Method and System for Displaying the Electric Field Generated on the Brain by Transcranial Magnetic Stimulation

• US 20080161636A1
• Filed: 09/11/2007
• Published: 07/03/2008
• Est. Priority Date: 09/13/2006
• Status: Active Grant

• Current Assignee: Nexstim Oyj
• Original Assignee: Nexstim Oyj
• Inventors: Autio, Ilkka, Hurme, Raine, Ruohonen, Jarmo, Sipila, Perttu
• Granted Patent: US 9,101,751 B2
• Time in Patent Office: Days
• US Class Current: 600/13
• CPC Class Codes: A61N 2/004 specially adapted for a specific therapy
• CPC Class Codes: A61N 2/006 for magnetic stimulation of nerve tissue
• CPC Class Codes: A61N 2/02 using magnetic fields produced by coils, including single turn loops or electromagnets A61N2/12 takes precedence
• CPC Class Codes: G06T 17/20 Finite element generation, e.g. wire-frame surface description, tesselation
• CPC Class Codes: G06T 19/00 Manipulating 3D models or images for computer graphics
• CPC Class Codes: G06T 2210/41 Medical

Abstract

A visualization surface representative of a portion of the brain at a depth below the head surface of the subject is generated by combining an actual representation of the head surface with an idealized representation of the head surface. The combining is a function of the depth and is performed to minimize in the visualization surface any irregularities existing in the actual head surface of the subject. A display shows the visualization surface overlaid on a volumetric image of the brain, the electric field induced on a region of the visualization surface by a transcranial magnetic stimulation (“TMS”) induction coil device positioned above the head surface and the TMS coil device. By viewing the display, a user of the TMS coil device can interactively position the TMS coil device in relation to the head surface and, for a target site on the brain at a selected depth, determine the position at which the TMS coil device induces a maximum E-field on a visualization surface corresponding to the selected depth.

Claims

1. A method for generating a representation of a portion of a brain for use in transcranial magnetic stimulation (“

TMS”

) comprising;

generating an actual representation of a head surface of a head;

generating an idealized representation of the head surface;

combining the actual and idealized representations to form a visualization surface, wherein the visualization surface is representative of a portion of the brain within the head at a depth beneath the head surface; and

displaying the visualization surface.

2. The method of claim 1 further comprising:

computing, based on the visualization surface, an electric field (“

E-field”

) induced by a TMS induction coil device on a portion of the brain at the depth; and

displaying the induced E-field on the visualization surface.

3. The method of claim 2 further comprising:

displaying the TMS coil device positioned in relation to the visualization surface, a representation of the head surface corresponding to the actual representation of the head surface and a volumetric representation of the head.

4. The method of claim 3 further comprising:

providing information representative of the position of the TMS coil device in relation to the head surface for a target site on the visualization surface stimulated by the TMS coil device.

5. The method of claim 4, wherein the position of the TMS coil device is provided or automatically stored after performing the step of:

identifying a single maximum E-field on the visualization surface for the target site.

6. The method of claim 2, wherein a maximum and a minimum of the induced E-field are displayed on the visualization surface.

7. The method of claim 1, wherein the combining further comprises:

weighting the actual and idealized representations with first and second weightings, respectively, wherein the first and second weightings are a function of the depth;

combining the actual and idealized representations weighted by the first and second weightings, respectively, to generate an unscaled visualization surface; and

scaling the unscaled visualization surface based on the depth to generate the visualization surface.

8. The method of claim 7, wherein the first and second weightings are determined by a linear function of the depth, wherein the sum of the first and second weightings equals one and each of the first and second weightings is not less than zero or more than one.

9. The method of claim 8, wherein the first weighting decreases as the depth increases and the second weighting decreases as the depth decreases.

10. The method of claim 1, wherein the idealized representation is an ellipsoid.

11. The method of claim 1, wherein the visualization surface is a substantially convex surface.

12. The method of claim 1, wherein the actual representation is a polyhedral surface mesh defined by a plurality of polygons and generated from a volumetric image of the head, the method further comprising:

generating a smallest convex surface mesh containing the surface mesh;

eliminating from the convex surface mesh polygons corresponding to a lower portion of the head, polygons having an area exceeding a predetermined area (“

large polygons”

) and polygons sharing vertices with the large polygons, to generate a scalp mesh; and

generating the idealized representation based on the scalp mesh.

13. The method of claim 12, wherein the generating of the idealized representation based on the scalp mesh further comprises:

computing a centroid of the brain based on vertices of all polygons in the scalp mesh, wherein the idealized representation is formed around the centroid and fitted to the vertices.

14. The method of claim 13, wherein the idealized representation is an ellipsoid.

15. The method of claim 1, wherein the idealized representation is formed from a plurality of idealized representations.

16. The method of claim 7, wherein the idealized representation is formed from a plurality of n idealized representations idealized_n, wherein each of the idealized_n representations has a second weighting w_ideal-n and wherein the weightings w_ideal-n are a function of a position of a projection of a vector V from a point on the surface mesh onto the corresponding idealized_n representation, in relation to a predetermined portion of the brain.

17. The method of claim 1, wherein the actual representation is derived from magnetic resonance imaging data representative of an anatomical configuration of the head.

18. The method of claim 1 further comprising:

comparing the visualization surface with the actual representation of the head surface;

computing a differential between the visualization surface and the actual representation based on the comparing; and

generating a new visualization surface by combining the actual and idealized representations with an adjustment, if the differential exceeds a predetermined threshold.

19. The method of claim 18, wherein the adjustment is a function of the differential.

20. The method of claim 18, wherein the combining for generating the visualization surface further comprises:

weighting the actual and idealized representations with first and second weightings, respectively, wherein the first and second weightings are a function of the depth;

wherein the combining for generating the new visualization surface comprises adjusting the weightings of the first and second weightings as a function of the depth.

21. The method of claim 1, wherein the combining is a function of at least one optimization criteria and a constraint.

22. The method of claim 21, wherein the constraint is a function of an area of interest in the brain and quality of image data representative of the head for the area of interest in the brain.

23. The method of claim 1 further comprising:

generating control information for controlling position and orientation of a TMS coil device in relation to the head, based on an actual position of the TMS coil device in relation to the head surface and a computation of an electric field induced on the visualization surface, to maintain a constant amplitude electric field induced on the visualization surface.

24. An apparatus for generating a representation of a portion of a brain for use in transcranial magnetic stimulation (“

TMS”

) comprising;

a processor for performing a process encoded on a computer readable medium, wherein the process includes the steps of;

generating an actual representation of a head surface of a head;

generating an idealized representation of the head surface;

combining the actual and idealized representations to form a visualization surface, wherein the visualization surface is representative of a portion of the brain within the head at a depth beneath the head surface; and

providing for display of the visualization surface.

25. The apparatus of claim 24, wherein the process further comprises:

computing, based on the visualization surface, an electric field (“

E-field”

) induced by a TMS induction coil device on a portion of the brain at the depth; and

providing for display of the induced E-field on the visualization surface.

26. The apparatus of claim 25, wherein the process further comprises:

providing for display of the TMS coil device positioned in relation to the visualization surface, a representation of the head surface corresponding to the actual representation of the head surface and a volumetric representation of the head.

27. The apparatus of claim 26, wherein the process further comprises:

generating information representative of the position of the TMS coil device in relation to the head surface for a target site on the visualization surface stimulated by the TMS coil device.

28. The apparatus of claim 27, wherein the position of the TMS coil device is provided or automatically stored after performing the step of:

identifying a single maximum E-field on the visualization surface for the target site.

29. The apparatus of claim 25, wherein the process further comprises:

providing for display of a maximum and a minimum of the induced E-field on the visualization surface.

30. The apparatus of claim 24, wherein the combining further comprises:

weighting the actual and idealized representations with first and second weightings, respectively, wherein the first and second weightings are a function of the depth;

combining the actual and idealized representations weighted by the first and second weightings, respectively, to generate an unscaled visualization surface; and

scaling the unscaled visualization surface based on the depth to generate the visualization surface.

31. The apparatus of claim 30, wherein the first and second weightings are determined by a linear function of the depth, wherein the sum of the first and second weightings equals one and each of the first and second weightings is not less than zero or more than one.

32. The apparatus of claim 31, wherein the first weighting decreases as the depth increases and the second weighting decreases as the depth decreases.

33. The apparatus of claim 24, wherein the idealized representation is an ellipsoid.

34. The apparatus of claim 24, wherein the visualization surface is a substantially convex surface.

35. The apparatus of claim 24, wherein the actual representation is a polyhedral surface mesh defined by a plurality of polygons and generated from a volumetric image of the head, the process further comprising:

generating a smallest convex surface mesh containing the surface mesh;

eliminating from the convex surface mesh polygons corresponding to a lower portion of the head, polygons having an area exceeding a predetermined area (“

large polygons”

) and polygons sharing vertices with the large polygons, to generate a scalp mesh; and

generating the idealized representation based on the scalp mesh.

36. The apparatus of claim 35, wherein the generating of the idealized representation based on the scalp mesh further comprises:

computing a centroid of the brain based on vertices of all polygons in the scalp mesh, wherein the idealized representation is formed around the centroid and fitted to the vertices.

37. The apparatus of claim 36, wherein the idealized representation is an ellipsoid.

38. The apparatus of claim 24, wherein the idealized representation is formed from a plurality of idealized representations.

39. The apparatus of claim 30, wherein the idealized representation is formed from a plurality of n idealized representations idealized_n, wherein each of the idealized_n representations has a second weighting w_ideal-n and wherein the weightings w_ideal-n are a function of a position of a projection of a vector V from a point on the surface mesh onto the corresponding idealized_n representation, in relation to a predetermined portion of the brain.

40. The apparatus of claim 24, wherein the actual representation is derived from magnetic resonance imaging data representative of an anatomical configuration of the head.

41. The apparatus of claim 24, wherein the process further comprises:

comparing the visualization surface with the actual representation of the head surface;

computing a differential between the visualization surface and the actual representation based on the comparing; and

generating a new visualization surface by combining the actual and idealized representations with an adjustment, if the differential exceeds a predetermined threshold.

42. The apparatus of claim 41, wherein the adjustment is a function of the differential.

43. The apparatus of claim 38, wherein the combining for generating the visualization surface further comprises:

weighting the actual and idealized representations with first and second weightings, respectively, wherein the first and second weightings are a function of the depth;

wherein the combining for generating the new visualization surface comprises adjusting the weightings of the first and second weightings as a function of the depth.

44. The apparatus of claim 24, wherein the combining is a function of at least one optimization criteria and a constraint.

45. The apparatus of claim 44, wherein the constraint is a function of an area of interest in the brain and quality of image data representative of the head for the area of interest in the brain.

46. The apparatus of claim 24, wherein the processor generates control information for controlling position and orientation of a TMS coil device in relation to the head, based on an actual position of the TMS coil device in relation to the head surface and a computation of an electric field induced on the visualization surface, to maintain a constant amplitude electric field induced on the visualization surface.