Abstract
Translocator protein (TSPO) is a biomarker for detecting neuroinflammation by PET. (11)C-(R)-PK11195 has been used to image TSPO since the 1980s. Here, we compared the utility of four (11)C-labeled ligands-(R)-PK11195, PBR28, DPA-713, and ER176-to quantify TSPO in healthy humans. For all of these ligands, BP (ND) (specific-to-non-displaceable ratio of distribution volumes) was measured by partially blocking specific binding with XNBD173 administration. In high-affinity binders, DPA-713 showed the highest BP (ND) of 7.3 followed by ER176 (4.2), PBR28 (1.2), and PK11195 (0.8). Only ER176 allows the inclusion of low-affinity binders because of little influence of radiometabolites and high BP (ND). If inclusion of all three genotypes is important for study logistics, ER176 is the best of these four radioligands for studying neuroinflammation.