 Use of Intracerebral Microdialysis to Quantitate temozolomide Concentrations Temozolomide is a FDA approved oral alkylating agent used in upfront and relapsed therapy of adult and pediatric patients with high grade glioma. While temozolomide TMZ with radiotherapy has assisted with improving overall survival rates of high grade gliomas, previous studies have proven approximately only 20 of the drug crosses the BBB after peripheral administration. The peak concentration of TMZ in the brain has been shown to be approximately 1-2 hours after ingestion. Once ingested, TMZ undergoes degradation from its prodrug form to the highly reactive alkylating agent, methyl-triazenyl imidazole carboxamide MTIC. Previous studies have utilized brain microdialysis catheters to measure TMZ brain interstitium levels post primary or metastatic brain resectionbiopsy. Both serum and dialysates were collected at 30 minute time intervals and analyzed to quantitate TMZ drug delivery to the tumor bed and surrounding tissue yet due to drug stability issues, MTIC concentrations were not feasible for measurement in the microdialysis setting. Thus, the investigators propose to measure TMZ concentrations pre and post Regadenoson administration with the hypothesis that transient BBB disruption will result in improved drug efficacy to the brain interstitium and tumor bed. If gross total resection cannot be achieved two microdialysis catheters will be placed after resection. One microdialysis catheter will be placed in the MRI enhancing tumor area and one catheter will be placed in a non-enhancing area, allowing for later assessment of the degree of BBB permeability both in the tumor and normal brain. These studies will be beneficial to evaluate the role of increasing temozolomide delivery in an effort to further increase tumor cytotoxicity and progression-free survival in such an aggressive tumor. 