Low Field Magnetic Stimulation (LFMS) in Subjects With Treatment-Resistant Depression (TRD)

The primary objective of this study: * To compare the relative efficacy, as measured by a change in the 6-item Hamilton Rating Scale for Depression (HAM-D6), of 20 and 60 minutes of LFMS compared to sham (placebo) in subjects with treatment resistant depression (TRD). Secondary objectives: * To determine if subjects with TRD may respond to 120 minutes of LFMS. * To determine the persistence of response to LFMS therapy during the observation period. * To evaluate the safety and tolerability of LFMS.