Outcome Measure: The primary outcome measure of this study is the degree of agreement between the radiographically predicted diagnosis of tumor recurrence or radiation necrosis using two-compartment DT-MRI and the histologic diagnosis of such. This outcome will be measured as the proportion of instances in which the two modalities identify a particular lesion as being tumor recurrence or as being radiation necrosis. The information gathered from this study will allow for the implementation of a larger study with more patients if there is a high degree of agreement between the two compartment DT-MRI and histologic diagnoses of surgical biopsy specimens. The long range goal of the larger study is to radiographically diagnose tumor recurrence or radiation necrosis with a high enough level of sensitivity and specificity to avoid a diagnostic surgical procedure with its attendant risks.