Surgical ferromagnetic object detection system and method

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.