• Comparison of Gd and Ferumoxytol contrast agents for assessing cerebral blood flow , mean transit time , and time-to-peak perfusion parameters, and evaluate if any of these perfusion parameters is promising for tracking GBM therapeutic response. [ Time Frame: 12 weeks ] [ Designated as safety issue: No ]
• To obtain qualitative assessment of tumor vascularity using time-of-flight(TOF) MR angiography techniques. [ Time Frame: 12 weeks ] [ Designated as safety issue: No ]
• To characterize changes in the apparent diffusion coefficient (ADC) of tumor water associated with standard radio/chemotherapy in GBM. [ Time Frame: 12 weeks ] [ Designated as safety issue: No ]

In this study the investigators would like to find out how a new iron containing Magnetic Resonance Imaging (MRI) contrast agent, called "ferumoxytol" can help the investigators to assess at the beginning of a therapy if it is effective or not in the treatment of a brain tumor called Glioblastoma Multiforme (GBM). For this purpose, after intravenous ferumoxytol injection, special MR scans (called: dynamic perfusion, blood-brain barrier (BBB) permeability measurement) will be performed to see the vascular changes in the brain and tumor.

Patients will be scanned at four time-points of their radiation/temozolomide treatment: before onset of radiation/temozolomide treatment, at 3 weeks, 6 weeks and 12 weeks following the onset of treatment. Each time-point will consist of three visits on three consecutive days. On first day: MRI with and without gadolinium (the usual MR contrast agent) infusion (0.1 mmol/kg). On second day: MRI with ferumoxytol infusion (1 mg/kg). On the third day: MRI without additional contrast agent, 24 hr post ferumoxytol infusion. There will be follow up visits 1 month and 6 months after the last ferumoxytol injection.

The ferumoxytol molecule contains iron-oxide and other components (carbohydrate), which makes ferumoxytol safe for short and fast (bolus) injections. This new contrast agent has not shown significant side effects, even using extremely high doses in animal experiments. A total of 516 human subjects have received one or more doses of ferumoxytol. There have been 3 cases with serious side effects possibly related to the administration of ferumoxytol. Two cases of peritonitis (the inflammation of the lining the abdomen) that were possibly related and one case of anaphylaxis (serious allergic reaction) related to ferumoxytol. (Of note is that gadolinium, the standard contrast agent, carries a serious risk for persons with kidney dysfunction. This risk is the condition called nephrogenic systemic fibrosis (NSF), which causes scar tissue to develop and can, in some cases, affect internal organs and even lead to death.)

The various types of MR measurement (Perfusion, blood-brain barrier permeability, diffusion) will be evaluated or measured at each time-point, for each contrast agent. Certain regions will be described and the data will be evaluated throughout the study in an attempt to correlate changes with tumor response to therapy. The tumor volume will be evaluated by 2 radiologists, measuring the diameters of the largest areas of contrast enhancement and signal intensities will be also compared (semi-quantitatively).

Inclusion Criteria:

• Patients must have radiologically and histologically confirmed diagnosis of glioblastoma multiforme
• Patients must have measurable disease, defined as evident tumors with gadolinium enhancement on MRI that is measurable in at least one diameter and visible on both axial and sagittal or coronal views.
• Patients have not had prior chemotherapy and/or radiotherapy
• Life expectancy of greater than 6 months
• ECOG performance status > or = 2 (Karnofsky > or =60%)
• Patients scheduled for standard therapy (6 weeks RT ~60Gy, plus temozolomide 75 mg/m2 during 6w RT, 200 mg/m2 5x wk post RT started 4wk after RT)
• Patients must be on a stable dose (up to 8mg daily) of dexamethasone throughout the study.
• After entry into the study, patients are expected to be followed for at least 1 month after the last infusion of ferumoxytol
• Women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation.
• Ability to understand and the willingness to sign a written informed consent document. All patients, or their legal guardians, must sign a written informed consent and HIPAA authorization in accordance with institutional guidelines.

Exclusion Criteria:

• Patients who have had chemotherapy or radiotherapy.
• Patients may not be receiving any other investigational agents.
• History of allergic reactions attributed to compounds of similar chemical or biologic composition to ferumoxytol: parenteral iron, parenteral dextran, parenteral iron-dextran, or parenteral iron-polysaccharide preparations (Ferumoxytol Investigator's Drug Brochure, 2005). Patients with significant drug or other allergies or autoimmune diseases may be enrolled at the Investigator's discretion.
• Patients with clinically significant signs of uncal herniation, such as acute pupillary enlargement, rapidly developing motor changes (over hours), or rapidly decreasing level of consciousness.
• Patients who require monitored anesthesia for MRI scanning
• Patient with history of hemochromatosis or iron overload
• Patients with stage IV or V renal insufficiency
• Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements.
• Pregnant women are excluded from this study. Because there is an unknown but potential risk for adverse events in nursing infants secondary to treatment of the mother with ferumoxytol, breastfeeding should be discontinued if the mother is treated with ferumoxytol
• HIV-positive patients on combination antiretroviral therapy are ineligible because of the potential for pharmacokinetic interactions with ferumoxytol.