18F-FLUC PET/MR in Patients With Brain Mets

Inclusion Criteria: * Age 18 years or older * Able and willing to provide informed consent * Has a brain metastasis diagnosis with at least one single visible contrast enhancing metastatic lesion on brain MRI * Received radiation therapy at some point in the last 2 years * Is currently being treated with or has been treated with any other concurrent systemic therapy (multi-modal therapy) in the past 6 months, which would include immunotherapy, targeted therapy, or systemic chemotherapy, immunotherapy, or chemotherapy following radiation therapy. * Patients are eligible for the study if their most recent standard-of-care MRI, used to assess disease location and extent, raises the question of tumor recurrence versus treatment-related changes. This concern can be noted by the radiologist or other members of the multidisciplinary care team, such as during a multidisciplinary conference. Additionally, if there are clinical concerns based on evolving exam findings or symptoms, and the treating physician suspects progression versus treatment-induced changes, the patient is also eligible for the study. * Be able to lie still for 30-60 minutes during the imaging procedure * Willing and able to undergo PET/MRI or PET/CT * Patients requiring intravenous (IV) conscious sedation for imaging are not eligible; patients requiring mild, oral anxiolytics for the clinical MRI will be allowed to participate as long as the following criteria are met: * The subject has their own prescription for the medication * The informed consent process is conducted prior to the self-administration of this medication * They come to the research visit with a driver Exclusion Criteria: * Subject unable or unwilling to provide informed consent * Subject is pregnant * Subject with contraindication(s) to or inability to undergo a PET/MR or PET/CT * Known allergy to 18F-Fluciclovine or any of its excipients