Experimental Verification of a Computational Real-Time Neuronavigation System for Multichannel Transcranial Magnetic Stimulation

AbstractMultichannel Transcranial Magnetic Stimulation (mTMS) provides the capability of stimulating multiple cortical areas simultaneously or in rapid succession by electronic shifting of the E-field hotspots. However, in order to target the desired brain region with intended intensity, the intracranial E-field distribution for all coil elements needs to be determined and subsequently combined to electronically synthesize a ‘hot spot’. Here, we assessed the performance of a computational TMS navigation system that was used to track the position of a 2×3-axis TMS coil array with respect to subject’s head and was integrated with a real-time high-resolution E-field calculation engine to predict the activated cortical regions as the array is moved around the subject’s head. For fast evaluation of the E-fields with high-resolution head models, we employed our previously proposed Magnetic Stimulation Profile (MSP) approach. Our preliminary tests demonstrated the capability of this system to precisely calculate and render E-fields with a frame rate of 6 Hz (6 frames/second). Furthermore, we utilized two z-elements from the 3-axis coils to form a figure of eight coil type and utilized it for suprathreshold stimulation of the hand first dorsal interosseous (FDI) muscle on a healthy human. The recorded motor evoked potentials (MEPs) showed clear activation of the FDI muscle comparable to the activation elicited by a commercial TMS coil. The estimated cortical E-field distributions showed a good agreement between the commercial TMS coil and the two z-elements of the 2×3-axis array.