Phase I, Open Label, Single Center Safety Study of [F-18]FLT

Inclusion Criteria: * Subject may be male or female and of any race / ethnicity; * At the time of study drug dosing, the subject has reached his or her 18th birthday; * Subject has histologic diagnosis of one of the following malignancies - glioblastoma gliosarcoma, anaplastic mixed/anaplastic oligodendroglioma or (anaplastic) astrocytoma with lesion visible on CT or MR and minimum histological grade of III/IV; * Subject with suspect radiation necrosis that are planned for re-section; * Subject or subject's legally acceptable representative provides informed consent; * Subject is capable of complying with study procedures and able to lie still in the PET scanner; * Subject is capable of communicating with study personnel; * Subject has adequate liver and kidney function Exclusion Criteria: * Subject is pregnant or nursing; * Subject is anemic (as defined as a hemoglobin level \<10); * Subject has not received chemotherapy or radiation therapy within the two weeks prior to imaging. * Subject has as reflected by a serum liver enzymes outside the normal laboratory reference range; * Subject has a history of chronic liver disease, which may compromise liver function; * Subject has kidney disease as reflected by a serum creatinine outside the normal laboratory reference range; * Subject has prior history of stroke or other condition of the head or neck that, in the investigator's opinion, might affect circulation to the brain or image interpretation (examples include, but are not limited to, previous stroke with cystic softening and cerebral deformity, or arteriovenous malformation); * Subject has a history of significant cerebrovascular disease; * Subject has any other condition or personal circumstance that, in the judgment of the investigator, might interfere with the collection of complete good quality data * Subject has previously received \[F-18\]FLT at any time, or any other investigational product within the past two weeks.