PROBE FOR DETERMINING MAGNETIC MARKER LOCATIONS

• US 20160051164A1
• Filed: 08/21/2015
• Published: 02/25/2016
• Est. Priority Date: 08/24/2014
• Status: Active Grant

• Current Assignee: Health Beacons, Inc. (Hologic Incorporated)
• Original Assignee: Health Beacons, Inc. (Hologic Incorporated)
• Inventors: Derichs, Kevin J., Petcavich, Robert J., Reicher, Murray A.
• Granted Patent: US 10,188,310 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: A61B 2034/2048 using an accelerometer or inertia sensor
• CPC Class Codes: A61B 2034/2051 Electromagnetic tracking systems
• CPC Class Codes: A61B 2090/3908 Soft tissue, e.g. breast tissue
• CPC Class Codes: A61B 2090/3954 magnetic, e.g. NMR or MRI
• CPC Class Codes: A61B 5/05 Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves impedance plethysmography A61B5/0295; measuring movement of the entire body or parts thereof A61B5/11; detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof A61B5/24
• CPC Class Codes: G01R 33/02 Measuring direction or magnitude of magnetic fields or magnetic flux G01R33/20 takes precedence

Abstract

A probe including a first sensor having a first magnetometer and a first accelerometer and a second sensor having a second magnetometer and a second accelerometer is configured for determining the distance and direction to a marker. The marker may be magnetic and may be surgically inserted into a patient'"'"'s body to mark a specific location. The probe may be used to locate the marker, thus identifying the location. The probe may include a microprocessor that receives an output from the first sensor and an output from the second sensor and determines the distance and direction to the marker.

Claims

1. A probe for detecting a magnetic marker, the probe comprising:

a first sensor including a first magnetometer and a first accelerometer located in a handheld housing;

a second sensor including a second magnetometer and a second accelerometer, the second sensor located in the housing and separated from the first sensor; and

a processor located in the housing and electrically connected to the first sensor and the second sensor, the processor configured to receive an output from the first sensor and an output from the second sensor and determine a distance and direction between one of the first sensor and the second sensor and a magnetic marker.

2. The probe of claim 1, wherein each of the first and the second magnetometers are configured to detect the field strength of the magnetic field of a magnetic maker within a range measured from each of the first and second magnetometers, and wherein the first and second sensors are separated by a distance greater than the range.

3. The probe of claim 2, wherein the distance separating the first and second sensors is at least twice the range of the first and second magnetometers, such that the field strength of the magnetic field of a magnetic marker can only be substantially detected by either the first magnetometer or the second magnetometer.

4. The probe of claim 2, wherein the processor is configured to determine the distance between one of the first sensor and the second sensor and a magnetic marker by calculating a difference between the output of the first sensor and the output of the second sensor.

5. The probe of claim 4, wherein the difference represents the field strength of the magnetic marker.

6. The probe of claim 5, further comprising a memory configured to store a lookup table containing data relating the magnetic field strength of a magnetic marker to a distance from the magnetic marker.

7. The probe of claim 1, wherein the handheld housing is configured as a wand comprising:

a base, wherein the first sensor is located in the base;

an extension member extending from the base, the extension member defining the distance; and

a tip, wherein the second sensor is located in the tip, and wherein the processor determines the distance and direction between the tip and a magnetic marker.

8. The probe of claim 1, wherein the first and second sensors are located with a sensing portion which is configured to be removable from the housing.

9. The probe of claim 8, wherein the sensing portion is disposable.

10. A method for determining the distance and direction between a probe and a magnetic marker, the method comprising:

providing a probe comprising

a first sensor including a first magnetometer and a first accelerometer, and

a second sensor including a second magnetometer a second accelerometer,

the probe configured to determine the position in three-dimensional space of a magnetic marker;

balancing the probe while away from the magnetic marker;

moving the balanced probe so that the magnetic marker is within a range of the magnetic marker; and

determining the distance and direction between the probe and the magnetic marker by comparing an output of the first sensor with an output of the second sensor.

11. The method of claim 10, wherein balancing the probe comprises compensating for a gain and an offset in the output of the first magnetometer and the output of the second magnetometer, wherein the gain and the offset are caused by hard and soft iron effects.

12. The method of claim 11, wherein the output of each of the first and second magnetometers comprises X, Y, and Z, values, and balancing the probe further comprises:

rotating the probe through 360 degrees around each of three orthogonal axes;

for each of the first and second magnetometers;

recording the minimum and maximum X, Y, and Z values output during the rotation;

calculating a length between the minimum and maximum values for each of X, Y, and Z;

calculating a gain factor by dividing the length for each of X, Y, and Z by dividing the length of each of X, Y, and Z by the average length of X, Y, and Z;

calculating an offset value for each of X, Y, and Z by, for each of X, Y, and Z, adding half the length of X, Y, and Z, to the minimum value for X, Y, and Z.

13. The method of claim 12, further comprising adjusting raw output data into balanced output data by subtracting the offset value from the raw output data and multiplying by the gain factor for each of X, Y, and Z.

14. The method of claim 11, wherein the output of the first sensor comprises first magnetometer output data and first accelerometer output data, and the output of the second sensor comprises second magnetometer output data and second accelerometer output data, and wherein determining the distance and direction between the probe and the magnetic marker further comprises:

calculating a difference between the first magnetometer output data and the second magnetometer output data to determine distance between the probe and the magnetic marker; and

determining the orientation of the probe using one of the first accelerometer data or the second accelerometer data.

15. The method of claim 14, wherein the difference represents the field strength of the magnetic marker at the location of the probe, and wherein determining the distance between the probe and the magnetic marker comprises looking up the distance in a look up table based upon the field strength.

16. The method of claim 10, further comprising marking a location with the marker.

17. The method of claim 16, wherein the location is the location of a breast tumor to be surgically removed.

18. The method of claim 16, where the location is one of the location of a lung nodule, a lymph node, a parathyroid nodule, a thyroid nodule, or a GI lesion.

19. The method of claim 10, further comprising inserting the marker into a patient'"'"'s body.

20. The method of claim 19, wherein the marker is coated in a layer of gold.