The purpose of this study is to develop and test a new magnetic resonance imaging (MRI) technique to see if it can be used to tell the difference between tumor growth from worsening of cancer and growth from the effects of treatment in participants who have brain tumors treated with radiation therapy called stereotactic radiosurgery (SRS).

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

The study investigators will discuss participant potentially eligible for research participation within their interdisciplinary brain metastasis disease management team. These potential participants will then be contacted by their treating physician or investigator team. Study investigators will prioritize consenting participants who are planned to undergo SRS and, when possible, will attempt to coordinate the research scan with their clinically necessary MRI scans to minimize time and disruption for the participant.

Memorial Sloan Kettering Cancer Center supports the international committee of medical journal editors (ICMJE) and the ethical obligation of responsible sharing of data from clinical trials. The protocol summary, a statistical summary, and informed consent form will be made available on clinicaltrials.gov when required as a condition of Federal awards, other agreements supporting the research and/or as otherwise required. Requests for deidentified individual participant data can be made beginning 12 months after publication and for up to 36 months post publication. Deidentified individual participant data reported in the manuscript will be shared under the terms of a Data Use Agreement and may only be used for approved proposals. Requests may be made to: crdatashare@mskcc.org.