Method for determining a position of a magnetic source

• US 20070167703A1
• Filed: 12/30/2005
• Published: 07/19/2007
• Est. Priority Date: 12/30/2005
• Status: Active Grant

• Current Assignee: DePuy Synthes Products LLC (Johnson & Johnson)
• Original Assignee: DePuy Synthes Products LLC (Johnson & Johnson)
• Inventors: Popovic, Radivoje, Sherman, Jason, DiSilvestro, Mark
• Granted Patent: US 8,862,200 B2
• Time in Patent Office: Days
• US Class Current: 600/407
• CPC Class Codes: A61B 2034/2051 Electromagnetic tracking systems
• CPC Class Codes: A61B 2090/3954 magnetic, e.g. NMR or MRI
• CPC Class Codes: A61B 5/06 Devices, other than using radiation, for detecting or locating foreign bodies for removing same A61B17/50 ; determining position of probes within or on the body of the patient
• CPC Class Codes: A61B 5/062 using magnetic field
• CPC Class Codes: A61B 5/064 using markers A61B5/062 takes precedence
• CPC Class Codes: A61B 5/4504 Bones A61B5/4547 takes precedence
• CPC Class Codes: A61B 5/4533 Ligaments
• CPC Class Codes: A61B 5/745 using a holographic display
• CPC Class Codes: A61B 90/36 Image-producing devices or illumination devices not otherwise provided for
• CPC Class Codes: A61B 90/39 Markers, e.g. radio-opaque or breast lesions markers
• CPC Class Codes: G01R 33/0206 Three-component magnetometers

Abstract

A method for determining a position of a magnetic source includes measuring a magnetic field generated by the magnetic source and determining components of the three-dimensional magnetic flux density of the magnetic field at a plurality of points in space based on such measurement. The method also includes estimating a position of the magnetic source and determining components of a theoretical three-dimensional magnetic flux density at the plurality of points in space based on the estimated position. The position of the magnetic source may then be determined by minimizing the difference between the components of the measured and corresponding theoretical three-dimensional magnetic flux density components.

Claims

1. A method for determining a position of a magnetic source coupled to a bone of a patient, the method comprising:

(i) measuring a magnetic field generated by the magnetic source with a magnetic sensor array, the magnetic field being defined by a plurality of three-dimensional magnetic flux densities;

(ii) generating first data indicative of components of the three-dimensional magnetic flux density of the magnetic source at a plurality of points in space based on the measuring step;

(iii) determining an estimated position of the magnetic source;

(iv) calculating second data indicative of a theoretical value of the components of the three-dimensional magnetic flux density of the magnetic source based on the estimated position;

(v) calculating a difference between the first data and the second data; and

(vi) repeating steps (iii)-(v) until the difference between the first data and the second data is less than a predetermined minimum threshold value.

2. The method of claim 1, wherein the measuring step comprises measuring an X-component and a Y-component of the three-dimensional magnetic flux density of the magnetic source at a point in space and positioning the magnetic sensor array over a longitudinal axis of the magnetic source such that the X-component and Y-component measurements are minimized.

3. The method of claim 1, wherein generating first data comprises generating voltage values indicative of an X-component value, a Y-component value, and a Z-component value of the three-dimensional magnetic flux density of the magnetic source at the plurality of points in space.

4. The method of claim 1, wherein determining an estimated position comprises estimating an X-coordinate value, a Y-coordinate value, and a Z-coordinate value of the location of at least one magnetic sensor of the magnetic sensor array with respect to the magnetic source.

5. The method of claim 4, wherein determining an estimated position comprises estimating a first value indicative of an amount of rotation about an X-axis of the magnetic source and a second value indicative of an amount of rotation about a Y-axis of the magnetic source.

6. The method of claim 1, wherein the estimating step comprises estimating values for at least five degrees of freedom of the magnetic source.

7. The method of claim 1, wherein calculating second data comprises calculating theoretical values of an X-component, a Y-component, and a Z-component of the three-dimensional magnetic flux density of the magnetic field at a point in space.

8. The method of claim 1, wherein calculating second data comprises calculating a theoretical value of an X-component of the three-dimensional magnetic flux density of the magnetic field using the following equation:

9. The method of claim 1, wherein calculating second data comprises calculating a theoretical value of a Y-component of the three-dimensional magnetic flux density of the magnetic field using the following equation:

10. The method of claim 1, wherein calculating second data comprises calculating a theoretical value of an Z-component of the three-dimensional magnetic flux density of the magnetic field using the following equation:

11. The method of claim 1, wherein calculating a difference between the first data and the second data comprises calculating a difference between a measured X-component and an estimated X-component of the three-dimensional magnetic flux density of the magnetic source at a point in space, calculating a difference between a measured Y-component and an estimated Y-component of the three-dimensional magnetic flux density of the magnetic source at a point in space, and calculating a difference between a measured Z-component and an estimated Z-component of the three-dimensional magnetic flux density of the magnetic source at a point in space.

12. The method of claim 1, wherein calculating a difference between the first data and the second data comprises calculating a sum of the squared difference between the first data and the second data.

13. The method of claim 12, wherein calculating the sum of the squared difference between the first data and the second data comprises calculating the sum of the squared difference between the first data and the second data using the following equation:

14. The method of claim 1, wherein calculating a difference between the first data and the second data comprises calculating a sum of the weighted square roots of the squared differences.

15. The method of claim 12, wherein determining the position of the magnetic source comprises using a local optimization algorithm to determine a minimum value of the sum of the squared difference between the first data and the second data by adjusting the estimated position.

16. The method of claim 12, wherein determining the position of the magnetic source comprises using a global optimization algorithm to determine a minimum value of the sum of the squared difference between the first data and the second data by adjusting the estimated position.

17. A method for determining a position of a magnetic source coupled to a bone of a patient, the method comprising:

measuring the three-dimensional magnetic flux density components of a magnetic field generated by the magnetic source at a plurality of points in space;

calculating components of a theoretical three-dimensional magnetic flux density at each of the plurality of points in space based on an estimated position of the magnetic source; and

calculating a sum of the squared difference between the measured three-dimensional magnetic flux density components and the theoretical three-dimensional magnetic flux density components; and

optimizing the sum such that the sum is reduced below a predetermined minimum threshold value.

18. The method of claim 17, wherein optimizing the sum comprises determining a local minimum value of the sum by adjusting the estimated position and determining the position of the magnetic source based on the local minimum value.

19. The method of claim 17, wherein determining the position of the magnetic source comprises determining values of at least five degrees of freedom of the magnetic source.

20. A method for determining a position of a magnetic source relative to a magnetic sensor array, the method comprising:

measuring the three-dimensional magnetic flux density components of a magnetic field generated by the magnetic source using the magnetic sensor array at a plurality of points in space;

determining an estimated position of the magnetic source relative to the magnetic sensor array;

calculating theoretical three-dimensional magnetic flux density components based on the estimated position at each of the plurality of points in space; and

reducing a sum of the squared difference between the measured three-dimensional magnetic flux density components at each point in space and the corresponding theoretical three-dimensional magnetic flux density components by adjusting the estimated position until the sum is below a predetermined threshold value.