Robotized TMS for motion compensated navigated brain stimulation

This paper describes the setup and first applications of a computer-aided robotized Transcranial Magnetic Stimulation (TMS) system for motion compensated brain stimulation The system uses a registration of the cranium to its 3D magnetic resonance imaging (MRI) data and constant infrared stereo optical tracking to establish a real-time link between the digital anatomical data and the head. Based on this registration the robot implements the planned stimulation. Tracking of the head and subsequent refinement of the robot position ensures that the stimulation coil is always at the right position relative to the cranium. The second part of the paper describes a novel approach to brain mapping. Assuming a functional relationship between electric field strength at the representation site of a muscle in the brain and its MEP response to stimulation, an algorithm is derived to calculate the representation site. The algorithm uses a map of the produced electric field of the TMS coil which is measured in a separate experiment. The results of a first mapping experiment that shows good correspondence between fMRI and TMS prediction is presented at the end of the paper.