Radiologic characterization of glial tumors relies predominantly on CT and MRI images; these studies provide good anatomic information regarding the size and location of the tumor, as well as surrounding structures, but are unable to evaluate viability or proliferative activity of tumors. Thus, the enhancing lesion on CT or MRI may not correspond precisely to areas of viable tumor, especially after surgery and radiotherapy. Also, because contrast enhanced MRI relies on regions of blood brain barrier (BBB) breakdown, it is not tumor specific, thus non-neoplastic processes may lead to findings similar to disease progression. This phenomenon can make conventional radiologic follow-up difficult in patients who have received radiotherapy, as such imaging techniques are limited in their ability to discern radiotherapy effect and necrosis from recurrence and progression. Finally, because they do not discriminate viable tumor, CT and MRI are of limited usefulness in assessing response to therapy, and are unable to effectively predict outcome. Magnetic Resonance Spectroscopy (MRS) is a relatively new technology which may be able to address these issues.