This study will begin with a screening whole-body scan to confirm that the radioactivity has fairly broad distribution in several organs. For absolute quantification of mGluR1, 22 healthy controls will have brain PET imaging using [18F]FIMX and an arterial line. Up to 12 of them will have a test-retest scan. Eight additional subjects will have a whole body PET scan for dosimetry, which does not require an arterial line.