Radionuclide Production     The materials or tracers injected for P.E.T. studies are radioactive. Starting from nonradioactive atoms, a device called a particle accelerator is used to produce radioactive isotopes or more correctly radionuclides. The specific device that is used at the University of Iowa is a compact medical cyclotron, which is a cyclic accelerator. Particles such as protons or deuterons (hydrogen and deuterium atoms without their orbital electrons) are brought to high energies by traversing several hundred orbits within the cyclotron. During each orbit the particle receives about 90 keV (90,000 electron volts) of energy. When the orbits near the maximum radius of the cyclotron, they are removed through electrostatic deflection and impinge upon small volume hollow metallic cylinders filled with a nonradioactive gas or liquid. Nuclear reactions take place within the cylinder (also called a target) between the high energy particle (proton or deuteron) and the contents of the target (also called target material) to produce the necessary radioactivity for incorporation into the P.E.T. radiotracers. The radionuclides produced with the cyclotron for P.E.T. imaging are shown in the following table. Nuclide Half-Life Target Nuclear Reaction O-15 2 min N2gas 14N(d,n)15O N-13 10 min water 16O(p,a)13N C-11 20 min N2gas 14N(p,a)11C F-18 110 min 18O water 18O(p,n)18F     The short half-lives of the routinely produced P.E.T. nuclides require that the cyclotron be located very near to where the nuclides will be synthesized into radiotracers for P.E.T. imaging. The Scanditronix MC-17F cyclotron shown in the figure below weighs 22 tons and is located within a vault that has 5 ft thick concrete walls. Unlike nuclear reactors, when the cyclotron is turned off, it immediately stops producing radionuclides.   A Rb-82 generator is also available for rest and stress myocardial perfusion studies. Scanditronix Cyclotron   Rb-82 Generator by 40 slice PET/CT Scanner

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