Bio-heat transfer model of transcranial DC stimulation: comparison of conventional pad versus ring electrode.

Transcranial Direct Current Stimulation (tDCS) is a non-invasive procedure where a weak electrical current is applied across the scalp to modulate brain function. The proliferation of this therapy has been accompanied by isolated reports regarding concern about their safety namely skin irritation. The potential cause of skin irritation has sometimes been attributed to increased scalp temperature during stimulation. We have developed novel technology for tDCS that improves spatial focality at the cost of increased stimulation electrode current density; high density tDCS (HD-tDCS). The goal of this paper was to provide information on the thermal effects of tDCS using a MRI-derived finite element human head model. The tissue temperature increases of tDCS using conventional rectangular-pad (7 x 5 cm(2)) and HD-tDCS using the ring (4 x 1) electrode configurations were compared using a bio-heat model. Our results indicate that clinical tDCS do not increase tissue temperature and 4 x 1 ring configurations leads to a negligible increase in scalp temperature.