gms | German Medical Science

Objective: rTMS with focussed coils is able to stimulate depolarization in circumscribed cerebral region of interest (ROI). During repetitive stimulations it is difficult to position the coil precisely above the target gyrus. Orientation on the 10-20-EEG system or calculation of bone markers by MRI imaging has been used to position the coil manually. We present a system which coordinates the MRI of the brain with an infrared camera system (ICS) guided robot to position the coil directly over the ROI.

Method: 25 patients with aphasia due to left hemispheric lesions stimulation of the homologous motor language area of the right hemisphere were included. A T1-MRI of the brain identified the ROI, here the gyrus frontal inferior (GFI). The patient was placed into a relaxing chair and head reference markers (HRM) were fixed to the head by a headband. HRM were tracked by an infrared camera system (ICS). The HRM were correlated to the cerebral MRI imaging. A robot system (smartmove™, 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 ICS identified both the position of the magnetic coil by another set of HRM fixed to the coil and the patient’s head by the HRM. MRI data were 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 to position precisely the coil over the underlying ROI.

Results: Correct position of the coil manoeuvred by the robot arm was successfully controlled in all patients by rTMS of the precentral hand knob and surface electromyography of 3 contralateral hand muscles. Movements of the head in all horizontal directions during therapeutic sessions (GFI in aphasia treatment, parietal lobe in pain treatment, handknob in central paresis) could be compensated with automatic roboter guided positioning of the coil. Compared to sham (vertex) 1-Hz-stimulation of the GFI for 20 min/day followed by speech therapy in a 14-days protocol resulted in significant speech improvement.

Conclusion: It is possible to manoeuvre precisely a magnetic coil for rTMS over brain tissue of interest by a robot arm. This allows both diagnostic tests like motoric mapping and speech mapping and therapeutic measures like treatment for aphasia, central paresis and pain. The robot arm is able to follow the head during limited movements.