Resolution of magnetic dipole ambiguity in position tracking measurements

• US 20060241394A1
• Filed: 03/03/2006
• Published: 10/26/2006
• Est. Priority Date: 02/22/2005
• Status: Active Grant

• Current Assignee: Biosense Webster Incorporated (Johnson & Johnson)
• Original Assignee: Biosense Webster Incorporated (Johnson & Johnson)
• Inventors: Ludwin, Doron, Bar-tal, Meir, Govari, Assaf, Shalgi, Avi, Keidar, Yaron, Reznick, Dudi
• Granted Patent: US 8,180,430 B2
• Time in Patent Office: Days
• US Class Current: 600/423
• CPC Class Codes: A61B 2034/2051 Electromagnetic tracking systems
• CPC Class Codes: A61B 2090/3958 emitting a signal
• 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 5/062 using magnetic field
• CPC Class Codes: A61B 90/36 Image-producing devices or illumination devices not otherwise provided for

Abstract

A method for position tracking includes using first and second field generators located at respective different first and second locations to generate respective first and second magnetic fields in a vicinity of first and second objects. The first and second fields are measured using first and second position sensors respectively associated with the first and second objects. First and second potential relative coordinates of the first object relative to the second object are calculated responsively to the first and second magnetic field. The potential relative coordinates are processed in order to determine a correct relative coordinate of the first object relative to the second object.

Claims

1. A method for position tracking, comprising:

using first and second field generators located at respective different first and second locations, generating respective first and second magnetic fields in a vicinity of first and second objects;

measuring the first and second fields using first and second position sensors respectively associated with the first and second objects;

calculating first potential relative coordinates of the first object relative to the second object responsively to the first magnetic field, and second potential relative coordinates of the first object relative to the second object responsively to the second magnetic field; and

processing the first and second potential relative coordinates in order to determine a correct relative coordinate of the first object relative to the second object by;

comparing the first potential relative coordinates to the second potential relative coordinates; and

comparing at least one of the first and second potential relative coordinates to a-priori positional information with respect to at least one of the field generators and at least one of the position sensors.

2. The method according to claim 1, wherein one of the first and second objects comprises an implant inserted into a body of a patient, wherein the other of the first and second objects comprises a tool, and wherein processing the first and second potential relative coordinates comprises tracking a relative position of the tool with respect to the implant.

3. The method according to claim 1, wherein processing the first and second potential relative coordinates comprises invalidating a relative coordinate value in one of the first and second potential relative coordinates that does not appear in the other of the first and second potential relative coordinates.

4. The method according to claim 1, wherein processing the first and second potential relative coordinates comprises invalidating a relative coordinate value in at least one of the first and second potential relative coordinates responsively to an inconsistency between the relative coordinate value and the a-priori positional information.

5. The method according to claim 1, and comprising providing the a-priori positional information by positioning the at least one of the field generators so as to cause at least one of the magnetic fields to have a known orientation with respect to the at least one of the position sensors.

6. The method according to claim 5, wherein positioning the at least one of the field generators comprises marking the at least one of the field generators with a mark indicative of the orientation of the at least one of the magnetic fields.

7. The method according to claim 1, and comprising providing the a-priori positional information by positioning the first field generator at a first distance from the first object along an axis, positioning the second field generator on an opposite side of the first object along the axis at a second distance from the first object different from the first distance, so as to cause the first and second fields measured at the first object to have different magnitudes.

8. The method according to claim 1, wherein the first and second field generators have respective first and second axes, and comprising providing the a-priori positional information by positioning the first and second field generators at a known distance from one another and so that the first and second axes are parallel.

9. The method according to claim 1, and comprising providing the a-priori positional information by defining a working volume specifying a valid range of location coordinates of the first and second objects, and positioning the first field generator at a sufficient distance from the first and second objects so that at least one of the first and second potential relative coordinates falls outside the working volume.

10. The method according to claim 1, wherein the first and second magnetic fields comprise at least one of dipole and semi-dipole magnetic fields.

11. A method for position tracking, comprising:

using a co-axial pair of first and second field generators fixed at a respective known offset from one another along a common axis in a location pad, generating respective first and second magnetic fields in a vicinity of an object;

measuring the first and second magnetic fields using a position sensor associated with the object; and

calculating unambiguous position coordinates of the object with respect to the location pad based on the measured first and second magnetic fields and the known offset.

12. The method according to claim 11, and comprising generating additional magnetic fields using one or more additional co-axial pairs of field generators fixed at respective known offsets from one another along respective different axes, and measuring the additional magnetic fields by the position sensor, wherein calculating the unambiguous position coordinates comprises calculating the coordinates responsively to the measured additional magnetic fields and the respective known offsets.

13. The method according to claim 11, wherein generating the first and second magnetic fields comprises driving the first and second field generators with respective first and second drive signals having respective different first and second frequencies.

14. A position tracking system, comprising:

first and second field generators located at respective different first and second locations, which are arranged to generate respective first and second magnetic fields in a vicinity of first and second objects;

first and second position sensors respectively associated with the first and second objects, which are arranged to measure the first and second fields;

a processor, which is arranged to calculate first potential relative coordinates of the first object relative to the second object responsively to the first magnetic field, to calculate second potential relative coordinates of the first object relative to the second object responsively to the second magnetic field, and to process the first and second potential relative coordinates in order to determine a correct relative coordinate of the first object relative to the second object by comparing the first potential relative coordinates to the second potential relative coordinates, and comparing at least one of the first and second potential relative coordinates to a-priori positional information with respect to at least one of the field generators and at least one of the position sensors.

15. The system according to claim 14, wherein one of the first and second objects comprises an implant inserted into a body of a patient, wherein the other of the first and second objects comprises a tool, and wherein the processor is arranged to track a relative position of the tool with respect to the implant.

16. The system according to claim 14, wherein the processor is arranged to invalidate a relative coordinate value in one of the first and second potential relative coordinates that does not appear in the other of the first and second potential relative coordinates.

17. The system according to claim 14, wherein the processor is arranged to invalidate a relative coordinate value in at least one of the first and second potential relative coordinates responsively to an inconsistency between the relative coordinate value and the a-priori positional information.

18. The system according to claim 14, wherein the at least one of the field generators is positioned so as to cause at least one of the magnetic fields to have a known orientation with respect to the at least one of the position sensors, thereby providing the a-priori positional information.

19. The system according to claim 18, wherein the at least one of the field generators comprises a mark indicative of the orientation of the at least one of the magnetic fields.

20. The system according to claim 14, wherein the first and second magnetic fields comprise at least one of dipole and semi-dipole magnetic fields.

21. A position tracking system, comprising:

a location pad comprising a co-axial pair of first and second field generators fixed at a known offset from one another along a common axis, which are arranged to generate respective first and second magnetic fields in a vicinity of an object;

a position sensor associated with the object, which is arranged to measure the first and second magnetic fields; and

a processor, which is arranged to calculate unambiguous position coordinates of the object with respect to the location pad based on the measured first and second magnetic fields and the known offset.

22. The system according to claim 21, wherein the location pad comprises one or more additional co-axial pairs of field generators fixed at respective known offsets from one another along respective different axes, which are arranged to generate additional magnetic fields, wherein the position sensor is further arranged to measure the additional magnetic fields, and wherein the processor is arranged to calculate the unambiguous position coordinates responsively to the measured additional magnetic fields and the respective known offsets.

23. The system according to claim 21, wherein the first and second field generators are driven with respective first and second drive signals having respective different first and second frequencies.

24. A computer software product used in a position tracking system, the product comprising a computer-readable medium, in which program instructions are stored, which instructions, when read by a computer, cause the computer to control first and second field generators located at respective different first and second locations so as to generate respective first and second magnetic fields in a vicinity of first and second objects, to accept measurements of the first and second fields from first and second position sensors respectively associated with the first and second objects, to calculate first potential relative coordinates of the first object relative to the second object responsively to the first magnetic field, to calculate second potential relative coordinates of the first object relative to the second object responsively to the second magnetic field, and to process the first and second potential relative coordinates in order to determine a correct relative coordinate of the first object relative to the second object by comparing the first potential relative coordinates to the second potential relative coordinates, and comparing at least one of the first and second potential relative coordinates to a-priori positional information with respect to at least one of the field generators and at least one of the position sensors.

25. The product according to claim 24, wherein one of the first and second objects comprises an implant inserted into a body of a patient, wherein the other of the first and second objects comprises a tool, and wherein the instructions cause the computer to track a relative position of the tool with respect to the implant.

26. The product according to claim 24, wherein the instructions cause the computer to invalidate a relative coordinate value in one of the first and second potential relative coordinates that does not appear in the other of the first and second potential relative coordinates.

27. The product according to claim 24, wherein the instructions cause the computer to invalidate a relative coordinate value in at least one of the first and second potential relative coordinates responsively to an inconsistency between the relative coordinate value and the a-priori positional information.