@misc{oai:repo.qst.go.jp:00072675,
 author = {Akamatsu, Go and Tashima, Hideaki and Iwao, Yuma and Wakizaka, Hidekatsu and Maeda, Takamasa and Yoshida, Eiji and Yamashita, Taichi and Yamaya, Taiga and 赤松 剛 and 田島 英朗 and 岩男 悠真 and 脇坂 秀克 and 前田 貴雅 and 吉田 英治 and 山下 大地 and 山谷 泰賀},
 month = {Feb},
 note = {Objectives: Brain PET imaging is frequently used in clinical practice and research. A high lesion detectability is required in neuro-oncology field because the brain tumor extent is clinically relevant. Therefore, we have developed a brain-dedicated high-resolution and high-sensitivity PET prototype. In this study, we evaluated the small lesion imaging performance of the brain PET prototype using a small sphere phantom. 
Materials and methods: The helmet-neck PET is our original brain PET system, in which 47 four-layer depth-of-interaction detectors are used to form a hemisphere and 7 of them are placed on the neck part. The phantom had six small spheres (Inner diameters: 22, 17, 13, 10, 8, and 5 mm), which were filled with three times higher radioactivity concentration of the background. The background radioactivity was 1.32kBq/mL, which was generally half radioactivity level compared with clinical neuro-oncology PET. PET data were acquired for 20-min and were reconstructed with ordered-subsets expectation-maximization algorithm. The %contrast in each sphere and coefficient-of-variation on the background area (CVBG) were calculated to evaluate lesion detectability and image quality. 
Results: On the images reconstructed with 8-iterations and 8-subsets, the 8-mm-sphere was clearly observed. The %contrast of the 8-mm-sphere was 35.8% and the CVBG was 16.0%. The %contrast obviously achieved the criteria described by the previous report (%contrast >13%). 
Conclusion: The novel helmet-neck PET showed great small lesion detectability even though the radioactivity level was a lower condition. Therefore, the helmet-neck PET has a potential to not only improve small lesion detectability but also reduce injection activity or scanning duration., ECR2018},
 title = {Small lesion imaging performance of a novel helmet-neck PET prototype: a phantom study},
 year = {2018}
}