[11C]methyl iodide was originally produced by using LiAlH4 to reduce [11C]CO2 to [11C]methanol, followed by reaction with
liquid hydriodic acid. However, it is difficult to obtain the desired high specific radioactivity of the end-product 11C-methylated tracer because
the lithium reagent solution is so easily contaminated by atmospheric [12C]CO2. The introduction of high temperature gas-phase
methodologies greatly enhanced the specific activity of 11C-labeled PET tracers by eliminating the lithium reagent entirely. Details for
three commercially available gas-phase synthesis modules are provided and discussed with respect to ease-of-operation and preventative
maintenance concerns. Lastly, C-11 target performance is discussed with respect to the in-target release of carrier [12C]carbon, the remaining
obstacle to ultra-high specific activity for 11C-labeled PET tracers.
Keywords: Automation, Gas-phase production, Methyl iodide, Methyl triflate, Specific activity.
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