Method and apparatus for determining position of object

• US 5,752,513 A
• Filed: 06/07/1995
• Issued: 05/19/1998
• Est. Priority Date: 06/07/1995
• Status: Expired due to Term

• Current Assignee: Biosense, Inc. (Cardinal Health, Inc.)
• Original Assignee: Biosense, Inc. (Cardinal Health, Inc.)
• Inventors: Gasparakis, Charidimos E., Acker, David E.
• Primary Examiner(s): Lateef, Marvin M.
• Assistant Examiner(s): SHAW, SHAWNA JEANNINE
• Application Number:
  US08/479,671
• Time in Patent Office: 1,077 Days
• Field of Search: 128/653.1, 128/653.2, 128/897, 128/899, 606/130, 324/309, 324/207.11, 324/204.13, 324/207.17, 324/207.22, 378/205, 340/686
• US Class Current: 600/424
• 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 5/064 using markers A61B5/062 takes precedence
• CPC Class Codes: G01B 7/004 for measuring coordinates of points

Abstract

Apparatus for determining the position of a probe in a sensing volume includes a plurality of magnetic field generating sources for generating different magnetic fields in the sensing volume, where the sources have a planar configuration and are positioned so that they at least partially overlap one another in horizontal extent and so that the sensing volume extends outwardly from the sources. The probe is provided with sensors which detect magnetic field components of fields generated by the sources. The position of the probe can be determined from the detected magnetic components. Methods for determining the probe position are also included.

Claims

1. Apparatus for determining the position of an object comprising:

(a) a plurality of magnetic field generating coils for generating a plurality of different magnetic fields in a sensing volume, said coils being arranged in a stacked, overlapping group such that the sensing volume is positioned on one side of said overlapping group of coils taken together and not between any of said coils;

(b) control means for actuating said coils to generate said magnetic fields in a predetermined sequence,

(c) a sensor connected to the object and movable within said sensing volume, and adapted to detect magnetic field components in at least two different local directions relative to the sensor, and

(d) calculation means for determining the position of said sensor from the magnetic field components detected by said sensor during generation of said magnetic fields.

2. Apparatus as claimed in claim 1, further comprising control means for generating a plurality of successive magnetic fields within said sensing volume, said control means being operative to actuate said coils to generate said magnetic fields in sequence, said calculation means being operative to determine the position of said object within said sensing volume from said magnetic field components detected during generation of said magnetic fields.

3. Apparatus as claimed in claim 2, wherein said coils are formed from a plurality of conductor segments, and said calculation means calculates the magnetic field contribution B of each said conductor segment in accordance with the equation:

space="preserve" listing-type="equation">|B(x,y,z)|=I(cos(A1)+cos(A2))/(cR)

where I is the current through said conductor segment, c is the speed of light, R is the distance between the location of the sensor at point r=(x,y,z) and said conductor segment, A1 is the angle between the sensor and one end of said conductor segment, and A2 is the angle between the sensor and the other end of said conductor segment.

4. Apparatus as claimed in claim 3, wherein said conductor segments of each said source form a polygonal shape.

5. Apparatus as claimed in claim 4, wherein said conductor segments of each said source form a triangular shape.

6. Apparatus as claimed in claim 5, wherein said conduct segments form an isosceles triangle.

7. Apparatus as claimed in claim 5, wherein said plurality of coils comprises three coils.

8. Apparatus as claimed in claim 5, wherein said plurality of coils comprises four coils.

9. Apparatus as claimed in claim 8, wherein said coils are arranged to overlap one another in horizontal extent to produce a eight-pointed star.

10. Apparatus as claimed in claim 5, wherein the conductor segments are rectangular in cross-section.

11. Apparatus as claimed in claim 5, wherein said coils have center points which are spaced apart from one another at a center distance.

12. Apparatus as claimed in claim 11, wherein said center distance is about 10 cm.

13. Apparatus as claimed in claim 5, wherein said sensing volume extends outwardly to a maximum distance of interest, and the ratio of said maximum distance of interest to an effective diameter of said coils is less than or equal to two, said effective diameter comprising a diameter of a circle circumscribing said coils.

14. Apparatus as claimed in claim 1, wherein said plurality of coils comprises at least two said coils, and said apparatus further includes dipole means for generating one or more magnetic dipole fields within said sensing volume, said calculation means being further operative to determine the position of said probe within said sensing volume from said magnetic field components detected by said sensor during generation of said magnetic fields by said coils and magnetic field components detected by said sensor from said dipole means.

15. Apparatus for determining the position of an object comprising:

(a) a plurality of magnetic field generating coils for generating a plurality of different magnetic fields in a sensing volume, said coils being arranged in a stacked, overlapping group such that the sensing volume is positioned on one side of said overlapping group of coils taken together and not between any of said coils, each of said coils including conductors encompassing an enclosed area, said coils being positioned so that said enclosed areas of said coils at least partially overlap one another in horizontal extent and define an overlap area, said overlap area encompassing at least about fifty percent of the enclosed area of each of said coils;

(b) control means for actuating said coils to generate said magnetic fields in a predetermined sequence;

(c) a sensor connected to the object and movable within said sensing volume, said sensor adapted to detect magnetic field components in at least two different local directions relative to the sensor; and

(d) calculation means for determining the position of said sensor from the magnetic field components detected by said sensor during generation of said magnetic fields.

16. A method of determining the position of an object within a sensing volume comprising the steps of:

(a) actuating a plurality of magnetic field-generating coils arranged in a stacked, overlapping group to generate a plurality of magnetic fields in a predetermined sequence such that at least two of said coils generate fields varying quasi-linearly with position within near-field volumes, the near-field volumes of said coils intersecting one another within a sensing volume positioned on one side of said overlapping group of coils taken together and not between any of said coils;

(b) measuring magnetic field components in the sensing volume above the near-field areas of said coils in at least two different local directions relative to a sensor connected to the object during generation of said fields; and

(c) determining the position of said sensor from said magnetic field components detected during generation of said magnetic fields.

17. A method a claimed in claim 16, wherein said coils are formed from a plurality of conductor segments, and said step of determining the position of said sensor includes the step of calculating magnetic field contributions of each of said conductor segments of said coils.

18. A method as claimed in claim 17, wherein said step of calculating comprises calculating the magnetic field contribution B of each said conductor segment in accordance with the equation:

space="preserve" listing-type="equation">|B(x,y,z)|=I(cos(A1)+cos(A2))/(cR)

where I is the current through said conductor segment, c is the speed of light, R is the distance between the location of the sensor at point r=(x,y,z) and said conductor segment, A1 is the angle between the sensor and one end of said conductor segment, and A2 is the angle between the sensor and the other end of said conductor segment.

19. A method of determining the position of an object within a sensing volume comprising the steps of:

(a) generating a plurality of different magnetic fields in a predetermined sequence in the sensing volume from a plurality of magnetic field generating coils arranged in a stacked, overlapping group such that the sensing volume is positioned on one side of said overlapping group of coils taken together and not between any of said coils;

(b) measuring magnetic field components of said magnetic fields generated from said plurality of coils in at least two different local directions relative to a sensor connected to the object during generation of said fields; and

(c) determining the position of said sensor from said magnetic field components detected during generation of said magnetic fields.

20. A method of determining the position of an object within a sensing volume comprising the steps of:

(a) generating a plurality of different magnetic fields in a predetermined sequence in the sensing volume from a plurality of magnetic field generating coils arranged in a stacked, overlapping group such that the sensing volume is positioned on one side of said overlapping group of coils taken together and not between any of said coils;

(b) generating one or more magnetic dipole fields within said sensing volume;

(c) measuring magnetic field components of said generated magnetic fields in at least two different local directions relative to a sensor connected to the object during generation of said fields; and

(d) determining the position of said object from the magnetic field components detected during generation of said magnetic fields.

21. Apparatus for generating magnetic fields inside the body of a patient, comprising a plurality of magnetic field generating coils for generating a plurality of different magnetic fields in a sensing volume, said coils being arranged in a stacked, overlapping group such that the sensing volume is positioned on one side of said overlapping group of coils taken together and not between any of said coils.