Inclusion Criteria:
* Subjects must have one of the following:
* Neurological findings (i.e. headache, loss of consciousness, paresis, cranial neuropathy, seizures, etc.)
* Radiological abnormalities in the brain (neoplastic or non-neoplastic in nature)
* Neoplastic process elsewhere in the body that may affect the brain (i.e. possible metastasis, vascular compromise, treatment related changes, etc.)
* Subjects must be able to undergo MRI imaging without anesthesia
* Subjects must be at least 10 years of age
* All subjects, or their legal guardians, must sign a written informed consent and Health Insurance Portability and Accountability Act (HIPAA) authorization in accordance with institutional guidelines
* Sexually active women of child-bearing potential must agree to use adequate contraception (hormonal or barrier method of birth control; surgical intervention i.e. tubal ligation or vasectomy; post-menopausal \< 6 months; or abstinence) for at least two months after each cycle of the study; should a female become pregnant or suspect she is pregnant while participating in this study, she should inform her treating physician immediately
Exclusion Criteria:
* Subjects with clinically significant signs of uncal herniation, such as acute pupillary enlargement, rapidly developing motor changes (over hours), or rapidly decreasing level of consciousness, are not eligible
* Subjects with known allergic or hypersensitivity reactions to parenteral iron, parenteral dextran, parenteral iron-dextran, or parenteral iron-polysaccharide preparations (Ferumoxytol Investigator's Drug Brochure, 2009); subjects with significant drug or other allergies or autoimmune diseases may be enrolled at the investigator's discretion
* Subjects who are pregnant or lactating or who suspect they might be pregnant
* Subjects who have a contraindication for MRI: metal in their bodies (a cardiac pacemaker or other incompatible device), are severely agitated, or have an allergy to gadolinium containing contrast material
* Subjects with known iron overload (genetic hemochromatosis); in subjects with a family history of hemochromatosis, hemochromatosis must be ruled out prior to study entry with normal values of the following blood tests: transferrin saturation (TS) test and serum ferritin (SF) test; all associated costs will be paid by the study
* Subject who have received ferumoxytol within 3 weeks of study entry
* Subjects with three or more drug allergies from separate drug classes
