Method and system for displaying the electric field generated on the brain by transcranial magnetic stimulation

The first method and system for displaying the electric field generated by transcranial magnetic stimulation in the brain. CROSS-REFERENCE TO RELATED APPLICATIONS This invention claims the rights of U.S. Provisional Application No. 60/825,454 filed on September 13, 2006, which has been assigned to The assignee of this application is incorporated herein by reference.

TECHNICAL FIELD The present invention generally relates to transcranial magnetic stimulation, and more specifically, to display an accurate representation of the electric field induced by a transcranial magnetic stimulation induction coil device in the brain of a subject. Background Art Transcranial magnetic stimulation (TMS) uses The induction coil generates a time-varying magnetic field in the induction coil to induce an electric field ("E-flled") in the brain. Neurons located in the brain that are exposed to a sufficiently strong electric field will be activated or stimulated. In navigated brain stimulation (NBS), the electric field induced in the brain by the TMS induction coil is shown as an overlap on the graphic display of the anatomical representation of the subject's brain. By observing the display, the user can visualize the electric field induced in the brain, and thereby interactively position the TMS coil device relative to the brain in real time to stimulate the target position of the brain.

The following data acquisition and processing steps are usually implemented as part of NBS.

1. A segmented data representation of the scalp or head surface of the subject is generated based on the data representing the anatomical structure of the subject's head. Generally, well-known software algorithms are used to process two-dimensional ("2D") magnetic resonance imaging ("MRI") data representing the head of the subject to generate a three-dimensional ("3D") representation of the volume of the head. Among them, the data representing two-dimensional magnetic resonance imaging was previously obtained using traditional MRI technology, and the image includes at least the brain, the upper part of the skull, and attached tissues and cartilage. Then, the 3D representation of the head is further processed by a known software algorithm to generate a segmented data representation of the head surface of the object.

2. The tracking element is implemented to track the position and orientation of the TMS coil device relative to the head. Like the conventional technology in this field, the easily recognizable reflection mark (tracking

20078003402&5) is placed on the selected points of the subject's head and the TMS coil device, so that the 3D coordinates and six degrees of freedom of these points can be automatically recorded. For example, the tracker on the TMS coil device may be a part of the tracking device attached to the TMS coil device, such as the one submitted on August 30, 2007 entitled "TRANSCRANIAL MA GNETIC STIMULA TION IND UCTION COIL DEVICE WITH ATTACHMENT PORTION FOR RECEIVING TRACKING DEVICE" described in US Patent Application No. 11/847,544, which is assigned to the assignee of this application and incorporated herein by reference. Like the conventional technology in this field, a dedicated camera is used to record the coordinates of the tracker.

3. Perform a registration process that combines the data (the second point above) representing the position of the TMS coil device and the tracker on the subject's head during the tracking calibration process with the image data (the first point above) that generates a 3D representation of the subject's head )Associated. Generally, multiple landmark points (for example, points on each ear or nose) on the head with reflection trackers are accurately positioned on the 2D MRI image or volumetric 3D image (if available) of the head. The same point can also be accurately positioned on the subject's head by using a digital pen tracker including a reflection tracker. After performing this point-to-point correspondence or point-to-point matching, a transformation that aligns the coordinate system used to represent the head in the MRI image data with the coordinate system used to represent the relative position of the tracker in the calibration process is calculated. By performing additional point-to-point matching, for example, the quality of the transformation is enhanced at least in the sense of the least square method, thus improving the accuracy of the NBS.

4. On a display commonly used in NBS, a graphical representation of the TMS coil device with respect to the graphical representation of the scalp and brain at the selected depth is displayed. It is particularly preferable to display only the housing of the TMS coil device containing the coil windings. The electric field induced by the TMS coil device in the brain is shown as an overlap on the representation of the brain. Therefore, when the user navigates the TMS coil device relative to the head of the subject, the display provides the user with a visual representation of the position and direction of the TMS coil device housing relative to the head and brain, thereby providing the coil windings relative to the head and the brain. A visual representation of the location and direction of the brain, and provides an electric field induced in the brain. The quality of the transformation calculated in the registration (point 3 above) affects the accuracy of the representation shown on the display and thus the navigation accuracy. It is well known that the electric field induced by the coil windings is calculated using a head model or a head conductivity distribution model (such as a spherical model), such as Ravazzani, P. et al. in Magnetic stimulation of the nervous system: induced electric field in unbounded, semi-infinite, spherical, and

20078003402& 5th Cylindrical mediaⁿ (Annals of Biomedical Engineering 24: 606-616, 1996) The model described in the article, the entire content of which is incorporated herein by reference, is based on the model of the shape and position of the copper wire winding in the TMS coil device. Then, the electric field is shown in the representation of the brain, for example, the intensity of the electric field is indicated by color, so that the user navigates the TMS coil device to stimulate the target point of the brain. To a large extent, the accuracy of the brain representation determines the accuracy of the representation of the electric field induced in the brain shown on the display, and greatly affects the accuracy with which the user navigates the TMS coil device to stimulate the target point on the brain.

It is known that the effect of TMS depends on the absolute intensity of the electric field of the target point on the brain and its relative intensity relative to the adjacent area of the target point. Therefore, it is very important for the NBS display to accurately show the user of the TMS coil device the position of the maximum electric field in the neighborhood of interest of the target point. For anatomical reasons, on existing NBS displays, the neighborhood of interest at a selected depth of the brain is usually represented as a direction approximately parallel to the surface of the subject's scalp above the neighborhood. Therefore, in the existing NBS, multiple so-called visualization surfaces are used to represent the brain, and each visualization surface represents a part of the brain at a selected depth.

In the prior art, the NBS display usually displays the visualization surface at a depth of approximately 20 to 25 mm below the scalp. The shape of the visualization surface approximates the shape of the brain and cortical brain structure at the selected depth. In addition, the NBS display displays the electric field induced at points along the visualization surface (including the location of the largest electric field on the visualization surface). The electric field is usually shown as a color map, where the colors indicate the intensity relative to the maximum. In addition, NBS displays usually show the TMS coil device in color relative to the visualization surface. In addition, real-time updated, polygonal colored and textured surfaces are also used to display the visualization surface, for example, when the TMS coil device or the head is moved in real time. In addition, on existing NBS displays, the TMS coil device and the visualization surface can be viewed from any angle and distance.

In the existing NBS, the visualization surface is directly obtained from the 2D MRI image data of the head, so that any protrusions (protrusions), depressions, or other irregularities in the scalp are correspondingly and substantially the same reflected in the visualization surface. Ideally, it is expected that the location of the strongest electric field will move along the visualization surface on the NBS display in response to the movement of the TMS coil device along the scalp.

However, it has been observed on existing NBS displays displaying the visualization surface that when the TMS coil device is gradually moved along the subject's scalp, the electric field representation on the visualization surface becomes irregular and does not completely correspond to the movement of the TMS coil along the scalp, where , In the existing NBS

20078003402& 5 The visualization surface displayed on the display has obvious ridges, depressions or irregularities relative to the TMS coil device and the electric field induced by the TMS coil device. For example, if the stimulus target point is located at the bottom of the surface depression of the visualization surface, the electric field intensity at the target point displayed on the visualization surface is significantly smaller than the points around the target point, even though the actual electric field intensity at the target point is comparable to the electric field of the surrounding points The intensity is the same or similar. It is well known in the art that the electric field induced by the TMS coil device rapidly weakens with the distance from the coil winding in the TMS coil device, for example, the electric field at a distance of 2 mm from the coil winding can be weakened by even about 5-20%. Therefore, if the visualization surface is very close to the shape of the scalp, the maximum electric field will most likely not appear as a depression in the visualization surface that constitutes the stimulation target point, but as a point on the visualization surface that is located near the target point and at the edge of the depression. Place. Therefore, when the visualization surface includes depressions corresponding to the target point, it will be difficult, if not impossible, to locate the TMS coil device so that the electric field is located at the target point on the visualization surface. Optionally, if the visualization surface is not very close to the brain shape, the area near the target point will probably not be oriented correctly, making it difficult to accurately position the TMS coil device relative to the head using NBS to induce induction at the target point The target of the strongest electric field.

Therefore, it is necessary to generate a visualization surface representing the part of the brain at the selected depth to display the electric field induced by the TMS coil device in the brain as a part of the NBS. The visualization surface accurately represents the brain at the selected depth and avoids the occurrence of interference on the visualization surface. Misrepresentation of electric field.

SUMMARY OF THE INVENTION According to the present invention, the visualization surface representing the brain part of the subject at a selected depth is obtained by combining the actual representation of the subjects head surface obtained from image data representing the anatomical structure of the subjects head and the ideal representation of the head surface It is generated, in which the combination eliminates or substantially reduces any protrusions, depressions or other irregularities on the visualization surface, and provides an electric field induced by the TMS coil device used to stimulate the brain of the subject in the part of the brain corresponding to the visualization surface The actual representation. The contribution of each of the actual and ideal representations of the brain surface is a function of the depth of the visualization surface, and the size of the visualization surface generated by this combination is proportional to the depth of the visualization surface.

In one embodiment, the visualization surface generated by this combination is substantially convex.

20078003402& 5 In another embodiment, the ideal representation of the head surface is a function of the raised area of the scalp, and there are no or substantially no protrusions, depressions or other irregularities in the scalp (it has been removed or substantially reduced) . In yet another embodiment, the ideal representation of the head surface is an ellipsoid.

In yet another embodiment, the visualization surface generated by the combination is compared with the actual representation of the head surface, and if the difference between the former and the latter exceeds a predetermined threshold, the contribution of the actual representation and the ideal representation to the combination is adjusted (Ie, the difference function) to generate a new visualization surface. In one embodiment, the difference is an average value that defines the distance between the actual representation of the head surface and the multiple corresponding points of the visualization surface.

BRIEF DESCRIPTION OF THE DRAWINGS According to the following detailed description of the current preferred embodiments in conjunction with the accompanying drawings, other objectives and beneficial effects of the present invention will be apparent, and similar reference numerals in the accompanying drawings indicate similar elements.

Figure 1A is a cross-sectional view of an exemplary head surface portion of an object, which includes a visualization surface corresponding to the actual and ideal representations of the head surface and the contour of the electric field induced by the TMS coil device located above the head surface; 1B is an enlarged view of a portion of the head surface shown in FIG. 1A; FIG. 2A is a cross-sectional view of the head of the subject of FIG. 1A, which includes a visualization surface corresponding to the actual representation of the head surface; FIG. 2E is the object of FIG. 1A A cross-sectional view of the head, which includes a visualization surface corresponding to an ideal representation of the head surface; FIG. 3 is a flowchart of an exemplary process of generating a visualization surface at the depth of the brain according to the present invention; FIG. 4A is an example of a subject's head Figure 4E is an exemplary scalp grid representation of the head of Figure 4A in accordance with the present invention; Figure 5 is a perspective view of an exemplary three-dimensional representation of the head in accordance with the present invention, overlaid on the figure The visualization surface of the brain and shows the electric field induced by the TMS coil device on the visualization surface.

Detailed ways

20078003402& 5 In NBS, use previously collected MRI image data representing the anatomical structure of the subject's head to generate a three-dimensional ("3D") image representing the head and the brain part at a selected depth below the scalp or head surface The visualization surface. The NBS display usually displays the visualization surface superimposed on the 3D image of the head, the position of the TMS coil device used to stimulate the target point on the brain relative to the head surface and the visualization surface, and the brain surrounding the target point on the visualization surface Electric field induced in the area.

In the existing NBS, the structure of the generated visualization surface basically corresponds to the actual structure of the head surface of the subject. 1A shows a typical head 10, a visualization surface 12 of the brain under the scalp 14 of the head 10 (which is generated according to the prior art), and a basic idealization of the brain part of the head 10 at the same depth as the surface 12 A cross-sectional view of the visualization surface 32 of the scalp, the TMS coil device 16 located above the scalp 14, and an isoplanar contour 18 representing the electric field induced by the TMS coil device 16 at various depths below the scalp 14. For ease of explanation, the device 16 shown in FIG. 1A, the visualization surface 12 includes bumps, protrusions, and irregularities 13, which basically correspond to the surface shape present in the scalp 14, that is, bumps, protrusions, and irregularities 15. FIG. 2A is a view of the head, which shows only the visualization surface 12. 2A, the visualization surface 12 includes points 11 that will be displayed on the visualization surface when the TMS coil device 16 moves along the scalp 14, representing the strongest electric field induced in the brain at the depth where the visualization surface 12 is located. In the prior art, the visualization surface 12 generally does not include points 11 in any depressions 13 in the visualization surface 12 that correspond to the depressions 15 covered on the scalp 14.

FIG. 1B is an enlarged view of a portion of FIG. 1A in which the scalp 14 includes depressions 15A. 1A and 1B, the electric field induced by the TMS coil device 16 has a maximum value at the point where the visualization surface (for example, the visualization surface 12) intersects the contour 18 having the maximum electric field value. In the exemplary embodiment of the TMS coil device 16 shown in FIGS. 1A and 1B, the target direction or the focusing direction of the TMS coil device 16 corresponds to the line AA extending orthogonally from the TMS coil device 16. Line AA extends through the recess The point A in 15A and the point E in the depression 13A on the visualization surface 12, the point A is located on the contour 18C and the distance from the TMS device 16 is L1, and the point E is located on the contour 18E and the distance from the TMS device 16 is L2. In addition, for exemplary purposes only, the scalp 14 is considered to have conductivity similar to that of the brain, so that when the TMS coil device 16 is in the position shown, the scalp 14 is

20078003402& 5 The strongest electric field is located at point A in recess 15A. On existing NBS displays, the strongest electric field induced by the TMS coil 16 will be represented as points D1 and D2 on the visualization surface 12, where the position of the TMS coil 16 is suitable for stimulating the recess 13A in the visualization surface 12 The target point at point E. Points D1 and D2 correspond to points on the contour 18D that are separated from the line AA and are close to the recess 13A. Although the point E in the recess 13A of the visualization surface 12 is a stimulation target, due to the shape of the recess 13A, the strongest electric field represented on the visualization surface 12 will not be located at the point E in the recess 13A. Similarly, if the stimulus target point is located below the point E, the visualization surface 12 will be located at a deeper depth in the brain, so that the actual target point of the point E is no longer on the visualization surface 12. In addition, if the stimulus target point is located above point E, for example on the idealized surface 32, the actual target point of point E will also be located on the idealized surface 32. Thus, based on the maximum electric field represented on the idealized surface 32, TMS The coil device 16 also cannot be located at the target point where the stimulus is actually at point E. Therefore, due to the shape of the recess 13A, the TMS coil device 16 cannot be positioned to point to the target point below, above, or at the point E by using the prior art to represent the brain surface at a certain depth.

As we all know, in NBS, it is desirable to recognize and know the position of the TMS coil device relative to the scalp. The TMS coil device induces the strongest electric field at a target point in a certain depth of the brain. Referring to the exemplary head 10 shown in FIGS. 1A and 1E, when the target position on the brain part corresponding to the depth represented by the visualization surface 12 is aligned with the point A on the scalp 14 of the head 10, the visualization surface 12 The recesses 13A in, generate a representation of the maximum electric field, as shown by points D1 and D2 in the visualization surface 12. Therefore, because the maximum electric field is shown at points D1 and D2, the position of the TMS coil device 16 that will induce the maximum electric field at the target position E of the brain part at the selected depth relative to the scalp 14 cannot be determined. In addition, if the TMS coil device 16 is moved slightly in the direction of arrow R or L along the surface of the scalp 14, the maximum electric field shown on the visualization surface 12 will probably still be at or near D1 and D2, only at D1. Or near, or only at or near D2. Therefore, since the target position on the brain part is aligned with the depression 15A in the scalp 14, the position of the TMS coil device 16 relative to the scalp 14 cannot be accurately determined for stimulating the point A corresponding to the scalp 14. The target location of the part of the brain directly below. Therefore, the position of the TMS coil device 16 cannot be determined and stored to align with the point A on the scalp 14. The precise target location on the brain provides repetitive, precise, and maximum stimulation.

20078003402& 5 Ideally, it is desirable to use a smooth or substantially convex curve to represent the brain part of the subject at a selected depth under the scalp, because this can accurately identify the TMS coil that generates the largest electric field at the target location of the brain The position of the device relative to the subject's head. 1A and 1B, if an ideal visualization surface 32 is used to represent the part of the brain at a selected depth, then the maximum electric field of the TMS coil device 16 aligned with point A on the scalp 14 will only represent the point on the visualization surface 32 At D, the point D is the intersection of the line AA and the contour 18D and the distance from the TMS coil device 16 is L3. 2B, FIG. 2E only shows a schematic view of the head 10 of the visualization surface 32. The smooth convex surface 32 allows when the TMS coil device 16 is gradually moved along the scalp 14 (for example, in the direction of the arrow R or L), The point 17 representing the maximum electric field induced on the surface 32 by the TMS coil device 16 is also substantially along the surface 32 accordingly. However, the visualization surface must also be very close to the shape of the brain to correctly orient the area adjacent to the target location to accurately identify the position of the TMS coil device relative to the head that generates the largest electric field at the target location.

According to the present invention, a visualization surface representing the brain part of the subject at a selected depth is generated so that when the TMS coil device is gradually moved on the subject's scalp, the anatomical position of the TMS coil device relative to the visualization surface and the subject's head is shown On the NBS display, the representation on the visualization surface of the maximum electric field induced by the TMS coil device at the target location on the selected depth of the brain portion correspondingly moves along the visualization surface. Therefore, the position of the TMS device with the maximum electric field induced at the target position on the brain part of the selected depth relative to the target's head can be identified, so that the TMS coil device can provide repetitive and precise stimulation to the target position.

FIG. 3 shows an exemplary process 50 for generating a substantially convex visualization surface of multiple depths of the brain according to the present invention, which can accurately identify the maximum electric field induced at the target location on the brain of the selected depth The position of the TMS coil device relative to the subject's head. It will be understood that the data processing steps shown in the process 50 can be easily performed by a processor with sufficiently high processing power to provide output data on the display in real time or substantially in real time, the processor including memory and coupled For displays such as monitors and data input devices such as mice and keyboards. For example, the processor may be a microprocessor programmed to perform TMS in conjunction with a TMS coil device, such as US Patent No. 6,849,040 assigned to the assignee of this application and incorporated herein by reference. In order to highlight the nature of the present invention, combined with the above

The exemplary header 10 described in 20078003402 & 5 illustrates the process 50. It will also be understood that although the data calculation and processing of the various steps in the exemplary process 50 may be well-known or customary in the art, the combination of the steps of the exemplary process 50 is creative and the resulting visualization The surface is creative and superior to the prior art visualization surface, for example in the use of NBS.

3, in step 52, using data processing techniques known in the art, the previously acquired 2D MRI image data representing the anatomy of the head 10 is combined and segmented to generate a head defined by a plurality of voxels Volume image. Likewise, the coordinates of the voxels that define the surface of the head or the scalp 14 of the head 10 are recognized using known techniques, and then stored in the memory.

Then, in step 54, a polyhedral surface mesh 100 representing the surface of the head 10 is generated using data processing techniques known in the art, as shown in FIG. 4A, where the surface mesh 100 is defined by a plurality of polygons 102. A typical polygon is a triangle with a length of about 1 to 2 mm and a width of about 1 to 2 mm. 4A, the size of each polygon 102 is proportional to the size of the voxel, so that the surface mesh 100 has substantially the same level of detail (resolution) as the MRI image data. For ease of reference, the surface grid 100 is hereinafter referred to as the actual representation of the head surface 14 or Rep-Actual.

In step 56, the smallest convex mesh or convex hull that includes or surrounds the surface mesh 100 is generated using data processing techniques known in the art. In addition, data processing techniques known in the art are still used to generate a bounding box that includes the surface mesh 100 and defines a set of coordinates, where the head 10 is in the bounding box.

In step 58, data processing techniques known in the art are still used to identify the polygon that defines the lower part of the head 10 (such as the part below the ear), and then generate a new convex mesh after the polygon is removed. In addition, we still use data processing techniques known in the art to identify polygons with areas exceeding a predetermined area in the new convex mesh ("large polygons") and polygons sharing vertices with the large polygons ("neighbor polygons"), and then pass Remove large polygons and neighboring polygons, and generate a synthetic convex mesh from the new convex mesh. The resultant convex mesh is the scalp mesh 110, as shown in FIG. 4B.

For a typical head, removing neighboring polygons from the convex mesh (performed in step 58) corresponds to the convex sub-region on the convex mesh corresponding to the head surrounded by the recessed area

20078003402& 5 The isolated part of the article is removed. 4A and 4B, due to the geometric properties of the convex mesh and the relatively small size of the polygons 102 in the surface mesh 100, the large polygons of the convex mesh correspond to the depressions in the surface mesh 100, for example, between the ears and the skull. The recessed area between. 4B, the convex mesh includes polygons 102 forming the skull cap shape of the head 10 with the protrusions and holes removed. A few polygons 102A are located in areas where the head 10 has a bulge, and most polygons 102B are densely located on the head 10. Other areas. Still referring to FIG. 4A, it can be seen that the raised sub-region above the left ear 103 of the head 10 generates many polygons 102, which are used to adapt the ideal representation of the head surface such as an ellipse to the actual head surface of the subject. Means (this will be discussed in detail in step 60 below), and that the irregular sub-region 108 on the left temple 105 of the head 10 generates only a small number of polygons.

Referring again to FIG. 3, in step 60, the vertices of all remaining polygons in the scalp mesh 110 are identified and stored. Based on the vertices of the remaining polygons, using a known technique, calculate the estimated value of the center of mass of the brain of the head. Then, by using the least square method, an ideal protrusion located around the center of mass and suitable for the extracted vertices of the scalp mesh 110 is formed. The shape is, for example, an ellipsoidal surface. The ideal convex shape is suitable for the convex area of the scalp 14, and the depressions in the scalp 14 are basically ignored. In one embodiment, the ellipsoidal surface is a sufficiently ideal convex shape because If the TMS coil device is located on or near the outer surface of an ellipsoidal body with conductive features (such as those already in the brain) and gradually moves along the outer surface of the ellipsoidal body, then follow the outer surface of the ellipsoid The electric field induced by the surface will correspondingly change with the movement of the TMS coil device. For ease of reference, the ideal convex shape of the head surface generated in step 60 is referred to as Rep-Ideal below.

In a preferred embodiment, in step 60, a technique known in the art is used to generate the topmost bounding box of the head 10 or the skull cap of the head 10. According to the content of the bounding box, calculate the estimated value of the centroid μ of the brain. Then, an ellipsoid with a centroid of μ and suitable for the apex of the scalp mesh 110 generated in step 58 is generated. As described above, the vertex density of the scalp mesh 110 is greatest at the top of the area on the skull cap corresponding to the most convex area of the actual head surface represented by the surface mesh 100. Therefore, the substantially convex area of the surface grid 100 has the greatest influence on the shape of the ellipsoid. In a preferred embodiment, the ellipsoidal surface is adapted to the apex of the head surface by using a well-known technique for minimizing the minimum mean square error (for example, pseudo-inverse).

20078003402& 5 In step 62, combine Rep-Actual and Rep-Ideal to generate a synthesized visualization surface V(D), as shown below:

V(D) = w_actuai* Rep-Actual + w_ldeai* Rep-Ideal (1) Among them, Wactual and Wide are weighting factors. It is the distance between the scalp 14 and the stimulation target position on the brain part of the head 10 ("the depth of the synthesized visualization surface" or "the depth of peeling"). Therefore, the synthesized visualization surface is the weighted average of the surface mesh 100, that is, the representation of the actual head surface and the ideal convex shape representation of the head surface generated by the scalp mesh no.

According to the present invention, by balancing the following objectives, equation (1) is used to generate a visualization surface of the brain at a specific depth with a structure favorable for use in NBS.

1. The shape of the brain part represented by the visualization surface should be anatomically reasonable. Because the volume segmentation of the brain is not performed routinely, the anatomical rationality is a function of how similar the shape of the brain is to the shape of the scalp or head surface.

2. The shape of the part of the brain represented by the visualization surface should be sufficiently smooth or convex so that the electric field represented on the visualization surface corresponds to the actual state of the electric field at the depth of the visualization surface in the brain. The second goal is clearly contradictory to the first goal. This is because if the brain is a perfect sphere, then it should be ideal to visualize the actual representation of the electric field on the surface.

Because the objective 1 and objective 2 are contradictory according to the present invention, the weights Wactual and Wjdeal in equation (1) are functions of D. In order to increase D, the influence of target 1 is reduced, so that the weight of Rep-Actual is reduced, which causes the weight of Rep-Ideal to increase. Because any surface of the brain will not be visible in the deeper part of the brain, therefore, for the deeper skinning depth, applying this weighting in equation (1) minimizes the error in the construction of the synthesized visualization surface Or there is no error. Therefore, the tiny cortex that protrudes deeper in the brain has no effect. In contrast, when the peeling depth is close to 0, the weight of Rep-Ideal is the same according to target 1, and the synthesized visualization surface is close to the structure of Rep-Actual.

In a preferred embodiment, the weights Wactual and Wide are determined by a linear function of the peeling depth, and additional constraints are implemented to prevent the weight from being less than 0 or greater than 1, so that Wactual+Wideal=1. In another embodiment, the Rep-Ideal is generated based on the experimental data related to the representation of the convex shape of the head surface of the head of another subject and appropriately

20078003402& 5th revision.

Referring again to FIG. 3, after step 62, in step 64, V(D) is adjusted proportionally according to the peeling depth D_O In the preferred embodiment of steps 62 and 64, the user selects the peeling depth D and the axial depth AD. The axial depth AD determines parts of the head other than the part where the scalp mesh 110 is generated, such as the jaw and neck. As described above, the peeling depth determines the parametric shape (step 62) and the zoom ratio (step 64) of the generated visualization surface to represent the part of the brain at the depth D. The axial depth specifies the axial range [0, AD] within which the head surface 14 is transparent to display the visualization surface on the NBS display. In one embodiment, the peeling depth indicates that the percentage ρ is from 0% to 50%, and the axial depth AD is between about 0 mm and 250 mm. For example, if ρ = 20% and AD = 50 mm, then the volume of the generated brain model is about 80% of the actual volume of the head, and the head surface 14 is transparent from the top of the head 10 down 50mm of. Therefore, if the peeling depth D is selected to make P close to the maximum value of 50%, then, referring to equation (1), Wactual is close to 0 and U^eal is close to 1. In one embodiment, the ratio of ρ is: if the head model represents the head of an adult male, P is approximately equal to the number of millimeters. For example, on the top of the head, ρ equal to 20% corresponds to a distance measured from the brain to the nearest surface point on the scalp 14 of about 20 mm.

In the exemplary embodiment of step 62, when the peeling depth ρ is between the minimum value and the maximum value, the weights Wactual and Wideal are determined by a linear model, where:

Wactual=f°*scale+fl (2) where the scale=1 -P, in other words, when the peeling depth ρ is equal to 0.1 (10%), the scale is equal to 0.9 (90%), so as to visualize the surface The size needs to be reduced to 90% of the original scalp size. When Actual +w_ideaWhen l = 1,

Wideal ⁼ 1-f°*scale-fl (3) If Pmin and pmax correspond to the minimum peeling depth and the maximum peeling depth, for example, 0% and 50%, then by rewriting the constraint condition of formula (1) as follows The parameter f can be easily determined₀And fl: f°*(I' Pmm) + fl = 1 (4), and f°*(l-Pmax) + f|=0 (5) by replacing p_minAnd p_mThe value of ax, formula (4) and formula (5) can be easily solved to obtain fo=

20078003402& 5th

2 and spinning = -1. Then, the known values of scale and fi can be used to calculate the scale, Wactual, and Wide using the p value selected by the user.

After calculating Wactuai and Wideai, by expressing the shapes represented by Rep-Actual and Rep-Ideal as a finite set or equation of points, according to formula (1), the weights Wactual and W_ideal combines the shapes represented by Rep-Actual and Rep-Ideal. In a preferred embodiment, when the equivalent equation becomes too complicated, the above-mentioned representation of the shape is a finite set of points. For example, it is difficult to accurately express the shape of the ear by using an equation.

In an exemplary embodiment, Rep-Actual is represented by a set of points, and Rep-Ideal of an ellipsoid is represented by an equation. In addition, the visualized surface synthesized according to formula (1) is represented by a set of points, where the number of points is equal to the number of points on the surface grid 100. This set of points corresponds to the vector Vi, where each vector contains the coordinates of the scalp point i, and the origin of the coordinate system is the center of mass J of the calculated ellipsoid Rep-Ideal. If h is a line that intersects μ and both, the person intersects the ellipsoid at two points. Further, if ® is the intersection point closest to Μ, then ei corresponds to Vi. In this sense, ei is the projection of V\ on the ellipsoid Rep-Ideal. Therefore, the combination of these shapes is achieved through the combination of corresponding points (that is, the scalp point and its projection). According to (M,_ei) Yes, calculate the new point corresponding to the brain surface modeling as follows: bj -Wactual*Vj + ^ideal*^i (6) For each i, repeat the calculation of formula (6) to obtain the corresponding A set of points on the model of the brain part (that is, the visualization surface at the skinning depth D). Since the point is located on the ellipsoid surface of the ideal representation of the scalp, in the data processing stage, the brain model and the scalp mesh model of the brain have approximately the same size. Then, according to step 64, each point 6 is scaled, that is, moved closer according to the peeling depth. Because the origin is at J, each point bj is a bj* scale.

In another embodiment, Rep-Ideal is composed of a plurality of ideal convex shapes Rep-Ideal_nEach Rep-Ideal is formed near the center of mass of the brain determined by the scalp mesh and suitable for the raised area of the scalp mesh. The use of multiple shapes (preferably, complex shapes) to form Rep-Ideal is advantageous and desirable for NBS, where the goal of TMS processing is to stimulate brain regions far away from the cortical motor area. In this embodiment, multiple ideal representations (for example, two ellipsoids) of the head surface form Rep-Ideal, so that there are M projections

20078003402& 5 No. pro] and the three rights Wi, W2 and W3, where: bi = Σ>1 P^r°Jj(X)* W/ (7 ), and work; Yan Guang1 (8) The weight Wi is equal to Wactual, W2 is the weight of the first ellipsoid surface Wjdeall, and W3 is the weight of the second ellipsoid surface ideal2. The projection pYOj 1 is projy (Vj) = Vj, and the projections pYOj? and pYOjs are simple projections of scalp points on two ellipsoid surfaces, where projziy^ = e,o sets dagger and W3 to 0 according to Vi as follows. When M is close to the cortical motor area of the brain, W3 is set to 0. According to normalization, W2 = Wideall, so that 4 is exactly the same, as if only one ellipsoid is used to form Rep-Ideal. Contrary to this, when V\ is far away from the cortex motion zone, it will be set to 0 and W3=Wideall to calculate di according to the second ellipsoid. Refer again to Fig. 3, in step 66 after step 64, according to the TMS coil device 16 With respect to the position of the scalp 14, the electric field induced on the visualization surface V(D) at the skinning depth selected by the user is calculated. Then, a three-dimensional image of the brain anatomy that contains the electric field induced by the TMS coil device and is covered by the visualization surface is displayed on a monitor as associated with performing NBS, as shown in FIG. 5. In a preferred embodiment, the maximum electric field at the target position and the electric field in the area near the target position are displayed on the visualization surface. Refer to Figure 5, The electric field 120 shown is overlaid on the image of the brain anatomy 122 of the head 10. In a preferred implementation on the display, the colored electric field 120 is overlaid on the anatomy 122 in gray scale, thus allowing the user to easily distinguish between the two types of information. The dark spot 124 under the white cylinder 126 represents the large value of the electric field, which is preferably represented by dark red, while the dark area 125 near the edge 130 of the circumference of the electric field 120 represents the minimum value of the electric field, which is preferably represented by dark blue .

In one embodiment of the present invention, the inner surface of the skull is used instead of the inner surface of the scalp to generate Rep-Actual, for example, when the outer shape of the head does not accurately conform to the shape of the cranial cavity.

In another embodiment, Rep-Actual is generated based on the actual shape of the brain or cortex, as determined by the segmentation of the MRI image. By using this Rep-Actual, the visualization surface generated by equation (1) can have increased anatomical fidelity, while also exhibiting irregularities representing the electric field induced on the visualization surface.

In yet another embodiment, the user can select one of a number of additional constraints

20078003402 & 5 The first application of formula (1) to generate a visual surface. These constraints, for example, correspond to and are based on experimental results obtained by generating visualization surfaces of other heads with a head surface configuration similar to that of the subject's head; these constraints are also selected to avoid generating users It will be difficult to interpret the visualization surface of the electric field information displayed on the visualization surface.

In yet another embodiment, Rep-Ideal is obtained by using one or more selected optimization criteria and constraints according to the current position of the TMS coil device. The optimization criteria and constraints may include, for example, generating a visualization surface only at a local area known in advance close to the target location of the stimulation. For example, in the MRI image data representing the head, if the data representing the right hemisphere of the brain is incomplete and the data representing the left hemisphere of the brain is complete and complete, and further, if the predetermined stimulation target position of interest is located on the left Hemisphere, then, only the part of the surface mesh 100 close to the predetermined position is used to fit the curved surface of the desired depth. In the fit of the curved surface, the part of the surface grid 100 far away from the stimulation position is ignored.

In another embodiment, the microcontroller for executing NBS and capable of generating a visualization surface in accordance with the present invention uses information representing the position of the TMS coil device relative to the head and the electric field induced on the visualization surface to automatically control Or provide the user with control information to control the position or direction of the TMS coil device relative to the head, so that the electric field induced on the visualization surface remains constant when the TMS moves along the surface of the head. The electric field with a constant amplitude can be defined by the user, for example. This controlled application of electric fields has special uses, for example, when the amplitude of the maximum electric field depends on the position or direction of the TMS coil device relative to the scalp, and when it is desired to stimulate the target area of the cortex with the TMS coil device in a uniform manner.

In yet another embodiment, referring to FIG. 3 again, after step 64, the coordinates of the visualization surface are compared with the corresponding coordinates of Rep-Actual to determine whether the difference between the shape of the visualization surface and the shape of Rep-Actual is Within the predetermined threshold. If yes, go to step 66. If not, a new value is assigned or calculated for Wactual or Wide, preferably the value is a function of the difference, and step 62 is performed again to generate a visualization surface. In a preferred embodiment, the difference is the average distance between Rep-Actual and a plurality of corresponding coordinates of the visualization surface.

In yet another embodiment, if the ideal representation of the head surface of the head is determined to be unsuitable for the subject's head, the ideal representation of other shapes (for example, other shapes

20078003402& 5 ellipsoid) used as Rep-Ideal.

Although the preferred embodiments of the present invention have been described and elucidated, it will be apparent to those skilled in the art that various modifications can be made without departing from the principle of the present invention.

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