Fast robotic compensation of spontaneous head motion during Transcranial Magnetic Stimulation (TMS)

As Transcranial Magnetic Stimulation (TMS) is spreading fast in neurology and neuroscience, advanced techniques for TMS are required. A robotized system is used for precise and repeatable TMS. The system is based on a serial industrial robot and an infrared tracking system for permanent position tracing of the head. For enhanced precision, a motion compensation module counterbalances head motions during stimulation. This avoids rigid fixations of the patient and leads to increased convenience and significant stress reduction. The motion compensation deals with two main scenarios: While the robot approaches the target point, the trajectory has to be adapted when the head moves. Once the point is reached, the robot keeps the coil at the given target position relative to the head. For safe robot operations around the patient's head, a metric is used that restricts big joint changes. Furthermore, a running average is used to compensate jitter in the tracking measurements. As a specific extension of the motion compensation method for TMS, an online coil pose adaptation and a manual coil placement are integrated. Our results have shown that the motion compensation latency is about 110 ms. The associated compensation is about 200 ms. Hence, the original position relative to the head will be re-established within about 300 ms. Our recent clinical trials for rTMS have practically proved that the motion compensation method is sufficient for medical applications.