[18F]BF3-BPA

1. Primary Objective: To evaluate the concordance between 18F-BR-02 injection PET/MRI and MRI using macrocyclic gadolinium contrast agents in detecting recurrent brain metastases after systemic therapy in patients with solid tumors. 2. Secondary Objectives: 1) To assess the diagnostic efficacy of 18F-BR-02 injection in detecting recurrent brain metastases in patients with solid tumors. 2) To assess the diagnostic efficacy of 18F-BR-02 injection in detecting lesion-level recurrent brain metastases in patients with solid tumors. 3) To assess the diagnostic performance of 18F-BR-02 injection in detecting recurrent brain metastases in patients with solid tumors. 4) To assess the safety of 18F-BR-02 injection in patients with solid tumors. 3. Exploratory Objective: To analyze the impact of different threshold levels for visual judgment of lesion uptake by 18F-BR-02 injection PET/MRI on the diagnostic efficacy at both the patient and lesion levels.