 In spite of numerous advances in neuroimaging techniques, the diagnosis of pediatric brain tumors relies on the pathologic evaluation of material obtained at the time of the initial operation. While 18F-FDG-positron emission tomography PET helps identify higher-grade lesions due to their increased glucose metabolism, the high tracer uptake of the normal adjacent brains makes this modality of limited value. Fluorine-18 fluorothymidine FLT is a new imaging agent that has two significant advantages in the imaging of CNS tumors. First, this agent detects cellular proliferation directly, and second, the normal brain does not take up the agent, making a positive areas easy to identify. Before embarking on a large pediatric disease stratified assessment of FLT imaging in pediatric neurooncology patients, the investigators are proposing a limited patient pilot study to evaluate the biodistribution, dosimetry and specificity of this compound when compared to immunohistochemical assessment of mitotic activity in newly diagnosed patients undergoing surgical resection. 