Method and system for marker localization

Abstract

A method and system for locating a source of a signal. The source may be a wireless marker that is implanted in an object, such as a human body. The signal generated by the marker is a magnetic field. The location system uses an array of sensors to measure the magnetic field of the marker at various sensor locations. The location system compares the set of actual measurements to sets of reference measurements for various known locations within a bounding volume. Based on the comparisons, the location system identifies the set of reference measurements that most closely matches the set of actual measurements. The location system then uses sets of reference measurements for known locations near the closest known location to more accurately determine the marker location when it is not actually at one of the known locations.

1 - 49 . (canceled) 
     
     
         50 . A method for locating a dipole source of a magnetic field, the dipole source being a marker implanted in or affixed to an organism, the method comprising:
 selecting a location associated with a set of reference measurements that most closely matches a set of actual measurements, an actual measurement being indicative of the magnetic field, a set of reference measurements being indicative of actual measurements expected when the dipole source is at the associated location; and   identifying a location associated with a set of interpolated reference measurements that most closely matches the set of actual measurements wherein the set of interpolated reference measurements is derived from sets of reference measurements.   
     
     
         51 . The method of  claim 50  wherein the identifying of the location includes searching for the location by iteratively determining how closely sets of interpolated reference measurements match the set of actual measurements. 
     
     
         52 . The method of  claim 50  wherein the marker is wireless. 
     
     
         53 . The method of  claim 50  wherein sets of reference measurements are calculated. 
     
     
         54 . The method of  claim 50  wherein the sets of reference measurements are experimentally derived. 
     
     
         55 . The method of  claim 50  wherein the locations associated with the sets of reference measurements are at grid points within a bounding box that contains the source. 
     
     
         56 . The method of  claim 50  wherein the closeness of a match between two sets of measurements is based on an evaluation of an objective function. 
     
     
         57 . The method of  claim 56  wherein the objective function is
     E   2   =s   T   H ( H   T   H ) −1   H   T   s.      
     
     
         58 . The method of  claim 50  wherein the approximation is a trilinear interpolation. 
     
     
         59 . The method of  claim 50  wherein the approximation is a combination of a trilinear and a second order difference interpolation. 
     
     
         60 . The method of  claim 50  wherein the identifying of a location includes identifying a location near a candidate location wherein a derivative of an objective function is near zero. 
     
     
         61 . The method of  claim 50  wherein the identifying of a location includes calculating a spatial offset from a current location according to
   ρ=− C   −1   b.      
     
     
         62 - 71 . (canceled)