An updated synthesis of [¹¹C]carfentanil for positron emission tomography (PET) imaging of the μ‐opioid receptor

[ 11 C]Carfentanil ([ 11 C]CFN) is a selective radiotracer for in vivo positron emission tomography imaging studies of the μ‐opioid system that, in our laboratories, is synthesized by methylation of the corresponding carboxylate precursor with [ 11 C]MeOTf, and purified using a C2 solid‐phase extraction cartridge. Changes in the commercial availability of common C2 cartridges have necessitated future proofing the synthesis of [ 11 C]CFN to maintain reliable delivery of the radiotracer for clinical imaging studies. An updated synthesis of [ 11 C]CFN is reported that replaces a now obsolete purification cartridge with a new commercially available version and also substitutes the organic solvents used in traditional production methods with ethanol.