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| This slide illustrates the method of PET (positron emission tomography) imaging. We produce a radioactive atom like 11C in an on-site cyclotron. The chemical form of this nuclide is often [11C]CO2. Because of its short half life (20 min), the 11C atom must be quickly incorporated in a drug that targets a specific protein in the body. In this cartoon, 11C is incorporated in a drug (e.g., raclopride) that binds to the dopamine D2 receptor. The 11C-labeled drug is injected intravenously in a human subject and localizes in the striatum, which has a high density of D2 receptors. The drug is administered at such low doses ("tracer doses") that it has no pharmacological effects. However, PET has such high sensitivity that it can detect the low levels of radioactivity in brain.
"P" in PET stands for "positron," since the radioactive atoms decay with the release of a positron. "E" stands for "emission", since the radioactivity is emitted from the body rather than transmitted through the body as with X-rays. "T" stands for "tomograph", because the image is reconstructed as a slice ("tomo") of the body. PET can localize and quantify the density of the target protein. PET ligands now exist to image many different receptors and enzymes. The goal of this laboratory is to discover, evaluate, and use new radiotracers to understand in vivo physiology and pathophysiology. Although our work to date has dealt exclusively with the brain, we are now working with tracers in other fields, including oncology. For background information on PET, see: M. Fujita, A. Kugaya, and R.B. Innis. Radiotracer Imaging: Basic Principles and Exemplary Findings in Neuropsychiatric Disorders. In Comprehensive Textbook of Psychiatry (8th edition), Kaplan, H.I. and Sadock, B.J. (eds), Williams and Wilkins, Baltimore, MD. pp. 222-235, 2005. (PDF File) |
