Locations & Hours | Radiology Services & Procedures | Insurance Info | Policies & Payments Positron Emission Tomography (PET) Imaging by Gregory R. Weaver, M. D. Introduction Positron Emission Tomography ,also known as PET or PET scan, is a type of imaging, which uses a minute quantity of a radioactive substance to generate images from a specialized camera. The substances most often used are fluorine-18 fluorodeoxy-glucose (FDG) and rubidium-82 (RB-82). FDG is a radioactive form of sugar. When it is injected into a vein, it localizes in the body in proportion to glucose metabolism (sugar use). Most malignant tumors use sugar (glucose) at a higher rate than benign tissues. Malignant tumors are imaged on a PET scan as “hot spots”. Cancer FDG PET imaging is used in cancer patients for the following indications: A. To differentiate benign from malignant nodules. B. Look for the spread and extent of tumors. C. Monitor the effects of therapy. D. Differentiate recurrent tumor from scar tissue or other effects of treatment. For FDG imaging, patients fast for at least four hours before the examination. A blood sugar measurement is obtained before the test. F-18 FDG is injected into a vein. Forty-five minutes is allowed for the FDG to distribute into the body. The scan is then begun. A series of pictures is taken to cover the area of concern. The FDG is only weakly radioactive and all radioactivity is gone within a few hours. Heart Rubidium-82 (RB-82) is distributed in the body in proportion to blood flow and is most often used to evaluate for decreased or absent blood flow to the heart. Most commonly, a baseline study is performed. The patient is then given a medication (Dipyridamole), which causes increased blood flow to the portions of the heart supplied by normal arteries. Blood flow to areas of the heart supplied by narrowed or blocked arteries does not increase. Another scan is done after Dipyridamole administration. A heart attack (myocardial infarction) is imaged as an area of deficient RB-82 activity on both sets of images due to dead heart muscle and decreased blood flow. If the artery carrying blood to the area of concern is narrowed and not completely blocked, this is imaged as a deficiency of RB-82 only on the images performed after Dipyridamole. As with FDG, the radioactivity quickly goes away. Brain FDG images brain metabolism (sugar use). Decreased metabolism can be seen in Alzheimer’s disease and in other dementias and in strokes and vasculitis. The pattern of activity often helps to distinguish among these conditions. PET scanning can show areas of abnormally decreased metabolism before abnormalities will show up with other imaging techniques. FDG is injected into a vein and the patient is kept in a quiet dark room. After the brain takes up the FDG (about 30-45 minutes), the patient is moved into the PET scanner room and a series of pictures is taken with the PET scanner.