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bioRxiv · 10.1101/2023.10.25.564044

Real-Time Computation of Brain E-Field for Enhanced Transcranial Magnetic Stimulation Neuronavigation and Optimization

Hasan, N. I.·Dannhauer, M.·Wang, D.·Deng, Z.-D.·Gomez, L. J.
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Abstract

Transcranial Magnetic Stimulation (TMS) coil placement and pulse wave-form current are often chosen to achieve a specified E-field dose on targeted brain regions. TMS neuronavigation could be improved by including real-time accurate distributions of the E-field dose on the cortex. We introduce a method and develop software for computing brain E-field distributions in real-time enabling easy integration into neuronavigation and with the same accuracy as 1st-order finite element method (FEM) solvers. Initially, a spanning basis set (< 400) of E-fields generated by white noise magnetic currents on a surface separating the head and permissible coil placements are orthogonalized to generate the modes. Subsequently, Reciprocity and Huygens principles are utilized to compute fields induced by the modes on a surface separating the head and coil by FEM, which are used in conjunction with online (real-time) computed primary fields on the separating surface to evaluate the mode expansion. We conducted a comparative analysis of E-fields computed by FEM and in real-time for eight subjects, utilizing two head model types (SimNIBSs headreco and mri2mesh pipeline), three coil types (circular, double-cone, and Figure-8), and 1000 coil placements (48,000 simulations). The real-time computation for any coil placement is within 4 milliseconds (ms), for 400 modes, and requires less than 4 GB of memory on a GPU. Our solver is capable of computing E-fields within 4 ms, making it a practical approach for integrating E-field information into the neuronavigation systems without imposing a significant overhead on frame generation (20 and 50 frames per second within 50 and 20 ms, respectively). O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=96 SRC="FIGDIR/small/564044v1_fig8.gif" ALT="Figure 8"> View larger version (27K): org.highwire.dtl.DTLVardef@1520141org.highwire.dtl.DTLVardef@d05835org.highwire.dtl.DTLVardef@4f1aa9org.highwire.dtl.DTLVardef@15f7b90_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFigure 8:C_FLOATNO Mean computational time for pre-processing stage (mode and field generation stage) for mri2mesh models (A) and headreco models (B). At any rank (mode), the time is calculated across 8 head models from 8 subjects.) C_FIG

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Hasan, N. I., Dannhauer, M., Wang, D., Deng, Z.-D., Gomez, L. J.. 2023-10-30. Real-Time Computation of Brain E-Field for Enhanced Transcranial Magnetic Stimulation Neuronavigation and Optimization. https://doi.org/10.1101/2023.10.25.564044

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