Introduction of transcranial magnetic stimulation

1. Numerical investigation of the electric field
distribution induced in the brain by
transcranial magnetic stimulation

2. Introduction

3. Magnetic Field Generator
Current
Magnetic Field Line

4. Energy efficiency of
coupling to the
brain is too LOW

5. Different
Configurations

6. Formulation

7. Field Computation
Sensitivity Formula
FEM, CDSA

8. Field Computation

9. Quasi-static Approximation
Equation keeps a static form
(do not involve time derivatives)
1.Electromagnetic wave is at LOW frequency.
2.Biological tissues have LINEAR material properties.

10. Analytical Sensitivity Formula

11. Objective Function Maxwell equation
Augmented Objective Function
Design Sensitivity Formula
Augmented Lagrangian Method
Derivative to Design Variable
Adjoint Variable Method

12. Analytical Sensitivity Formula

13. Implementation of FEM, CDSA

15. Results

16. Effect of Iron Core Shape

17. Initial shape Optimized shape Practical shape

19. Conclusion

20. CDSA
Þ An optimized core
Þ magnitude & localization of the electric field induced
Þ Energy efficiency of coupling to the brain

22. TMS Coil Analysis

26. Case1: Circular Coil

27. Schematic

28. Parameters
Permeability (air): 1
Permeability (copper): 0.99994
Radius (cross-section): 0.5 cm
Side Length (Square): 50 cm
Excitation Current: 1000A

29. Results

30. Results

31. Case2: Figure-8 Coil

32. Using Superposition theorem

33. Results

34. Comparison