Abstract
Abstract Introduction: During transcranial magnetic stimulation (TMS), a coil placed on the scalp driven by a low-frequency pulse is used to modulate brain activity. The TMS induced E-field has been shown to correlate well with stimulated cortical region. As a result, E-field information is essential for the determining where to place the coil and the necessary pulse intensity. A bottleneck to E-field informed TMS is that FEM requires the solution of a large linear systems of equations for each coil placement, making repeated execution of FEM for finding optimum coil placement impractical. Objectives: The goal is to develop a practical tool for E-field dosimetry that allows determination of E-fields in real-time, thereby, enabling the fast computation of optimum coil placement. Methods: We arrange E-field results into a matrix with each column consisting of E-field samples determined from a single coil placement via FEM. Its rows consist of the E-field at a single coil position for all possible coil placements and can be sampled using our previously proposed auxiliary dipole method (ADM). We use the adaptive cross approximation (ACA) to estimate the whole matrix from a few sample columns and rows. Results: This method can evaluate the E-field distribution in a 2 cm diameter ROI from for ∼1000 coil positions and 360 coil orientations with error <2% in under 10 and 20 simulations in a spherical and MRI-derived head model, respectively. For the MRI-derived head model, this method obtained all the fields in <20 minutes. Conclusion: The proposed method enables the fast computation of optimal coil placement and pulse intensity, as well as, it provides E-field distribution inside the ROI for each coil placement.View Large Image Figure ViewerDownload Hi-res image Download (PPT)View Large Image Figure ViewerDownload Hi-res image Download (PPT)View Large Image Figure ViewerDownload Hi-res image Download (PPT)View Large Image Figure ViewerDownload Hi-res image Download (PPT) Keywords: TMS, Low-rank approximation, Coil placement optimizaiton, E-field dosimetry
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