 - Children age 18 are excluded from the study plan because the incidence of astrocytomas and glioblastoma in children is far less than in adults. Although children frequently develop brain tumors, the glial tumors are most often pilocytic astrocytomas. In addition, enrollment of adults will be beneficial for the MRS sequence validation tests in healthy subjects since adults can remain motionless during the MR scans compared to children, giving minimal motion artifacts om the MR data. 