RecruitingDevice study7T Brain MRI Scan for Micro-brain Metastasis (microBM) Detection for Patients With Small-cell Lung Cancer (SCLC), Who Decline Prophylactic Cranial Irradiation (PCI)Comparison of a 7t MRI to standard of care 1.5t/3t MRI scans to determine if earlier detection of brain metastases are possible on a 7t.