Electromagnetic position single axis system

• US 6,484,118 B1
• Filed: 07/20/2000
• Issued: 11/19/2002
• Est. Priority Date: 07/20/2000
• Status: Active Grant

• Current Assignee: Biosense, Inc. (Cardinal Health, Inc.)
• Original Assignee: Biosense, Inc. (Cardinal Health, Inc.)
• Inventors: Govari, Assaf
• Primary Examiner(s): Hilten, John S.
• Assistant Examiner(s): Sun, Xiuqin
• Application Number:
  US09/620,316
• Time in Patent Office: 852 Days
• Field of Search: 600/424, 733/04.C, 702/150
• US Class Current: 702/150
• CPC Class Codes: A61B 2034/2051 Electromagnetic tracking systems
• CPC Class Codes: A61B 2034/2072 Reference field transducer attached to an instrument or patient
• 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: G01B 7/004 for measuring coordinates of points
• CPC Class Codes: H01F 2005/027 wound on formers for receiving several coils with perpendicular winding axes, e.g. for antennae or inductive power transfer

Abstract

A system for determining the position of a medical device having a sensor comprises a plurality of field radiators wherein each field radiator has a plurality of radiator elements. Each radiator element generates a magnetic field such that each magnetic field is distinct from one another due to the use of a different frequency through simultaneous energizing of the radiator elements. A signal processor is operatively connected to the field radiators and the sensor of the medical device for receiving a sensing signal from the sensor indicative of the magnetic field sensed at the sensor. Alternative field radiator arrangements are also provided in conjunction with a novel algorithm utilizing a global convergent technique.

Claims

1. A system for determining the position of a medical device having a sensor, said system comprising:

a plurality of field radiators, each field radiator having a plurality of radiator elements, each radiator element generating an electromagnetic field distinct from one another through simultaneous energizing of said radiator elements;

a signal processor operatively connected to said field radiators and said sensor of said medical device, said signal processor receiving a sensing signal from said sensor indicative of the electromagnetic field sensed at said sensor, said sensing signal defining a measured electromagnetic field at said sensor, said signal processor also having a desired range of accuracy for said system stored therein, said signal processor including;

(a) an initial position estimator for establishing an initial position estimate for said sensor;

(b) a magnetic field calculator for calculating the electromagnetic field at said initial position estimate;

(c) a steepest descent calculator for calculating a steepest descent of said calculated electromagnetic field to said measured electromagnetic field; and

(d) a new position estimate calculator for calculating a new position estimate of said sensor based on said steepest descent;

wherein said signal processor determines said position of said sensor when said new position estimate of said sensor is within said desired range of accuracy.

2. The system according to claim 1, wherein said signal processor includes pre-stored calibration information.

3. The system according to claim 1, wherein said desired range of accuracy is ≦

0.0001 cm.

4. The system according to claim 2, wherein said desired range of accuracy is ≦

0.0001 cm.

5. The system according to claim 1, wherein said field radiators are arranged in a fixed arrangement.

6. The system according to claim 5, wherein said signal processor determines a position and orientation of said sensor.

7. The system according to claim 6, wherein said position is in three different directions (X, Y, Z) and at least two orientations (pitch and yaw).

8. The system according to claim 7, wherein said radiator elements of said field radiators are mutually orthogonal.

9. The system according to claim 7, wherein said radiator elements of said field radiators are not mutually orthogonal.

10. The system according to claim 8, wherein said radiator elements of said field radiators are not co-located.

11. The system according to claim 9, wherein said radiator elements of said field radiators are not co-located.

12. The system according to claim 8, wherein said radiator elements of said field radiators are co-located.

13. The system according to claim 9, wherein said radiator elements of said field radiators are co-located.

14. The system according to claim 7, wherein said system further comprises a display operatively connected to said signal processor for displaying said position and said orientation of said sensor.

15. The system according to claim 14, wherein said display displays said position and said orientation of said sensor with respect to an anatomical feature of a patient.

16. The system according to claim 15, wherein said system further comprises a reference device for establishing a frame of reference.

17. A system for determining the position of a medical device having a sensor, said system comprising:

a plurality of field radiators, each field radiator having a plurality of radiator elements, each radiator element generating an electromagnetic field distinct from one another through simultaneous energizing of said radiator elements;

a signal processor operatively connected to said field radiators and said sensor of said medical device, said signal processor receiving a sensing signal from said sensor indicative of the electromagnetic field sensed at said sensor, said sensing signal defining a measured electromagnetic field at said sensor, said signal processor also having a desired range of accuracy for said system stored therein, said signal processor including;

(a) an initial position estimator for establishing an initial position estimate for said sensor;

(b) a magnetic field calculator for calculating the electromagnetic field at said initial position estimate;

(c) a global converger for determining the minimum field at said sensor based on a direction of the initial position estimate; and

(d) a new position estimate calculator for calculating a new position estimate of said sensor based on said steepest descent;

wherein said signal processor determines said position of said sensor when said new position estimate of said sensor is within said desired range of accuracy.

18. The system according to claim 17, wherein said signal processor includes pre-stored calibration information.

19. The system according to claim 18, wherein said desired range of accuracy is ≦

0.0001 cm.

20. A method of determining the position and orientation of a sensor relative to a plurality of field radiators of known location, each of said field radiators comprising a plurality of co-located radiator elements, each radiator element generating an electromagnetic field distinct from one another through simultaneous energizing of said radiator elements, said sensor producing sensing signals indicative of a measured electromagnetic field at said sensor, said method comprising the steps of:

(a) establishing a desired range of accuracy;

(b) determining an initial estimate of sensor position and orientation;

(c) calculating an electromagnetic field at the estimated sensor position and orientation;

(d) calculating the steepest descent from the calculated electromagnetic field at the estimated sensor position and orientation to the measured electromagnetic field at the sensor;

(e) calculating a new estimate for said sensor position and orientation from said steepest descent;

(f) iterating steps (c)-(e) based on said newly calculated sensor position and orientation estimate of step (e) to refine the sensor position and orientation estimate.

21. The method according to claim 20, wherein said desired range of accuracy is ≦

0.0001 cm.

22. The method according to claim 21, including establishing and storing calibration information for said field radiators.

23. The method according to claim 22, wherein said calibration information is used at steps (c) and (d) for calculating a new estimate for said sensor position and orientation.

24. The method according to claim 23, including refining said initial estimate of sensor position and orientation using a dipole approximation after step (b).

25. The method according to claim 24, including determining the position of said sensor in three different directions (X,Y,Z) and orientation of said sensor in at least two orientations (pitch and yaw).

26. The method according to claim 25, including displaying said position and orientation of said sensor.

27. The method according to claim 26, including displaying said position and orientation of said sensor with respect to an anatomical feature of a patient.

28. A method of determining the position and orientation of a sensor relative to a plurality of field radiators of known location, each of said field radiators comprising a plurality of co-located radiator elements, each radiator element generating an electromagnetic field distinct from one another through simultaneous energizing of said radiator elements, said sensor producing sensing signals indicative of a measured electromagnetic field at said sensor, said method comprising the steps of:

(a) establishing a desired range of accuracy;

(b) determining an initial estimate of sensor position and orientation;

(c) calculating an electromagnetic field at the estimated sensor position and orientation;

(d) determining a minimum electromagnetic field at said sensor based on a direction of the initial position estimate using a global convergent technique;

(e) calculating a new estimate for said sensor position and orientation based on said minimum electromagnetic field;

(f) iterating steps (c)-(e) based on said newly calculated sensor position and orientation estimate of step (e) to refine the sensor position and orientation estimate.

29. The method according to claim 28, wherein said desired range of accuracy is ≦

0.0001 cm.

30. The method according to claim 29, including establishing and storing calibration information for said field radiators.

31. The method according to claim 30, wherein said calibration information is used at steps (c) and (d) for calculating a new estimate for said sensor position and orientation.