The most difficult and sophisticated part of a PET installation is the cyclotron. It is a machine used to produce the radioisotopes (radioactive chemical elements) which are used to synthesize the radiopharmaceuticals (the actual substances which are used to make the functional images of the body).
The cyclotron is an accelerator of subatomic particles. It produces a large quantity of protons (heavy particles with an electrical positive charge) and get them moving at an accelerated rate along a circular orbit, inside a chamber controlled by powerful alternating electromagnetic fields. Thus, the particles gain energy and are smashed against a target at nearly the speed of light. The atoms of a substance placed in this target are transformed by this bombardment into radioactive, unstable isotopes, by means of a nuclear reaction.
There are many radioactive isotopes that can be produced in the cyclotron. In order to use them in a PET apparatus for imaging the body, they must:
This is why most of the PET installations in the world have the cyclotrons just by the side of the PET machine. It is truly a race against the clock, once the radioactive isotope is produced, to synthesize the radiopharmaceutical and get injected into the patient, so the PET and the cyclotron should be a few minutes away from each other.
The RDS cyclotron, manufactured by Siemens is one of the most frequently used in PET installations around the world. It is shown in the picture above. It incorporates a computer terminal to control the flow of production, and a biosynthesizer unit, which has several kinds of specialized apparatuses to carry out the chemical synthesis of radiopharmaceuticals.
Image credits: The Crump Institute for Biological Imaging, Department of Pharmacology, University of California at Los Angeles. The Center for Positron Emission Tomography, State University of New York at Buffalo, USA
From: The PET Scan: A New Window Into the
By: Renato M.E. Sabbatini, PhD
In: Brain & Mind Magazine, March 1997.