An improved synthesis of the inert, diffusible blood-flow tracer, [18F]fluoromethane

An improved procedure for producing [18F]fluoromethane ([18F]FM) in batches of several hundred mCi is reported. 18F prepared by the 18O (p, n) 18F reaction in a H2(18)O target is trapped on a small column of Dowex 1 (x 10) resin to allow recovery of H2(18)O. One new feature is elution of 18F- from the column with 3 mL of CH3CN containing 67 microL 1.5 M aqueous (Bu)4N+ OH-, after residual H2(18)O has been removed with dry CH3CN. This 18F- solution reacts with CH3I in the presence of Ag2O directly to give [18F]FM, which is swept out of the reaction vessel with a stream of air, from which CH3I and other vapors are removed with a C18 SEP-PAK at room temperature. Another new technique is trapping of [18F]FM on a second SEP-PAK cooled in ethanol/dry ice. After warming the SEP-PAK to room temperature, the trapped [18F]FM can be recovered with either H2O or air. The improvements speed the preparation and minimize hands-on operations. The product has no detectable radiochemical impurities, and a specific activity of greater than 1 Ci/mumol. Non-radioactive CH3CN, CH3I and CH3OH are present at less than 0.2 mumol per batch.