This clinical trial studies dynamic susceptibility-weighted contrast enhanced magnetic resonance imaging (DSC-MRI) after administration of ferumoxytol and dynamic contrast-enhanced MRI (DCE-MRI) after administration of a gadolinium-based contrast agent (GBCA) in viewing the vessels of the brain in younger patients with brain tumors. Ferumoxytol is an experimental form of very small iron particles that are taken by the blood stream to cells adjacent and inside the tumor. These iron particles may make it easier to see the areas of the brain that are affected by tumor. Ferumoxytol may work better than standard GBCA in viewing the vessels of the brain and brain tumor on MRI. Using ferumoxytol and GBCA in the same MRI session may provide more information about tumor blood supply and the extent of the tumor.

PRIMARY OBJECTIVES:

I. To describe the vascular properties of pediatric brain tumors using ferumoxytol for DSC-MRI and GBCA for DCE-MRI in pediatric brain tumor (proven or presumptive) patients in a single MRI session.

II. To describe evolving imaging characteristics of tumor vasculature using DSC-MRI with ferumoxytol and DCE-MRI with GBCA in pediatric brain tumor patients.

SECONDARY OBJECTIVES:

I. Compare and evaluate magnetic resonance angiogram (MRA) with ferumoxytol between different time points.

II. To describe number and size of tumors imaged. III. To assess histology and electron microscopy (EM) on tissue samples. IV. To demonstrate differences in patients with prior therapy versus (vs.) no prior therapy (radiation and/or chemotherapy).

OUTLINE:

Patients receive ferumoxytol and gadolinium intravenously (IV) and then undergo DSC-MRI and DCE-MRI. An optional MRI without injection of a contrast agent may be obtained after 20-24 hours at the discretion of the clinician. Patients may receive up to 3 more scans at least 3 weeks apart over up to 2 years.

After completion of study treatment, patients are followed up at approximately 4-6 weeks.

Inclusion Criteria:

• Participant must have either radiological (presumptive) or established (proven) histological diagnosis of a brain tumor or lesion
• Previously untreated participants must have a measureable lesion on an imaging study
• Participants undergoing active treatment, or who have completed treatment, will have radiographic abnormalities that may or may not be recurrent tumor
• Those participants requiring surgical intervention for diagnostic and/or therapeutic purposes as necessary for their disease are eligible; the tissue may be assessed by histology and/or EM for iron particles; only clinically indicated biopsy and/or surgery will be done
• Participants may have had prior therapy for the primary brain tumor, including surgery, radiotherapy or chemotherapy
• After entry into the study, participants agree to be followed for up to 6 weeks after the final infusion of ferumoxytol
• All participants, or their legal guardians, must sign a written informed consent and Health Insurance Portability and Accountability Act (HIPAA) authorization in accordance with institutional guidelines
• Baseline MRI studies for participants receiving ferumoxytol must be performed within 16 weeks of study entry
• Sexually active women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study treatment and for the duration of study treatment; should a female become pregnant or suspect she is pregnant while participating in this study, she should inform her treating physician immediately

Exclusion Criteria:

• Participants 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
• Participants with known allergic or hypersensitivity reactions to parenteral iron, parenteral dextran, parenteral iron-dextran, or parenteral iron-polysaccharide preparations, are not eligible; participants with significant drug or other allergies or autoimmune diseases may be enrolled at the Investigator's discretion
• Participants who are pregnant, lactating, or who suspect they might be pregnant are not eligible
• Aspartate aminotransferase (AST) and/or alanine aminotransferase (ALT) greater than 2.5 x upper limits of normal
• Glomerular filtration rate (GFR) < 50
• Participants 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 GBCA
• Participants with known hepatic insufficiency or cirrhosis
• Human immunodeficiency virus (HIV)-positive participants on combination antiretroviral therapy are ineligible
• Participants that have a known or suspected iron overload (genetic hemochromatosis or history of multiple transfusions)