Continuous modeling for dipole localization from 2D MCG images with unknown depth

• US 9,125,581 B2
• Filed: 05/23/2012
• Issued: 09/08/2015
• Est. Priority Date: 05/23/2012
• Status: Active Grant

• Current Assignee: Columbia Peak Ventures, LLC (Dominion Harbor Enterprises, LLC)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Wu, Chenyu, Xiao, Jing
• Primary Examiner(s): Luong, Peter
• Application Number:
  US13/478,682
• Publication Number:
  US 20130317337A1
• Time in Patent Office: 1,203 Days
• Field of Search: 600/407, 600/409
• US Class Current: 1/1
• CPC Class Codes: A61B 2576/023 for the heart
• CPC Class Codes: A61B 5/05 Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves impedance plethysmography A61B5/0295; measuring movement of the entire body or parts thereof A61B5/11; detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof A61B5/24
• CPC Class Codes: A61B 5/243 specially adapted for magnetocardiographic [MCG] signals
• CPC Class Codes: A61B 5/245 specially adapted for magnetoencephalographic [MEG] signals
• CPC Class Codes: G16H 30/40 for processing medical images, e.g. editing

Abstract

A system identifies double-layer dipoles in a magnetic image by defining two-dimensional patches of distributed point charges that simulate the double-layer dipoles. The geometric center of a two-dimensional patch is used as the location of an equivalent dipole moment of the double-layer dipole. The momentum of the equivalent dipole moment is determined by submitting the magnetic image to a dipole construction system that identifies the location and momentum based on the submitted magnetic image.

Claims

1. A method of constructing a magnetocardiogram (MCG) image of a double-layer dipole, comprising:

acquiring a magnetic image provided by a sensor unit including a plurality of electromagnetic sensors, each electromagnetic sensor contributing its output data to said magnetic image;

providing a data processing device to implement the following steps;

obtaining the magnetic image, said magnetic image being of an image of a magnetic field generated by a double-layer dipole, wherein said double-layer dipole is of an undefined shape, size, depth and orientation;

submitting said magnetic image to a current dipole constructing system to determine a 3D position and momentum of an electric current in accord with the magnetic image;

using the Biot-Savart Law to construct said MCG image based on the identified 3D position and moment of the electric current, including;

assigning the 3D position of the electric current to the geometric center of a single double-layer 2D patch; and

assigning the geometric center of the single double-layer 2D patch to the position of an equivalent dipole moment of said double-layer dipole, said equivalent dipole moment being characterized by the generation of an electric field substantially similar to that produced by said double-layer dipole; and

displaying the constructed MCG image.

2. The method of claim 1, further comprising:

assigning the momentum of the electric current to said equivalent dipole moment.

3. The method of claim 1, wherein said single double-layer 2D patch is an approximation of said double-layer dipole.

4. The method of claim 1, wherein said single double-layer 2D patch is of undefined size.

5. The method of claim 1, wherein said double-layer 2D patch is a distribution of point sources of electric charge having a common polarity.

6. The method of claim 1, wherein said single double-layer 2D patch defines an isochronal activation surface.

7. The method of claim 6, wherein said single double-layer 2D patch is one of two opposing surfaces that define said equivalent double-layer dipole, said equivalent double-layer dipole being equivalent to the double-layer dipole whose magnetic field is represented in said magnetic image.

8. The method of claim 1, wherein the electric field produced by said equivalent dipole moment is substantially similar to that produced by said double-layer dipole when viewed from a distance of multiple times the diameter of the surface of said double-layer dipole.

9. The method of claim 1, wherein:

the magnetic image of the magnetic field generated by a double-layer dipole is a first magnetic image having an M×

M resolution of data points; and

the current dipole constructing system determines the 3D position and momentum of an electric current by;

(a) using a high resolution image synthesizer to receive said first magnetic image and produce an intermediate magnetic image, said intermediate magnetic image being a higher resolution image representation of said first magnetic image by;

(i) accessing a linear model defining a model magnetic image of higher resolution than said first magnetic image, said linear model establishing interpolation patterns between characteristics of the linear model and the M×

M data values of the first magnetic image; and

(ii) producing said intermediate magnetic image by projecting said first magnetic image onto the subspace of the linear model, and establishing coefficients for said intermediate magnetic image in accordance with the linear model and said M×

M data values;

(b) submitting the intermediate magnetic image to an electric current localizer for determining the position and momentum of the electric current in accord with said intermediate magnetic image, said electric current localizer evaluating electromagnetic data in an x-y orientation (Bxy) assuming single dipole moment, computing dense Bxy from dense Bz, finding the image maximum in said intermediate magnetic image, and using this determined position information as a starting point in an iterative process for identifying a three-dimensional position vector {right arrow over (p)} and momentum vector {right arrow over (J)} for said electric current, said three-dimensional position vector {right arrow over (p)} and momentum vector {right arrow over (J)} defining said position and momentum of the electric current, respectively.

10. The method of claim 9, wherein said linear model is defined by creating a plurality of synthesized magnetic images having the same resolution as said intermediate magnetic image, said synthesized magnetic images being based on simulated electrical impulses within a three-dimensional spatial conductive volume.

11. The method of claim 10, wherein the electrical impulses are double-layer dipoles and said synthesized magnetic images are based on randomly generated double-layer dipoles.

12. The method of claim 11, wherein said randomly generated double-layer dipoles have random depths, shapes and locations within the three-dimensional spatial conductive volume.

13. The method of claim 11, wherein said linear model is created by using principal component analysis (PCA) and said three-dimensional spatial conductive volume is representative of cardiac tissue.

14. The method of claim 10, wherein said synthesized magnetic images are based on randomly generated currents (single dipole moments) within the three-dimensional spatial conductive volume.

15. The method of claim 14, wherein said linear model is created by using principal component analysis (PCA) and said three-dimensional spatial conductive volume is representative of cardiac tissue.

16. The method of claim 10, wherein said interpolation patterns are established by the following steps:

(A) defining the following notation;

N×

N dense Bz magnetic field map to form a vector;

M×

M sparse measurement to form a vector;

K randomly generated single current dipoles Q;

(B) for each randomly generated current Q, computing an N×

N magnetic field map using Biot-Savart equation and stack the resultant image to a vector f₁;

(C) repeating step (B) to obtain K samples and getting a data matrix A=≡

f₁, f₂, . . . f_K┘

; and

(D) training a PCA model given input data A, to obtain the eigenmatrix Σ

_f.

17. The method of claim 16, wherein said intermediate magnetic image is created by:

given a new dipole and M×

M sparse measurements g_j, finding the corresponding rows in the eigenmatrix, and denoting a resultant submatrix as Σ

_g;

projecting the sparse measurement to the PCA subspace and computing the coefficients as c_g=Σ

_g⁺(g_j−

g_mean), where Σ

_g⁺ is the pseudo inverse of Σ

_g; and

using the computed coefficients and original PCA space to reconstruct the dense magnetic field map Bz, as f_j=Σ

_fc_g+f_mean.

18. The method of claim 9, wherein the producing of said intermediate magnetic image includes:

defining the M×

M data points as a vector g;

defining the linear model as Σ

;

extracting from Σ

the row corresponding to each of the M×

M data points to form a sub-eigenmatrix Σ

_g;

projecting g onto Σ

_g;

defining the establishment of coefficients as c_g=Σ

⁺_g(g_i−

μ

_g), where Σ

_g⁺ is the pseudo inverse of Σ

_g, μ

_g are extracted coefficients from a mean vector μ

of linear model Σ

; and

defining the intermediate magnetic image vector h as h=Σ

·

c_g+μ

.

19. The method of claim 9, wherein the identifying a three-dimensional position vector {right arrow over (p)} and momentum vector {right arrow over (J)} for said electric current further includes:

defining said intermediate magnetic image as B_z(i,j)(i=1, 2, . . . , N;

j=1, 2, . . . , N), the maximal point of the tangential components B′

_xy(i,j) of B_z (i,j) as referring to the 2D position (x_p, y_p) of the electric current, and the tangential components of B_z(i,j) as B_xy(i,j)=√

{square root over ((∂

B_z(i, j)/∂

x)²+(∂

B_z(i, j)/∂

y)²)}{square root over ((∂

B_z(i, j)/∂

x)²+(∂

B_z(i, j)/∂

y)²)}; and

said iterative process for identifying position vector {right arrow over (p)} and momentum vector {right arrow over (J)} for said electric current includes;

(a) defining the Biot-Sarvart Law as {right arrow over (B)}^m={right arrow over (J)}×

{right arrow over (R)}_m=−

{right arrow over (R)}_m×

{right arrow over (J)}, where {right arrow over (B)}^m={right arrow over (B)}({right arrow over (r)}_m), {right arrow over (J)}={right arrow over (J)}({right arrow over (p)}) and