Transcranial Magnetic Stimulation: Development of a Novel Deep-Brain Triple-Halo Coil

Transcranial magnetic stimulation (TMS) is a noninvasive treatment for major depressive disorder. TMS coil design plays an important role in maximizing the magnetic field strength at the required location in the brain. Development of deep-brain TMS coils to stimulate subcortical structures will expand the uses of TMS beyond the simulation of superficial cortical targets. The simulation of deep-brain regions may have beneficial effects on neurological disorders such as Parkinson's disease, posttraumatic stress disorder, and mild traumatic brain injury. In this letter, a multicoil configuration, the triple-halo coil (THC), which can stimulate deep brain structures such as the hippocampus and amygdala, is designed and tested. A finite element tool is used to determine the induced electric field and magnetic field in these regions due to the THC alone and in combination with a figure-of-8 coil. Analysis of the results is done with the help of an anatomically accurate heterogeneous head model of a 34-year-old man derived from magnetic resonance imaging. The magnetic field of the THC is measured and compared with the simulated field.