Method and device for locating magnetic implant source field

Abstract

An apparatus and method for locating a magnetic implant in a surgical application using the field of a source magnet for the implant guiding field. The source magnet is an electromagnet having a separate calibrated magnetic field component in addition to the guiding field, so that both the magnitude and orientation of the magnetic field as a function of position around the magnet are known. A magnetic implant is provided with a sensor, such as a three-axis Hall effect sensor, to provide an indication of the magnitude and orientation of an applied magnetic field when the implant is surgically implanted in a patient. After implantation, the source magnet is energized with a current having a modulated component. The modulated component is received and filtered from the signal received from the Hall effect sensor in the implant, and provided to a processor that computes the location of the implant relative to the electromagnet based upon the detected magnitude and orientation of the modulated component of the magnetic field, and the location and orientation of the electromagnet. Localizers may be used to supply the relative locations of the patient and the electromagnet to the processor. A display may be provided to display a representation of the location of the implant in the patient, which may also be superimposed over a preoperative image of the patient.

1 . A magnetic surgical implant comprising a flexible probe having a magnetic seed mounted at a distal end thereof and a magnetic field sensor mounted near the magnetic seed and in a fixed relationship thereto so that as an external magnetic field acts on said magnetic seed to guide or propel it through a patient's body, the magnetic field sensor is also acted upon and provides an output which can be correlated with the position of the magnetic seed.  
     
     
         2 . The magnetic surgical implant of  claim 1  wherein the magnetic field sensor comprises a  3- axis magnetometer probe.  
     
     
         3 . The magnetic surgical implant of  claim 2  wherein the magnetic field sensor is mounted within the flexible probe.  
     
     
         4 . The magnetic surgical implant of  claim 3  further comprising at least one sensor conductor connected to the magnetic field sensor and extending through the flexible probe for carrying signals from the magnetic field sensor to a receiver.  
     
     
         5 . The magnetic surgical implant of  claim 4  wherein the flexible probe is an endoscope.  
     
     
         6 . The magnetic surgical implant of  claim 4  wherein the flexible probe is a catheter.  
     
     
         7 . The magnetic surgical implant of  claim 4  wherein the magnetic seed is also mounted within the flexible probe and at the tip thereof.  
     
     
         8 . The magnetic surgical implant of  claim 4  wherein the sensor conductor comprises at least one electrical conductor.  
     
     
         9 . A device for providing position data for a magnetic surgical implant having a magnetic field sensor which is guided or propelled through a patient's body by an external magnet, said device comprising a current source for supplying a modulated electrical current to the external magnet to thereby generate an oscillating magnetic field component, a demodulator coupled to the magnetic field sensor and responsive to a magnetic field direction and magnitude of the oscillating magnetic field component to provide a signal indicative of the oscillating magnetic field component at the location of the magnetic field sensor, a memory containing a representation of a relationship of spatial locations to a magnetic field pattern produced by the external magnet, and a data processor coupled to the demodulator and the memory and configured to compute a spatial location of the magnetic field sensor as a function of the signal indicative of the oscillating magnetic field component.  
     
     
         10 . The device of  claim 9 , wherein the representation of the relationship of spatial locations to the magnetic field pattern produced by the electromagnet is a representation in a reference frame, the electromagnet is moveable, and the device further comprises a localizer configured to provide a signal representative of a position and orientation of the electromagnet to the processor, and the processor is configured to apply a correction based upon the position and orientation provided by the locator.  
     
     
         11 . The device of  claim 10  wherein the localizer comprises a sensor mounted on the electromagnet and a first plurality of fiducial markers positioned on the patient and a second plurality of fiducial markers positioned on the electromagnet.  
     
     
         12 . The device of  claim 9  and further comprising a display coupled to the processor, the processor further being configured to display on said display an image representing the spatial location of the magnetic field sensor and a preoperative image of a patient in which the magnetic field sensor is implanted, the location image and the preoperative image being superimposed on one another.  
     
     
         13 . The device of  claim 9 , in which the electromagnet is configured to generate a hemispherically symmetrical field.  
     
     
         14 . The device of  claim 9 , in which the electromagnet is configured to generate a hemispherically asymmetric field.  
     
     
         15 . The device of  claim 9  in which the electromagnet comprises a plurality of separate coils.  
     
     
         16 . A method for locating a magnetic surgical implant, comprising the steps of: 
 (a) surgically implanting a magnetic implant including an associated magnetic field probe in a patient;    (b) applying a modulated magnetic field from an external electromagnet;    (c) detecting signals from the magnetic probe resulting from the application of the modulated magnetic field; and    (d) computing the relative location of the magnetic probe, and therefore, the magnetic implant, with respect to the electromagnet, from the detected signals from the magnetic probe.    
     
     
         17 . The method of  claim 16 , and further comprising the steps of locating the patient and electromagnet with a localizer and displaying an indication of the location of the magnetic probe relative to the patient on a display.  
     
     
         18 . The method of  claim 17 , and further comprising the step of superimposing a preoperative image of the patient on the display with the indication of the location of the magnetic probe.  
     
     
         19 . The method of  claim 18  wherein the step of applying a modulated magnetic field from an external electromagnet comprises the steps of selecting a current required by the external electromagnet to guide the magnetic implant and modulating the selected current with a modulating signal; 
 and further comprising the step of guiding the magnetic probe with the modulated magnetic field.    
     
     
         20 . The method of  claim 16  wherein the step of applying a modulated magnetic field from an external electromagnet comprises the steps of selecting a current required by the external electromagnet to guide the magnetic implant  5  and modulating the selected current with a modulating signal; 
 and further comprising the step of guiding the magnetic probe with the modulated magnetic field.