18Fmärkning

18F-märkning, or fluorine-18 märkning, is the process of attaching the positron-emitting isotope fluorine-18 to organic molecules to create radiopharmaceuticals for positron emission tomography (PET). Fluorine-18 has a half-life of about 109.8 minutes and yields sufficient positrons for high-resolution imaging, making it the most widely used isotope in clinical PET tracers.

Production and basic chemistry

Fluorine-18 is commonly produced in a cyclotron by irradiating 18O-enriched water with protons, generating [18F]fluoride in aqueous solution. The fluoride is then dried and activated, typically with a phase-transfer catalyst such as Kryptofix 2.2.2 and potassium carbonate, to form reactive [18F]F− suitable for nucleophilic substitution. Two main strategies are employed: nucleophilic fluorination of precursors bearing good leaving groups (for example tosylates or mesylates) and prosthetic-group labeling, where a small 18F-containing fragment is synthesized first and later conjugated to the target molecule. Reactions often use polar aprotic solvents and elevated temperatures, followed by purification by semi-preparative HPLC or solid-phase extraction.

Purity, validation and quality control

Radiopharmaceutical production requires rapid purification and stringent quality control. Typical measures include radiochemical purity above 95%, verification of identity, determination of specific activity, and assessment of pH and residual solvents. Sterility and pyrogen testing are performed for injectable products. The short half-life of 18F necessitates fast, automated, and often centralized production workflows.

Applications and challenges

18F-märkning enables PET imaging across oncology, neurology and cardiology through tracers such as FDG and various receptor- or metabolism-targeted compounds. Challenges include the need for specialized infrastructure, regulatory oversight, and adherence to good manufacturing practices (GMP) to ensure patient safety and tracer reliability. Alternative electrophilic fluorination methods exist but generally offer lower specific activity and are less commonly used in routine radiopharmacy.