 The objectives of this exploratory study is to preliminarily evaluate the complementary value of FDG, FLT, ACE, and H2O PET in patients with primary glial neoplasms. Multi-tracer PET profiles with these four tracers will be obtained in 20 patients with primary glial neoplasms at up to three timepoints: 1 at baseline prior to surgery or immediately after surgery providing a complete surgical resection was not possible and confirmed by a post-operative contrast MRI scan where residual tumor greater than 1.0 cm in diameter was present and prior to any tumor-directed therapy; 2 at the conclusions of the initial 6-8 weeks chemoradiotherapy; and 3 at the time of MRI-documented recurrence within 2 years. In addition, patients with a known primary brain tumor who have previously undergone treatment and have recurred based on standard clinical and imaging criteria will be eligible for the study. A number of quantitative and pseudo-quantitative imaging biomarkers for each tracer will be computed at each imaging timepoint, and the change in each biomarker between timepoints will also be computed. These data will be compared with clinical endpoints survival, time to progression, and with tumor biologic information histology, WHO grade, vascularity, Ki-67, VEGF, EGFR, p53 in cases when tumor tissue becomes available from standard care. These data will provide pilot information into the potential value of concurrent multiple PET biomarkers for predicting tumor behavior prior to the start of therapy, for improved prognostication, for more efficient and effective tumor surveillance, andor for more appropriate assignment of patients to conventional, aggressive, or investigational therapies early in their clinical courses. 