In this study, we will establish the MR imaging characteristics of macrophages in malignant brain tumors and other CNS conditions in the pediatric and adult populations using ferumoxytol, an ultrasmall superparamagnetic iron oxide (USPIO) particle that is approved for the treatment of iron deficiency anemia in patients with chronic kidney disease. The investigators will correlate the MR signal of ferumoxytol uptake with the number of macrophages in surgical specimen at histopathology. This information may potentially offer clinicians a new means for risk stratification and monitoring treatment efficacy.
