Radiotracer Production

Cyclotron-Produced Radiotracers

The synthesis of most PET radiotracers requires a machine called a cyclotron. This is a circular particle accelerator that is used to bombard chemical targets with charged particles to form new isotopes.

Interior of a cyclotron

The cyclotron opened to show the path taken by the accelerated charged particles. Different targets are stored in the chambers at the upper left. Photo credit: John Clark

By using different target materials, four of the most commonly produced radioisotopes for PET imaging are shown in the table below:

Radioisotope Target Half-life
18F 18O 110 minutes
11C 14N 20 minutes
13N 16O 10 minutes
15O 15N 2 minutes

The newly formed radioisotope is automatically transferred to a hot cell. Hot cells are shielded chambers where a series of automated chemical reactions incorporate the radioisotope into a useful chemical compound. Shielding is required throughout the process due to the high amounts of radioactivity involved.

Hot cells

Hot cells used for radiotracer production

Synthesis unit

Automated synthesis unit for producing FDG

After the radiopharmaceutical has been synthesized in the hot cell, it undergoes quality checks to ensure it is safe for injection into a patient.

18F-based radiopharmaceuticals have a long enough half-life that a large quantity can be synthesized in the morning for use throughout the day. Shorter-lived isotopes (such as 15O) have to be synthesized just before they are delivered for injection.

The radiopharmaceuticals formed in this process will all have different biological pathways in the body (known as pharmacokinetics), each giving different physiological information about the patient.