Inclusion Criteria:

- Pathological or clinical/radiological diagnosis of a brain mass, either primary
(e.g., malignant glioma) or secondary (metastasis from systemic malignancy)

- Completed fractionated radiation therapy (to 60 Gy for high grade gliomas) or
stereotactic radiosurgery or hypofractionated radiation therapy (e.g. for brain
metastases, anaplastic meningiomas), without or with concurrent chemotherapy

- New or increased enhancing brain lesion(s) OR nonenhancing brain lesion(s) if
receiving anti-angiogenic therapy, which is considered indeterminate for tumor
progression vs. radiation injury by the neuroradiologist or clinician

- Patient and/or guardian is able to provide written informed consent prior to study
registration

- Age ≥ 18 years old

Exclusion Criteria:

- Claustrophobia

- Known allergic reaction to Gd-DTPA

- Renal insufficiency with recent (< 3 month old) creatinine > 2.0

- Any contraindication to MRI (e.g., pacemaker, aneurysm clip, tissue expander).

- Pregnant or nursing female

- Unable to cooperate for MRI and/or PET/CT