Positron Emission Tomography

Industry Experts

The Essential Role of Enriched Stable Nuclides in Positron Emission Tomography (PET)

Professor Michael J. Welch
Division of Radiological Sciences
Washington University School of Medicine

Positron Emission Tomography (PET) is one of the most rapidly expanding areas of medical diagnosis. PET is routinely used in determining the extent of tumor metastases, utilizing an analog of glucose in which the hydroxy group at the two position is replaced by a radioactive fluorine atom. This compound, 2-fluoro-2-deoxy-Dglucose (FDG), is taken up in tissues in an amount very similar to glucose, but is retained in the tissue unlike normal glucose, which is rapidly metabolized largely to water and carbon dioxide. This retention of the radioactivity allows the visualization of tumors, which metabolize glucose to a greater extent than normal tissue. In research studies, the glucose utilization of the tumors can be quantified. Due to the two-hour half-life of fluorine-18, this compound must be distributed from regional centers. All of these centers utilize enriched oxygen-18 to produce the fluoride used to make FDG. Fluorine-18 is reacted with agents also supplied by Sigma-Aldrich to produce the radioactive drug used in the medical diagnostic studies.

Other enriched compounds include enriched molecular oxygen and nitrogen enriched in nitogen-13 and are also used as target materials to produce PET radiopharmaceuticals. Oxygen gas is used in several centers to produce another radioactive drug, fluorine-18-labeled dopamine, used to study brain function, particularly in patients with schizophrenia and other psychiatric diseases. In the most common cyclotron used to produce PET radiopharmaceuticals, the enriched nitrogen is used to produce a series of very simple compounds containing radioactive oxygen-15. Oxygen-15, which has a two-minute half-life, can be used to study brain blood flow and brain oxygen metabolism. In a multicenter study funded by the National Institutes of Neurological Diseases and Stroke, labeled oxygen is being used to predict which patients will benefit from a brain surgery intracranial/extracranial bypass surgery, which restores blood flow to areas of the brain where delivery of oxygen is significantly reduced. Imaging relies upon the supply of enriched stable isotopes. In the future, it is anticipated that a whole battery of new compounds will be used to study many other parameters in tumors, brain and heart diseases, and they will rely upon the continued supply of stable isotopes.

Literature of Interest

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