Surgical ferromagnetic object detection system and method

1. A surgical system for detecting a ferromagnetic object in a living organism, wherein:

the system comprises:

a probe shaft comprising:

a distal end configured for insertion into the living organism; and

a proximal end configured for remaining outside the livin organism;

a probe tip magnetoresistance module wherein the probe tip magnetoresistance module is located at the distal end of the probe shaft;

a probe base magnetoresistance module wherein the probe base magnetoresistance module is located on the proximal end of the probe shaft;

the probe tip magnetoresistance module comprises a probe tip X-axis magnetoresistance sensor, a probe tip Y-axis magnetoresistance sensor, and a probe tip Z-axis magnetoresistance sensor wherein the probe tip X-axis magnetoresistance sensor, the probe tip Y-axis magnetoresistance sensor, and the probe tip Z-axis magnetoresistance sensor are responsive to an ambient magnetic field in three orthogonal axes at the distal end of the shaft and wherein:

the probe tip X-axis magnetoresistance sensor comprises a probe tip X-axis tunneling magnetoresistance sensor;

the probe tip Y-axis magnetoresistance sensor comprises a probe tip Y-axis tunneling magnetoresistance sensor;

the probe tip Z-axis magnetoresistance sensor comprises a probe tip Z-axis tunneling magnetoresistance sensor;

the probe tip X-axis magnetoresistance sensor generates a probe tip X-axis electrical signal in response to the ambient magnetic field at the distal end of the shaft;

the probe tip Y-axis magnetoresistance sensor generates a probe tip Y-axis electrical signal in response to the ambient magnetic field at the distal end of the shaft; and

the probe tip Z-axis magnetoresistance sensor generates a probe tip Z-axis electrical signal in response to the ambient magnetic field at the distal end of the shaft;

the probe base magnetoresistance module comprises a probe base X-axis magnetoresistance sensor, a probe base Y-axis magnetoresistance sensor, and a probe base Z-axis magnetoresistance sensor wherein the probe base X-axis magnetoresistance sensor, the probe base Y-axis magnetoresistance sensor, and the probe base Z-axis magnetoresistance sensor are responsive to the ambient magnetic field in three orthogonal axes at the proximal end of the shaft and wherein:

the probe base X-axis magnetoresistance sensor comprises a probe base X-axis tunneling magnetoresistance sensor;

the probe base Y-axis magnetoresistance sensor comprises a probe base Y-axis tunneling magnetoresistance sensor;

the probe base Z-axis magnetoresistance sensor comprises a probe base Z-axis tunneling magnetoresistance sensor;

the probe base X-axis magnetoresistance sensor generates a probe base X-axis electrical signal;

the probe base Y-axis magnetoresistance sensor generates a probe base Y-axis electrical signal; and

the probe base Z-axis magnetoresistance sensor generates a probe base Z-axis electrical signal

in response to the ambient magnetic field at the proximal end of the shaft;

all tunneling magnetoresistance sensors comprise magnetic tunnel junctions comprising two ferromagnetic layers separated by an insulating barrier wherein one of the ferromagnetic layers has a magnetization that does not move in response to an applied magnetic field and the other ferromagnetic layer moves in response to an applied magnetic field;

the system is configured to detect the ferromagnetic object in response to a difference between at least one pair of signals selected from a group of:

the probe tip X-axis electrical signal and the probe base X-axis electrical signal;

the probe tip Y-axis electrical signal and the probe base Y-axis electrical signal; and

the probe tip Z-axis electrical signal and the probe base Z-axis electrical signal;

gain and offset of the probe tip X-axis electrical signal, the probe tip Y-axis electrical signal, the probe tip Z-axis electrical signal, the probe base X-axis electrical signal, the probe base Y-axis electrical signal; and the probe base Z-axis electrical signal are adjusted in response to digital gain and digital offset values stored in a non-volatile memory in the surgical system wherein the digital gain and the digital offset values are determined from a calibration process comprising the steps of:

measuring the probe tip X-axis electrical signal, the probe tip Y-axis electrical signal, the probe tip Z-axis electrical signal, the probe base X-axis electrical signal, the probe base Y-axis electrical signal, and the probe base Z-axis electrical signal at a variety of angles in a calibrated constant magnetic field; and

calculating gain and offset values for the probe tip and probe base electrical signals in response to an optimized least squares linear regression calculation of a relationship of the probe tip and probe base electrical signals; and

the system is configured for detecting the ferromagnetic object without generating a magnetic field to detect the ferromagnetic object.

2. The surgical system for detecting a ferromagnetic object as recited in claim 1 , wherein:

the probe tip magnetoresistance module comprises a Wheatstone bridge circuit;

the probe base magnetoresistance module comprises a Wheatstone bridge circuit;

the probe tip X-axis electrical signal is amplified and digitized to produce a probe tip digital X-axis electrical signal;

the probe tip Y-axis electrical signal is amplified and digitized to produce a probe tip digital Y-axis electrical signal;

the probe tip Z-axis electrical signal is amplified and digitized to produce a probe tip digital Z-axis electrical signal;

the probe base X-axis electrical signal is amplified and digitized to produce a probe base digital X-axis electrical signal;

the probe base Y-axis electrical signal is amplified and digitized to produce a probe base digital Y-axis electrical signal;

the probe base Z-axis electrical signal is amplified and digitized to produce a probe base digital Z-axis electrical signal;

the system is configured to detect the ferromagnetic object in response to the calibration process and said difference between at least one of the following pairs of signals:

the probe tip digital X-axis electrical signal and the probe base digital X-axis electrical signal;

the probe tip digital Y-axis electrical signal and the probe base digital Y-axis electrical signal; and

the probe tip digital Z-axis electrical signal and the probe base digital Z-axis electrical signal;

the ferromagnetic object comprises an unintended retained post-surgical foreign body comprising at least one material selected from a group of martensitic stainless steel, nickel, and cobalt; and

the system is configured not to be responsive to at least one material selected from a group of austenitic stainless steel, aluminum, and titanium.

3. The surgical system for detecting a ferromagnetic object as recited in claim 2 , wherein:

the system further comprises a force feedback vibration motor;

the force feedback vibration motor is responsive to the detection of a ferromagnetic object; and

the probe shaft is user attachable and replaceable.

4. The surgical system for detecting a ferromagnetic object as recited in claim 1 , wherein:

the probe tip magnetoresistance module comprises a Wheatstone bridge circuit; and

the probe base magnetoresistance module comprises a Wheatstone bridge circuit.

5. The surgical system for detecting a ferromagnetic object as recited in claim 1 , wherein:

the ferromagnetic object comprises an unintended retained post-surgical foreign body comprising at least one material selected from a group of martensitic stainless steel; nickel, and cobalt; and

the system is configured not to be responsive to at least one material selected from a group of austenitic stainless steel, aluminum, and titanium.

6. The surgical system for detecting a ferromagnetic object as recited in claim 1 , wherein:

the probe tip X-axis electrical signal is amplified and digitized to produce a probe tip digital X-axis electrical signal;

the probe tip Y-axis electrical signal is amplified and digitized to produce a probe tip digital Y-axis electrical signal;

the probe tip Z-axis electrical signal is amplified and digitized to produce a probe tip digital Z-axis electrical signal;

the probe base X-axis electrical signal is amplified and digitized to produce a probe base digital X-axis electrical signal;

the probe base Y-axis electrical signal is amplified and digitized to produce a probe base digital Y-axis electrical signal;

the probe base Z-axis electrical signal is amplified and digitized to produce a probe base digital Z-axis electrical signal;

the system is configured to detect the ferromagnetic object in response to the calibration process and said difference between at least one of the following pairs of signals:

the probe tip digital X-axis electrical signal and the probe base digital X-axis electrical signal;

the probe tip digital Y-axis electrical signal and the probe base digital Y-axis electrical signal; and

the probe tip digital Z-axis electrical signal and the probe base digital Z-axis electrical signal.

7. The surgical system for detecting a ferromagnetic object as recited in claim 1 , wherein:

the system is configured to detect the ferromagnetic object based on a change in earth's ambient magnetic field caused by the ferromagnetic object;

the system further comprises a temperature sensor; and

the system is configured to detect the ferromagnetic object in response to the temperature sensor.

8. The surgical system for detecting a ferromagnetic object as recited in claim 1 , wherein:

the distal end of the probe shaft is configured for insertion into an internal cavity of a human through a trocar cannula placed in a body wall of the human as part of a laparoscopic surgical procedure.

9. The surgical system for detecting a ferromagnetic object as recited in claim 1 , wherein:

the system is configured to display a location of the detected ferromagnetic object relative to the distal end of the probe shaft in response to:

the probe tip X-axis electrical signal;

the probe base X-axis electrical signal;

the probe tip Y-axis electrical signal;

the probe base Y-axis electrical signal;

the probe tip Z-axis electrical signal; and

the probe base Z-axis electrical signal.

10. The surgical system for detecting a ferromagnetic object as recited in claim 1 , wherein:

the probe shaft is configured for connection to a probe handle;

the probe handle is configured for manual movement;

the probe handle is configured for tactile input;

the system further comprises a force feedback vibration motor;

the force feedback vibration motor is responsive to the detection of a ferromagnetic object; and

the system is configured for wireless digital telemetry.

11. The surgical system for detecting a ferromagnetic object as recited in claim 1 , wherein:

the system further comprises an additional magnetoresistance module comprising an additional X-axis magnetoresistance sensor, an additional Y-axis magnetoresistance sensor, and an additional Z-axis magnetoresistance sensor, wherein;

the additional X-axis magnetoresistance sensor generates an additional X-axis electrical signal;

the additional Y-axis magnetoresistance sensor generates an additional Y-axis electrical signal; and

the additional Z-axis magnetoresistance sensor generates an additional Z-axis electrical signal; and

the system is configured to detect the ferromagnetic object in response to a comparison between at least one set of signals selected from a group of:

the probe tip X-axis electrical signal, the probe base X-axis electrical signal, and the additional X-axis electrical signal;

the probe tip Y-axis electrical signal, the probe base Y-axis electrical signal, and the additional Y-axis electrical signal; and

the probe tip Z-axis electrical signal, the probe base Z-axis electrical signal, and the additional Z-axis electrical signal.

12. The surgical system for detecting a ferromagnetic object as recited in claim 1 , wherein:

the probe shaft is user attachable and replaceable.

13. The surgical system for detecting a ferromagnetic object as recited in claim 1 , wherein:

ferromagnetic object comprises an unintended retained post-surgical foreign body selected from a group of a ferromagnetic surgical tool, a ferromagnetic surgical needle, and a ferromagnetic surgical sponge.

14. The surgical system for detecting a ferromagnetic object as recited in claim 1 , wherein:

the surgical system further comprises a two-dimensional display:

the two-dimensional display is configured to show a relative position of the ferromagnetic object to the probe tip magnetoresistance module in three dimensions wherein:

relative vertical position is shown as a vertical distance of a displayed object from the center of a display element;

relative horizontal position is shown as a horizontal distance of the displayed object from the center of the display element; and

relative in-out position is shown as a change in size of the displayed object.

15. The surgical system for detecting a ferromagnetic object as recited in claim 1 , wherein:

the digital gain and digital offset values for the tunneling magnetoresistance sensors in the probe tip and the probe based are set when calibrating the tunneling magnetoresistance sensors in a magnetic field that is within the linear analysis range of the tunneling magnetoresistance sensors.

16. The surgical system for detecting a ferromagnetic object as recited in claim 1 , wherein:

the system further comprises a display; and

the display is configured to record a count of detected ferromagnetic objects.

17. A ferromagnetic object detection system, wherein:

the system comprises a probe shaft that comprises:

a probe tip magnetoresistance module located at the distal end of the probe shaft wherein the probe tip magnetoresistance module comprises three orthogonally-oriented tunneling magnetoresistance sensors configured for:

insertion into a body cavity of a living organism during surgery; and generating three orthogonal probe tip electrical signals in response to an ambient magnetic field in three orthogonal axes in the body cavity;

a probe base magnetoresistance module located at the proximal end of the probe shaft wherein the probe base magnetoresistance module comprises three orthogonally-oriented tunneling magnetoresistance sensors configured for:

remaining outside the body cavity; and

generating three orthogonal probe base electrical signals in response to an ambient magnetic field in three orthogonal axes outside the body cavity;

the system is configured to detect the ferromagnetic object in response to a difference in the electrical signals generated by the probe tip magnetoresistance module and the probe base magnetoresistance module; and

said difference in electrical signals is responsive to digital gain and digital offset values stored in non-volatile memory in the ferromagnetic object detection system wherein in the digital gain and the digital offset values are determined from a calibration process comprising the steps of:

measuring probe tip electrical signals and probe base electrical signals at a variety of angles in a calibrated constant magnetic field; and

calculating the digital gain and the digital offset values in response to an optimized least squares linear regression calculation of a relationship of the measured probe tip and probe base electrical signals in the calibrated constant magnetic field.

18. The ferromagnetic object detection system as recited in claim 17 , wherein:

the system does not generate a magnetic field to detect the ferromagnetic object.

19. The ferromagnetic object detection system as recited in claim 17 , wherein:

each tunneling magnetoresistance sensor comprises a magnetic tunnel junction comprising two ferromagnetic layers separated by an insulating barrier wherein one of the ferromagnetic layers has a magnetization that does not move in response to an applied magnetic field and the other ferromagnetic layer moves in response to an applied magnetic field.

20. A method for detecting a ferromagnetic object in a body cavity of a living organism during surgery, the method comprising the steps of:

establishing a probe shaft that comprises:

a probe tip magnetoresistance module comprising three orthogonally-oriented tunneling magnetoresistance sensors configured for:

insertion into a body cavity of a living organism during surgery; and generating three orthogonal probe tip electrical signals in response to an ambient magnetic field in three orthogonal axes in the body cavity; and

a probe base magnetoresistance module comprising three orthogonally-oriented tunneling magnetoresistance sensors configured for:

remaining outside the body cavity; and

generating three orthogonal probe base electrical signals in response to the ambient magnetic field in three orthogonal axes outside the body cavity;

generating digital gain and digital offset values for the three orthogonal probe tip electrical signals and the three orthogonal probe base electrical signals by:

measuring the three orthogonal probe tip electrical signals and the three orthogonal probe base electrical signals at a variety of probe shaft angles in a calibrated constant magnetic field; and

calculating the digital gain and the digital offset values in response to an optimized least squares linear regression of the measured probe tip and probe base electrical signals at the variety of angles;

storing the generated digital gain and digital offset values in a non-volatile memory; and

detecting the ferromagnetic object in response to:

the three orthogonal probe tip electrical signals;

the three orthogonal probe base electrical signals; and

the stored digital gain and digital offset values.