@misc{oai:repo.qst.go.jp:00069144,
 author = {Lam, ChihFung and Yamaya, Taiga and Obi, Takashi and Yoshida, Eiji and Inadama, Naoko and Shibuya, Kengo and Murayama, Hideo and Ｌａｍ ＣｈｉｈＦｕｎｇ and 山谷 泰賀 and 小尾 高史 and 吉田 英治 and 稲玉 直子 and 澁谷 憲悟 and 村山 秀雄},
 month = {Nov},
 note = {The use of small crystals in new PET scanners results in large number of line-of-response (LOR). Thus, fully 3D image reconstruction becomes time consuming especially for iterative algorithms. One of the methods to speed-up image reconstruction is by master-slave parallel computing. However, as number of computing nodes increases, the parallel efficiency decreases due to network transfer delay and other overheads. Network delay becomes significant particularly for high converging algorithm such as dynamic RAMLA, where image reconstruction is possible with large subset size. In this paper, we propose a way to reduce data transfer between nodes by allowing intra-node image update. In details, few intra-node updates for L-1 number of sub-iterations are performed in each slave thread before a global update is done at the master thread. We implemented a normal parallel version and the proposed intra-node update version of dynamic RAMLA for the jPET-D4 scanner by using MPICH2 library. We evaluated it with four servers, each contain two dual-core opteron 2.8GHz processors. Firstly, we compare the parallel efficiency (PE) gain by the proposed method with several L parameters: 1, 4, 8, and 12 for subset size of 192. PE gain is significant for L=4, after which no much gain is obtained as other factors such as load balancing become more prominent. Next, we accessed image quality of the proposed method with a hotspot phantom generated by GATE simulator, and a human brain experiment data. In both cases, no significant image artifact was found by using the proposed method. We showed that, by distributing the calculation load in a way where LORs in each slave thread covers the FOV substantially, it is possible to achieve almost the same image quality by allowing intra-node update. With proposed method, image reconstruction time is reduced by more than 22%., IEEE 2007 Nuclear Science Symposium and Medical Imaging Conference},
 title = {Parallel Implementation of 3-D Dynamic RAMLA with Intra-node Image Update for the jPET-D4.},
 year = {2007}
}