Comparaison Between MRI Alone or Combined With Positron Emission Tomography for Brain Metastasis Diagnosis

Inclusion Criteria: * Male or female over 18 years of age; * Having undergone gamma knife radiosurgery for brain metastasis; * Presenting for a first MRI follow-up (Cohort C1); * Presence of one or more brain metastases with increased enhancement on follow-up MRI (Cohort C2.1 and C2.2); A participant recruited for Cohort C1 could be recruited for follow-up in Cohort C2.1 or C2.2 if the MRI result is ambiguous. Exclusion Criteria: * Pregnancy or breastfeeding; * Other condition that may influence the imaging result; * Renal impairment (\<30 mL/min/1.73 m2). This threshold is consistent with recent RAC recommendations; Note: For participants with intermediate renal clearance (30-60 mL/min/1.73 m2), the total gadobutrol dose injected is set at the manufacturer's recommended clinical dose. For patients with renal clearance greater than 60 mL/min/1.73 m2, a dose of 1.5x the normal dose is used. These dose values have been approved by Dr. Chénard and are consistent with the RAC recommendations. * Inability to maintain supine position for the required duration (variable, depending on the sequence); * Patients who have previously received full brain irradiation; * Patients who are claustrophobic and cannot tolerate insertion into the MRI scanner;