 PBR has been imaged with positron emission tomography PET using 11C1-2-chlorophenyl-N-methylpropyl-3-isoquinoline carboxamide PK11195. However, this classical ligand provides only low levels of specific signals and is not sensitive to detect changes that occurred in vivo. Recently we developed a new ligand, N-acetyl-N-2-11Cmethoxybenzyl-2-phenoxy-5-pyridinamine 11CPBR28, which showed much greater specific signals than 11CPK11195 in non-human primates. Therefore, 11CPBR28 is a promising PET ligand. However, radiation absorbed doses have not been estimated from human whole body imaging. 