Developing a New MRI Technique to Understand Changes in Brain Tumors After Treatment

Inclusion Criteria: Healthy volunteers \[for Study Aim 1 (SA1) and Study Aim 2 (SA2)\] will be entered into the study if they meet the following criteria: * Age ≥ 18 years * Able to understand and give informed consent * No known cancer diagnosis Patients \[for Study Aim 1 (SA1)\] will be entered into the study if they meet the following criteria: * Age ≥ 18 years * Able to understand and give informed consent * At least one untreated brain metastasis \> 1cm (e.g., an enhancing lesion in the brain of a patient with known systemic cancer determined likely to represent metastasis by neuroradiologist) Patients \[for Study Aim 3 (SA3)\] will be entered into the study if they meet the following criteria: * Age ≥ 18 years * Able to understand and give informed consent * At least one untreated brain metastasis \> 1cm (e.g., an enhancing lesion in the brain of a patient with known systemic cancer determined likely to represent metastasis by neuroradiologist) * Planned SRS treatment Exclusion Criteria: Healthy volunteers (SA1 \& SA2) and patients (SA1 \& SA3) exclusion criteria: * Pregnant or breastfeeding women * Pre-existing medical conditions, including the likelihood of developing seizures or claustrophobic reactions, and any greater than normal potential for cardiac arrest * Age \< 18 years