MAPPING TRANSCRANIAL MAGNETIC STIMULATION (TMS) FIELDS IN-VIVO WITH MRI

TRANSCRANIAL magnetic stimulation (TMS) is a noninvasive technique for investigating brain function that uses pulsed magnetic fields created by special coils to induce localized neuronal depolarization. Despite the technique's expanding application, the exact magnetic field produ ced by TMS coils have never been directly measured in human subjects. Using a standard 1.5T MR scanner and TMS coils constructed from non ma gnetic materials, we have obtained 3D maps of the magnetic field creat ed by TMS coils in human volunteers. Further, we mapped the combined f ield of two coils and demonstrated that combinations of coils might be used to focus the magnetic field to achieve improved stimulation patt erns and, perhaps, reach areas out of reach of single coils.