System and Method for Measuring Position and Orientation Using Distortion-Compensated Magnetic Fields

• US 20080162074A1
• Filed: 02/26/2008
• Published: 07/03/2008
• Est. Priority Date: 09/20/2004
• Status: Active Grant

• Current Assignee: Northern Digital Inc. (Roper Technologies, Inc.)
• Original Assignee: Ascension Technology Corporation (Roper Technologies, Inc.)
• Inventors: Schneider, Mark R.
• Granted Patent: US 7,788,060 B2
• Time in Patent Office: Days
• US Class Current: 702/150
• CPC Class Codes: A61B 2034/2051 Electromagnetic tracking systems
• CPC Class Codes: A61B 34/20 Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis
• CPC Class Codes: A61B 90/36 Image-producing devices or illumination devices not otherwise provided for

Abstract

An electromagnetic tracking system and a distortion compensation method that utilize a lead-lag network model to compensate for position and orientation distortion caused by eddy currents formed in one more conductive distorters located within a tracking environment during electromagnetic tracking of one or more objects. The method is adaptive relative to the amount of distortion cause by the conductive distorters.

Claims

1. A method of determining the location of an object using a tracking system having a distortion threshold, comprising the steps of:

a) collecting magnetic field data from at least one sensor, said magnetic field data containing frequency data for at least one frequency;

b) processing said frequency data so as to obtain a real response component and an imaginary response component for said at least one frequency; and

c) determining whether to compensate for magnetic field distortion as a function of said real response component, said imaginary response component and the distortion threshold.

2. A method according to claim 1, wherein the distortion threshold is a function of a norm of residuals and step c) includes the step comparing to the distortion threshold a ratio of said imaginary component to said real component.

3. A method according to claim 2, further comprising, when said ratio is no less than said distortion threshold, the step of compensating for magnetic field distortion based on a representation of said frequency data comprising at least one lead-lag network having a plurality of parameters.

4. A method according to claim 3, further comprising, when said ratio is no less than said distortion threshold, the steps of:

a) calculating said plurality of parameters and a norm that is a function of said parameter; and

b) comparing said norm to said distortion threshold.

5. A method according to claim 4, further comprising, when said norm is less than said distortion threshold, the step of calculating an adjusted B-field.

6. A method according to claim 4, further comprising, when said norm is not less than said distortion threshold, the step of compensating for magnetic field distortion based on a representation of said frequency data comprising at least two lead-lag networks.

7. A computer readable medium containing computer instructions for determining the location of an object using a tracking system having a distortion threshold, said computer instructions comprising:

a) a first set of instruction for collecting magnetic field data from at least one sensor, said magnetic field data containing frequency data for at least one frequency;

b) a second set of instructions for processing said frequency data so as to obtain a real response component and an imaginary response component for said at least one frequency; and

c) a third set of instructions for determining whether to compensate for magnetic field distortion as a function of said real response component, said imaginary response component and the distortion threshold.

8. A computer readable medium according to claim 7, wherein the distortion threshold is a function of a norm of residuals and said third set of instructions includes instructions for comparing to the distortion threshold a ratio of said imaginary component to said real component.

9. A computer readable medium according to claim 8, further comprising a fourth set of instructions for compensating, when said ratio is no less than said distortion threshold, for magnetic field distortion based on a representation of said frequency data comprising at least one lead-lag network having a plurality of parameters.

10. A computer readable medium according to claim 9, further comprising:

a) a fifth set of instructions for calculating, when said ratio is no less than said distortion threshold, said plurality of parameters and a norm that is a function of said parameter; and

b) a sixth set of instructions for comparing said norm to said distortion threshold.

11. A computer readable medium according to claim 10, further comprising a seventh set of instructions for calculating an adjusted B-field when said norm is less than said distortion threshold.

12. A computer readable medium according to claim 10, further comprising an eighth set of instructions for compensating for magnetic field distortion based on a representation of said frequency data comprising at least two lead-lag networks when said norm is not less than said distortion threshold.

13. A system for determining the location of an object using a tracking system having a distortion threshold based on a norm of residuals, comprising:

a) a distortion threshold;

b) at least one sensor; and

c) a processor having an input for receiving magnetic field data from said at least one sensor and operatively configured to;

i) collect said magnetic field data, said magnetic field data containing frequency data for at least one frequency;

ii) process said frequency data so as to obtain a real response component and an imaginary response component for said at least one frequency; and

iii) determine whether to compensate for magnetic field distortion as a function of said real response component, said imaginary response component and the distortion threshold.

14. A system according to claim 13, wherein the distortion threshold is a function of a norm of residuals and said processor is further operatively configured to compare to the distortion threshold a ratio of said imaginary component to said real component.

15. A system according to claim 14, wherein said processor is further operatively configured to compensate, when said ratio is no less than said distortion threshold, for magnetic field distortion based on a representation of said frequency data comprising at least one lead-lag network having a plurality of parameters.

16. A system according to claim 15, wherein said processor is further operatively configured to:

a) calculate, when said ratio is no less than said distortion threshold, said plurality of parameters and a norm that is a function of said parameter; and

b) comparing said norm to said distortion threshold.

17. A system according to claim 16, wherein said processor is further operatively configured to calculate an adjusted B-field when said norm is less than said distortion threshold.

18. A system according to claim 16, said processor is further operatively configured to compensate, when said norm is not less than said distortion threshold, for magnetic field distortion based on a representation of said frequency data comprising at least two lead-lag networks.