DISTORTION-IMMUNE POSITION TRACKING USING FREQUENCY EXTRAPOLATION

• US 20080125646A1
• Filed: 08/21/2006
• Published: 05/29/2008
• Est. Priority Date: 08/21/2006
• Status: Active Grant

• Current Assignee: Biosense Webster Incorporated (Johnson & Johnson)
• Original Assignee: Biosense Webster Incorporated (Johnson & Johnson)
• Inventors: Govari, Assaf, Bar-Tal, Meir, Goldin, Alexander
• Granted Patent: US 8,326,402 B2
• Time in Patent Office: Days
• US Class Current: 600/424
• 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 34/20 Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis
• 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 90/36 Image-producing devices or illumination devices not otherwise provided for

Abstract

A method for tracking a position of an object includes generating alternating current (AC) magnetic fields at two or more frequencies in a vicinity of the object using at least one field generator. The AC fields are sensed using a field sensor associated with the object. Corresponding AC data points that are indicative of amplitudes and directions of the AC fields at the field sensor are produced, wherein at least some of the sensed AC fields are subject to a distortion. A dependence of the AC data points on the frequencies of the AC fields is extrapolated to a target frequency so as to determine the amplitudes and directions of the AC fields with a reduced level of the distortion. Position coordinates of the object relative to the at least one field generator are calculated responsively to the extrapolated data points.

Claims

1. A method for tracking a position of an object, comprising:

using at least one field generator, generating alternating current (AC) magnetic fields at two or more frequencies in a vicinity of the object;

using a field sensor associated with the object, sensing the AC fields and producing corresponding AC data points that are indicative of amplitudes and directions of the AC fields at the field sensor, wherein at least some of the sensed AC fields are subject to a distortion;

extrapolating a dependence of the AC data points on the frequencies of the AC fields to a target frequency so as to determine the amplitudes and directions of the AC fields with a reduced level of the distortion; and

calculating position coordinates of the object relative to the at least one field generator responsively to the extrapolated data points.

2. The method according to claim 1, and comprising inserting the object into an organ of a patient, wherein calculating the position coordinates of the object comprises tracking the position of the object inside the organ.

3. The method according to claim 2, wherein the at least one field generator is associated with the object, and wherein the field sensor is located externally to the organ.

4. The method according to claim 1, wherein the distortion is caused by a field-distorting object subjected to at least some of the AC fields, and wherein the object comprises a material selected from a group consisting of metallic, paramagnetic and ferromagnetic materials.

5. The method according to claim 1, wherein the target frequency comprises a zero frequency.

6. The method according to claim 1, wherein the target frequency comprises an infinite frequency.

7. The method according to claim 1, wherein extrapolating the dependence comprises fitting a function to the AC data points and the frequencies of the AC fields, and determining a value of the function at the target frequency.

8. The method according to claim 7, wherein the function is selected from a group consisting of a polynomial function and a rational function, and wherein fitting the function comprises assigning values to coefficients of the function.

9. The method according to claim 7, wherein extrapolating the dependence comprises defining the function based on previously-acquired field measurements.

10. The method according to claim 9, wherein defining the function comprises applying a principal components analysis (PCA) method to produce PCA base functions based on the previously-acquired field measurements and defining the function using the PCA base functions.

11. A system for tracking a position of an object, comprising:

at least one field generator, which is arranged to generate alternating current (AC) magnetic fields at two or more frequencies in a vicinity of the object;

a field sensor associated with the object, which is arranged to sense the AC fields and to produce corresponding AC data points that are indicative of amplitudes and directions of the AC fields at the field sensor, wherein at least some of the sensed AC fields are subject to a distortion; and

a processor, which is arranged to extrapolate a dependence of the AC data points on the frequencies of the AC fields to a target frequency so as to determine the amplitudes and directions of the AC fields with a reduced level of the distortion, and to calculate position coordinates of the object relative to the at least one field generator responsively to the extrapolated data points.

12. The system according to claim 11, wherein the object is adapted to be inserted into an organ of a patient, and wherein the processor is arranged to track the position of the object inside the organ.

13. The system according to claim 12, wherein the at least one field generator is associated with the object, and wherein the field sensor is located externally to the organ.

14. The system according to claim 11, wherein the distortion is caused by a field-distorting object subjected to at least some of the AC fields, and wherein the object comprises a material selected from a group consisting of metallic, paramagnetic and ferromagnetic materials.

15. The system according to claim 11, wherein the target frequency comprises a zero frequency.

16. The system according to claim 11, wherein the target frequency comprises an infinite frequency.

17. The system according to claim 11, wherein the processor is arranged to fit a function to the AC data points and the frequencies of the AC fields, and to determine a value of the function at the target frequency.

18. The system according to claim 17, wherein the function is selected from a group consisting of a polynomial function and a rational function, and wherein the processor is arranged to fit the function by assigning values to coefficients of the function.

19. The system according to claim 17, wherein the processor is arranged to define the function based on previously-acquired field measurements.

20. The system according to claim 19, wherein the processor is arranged to apply a principal components analysis (PCA) method to produce PCA base functions based on the previously-acquired field measurements, and to define the function using the PCA base functions.

21. A computer software product used in a system for tracking a position of an object, the product comprising a computer-readable medium, in which program instructions are stored, which instructions, when read by the computer, cause the computer to control at least one field generator so as to generate alternating current (AC) magnetic fields at two or more frequencies in a vicinity of the object, to accept from a field sensor associated with the object AC data points indicative of amplitudes and directions of the respective AC fields sensed by the field sensor, wherein at least some of the sensed AC fields are subject to a distortion, to extrapolate a dependence of the AC data points on the frequencies of the AC fields to a target frequency so as to determine the amplitudes and directions of the AC fields with a reduced level of the distortion, and to calculate position coordinates of the object relative to the at least one field generator responsively to the extrapolated data points.