In each study, the patient was injected with 10 mCi of 18-FDG IV and after allowing 30 min. A focus of hypermetabolic activity in the cerebellum suggesting active tumor. One month post therapy markedly diminished metabolism of the tumor focus is noted. Typically, T1 gadolinium-enhanced MRI images often demonstrate enhancement around the relatively vascular expanding margins of tumors but a similar appearance can be seen with radiation necrosis. Additionally, PET can direct biopsies toward more metabolically active tumor sites thus reducing sampling error and improving pathological diagnosis.
Serial studies can also detect transformation of low grade astrocytomas to higher grades.
Metabolism is often graded on relative intensity using a scale of 1 to 5. The lesions seen in the first study were graded as 5. Schifter T, Hoffman JM, Hanson MW, et al. Serial FDG-PET studies in the prediction of survival in patients with primary brain tumors.