@misc{oai:repo.qst.go.jp:00061740,
 author = {Shibuya, Kengo and Yoshida, Eiji and Nishikido, Fumihiko and Suzuki, Tosikazu and Tsuda, Tomoaki and Inadama, Naoko and Yamaya, Taiga and Murayama, Hideo and 澁谷 憲悟 and 吉田 英治 and 錦戸 文彦 and 鈴木 敏和 and 津田 倫明 and 稲玉 直子 and 山谷 泰賀 and 村山 秀雄},
 month = {Sep},
 note = {In a PET scanner, a line of response is drawn between the two scintillators detecting the pair of annihilation radiation. However, the non-collinearity of the two photons limits the special resolution. The slight deviation from 180 degrees is known to be 0.47 degrees in the full width half maximum (FWHM) for pure water; however, the value may be changed by chemical and physical conditions for the positrons in vivo. The aim of this study is an experimental determination of the angular correlation of the annihilation radiation from a human body.
\nUsually, the angle is measured by using plural position sensitive detectors such as gamma-cameras; however, this method cannot be used when the radiation source is specially distributed and the acquisition time is limited. The authors overcame this problem by measuring the energy distribution instead of the angular distribution; the two distributions can be converted each other by the conservation laws of momentum and energy.
\nThe photopeak due to in vivo [18F]-FDG was measured by using a germanium detector with the energy resolution of 1.17 keV at 511 keV (0.23%), and the Gaussian distribution was determined to be 2.68 keV in FWHM. Therefore, the energy deviation due to the momentum of electron-positron pair before annihilation was calculated to be 2.41 keV in FWHM. This value is corresponding to 0.54 degree in the angular distribution and about 15% larger than that had obtained for pure water. 
\nBy the convolution of the annihilation radiation non-collinearity into the positron range, the physical limit of spatial resolution of FDG-PET with ideal radiation detectors can be estimated: 0.5 mm for a small animal PET with a 10-cm diameter, 1.2 mm for a human brain PET with a 40-cm diameter, and 2.1 mm for a human whole-body PET with a 80-cm diameter., World Congress on Medical Physics and Biomedical Engineering 2006},
 title = {Limit of Spatial Resolution in FDG-PET due to Annihilation Photon Non-Collinearity},
 year = {2006}
}