PET/CT Imaging of Malignant Brain Tumors With 124I-NM404

Inclusion Criteria: 1. Participants will have a contrast enhanced brain MRI which documents evidence of GBM or metastatic brain tumor 2. Tumor size at least 1.5 cm in greatest axial dimension on MRI. MRI must be obtained within 2 months of study inclusion 3. Female patients must not be pregnant or breast feeding and both women of childbearing potential, and men, must use appropriate means of contraception and must be maintained for at least 45 days after injection of I-124 NM404. Participants must not attempt to become pregnant during this time 4. Platelet count must be ≥ 160,000/µl, Hematocrit must be ≥ 22%, Leukocyte count must be ≥ 3,000/µL, Creatinine must be ≤ 2.5 mg/dL, ALT must be ≤ 130 U/L, AST must be ≤ 100 U/L, and urine or serum pregnancy test must be negative for pregnancy 5. Karnofsky score ≥ 60 6. For brain metastases patients: targeted brain therapy (radiation or drug) must have concluded ≥2 months prior to injection of 124I-NM404 7. For GBM tumors confirmed by surgical biopsy or suspected by MRI: no previous surgical resection (except for biopsy) or systemic or radiation therapy targeted to the GBM tumor - Exclusion Criteria: 1. Life expectancy of \< 3 months 2. Allergy to potassium iodide (SSKI or Thyroshield) 3. Planned surgical resection or biopsy after injection of 124I-NM404 and prior to completion of the 3rd PET/CT scan 4. Unwilling or unable to complete 3 separate PET/CT imaging sessions of 90 minutes each over 3 days -