 Resting state fMRI will be used to measure the functional connectivity within the default mode network DMN and other circuits that are known to function abnormally in MDD Greicius et al. 2007. ASL will be used to measure the regional blood flow within individual nodes of this circuitry, while DTI will measure the structural integrity of the connections between nodes. Measurements at baseline will be compared to measurements post-LFMS in both active treatment and sham groups. 