Synthesis of D4-FCH. (a) No-carrier-added D4-FCH was synthesized by reacting [18F]fluorobromomethane with N,N-dimethylaminoethanol or d4-N,N-dimethylaminoethanol. (b) Analysis of the metabolism of FCH to FCH-betaine and D4-FCH to D4-FCH-betaine by radio-HPLC in mouse plasma samples obtained 15 min after injecting the tracers intravenously into mice (c) A summary of the conversion of parent tracers, FCH and D4-FCH, to metabolites, FCH-betaine (FCHB) and D4-FCH betaine (D4-FCHB), in plasma. Data are mean (± SE); n=3 mice.