In one aspect, a portable transcranial magnetic stimulation (TMS) device for delivering a TMS procedure is provided. The portable TMS device comprises at least one coil that, when energized, generates electromagnetic energy, a helmet adapted to fit a user's head and configured to hold the at least one coil in a predetermined position with respect to the user's head, and a port having at least one power connection coupled to the at least one coil, the at least one power connection adapted to connect the at least one coil to a power source capable of energizing the at least one coil, the port further comprising at least one data connection adapted to exchange data with at least one external component, the port being located on the helmet. In another aspect a method of positioning a coil with respect to a person's head to target a desired region of the person's brain with transcranial magnetic stimulation (TMS) is provided. The method comprises obtaining a dielectric property map of a portion of the brain, the dielectric map indicating a spatial distribution of at least one dielectric property over the portion of the brain, determining a location for the coil based, at least in part, on the dielectric property map, the location being such that when the coil is positioned at the location, magnetic energy generated by the coil is focused on the desired region, and positioning the coil at the determined location.