RESTON, Va.--Before you take that walk or ride a bike, think again--especially if you will be undergoing a positron emission tomography (PET) scan any time soon.

"Any type of physical activity--from tapping your feet while in the waiting room to jogging the neighborhood the day before--can affect the results of a PET scan and lead to false-positive results," said Medhat M. Osman, M.D., ScM, Ph.D., assistant professor in the department of internal medicine's division of nuclear medicine and director of PET at St. Louis University Hospital, St. Louis, Mo. "Knowing whether a patient has participated in physical activity is relevant in interpreting a PET imaging study," added the co-author of "Prevalence and Patterns of Physiologic Muscle Uptake Detected With Whole-Body 18F-FDG PET," which appears in the March issue of the Journal of Nuclear Medicine Technology.

"Individuals undergoing PET scans should take it easy--and if you do any kind of physical activity outside of the ordinary--you should let your nuclear medicine technologist know so it can be noted," said Thomas C. Schlarman, MBA, CNMT, educational coordinator with the department of nuclear medicine technology at St. Louis University. Physical activity may trigger a potential source of false-positive results on a PET scan in about one out of eight patients, he noted. In order to obtain the most accurate reading of PET scans, patients should not exercise excessively 48 hours prior to having a PET scan and should remain quiet prior to scanning, Schlarman said.
PET is a powerful medical imaging procedure that noninvasively demonstrates the function of organs and other tissues. It is used primarily as a diagnostic tool in oncology, cardiology, neurology and many other medical specialties. To image cancer, a radiopharmaceutical such as fluorodeoxyglucose (FDG), which includes both sugar (metabolized at a higher rate by cancer cells) and a radionuclide, is injected into the patient. Because cancer cells metabolize sugar at higher rates than normal cells, the radiopharmaceutical is drawn in higher concentrations (called "uptake") to cancerous areas. The PET scan shows where the radiopharmaceutical is by tracking the gamma ray signals given off by the radionuclides. PET scans are very sensitive, and increased physical activity can create problems in differentiating between normal and pathologic uptake, explained Osman. Normal muscles accumulate little FDG, but muscles exercised just before or around the time of the scanning can exhibit intense uptake into those muscles--for example, possibly mimicking cancer, he added.

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