Fluoro-L-Thymidine Positron Emission Tomography (FLT PET) vs. Adv. Magnetic Resonance (MR) Techniques in Recurrent Glioma

Inclusion Criteria:

1. Patient is \>/= 18 years old, agrees to participate in the clinical study and to complete all required visits and evaluations. The pediatric population has a different disease profile from the glioma patients we hope to recruit. To reduce heterogeneity in the patient population we will not consider patients younger than 18 for this study.
2. Patient is a candidate for cerebral tumor resection due to an enhancing brain lesion, with history of previous pathologically proven primary brain tumor (WHO grade II-IV diffuse glioma)
3. Patient had diffuse glioma (WHO grade 2 - 4) and as part of their treatment received radiation therapy and Temozolomide (a first-line chemotherapeutic agent).
4. Patient will have subsequently developed an enhancing brain mass greater than 1cm in diameter, at least 6 months after finishing radiation therapy (to differentiate from the more acute treatment related effect of "pseudo-progression").
5. As the predominate means of determining TRN versus recurrent glial tumor at MD Anderson, a brain tumor/ necrosis protocol is ordered as clinically indicated.
6. Patient's clinician based on the clinical and MR information wants to proceed with biopsy or surgical resection within 30 days from when the brain tumor MR protocol was performed. The patient meets with the neurosurgeon and agrees to surgical biopsy or resection.
7. Patient is able to understand and give consent to participation in the study
8. Patient has received as part of their care the Brain Tumor Imaging protocol.
9. Patient agrees to undergo, prior to the procedure, FLT PET at CABI

Exclusion Criteria:

1. The patient is found to have unfavorable anatomy to indicate that stereotactic biopsy/ resection could not be safely performed
2. Claustrophobia that does not readily respond to oral medication
3. Allergy to Fluoro-L-Thymidine
4. Pregnant or lactating (Based on self-reported and clinical care testing with physicians before study participation)