Radial and Tangential Stimulation of same ROI

1. Multi-electrode current optimization for targeted and directional tDCS in a realistic head model Seyhmus Guler1,2, Moritz Dannhauer2, Burak Erem1,2, Rob Macleod2, Don Tucker3, Sergei Turovets3, Chelsea Mattson3 and Dana Brooks1,2 1 Department of Electrical and Computer Engineering, Northeastern University, Boston, MA 2 Scientific Computing and Imaging Institute, University of Utah, Salt Lake, UT 3 Electrical Geodesics Inc. (EGI), Eugene, OR • Transcranialdirect current stimulation (tDCS) stimulates the brain by injecting low amplitude currents through the electrodes on the scalp. • Targeting a specific region and Polarity of the stimulation are important depending on the clinical purpose. • Using smaller electrodes instead of patch electrodes might increase the focality. • Manual optimization is very hard, the parameter space is huge. • Goal: Maximize the directional current density in region of interest without violating safety constraints. Introduction ROI #1 ROI#2 ROI#3 ROI#4 Fig 2: 4 ROIs Head Model Optimization FEM CVX Anterior Superior Transfer Matrix Electrode Currents • ROI is directionally stimulated • Desired direction has a critical effect • Isolated source and sinks!!! ROI Electrodes Skin Skull CSF Gray Matter (GM) ROI Internal Air *Eyes and White Matter not seen in the figure Radial DISCUSSION AND FUTURE WORK tDCS Optimization Stimulation of different ROIs in Anterior and Superior Directions Radial and Tangential Stimulation of same ROI Head Model and FEM • ROI may be stimulated in the desired direction • Add current density constraints to prevent hotspots and skin burns • Number of constraints increases considerably • Might be computationally heavy • Problem specific optimization solver may be needed • Include anisotropy for more accurate simulations Fig 3: Current paths going through ROI (purple) for different ROIs and different desired directions. The desired directions are shown on top left of each image. • Linear Tetrahedral Mesh using Biomesh3D1 • 40 x 106 elements • 6 x 106 nodes • 8 Materials • Detailed tissue boundaries • Forward tDCS solution by using FEM and Complete Electrode Model. ROI Current Density (100 Samples) Gray Matter Current Intensity ROI Fig 1: Head Mesh and ROI (red color) Tangential Original Problem Equivalent Convex Problem Maximize the current density in preferred direction in ROI Figure 3: Optimization results of 4 ROIs in x,y,z directions. Individual electrode current Constraints Figure 2: Optimization Results for radial (purple ) and direction. The total current constraint Current power constraint in the brain outside ROI ROI References: 1Biomesh3D: Quality Mesh Generator for Biomedical Applications. Scientific Computing and Imaging Institute (SCI) http://www.biomesh3d.org • a and B in convex problem are calculated using Forward Matrix and Linear FE Mesh. Acknowledgment:This work was made possible in part by the NIH/NIGMS Center for Integrative Biomedical Computing, 2P41 RR0112553-12 ROI