The purpose of this study is to help us understand gliomas, one type of brain tumor. This research protocol makes pictures of gliomas. We will take pictures of the glioma before and after treatment. The pictures are made with a positron emission tomography (PET) scanner. PET scans use radioactive markers to "see" cancer cells. We plan to use two different radioactive markers, [18F]FACBC and [18F]FLT, to "see" if the glioma responds to the treatment being recommended by the doctor. We are investigating whether one or both of these types of PET scans can help us to better understand gliomas and their response to treatment.