System and method for measuring, estimating and displaying RMS current density maps

• US 6,370,414 B1
• Filed: 07/20/2000
• Issued: 04/09/2002
• Est. Priority Date: 01/23/1998
• Status: Expired due to Term

• Current Assignee: VSM Medtech Systems Incorporated (VSM Medtech, Ltd.)
• Original Assignee: CTF Systems, Inc. (VSM Medtech, Ltd.)
• Inventors: Robinson, Stephen E.
• Primary Examiner(s): Lateef, Marvin M.
• Assistant Examiner(s): Lin, Jeoyuh
• Application Number:
  US09/600,730
• Time in Patent Office: 628 Days
• Field of Search: 600/407, 600/409, 600/345, 600/373, 600/374, 600/378, 600/425, 324/300, 324/301, 324/302, 324/248, 324/244, 324/260, 324/262, 382/128
• US Class Current: 600/409
• CPC Class Codes: A61B 5/242 Detecting biomagnetic fields, e.g. magnetic fields produced by bioelectric currents
• CPC Class Codes: A61B 5/245 specially adapted for magnetoencephalographic [MEG] signals
• CPC Class Codes: G06F 2218/22 Source localisation; Inverse modelling

Abstract

A method of performing synthetic aperture magnetometery on the signals from a target organ using an array of biomagnetic sensors positioned in a predetermined manner around the target organ, each sensor in the array having a position vector and an orientation vector relative to a common coordinate system encompassing the target organ. The method includes the steps of: simultaneously measuring EM signals from each sensor positioned in the array for a selected time interval; computing a covariance matrix of the measured EM signals over a user-selected time sub-interval within the selected time interval; selecting a set of coordinates for a region of interest to be imaged and a distance between voxels to form a grid of voxels; computing a forward solution for a current element at each of the voxels for each of the sensors in the array sensors; computing an RMS current density estimate for each voxel from the covariance matrix and the forward solution for that voxel; and displaying the voxels estimating RMS current density as a first image. The method is particularly well suited for evaluating brain activity in a human subject.

Claims

1. A method of performing synthetic aperture magnetometry on the signals from a target organ using an array of biomagnetic sensors positioned in a predetermined manner around a target organ, each sensor in the array having a position vector and an orientation vector relative to a common coordinate system encompassing the target organ, the method comprising the steps of:

(i) simultaneously measuring EM signals from each sensor positioned in the array for a selected time interval;

(ii) computing a covariance matrix of the measured EM signals over a user-selected time sub-interval within the selected time interval;

(iii) selecting a set of coordinates for a region of interest to be imaged and a distance between voxels to form a grid of voxels;

(iv) computing a forward solution for a current element at each of the voxels for each of the sensors in the array sensors;

(v) computing an RMS current density estimate for each voxel from the covariance matrix and the forward solution for that voxel; and

(vi) displaying the voxels estimating RMS current density as a first image.

2. The method defined in claim 1, wherein the organ is a brain.

3. The method defined in claim 1, wherein the voxels are spaced to form Cartesian coordinate grid.

4. The method defined in claim 1, wherein the EM signals are magnetoencephalagraphic (MEG) signals.

5. The method defined in claim 1, wherein the EM signals are electroencephalographic (EEG) signals.

6. The method defined in claim 1, wherein the EM signals are a combination of MEG and EEG signals.

7. The method defined in claim 1, comprising, prior to Step (ii), the further Step of filtering the EM signals to a specified frequency band of interest.

8. The method defined in claim 1, wherein the further steps of repeating Steps (ii) through (vi) thereby computing a second RMS current density image over a second selected time interval and subtracting the second RMS current density image, voxel by voxel, from the first image to form a third difference image.

9. The method defined in claim 1, wherein the first RMS current density image is displayed relative to the anatomy of the organ.

10. The method defined in claim 8, wherein the second RMS current density image is displayed relative to the anatomy of the organ.

11. The method defined in claim 8, wherein the third difference image is displayed relative to the anatomy of the organ.

12. A method of performing synthetic aperture magnetometery on an electrically active organ comprising the steps of:

(i) measuring a plurality of EM data simultaneously from an array of sensors positioned around the organ;

(ii) measuring the position of an organ in a common frame of reference with the array of sensors;

(iii) computing a covariance matrix of the signals over a first selected interval of time;

(iv) selecting a set of coordinates of a region of interest to be imaged and a distance between voxels to form a grid of voxels;

(v) computing a forward solution for each sensor in the array of sensors at each of the voxels with each of the sensors current vector;

(vi) computing an RMS current density estimate for each voxel from said covariance matrix and from said forward solution for each said voxel; and

(vii) displaying the voxels estimating RMS current density as a first image.

13. The method defined in claim 12, wherein the organ is a brain.

14. The method defined in claim 12, wherein the voxels are spaced to form Cartesian coordinate grid.