Surgical navigation

• US 20030163037A1
• Filed: 12/17/2002
• Published: 08/28/2003
• Est. Priority Date: 08/14/1992
• Status: Active Grant

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: British Telecommunications PLC (BT Group PLC)
• Inventors: Bladen, John Stuart, Anderson, Alan Patrick
• Granted Patent: US 7,174,202 B2
• Time in Patent Office: Days
• US Class Current: 600/424
• CPC Class Codes: A61B 2017/00207 with hand gesture control or hand gesture recognition
• CPC Class Codes: A61B 2034/107 Visualisation of planned trajectories or target regions
• CPC Class Codes: A61B 2034/2051 Electromagnetic tracking systems
• CPC Class Codes: A61B 2034/742 Joysticks
• 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 5/064 using markers A61B5/062 takes precedence
• CPC Class Codes: A61B 5/6806 Gloves
• CPC Class Codes: G01B 7/004 for measuring coordinates of points
• CPC Class Codes: G01V 3/08 operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices with electromagnetic waves G01V3/12
• 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

Methods and apparatus are provided for locating the position, preferably in three dimensions, of a sensor by generating magnetic fields which are detected at the sensor. The magnetic fields are generated from a plurality of locations and, in one embodiment of the invention, enable both the orientation and location of a single coil sensor to be determined. The present invention thus finds application in many areas where the use of prior art sensors comprising two or more mutually perpendicular coils is inappropriate.

Claims

1. A method of determining the location of a field sensor relative to a plurality of field generators of known location, each field generator comprising a plurality of co-located field generating elements, the method comprising the steps of:

1) for each generator, energising each generating element and measuring the respective field generated by each generating element at the field sensor,

2) for each field generator calculating, from the measurements of the fields generated by each of its generating elements, an estimate of the distance from that particular field generator to the sensor, and

3) utilising the estimates of the distances from each of the field generators to the sensor, and the known location of the field generators to calculate the location of the sensor relative to the field generators.

2. A method as claimed in claim 1, wherein in step 1) each generating element of each field generator is energised in sequence so that only one generating element is energised at any given time.

3. A method as claimed in claim 1, wherein in step 1) at least two generating elements are simultaneously energised, each of these at least two generating elements being energised at a different frequency from the other simultaneously energised generating element(s).

4. A method as claimed in any one of claims 1, 2 or 3 for determining the location of a field sensor and for further determining the orientation of said sensor, the method further comprising the steps of:

4) employing the location of the sensor calculated in step

     3), and a knowledge of the form of the field generated by a field generating element, to calculate an estimate of the orientation of the sensor relative to each of the field generators,

5) repeating steps

     2) to

     4) iteratively until the location and orientation of the sensor relative to the field generators is found to a desired level of accuracy.

5. A method as claimed in any one of claims 1, 2 or 3 for determining the location of a field sensor and for further determining the orientation of said sensor, the method further comprising the steps of:

4) employing the location of the sensor calculated in step

     3), and the known relative orientations of the field generating elements to calculate the angle of the respective field to the direction vector of the sensor from each field generator,

5) calculating from the field angles and a knowledge of the form of the field generated by a field generating element the angle of the field sensor relative to each field generator,

6) repeating steps

     2) to

     5) iteratively until the position of the sensor relative to the field generators is found to a desired level of accuracy, and

7) calculating the orientation of the sensor relative to each of the field generators.

6. A method of determining the location of a field sensor, comprising a plurality of co-located field sensing elements, relative to a field generator, comprising a plurality of co-located field generating elements, the method comprising the steps of:

1) energising a single field generating element to establish a field,

2) measuring a value of the field strength at the field sensor which is dependent on the location and orientation of the sensor within the field,

3) repeating steps

     1) and

     2) for each field generating element,

4) calculating, by utilising all the values measured in step 2 and an estimate of the location of the sensor, an estimate of the field strength B that would exist at the sensor if the axis of the field were directed towards the sensor, and

5) maximising the value of B by iteratively altering the estimate of the location of the sensor until the location of the sensor relative to the field is found to a desired level of accuracy.

7. Apparatus for determining the location of a field sensor comprising:

a plurality of field generators each comprising a plurality of field generating elements,

energising means operable for each field generator to energise each of the Plurality of field generating elements to produce a field within which the location of the object may be determined,

measurement means, connected to the field sensor, for measuring and outputting a parameter of the field at the sensor,

control means for controlling the energising means, storing parameters output by the measurement means, and calculating the location of the sensor relative to the plurality of field generators.

8. Apparatus as claimed in claim 7, wherein the energising means are operable to sequentially energise each field generating element.

9. Apparatus as claimed in claim 7 wherein the energising means are operable to simultaneously energise at least two field generating elements, and to energise each simultaneously energised field generating element at a distinct frequency.

10. Apparatus for determining the location of a field sensor as claimed in any one of claims 7, 8 or 9, wherein the field sensor comprises a single field sensing element and the parameter of the field sensed by said single field sensing element is dependent on the orientation of the field sensing element within the field.

11. Apparatus for determining the location of a field sensor as claimed in claim 10, wherein the field sensing element comprises a coil of electrically conducting wire.

12. Apparatus for determining the location of a field sensor as claimed in any one of claims 7 to 11, having three field generators, each comprising three mutually orthogonal co-located field generating elements.

13. Apparatus for determining the location and orientation of a field sensor as claimed in any one of claims 7 to 12, wherein the control means calculates the location and orientation of the sensor by

estimating the distance of the sensor from each of the three field generators, having no regard for the orientation of the sensor,

estimating the location of the sensor relative to the field generators from the estimates of the distance of the sensor from each field generator, and a knowledge of the relative locations of the three field generators,

iteratively improving the estimate of the location of the sensor, and additionally determining the orientation of the sensor, by including the effect of the orientation of the sensor in subsequent estimates of the distance of the sensor From each of the field generators.

14. Apparatus for determining the location of an object relative to a field generator, the apparatus comprising

a field generator comprising a plurality of field generating elements,

energising means for sequentially energising each of the field generating elements to produce a field within which the object may be located,

a sensor, to be attached to the object, comprising a plurality of co-located field sensing elements, each able to sense a parameter of the field,

measurement means for measuring and outputting the parameter of the field sensed by each field sensing element when each field generating element is energised, and

control means for controlling the energising means, storing the parameters output by the measurement means and calculating the location of the sensor, relative to the field generator

wherein the control means is operable to determine the location of the sensor by,

weighting each of the parameters, sensed by the sensor, by a location dependent weighting factor,

calculating from all the parameters sensed at the sensor an estimate of the field strength at the sensor,

iteratively altering the location dependent weighting factors until a maximum value of the field strength is found.

15. Apparatus for determining the location of an object as claimed in claim 14, wherein the field generator comprises three mutually orthogonal field generating elements and the sensor comprises three mutually orthogonal field sensing elements.

16. Apparatus for determining the location of an object substantially as hereinbefore described, with reference to, and as shown in, the accompanying drawings.

17. A method of locating an object substantially as hereinbefore described, with reference to, and as shown in, the accompanying drawings.