Method and apparatus for calibrating a magnetic field generator

• US 6,335,617 B1
• Filed: 03/08/1999
• Issued: 01/01/2002
• Est. Priority Date: 05/06/1996
• Status: Expired due to Term

• Current Assignee: Biosense, Inc. (Cardinal Health, Inc.)
• Original Assignee: Biosense, Inc. (Cardinal Health, Inc.)
• Inventors: Govari, Assaf, Osadchy, Daniel
• Primary Examiner(s): Snow, Walter E.
• Application Number:
  US09/180,244
• Time in Patent Office: 1,030 Days
• Field of Search: 324/202, 324/207.12, 324/207.17, 324/207.23, 324/207.26, 324/225, 324/239, 324/244, 324/246, 324/260, 324/320, 73/10.1, 73/17.9, 702/85, 702/94, 702/95, 702/104
• US Class Current: 324/202
• 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 33/02 Measuring direction or magnitude of magnetic fields or magnetic flux G01R33/20 takes precedence
• CPC Class Codes: G01R 33/246 Spatial mapping of the RF magnetic field B1
• CPC Class Codes: G01R 33/58 Calibration of imaging systems, e.g. using test probes , Phantoms; Calibration objects or fiducial markers such as active or passive RF coils surrounding an MR active material
• CPC Class Codes: G01R 35/00 Testing or calibrating of apparatus covered by the other groups of this subclass

Abstract

A method for calibrating a magnetic field generator, including fixing one or more magnetic field sensors to a probe in known positions and orientations and selecting one or more known locations in the vicinity of the magnetic field generator. The magnetic field generator is driven so as to generate a magnetic field. The probe is moved in a predetermined, known orientation to each of the one or more locations, and signals are received from the one or more sensors at each of the one or more locations. The signals are processed to measure the amplitude and direction of the magnetic field, at the respective positions of the one or more sensors and to determine calibration factors relating to the amplitude and direction of the magnetic field in the vicinity of the magnetic field generator.

Claims

1. A method for calibrating a magnetic field generator, comprising:

fixing one or more magnetic field sensors to a probe in known positions and orientations;

selecting one or more known locations in a vicinity of the magnetic field generator;

driving the magnetic field generator so as to generate a magnetic field;

moving the probe in a predetermined, known orientation to each of the one or more locations;

receiving signals from the one or more sensors at each of the one or more locations;

processing the signals to measure the amplitude and direction of the magnetic field, at the respective positions of the one or more sensors; and

determining calibration factors relating to the amplitude and direction of the magnetic field in the vicinity of the magnetic field generator.

2. A method according to claim 1, wherein fixing one or more magnetic sensors to a probe comprises fixing sensor coils to the probe.

3. A method according to claim 2, wherein fixing the sensor coils to the probe comprises fixing two or more sensor coils in orientations such that respective axes of the coils are mutually substantially orthogonal.

4. A method according to claim 3, wherein fixing the one or more magnetic sensors to a probe comprises fixing three sensors to the probe, such that the positions of the sensors on the probe are substantially collinear.

5. A method according to claim 3, wherein fixing the one or more magnetic sensors to the probe comprises fixing sensors to a cube.

6. A method according to claim 5, wherein selecting one or more known locations comprises selecting a plurality of locations, and wherein moving the probe comprises moving the probe along an axis defined by the one or more sensors on the probe and passing through two or more of the plurality of locations.

7. A method according to claim 6, wherein moving the probe along the axis comprises moving the probe in steps of substantially equal length, such that the distance between any two of the sensors is substantially integrally divisible by the length of the steps.

8. A method according to claim 7, where calibrating the magnetic field generator comprises calibrating a field generator that is substantially rotationally symmetrical, and

wherein selecting the one or more known locations comprises selecting one or more locations in a quadrant defined by the axis of rotational symmetry of the magnetic field generator and by a second axis in a plane defined by the magnetic field generator and normal to the axis of rotational symmetry, and

wherein moving the probe comprises orienting the probe so that the one or more sensors are positioned in the plane.

9. A method according to claim 8, wherein determining calibration factors comprises:

calculating theoretical values of the amplitude and direction of the magnetic field generated by the magnetic field generator at the one or more known locations;

comparing the theoretical values to the amplitude and direction of the magnetic field measured at said locations; and

computing arithmetic factors based on the difference between the theoretical values and the measured amplitude and direction of the magnetic field at each such location.

10. A method according to claim 9, wherein computing arithmetic factors comprises fitting the theoretical values to the measured amplitude and direction of the field.

11. A method according to claim 10, wherein calculating theoretical values comprises:

deriving a theoretical model of the magnetic field in the presence of an air core within the magnetic field generator; and

modifying the model to account for the presence of a ferromagnetic core within the magnetic field generator.

12. A method according to claim 11, wherein modifying the model comprises determining a perturbation of the field due to the core.

13. A method according to claim 12, wherein determining the perturbation of the field comprises determining a perturbation due to a nonlinearity of the core.

14. A method according to claim 13, wherein determining the perturbation of the field comprises determining a perturbation due to eddy currents in the core.

15. A method according to claim 14, and comprising:

fixing a magnetic-field-responsive position-sensing device to an object;

placing the object in the vicinity of the magnetic field generator;

receiving signals from the position-sensing device;

processing the signals so as to calculate the position or orientation of the object; and

applying the calibration factors so as to improve the accuracy of calculation of the position or orientation.

16. A method according to claim 15, and comprising storing the calibration factors in a memory associated with the radiator coil.

17. Apparatus for calibrating a magnetic field generator comprising:

a plurality of magnetic field sensors, which generate electrical signals in response to magnetic fields applied thereto by the field generator;

a positioning device, for moving the sensors;

wherein the positioning device has an axis of motion that is parallel to an axis defined by two or more of the plurality of the coils, the magnetic field sensors comprising sensor coils, which are fixed so that respective axes of the coils are mutually substantially orthogonal, the sensors being fixed to the positioning device in a substantially linear arrangement, wherein the sensors are fixed to the faces of a cube, which is fixed to the positioning device; and

a computer, which receives the signals from the sensors and compares them to a theoretical model, so as to calibrate the magnetic field generator.