Errors in systems using magnetic fields to locate objects

• US 6,553,326 B1
• Filed: 04/07/2000
• Issued: 04/22/2003
• Est. Priority Date: 04/07/2000
• Status: Expired due to Term

• Current Assignee: Northern Digital Inc. (Roper Technologies, Inc.)
• Original Assignee: Northern Digital Inc. (Roper Technologies, Inc.)
• Inventors: Kirsch, Stefan R., Schilling, Christian J.
• Primary Examiner(s): Barlow; John
• Assistant Examiner(s): LE, JOHN H
• Application Number:
  US09/544,539
• Time in Patent Office: 1,110 Days
• Field of Search: 702/36,38,57,72,65,84,153 324/207.12,207.17,248,318,345 600/407,424
• US Class Current: 702/65
• 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: G01R 33/00 Arrangements or instruments for measuring magnetic variables
• CPC Class Codes: G01V 3/08 operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices with electromagnetic waves G01V3/12

Abstract

A process detects distortions to magnetic location or orientation determinations. The process includes measuring a plurality of magnetic field values, determining one of a probe'"'"'s location and a probe'"'"'s orientation from an extremum of an optimization function. The measured values depend on the probe'"'"'s location and orientation. The optimization function depends on the measured field values and field values calculated from a model. The process also includes indicating that a distortion to the determining exists in response to the extremum belonging to a preselected range.

Claims

1. A process for detecting distortions to probe location or orientation determinations, comprising:

measuring a plurality of magnetic field values, the measured values depending on a probe'"'"'s location and a probe'"'"'s orientation;

determining one of the probe'"'"'s location and the probe'"'"'s orientation from an extremum of an optimization function, the function depending on differences between the measured field values and field values from a model, determining one of the probe'"'"'s location and the probe'"'"'s orientation includes;

guessing a location and orientation of the probe,

calculating magnetic field values associated with the guessed location and orientation from a model, and

evaluating a new value of the optimization function from the calculated and measured values;

rejecting the guessed location and orientation in response to the new value being farther from an extremum of the function than an earlier calculated value of the function; and

indicating that a distortion to the determining exists in response to the extremum belonging to a preselected range of values associated with presence of distortion.

2. The process of claim 1, further comprising:

providing a predicted value for one of the probe'"'"'s location and the probe'"'"'s orientation in response to the extremum belonging to another preselected range of values.

3. The process of claim 2, reperforming the determining to find another extremum in response to the extremum not corresponding to a global extremum of the function.

4. The process of claim 2, wherein values of the preselected ranges correspond to global extrema of the function.

5. The process of claim 2, wherein the optimization function is a least-squares sum of the measured field values and calculated field values.

6. The process of claim 2, wherein the another preselected range corresponds to a global minimum of the optimization function.

7. The process of claim 2, wherein the preselected range includes a value corresponding to a global minima of the least-squares function.

8. The process of claim 1, wherein the act of indicating is responsive to presence of a passive distortion to the measured magnetic field by one of a nearby conductor and a ferromagnetic object.

9. The process of claim 1, wherein the act of indicating is responsive to presence of a active distortion to the measured magnetic field by a nearby field source.

10. The process of claim 1, wherein the act of indicating is responsive to presence of a malfunction of one of hardware and software that processes data from a field sensor.

11. The process of claim 1, wherein the act of indicating is responsive to presence of a malfunction of one of hardware and software that controls a field source.

12. The process of claim 1, further comprising:

discarding one of the measured field values; and

redetermining one of the probe'"'"'s location and the probe'"'"'s orientation from remaining measured field values in response to finding that a distortion is present.

13. A program storage medium storing computer executable instructions, the instructions to cause a computer to:

receive data representative of measured magnetic field values that depend on a probe'"'"'s location and orientation;

determine one of the probe'"'"'s location and the probe'"'"'s orientation from an extremum of an optimization function, the function depending on differences between the measured field values and field values from a model, determine one of the probe'"'"'s location and the probe'"'"'s orientation includes;

guess a location and orientation of the probe,

calculate magnetic field values associated with the guessed location and orientation from a model, and

evaluate a new value of the optimization function from the calculated and measured values;

reject the guessed location and orientation in response to the new value being farther from an extremum of the function than an earlier calculated value of the function;

indicate that a distortion to the determining exists in response to the extremum belonging to a preselected range associated with presence of distortion; and

provide a predicted value for one of the probe'"'"'s location and the probe'"'"'s orientation in response to the extremum belonging to another preselected range of values.

14. The medium of claim 13, the instructions further causing the computer to:

find another extremum of the optimization function in response to a previously found extremum not corresponding to a global extremum of the function.

15. The medium of claim 13, wherein values of the preselected sets correspond to global extrema of the function.

16. The medium of claim 13, wherein the optimization function is a least-squares sum of the measured field values and calculated field values.

17. The medium of claim 16, wherein the another preselected range corresponds to a global minimum of the least-squares function.

18. The medium of claim 13, wherein the preselected range includes a value corresponding to a global extremum of the optimization function.

19. The medium of claim 13, wherein the instructions causing the computer to indicate are responsive to presence of a distortion to the measured magnetic field by one of a nearby conductor and a ferromagnetic object.

20. The medium of claim 13, wherein the instructions causing the computer to indicate are responsive to presence of a malfunction of one of hardware and software that processes data from a field sensor.

21. A process for detecting distortions to probe location or orientation determinations, comprising:

determining a preselected range of values associated with the presence of a certain condition;

measuring a plurality of magnetic field values, the measured values depending on a probe'"'"'s location and a probe'"'"'s orientation;

determining one of the probe'"'"'s location and the probe'"'"'s orientation from an extremum of an optimization function, the function depending on differences between the measured field values and field values from a model; and

indicating that a distortion to the determining exists in response to the extremum belonging to the preselected range of values associated with presence of a certain condition;

wherein determining a preselected range includes;

setting up a condition that distorts determinations of the probe'"'"'s location and the probe'"'"'s orientation from measured fields,

determining an actual probe location and orientation,

measuring magnetic field values depending on the location and orientation,

finding an extremum of an optimization function that depends on differences between the measured field values and field values calculated from a model and guessed probe location and position, and

assigning the extremum to the preselected range of values associated with the presence of the certain condition.

22. The process of claim 21, further comprising:

rejecting the extremum in response to the extremum being a local extremum.

23. The process of claim 21, wherein the finding comprises:

selecting an initial guess for the probe'"'"'s location and the probe'"'"'s orientation;

calculating magnetic field values associated with the initial guess from the model; and

evaluating a new value of the optimization function from the calculated and measured magnetic field values.

24. The process of claim 21, wherein the condition is a failure of one of an electronics module and software that processes data on magnetic field values received from one or more field sensors.

25. The process of claim 21, wherein the condition is a presence of a source of a magnetic field absent from the model.

26. The process of claim 21, wherein the condition is a presence of one of a conductive object and a ferromagnetic object.

27. The process of claim 21, further comprising repeating the acts of setting up a condition, determining, measuring, finding, and assigning for a second type of condition.