This Funding Opportunity Announcement (FOA) invites research grant applications that propose the preclinical development of novel radioligands for positron emission tomography (PET) or single photon emission computed tomography (SPECT) imaging in rodent and nonhuman primate brain and incorporation of pilot or clinical feasibility evaluation in pre-clinical studies and appropriate model development. Projects proposing clinical assessments of novel radioligands should respond to FOA PAR XX-XXX .: