Magnetic location system with feedback adjustment of magnetic field generator

• US 5,729,129 A
• Filed: 06/07/1995
• Issued: 03/17/1998
• 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: Acker, David E.
• Primary Examiner(s): Snow, Walter E.
• Application Number:
  US08/476,380
• Time in Patent Office: 1,014 Days
• Field of Search: 324/232, 324/207.12, 324/225, 324/207.17, 324/207.22, 324/207.23, 128/653.1, 128/899
• US Class Current: 324/207.12
• CPC Class Codes: A61B 2034/2051 Electromagnetic tracking systems
• 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

A system for locating objects in space, such as medical instruments within the body of a patient, based upon transmission of magnetic fields from coils in a fixed frame of reference to sensors on the object or visa-versa. The current supplied to the coils is adjusted to assure that the sensors receive fields within a preselected range of magnitudes regardless of the location of the object in space. This assures that the sensor operates within its optimum range, and permits use of compact transmitters and sensors.

Claims

1. Apparatus for determining position comprising:

(a) field generating means for producing a plurality of magnetic fields, each said field having parameters varying with location within a sensing volume according to a known pattern of variation, said patterns of variation being different for different ones of said fields;

(b) at least one sensor adapted to detect one or more of said parameters of said fields generated by said field generating means prevailing at such sensor when said sensor is at an unknown location within said sensing volume and to provide one or more sensor signals representing said one or more parameters;

(c) calculation means for determining a calculated location of said sensor based upon said sensor signals and said known patterns of variation; and

(d) feedback control means for adjusting said field generating means to alter said known pattern of variation of at least one of said fields responsive to said sensor signals, said calculated location or both so as to maintain said parameters of each such altered field prevailing at said sensor within a preselected range.

3. Apparatus as claimed in claim 1 or claim 2 wherein said field generating means is operative to provide DC magnetic fields within said sensing volume.

4. Apparatus as claimed in claim 3 wherein said field generating means includes a plurality of coils and means for intermittently actuating each said coil with a direct current, said feedback control means includes means for altering the magnitude of each said direct current, and wherein said calculation means includes means for sampling the signals from each sensor when a delay time has elapsed after commencement of each said intermittent actuation, said feedback control means further including means for varying the delay time for each actuation in accordance with the magnitude of the current applied in such actuation so as to reduce the delay time when lesser currents are employed and increase the delay time when greater currents are employed.

5. Apparatus as claimed in claim 1 or claim 2 wherein said field generating means is operative to provide AC magnetic fields within said sensing volume.

6. Apparatus as claimed in claim 1 or claim 2 wherein each said sensor has maximum accuracy within a preselected optimum operational range for each said parameter and said preselected range for each said parameter substantially corresponds to said optimum operational range.

7. Apparatus as claimed in claim 1 or claim 2 wherein said preselected range for each said parameter consists of a single value, and wherein said feedback control means is operative to maintain each said parameter of the field at each sensor substantially at said single value.

8. Apparatus as claimed in claim 1 wherein said field generating means includes a plurality of transmitters disposed adjacent said sensing volume.

10. Apparatus as claimed in claim 1 further comprising a sensor body, said at least one sensor including a plurality of component sensors disposed on said sensor body, each said component sensor being operative to measure the magnitude of a magnetic field component in a preselected local direction relative to the sensor body.

11. Apparatus as claimed in claim 10 wherein said field generating means includes a plurality of transmitters disposed at spaced-apart locations adjacent said sensing volume, said feedback control means being operative to adjust each said transmitter to transmit a plurality of fields so that for each said field, the magnitude of a component of such field in the local direction of one said component sensor will be within a preselected range.

12. Apparatus as claimed in claim 10 wherein each said component sensor is a Hall effect sensor, a magnetoresistive sensor, a magnetooptical sensor or a flux gate magnetometer.

13. Apparatus as claimed in claim 1 or claim 2 wherein each said sensor includes a coil and wherein said field generating means is arranged to provide AC fields in said sensing volume.

14. Apparatus as claimed in claim 1 wherein said field generating means includes a plurality of transmitters disposed at spaced-apart locations on one side of a reference plane and wherein said sensing volume extends to the other side of said reference plane.

15. Apparatus as claimed in claim 14 wherein said transmitters are disposed substantially in a common plane.

18. Apparatus as claimed in claim 1 or claim 2 wherein said at least one sensor includes a plurality of sensors, and wherein said sensors can be impaired by exposure to fields having components above a predetermined threshold magnitude, and wherein said feedback control means includes means for controlling said field generating means to assure that no sensor is exposed to a field component having magnitude above its threshold value.

19. Apparatus as claimed in claim 1 or claim 2 wherein said at least one sensor includes a plurality of sensors and wherein said sensors can be impaired by exposure to fields having components above a predetermined threshold magnitude but can be restored after such exposure upon application of a reset routine, said feedback control means including means for initiating such reset routine in the event of such exposure.

2. Apparatus for determining position comprising:

(a) a plurality of sensors, said sensors being disposed adjacent a sensing volume at different positions, different orientations or both;

(b) field generating means including at least one magnetic field transmitter movable to an unknown location within said sensing volume and adapted to provide at least one magnetic field in said sensing volume, so that the magnetic field from each transmitter varies in according to a known pattern of variation with location relative to such transmitter, said sensors being adapted to detect one or more parameters of the at least one magnetic field provided by said field generating means and to provide said sensor signals representing one or more parameters of the field or fields from said at least one transmitter;

(c) calculation means for determining a calculated location of said at least one transmitter based upon said sensor signals and said known patterns of variation; and

(d) feedback control means for adjusting said field generating means to alter said known pattern of variation of at least one of said fields responsive to said sensor signals, said calculated location or both so as to maintain said parameters of each such altered field prevailing at each said sensor within a preselected range.

9. Apparatus as claimed in claim 2 or claim 8 wherein each said transmitter is operative to radiate a field having magnitude decreasing with rⁿ where r is distance from the transmitter and n is a number greater than 1.

16. Apparatus as claimed in claim 2 wherein said plurality of sensors are disposed at spaced-apart locations on one side of a reference plane and wherein said sensing volume extends to the other side of said reference plane.

17. Apparatus as claimed in claim 16, wherein said sensors are disposed substantially in a common plane.

20. Apparatus for sensing the disposition of an object in a frame of reference comprising:

(a) transmitter means including at least one transmitter for providing a field;

(b) sensor means including at least one sensor for sensing one or more parameters of a field prevailing at each such sensor, said transmitter means and said sensor means cooperatively defining a plurality of transmitter-sensor pairs, each including one transmitter and one sensor as elements of the pair, one element of each such pair being disposed on the object and the other element of each such pair being disposed at a known disposition in said frame of reference, the sensor means of each such pair being operative to provide sensor signals representing parameters of a field provided by said transmitter means;

(c) calculation means for determining the disposition of said object in said frame of reference based upon said sensor signals; and

(d) feedback control means for adjusting said transmitter means responsive to said sensor signals to thereby maintain at least one of said sensor signals within a preselected range.

21. Apparatus for determining position comprising:

(a) a plurality of sensors adapted to detect one or more parameters of a magnetic field prevailing at each such sensor and to provide one or more sensor signals representing said one or more parameters, said sensors being disposed adjacent a sensing volume at different positions, different orientations or both;

(b) field generating means including at least one magnetic field transmitter movable to an unknown location within said sensing volume and adapted to provide at least one magnetic field in said sensing volume, so that the magnetic field from each transmitter varies in according to a known pattern of variation with location relative to such transmitter whereby said sensor signals will represent one or more parameters of the field or fields from said at least one transmitter;

(c) calculation means for determining a calculated location of said at least one transmitter based upon said sensor signals and said known patterns of variation; and

(d) feedback control means for adjusting said field generating means to alter said known pattern of variation of at least one of said fields responsive to said sensor signals, said calculated location or both so as to maintain said parameters of each such altered field prevailing at each said sensor within a preselected range, each said transmitter being operative to radiate a field having magnitude substantially equal to K/r³ where r is distance from the transmitter and K is a real number, and wherein said feedback control means is operative to adjust K.

22. Apparatus for determining position comprising:

(a) field generating means for producing a plurality of magnetic fields, each said field having parameters varying with location within a sensing volume according to a known pattern of variation, said patterns of variation being different for different ones of said fields;

(b) at least one sensor adapted to detect one or more of said parameters prevailing at such sensor when said sensor is at an unknown location within said sensing volume and to provide one or more sensor signals representing said one or more parameters;

(c) calculation means for determining a calculated location of said sensor based upon said sensor signals and said known patterns of variation; and

(d) feedback control means for adjusting said field generating means to alter said known pattern of variation of at least one of said fields responsive to said sensor signals, said calculated location or both so as to maintain said parameters of each such altered field prevailing at said sensor within a preselected range, said field generating means including a plurality of transmitters disposed adjacent

said sensing volume, each said transmitter being operative to radiate a field having magnitude substantially equal to K/r³ where r is distance from the transmitter and K is a real number, and wherein said feedback control means is operative to adjust K.