactivity was almost equally to clinical auto-activation settings, whilethe true coincidence was 0.2M counts. The true/random ratio was 24.3%, bycontrast, that of other PET systems was 99.9%. The reason why serious imagedegradation occurred when scanned with LSO-based PET system might be due topresence of 176Lu in LSO crystals[Conclusion]According to analysis of coincidenceevents, LSO-based PET system was not suitable for detecting infinitesimalradioactivity due to intrinsic radioactivity of 176Lu. An evaluation of imagequality suggested that high sensitive PET system, like jPET D4, was necessaryto detect infinitesimal radioactivity. To image the auto-activation using PETscanner, we must take characteristics of crystals and sensitivity of PET systeminto consideration., EANM Annual Congress 2010},
 title = {A comparative study of PET images among different PET scanners for detection infinitesimal radioactivity},
 year = {2010}
}