• 12/2/2004
  • Adam S. Jacobson, MD; Mark L. Urken, MD, FACS
  • ACS Surgery: Principles & Practice

Sources of False Negative PET Scans Using FDG

A range of physiologic tracers has been developed for positron emission tomography (PET), with the glucose analogue F-18 fluorodeoxyglucose (FDG) the most commonly used. FDG has a half-life of 110 minutes. Once given to the patient, FDG is taken up by glucose transporters and is phosphorylated by hexokinase to become FDG-6-phosphate (FDG-6-P). Further metabolism of FDG-6-P is blocked by the presence of an extra hydroxyl moiety, which allows FDG-6-P to accumulate in the cell and serve as a marker for glucose metabolism and utilization.

Because FDG is nonspecifically accumulated in glycolytically active cells, it demarcates areas of inflammation as well as neoplastic tissue; this can lead to a false positive scan. Muscular activity during the scan can also lead to areas of increased uptake in nonneoplastic tissue. Furthermore, healing bone, foreign-body granulomas, and paranasal sinus inflammation can produce false positive results.

False negative scans occur when tumor deposits are very small (3 to 4 mm or less in diameter). Thus, micrometastases are not reliably detected using an FDG-PET image. Furthermore, a false negative scan can occur if the PET is performed too soon after radiation therapy.