A Tour of the Feinstein Cyclotron, conducted by Dr. Vijay Dhawan.
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Our first stop is the radiochemistry laboratory, where radioactive products of the cyclotron are processed and measured in isolation, behind the thick glass windows of a “hot cell.”
To reach the cyclotron, we pass through a “quality control room,” which also serves as an air lock between the radiochemistry lab and the radioactively “hot” area where the cyclotron operates.
Disposable overshoes just outside the cyclotron area keep radioactive dirt and dust out of the radiochemistry lab.
Once inside the “hot” area, we follow Dr. Dhawan down a hallway and through a massive door that leads to the cyclotron room. The room is underground and shielded behind eight feet of concrete.
We can visit the cyclotron room only when the machine is “down,” or not running, and even then we must carefully monitor our exposure to radioactivity. The cyclotron itself is housed in a white sheet-metal box, or “yoke.” Large input-power cables are visible overhead.
Copper electromagnets are mounted vertically within the housing. The magnets generate a rapidly oscillating electromagnetic field that accelerates charged particles into an ever-widening spiral inside a highly evacuated chamber (watch this brief animated video
to see how that happens).
Flexible plastic tubing for maintaining the vacuum and electronics packages for controlling the trajectory of the fast-moving particles are all that is visible of the cyclotron beam exit ports, where target raw materials for making radiotracers are mounted.
Massive lead containers provide safe storage for radioactive materials.
Back in the radiochemistry lab, Dr. Dhawan demonstrates how radioactive materials behind the thick glass of the hot cell can be handled safely, with an elaborate mechanical manipulator.
Essential to PET imaging are minute quantities of radioactive isotopes with half-lives measured in seconds, minutes or hours. These isotopes are injected into the body of a patient, where they “decay” by emitting positrons that act as tracers for the PET camera to detect.
To produce an isotope, a cyclotron accelerates a beam of charged particles (usually protons or deuterons) around in an ever-widening spiral by rapidly changing its electromagnetic field. When the beam is reaches its desired energy, it is extracted from the cyclotron and directed at a suitable target.
Click the link to watch a brief animated video that illustrates how the machine works.
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A particle in the beam that happens to collide with an atomic nucleus in the target can stick to that nucleus or kick out one or more of its nuclear particles—thereby transforming the target atom into another isotope or even into another chemical element (changing oxygen-18 into fluorine-18, for instance, to yield fluorine-18 fluorodeoxyglucose (FDG)).
By picking the original target atoms and adjusting the energy of the particles in the beam, a radiochemist can control the radiochemical process and create the kind of radioactive isotope the PET imaging calls for.
The Center for Neurosciences at The Feinstein Institute houses a General Electric PETtrace cyclotron, an automated, compact, self-shielded medical cyclotron that can generate 16.5-MeV protons and 8.4-MeV deuterons. (One MeV, a measure of energy, is one million electron-volts.) The cyclotron can also be tuned to to make such other important radionuclides as carbon-11, nitrogen-13, and oxygen-15. A remotely operated semiautomatic system for producing the isotope of water made from oxygen-15 is mounted on the wall of the cyclotron vault. In addition, an automated injection system for the oxygen-15 water isotope is located in the PET suite.
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