P 226. Robot guided positioning of a magnetic coil for rTMS over the cortex in patients with cerebral lesions

Introduction rTMS with narrow focus coils is able to stimulate or inhibit depolarization in circumscribed cerebral areas. However, it is difficult to position the coil over the skull precisely above the target gyrus. Orientation on the 10–20-EEG system or calculation of bone markers of the skull in MRI imaging with transfer of the data to the skull of the living patient has been used to position the coil manually. These procedures are rather imprecise. We here present a system which coordinates the MRI imaging of the brain with an infrared camera system guided robot to position the coil directly over the region of interest (ROI). Protocol 5 patients have been included into this protocol. A T1-MRI of the brain was used to identify the ROI, here the precentral motor area of the hand (handknob). The sedantary patient was placed into a relaxing chair and small passive sphere markers (head reference markers) were fixed to the head by a headband. These skull markers were tracked by an infrared camera system positioned in front of and above the patient’s head in a distance of about 1.3 m and correlated to the cerebral MRI imaging. A robot system (Smart Move R , ANT) with a 6 joint metal arm allowing positioning of the coil with 6 degrees of freedom (DoF) was placed beside the patient. The magnetic coil (8-shaped) was fixed to the robot arm. The infrared camera system identified the position of the magnetic coil and the patient’s head by the passive sphere markers fixed to the magnetic coil and the patient. The MRI data were stored into a PC and the surface image of the brain was coordinated with the position of the patient’s skull and of the magnetic coil. By this technique, it was possible to identify the ROI of the cortex and direct the coil precisely by the robot arm over the skull area of the underlying ROI. Results Immediate correct position of the coil manoeuvred by the robot arm over the ROI was successfully controlled by rTMS of the precentral hand knob and surface electromyography of the contralateral hand muscles. Summary It is possible to manoeuvre precisely a magnetic coil for rTMS over brain tissue of interest using a robot arm by coordinating the cortical surface MRI of the patient with the skull and the magnetic coil. Registration of the positions is achieved by an infrared camera system. The robot arm is able to follow the head during limited movements.