Navigation Field Distortion Detection

Abstract

Disclosed is a method and system for navigating an instrument relative to a patient that can be near a field distorting feature. A localizer can generate an electromagnetic field that is sensed by a tracking device to determine a location of the tracking device with the sensed electromagnetic field. The system and related method can assist in determining whether a navigation field is distorted near a tracking device of the instrument.

What is claimed is: 
     
         1 . A method to determine proper navigation of a flexible instrument in a navigation field, comprising:
 evaluating and predetermining physical constraints of the flexible instrument;   predetermining a calibrated position of a first tracking device and a second tracking device fixed to the flexible instrument;   storing with a first storage device the physical constraints; and   storing with a second storage device the calibrated position of the first tracking device and the second tracking device fixed to the flexible instrument;   wherein the stored physical constraints and stored calibrated position are accessible by a processor to execute an algorithm to determine an energy of bending of the flexible instrument based on the accessed stored physical constraints and accessed stored calibrated position.   
     
     
         2 . The method of  claim 1 , further comprising:
 operating the processor to:
 determine the energy of bending based on (i) a current tracked position of both the first tracking device and the second tracking device and (ii) the stored physical constraints, and (iii) the stored calibrated position of the first tracking device and the second tracking device; and 
 based on the determined energy of bending, determine whether the determined energy of bending is probable based on the stored physical constraints and the stored calibrated position of the first tracking device and the second tracking device. 
   
     
     
         3 . The method of  claim 1 , wherein evaluating physical constraints of a flexible instrument includes:
 predetermining a parameterized energy of the flexible instrument between the first tracking device and the second tracking device; and   predetermining an energy functional based on the parameterized energy of the flexible instrument between the first tracking device and the second tracking device.   
     
     
         4 . The method of  claim 3 , further comprising:
 operating the processor to determine a minimization of the energy functional to determine a probable location and orientation of the flexible instrument.   
     
     
         5 . The method of  claim 2 , further comprising:
 executing the algorithm with the processor to determine the energy of bending based on at least one of a distance between a tracked location of the first tracking device and the second tracking device or determining an estimated arc length of the flexible instrument between the first tracking device and the second tracking device.   
     
     
         6 . The method of  claim 5 , wherein evaluating and predetermining physical constraints of the flexible instrument includes determining of the flexible instrument at least one of a wire constant, a modulus of elasticity, a dimension, or combinations thereof. 
     
     
         7 . The method of  claim 5 , further comprising:
 operating the processor to determine whether the determined energy of bending is expected, unlikely, or forbidden.   
     
     
         8 . The method of  claim 7 , further comprising:
 determining a probability value of the determined energy of bending based on whether a value of the determined energy of bending is greater than a threshold energy value.   
     
     
         9 . The method of  claim 5 , further comprising:
 determining an intra-procedure physical constraint based at least on a physical feature of the subject and the evaluated and predetermined physical constraints;   determining a maximum energy of bending based on the determined intra-procedure physical constraint; and   comparing the maximum energy of bending to the determined energy of bending.   
     
     
         10 . An instrument system operable with a navigation system within a navigation field to determine proper navigation of the instrument in the navigation field, comprising:
 a flexible instrument extending at least between a first portion and a second portion;   a first tracking device fixed to the flexible instrument at the first portion; and   a second tracking device fixed to the flexible instrument at the second portion;   wherein,
 the first tracking device is configured to generate a first signal and transmit the first signal to the navigation system; 
 the second tracking device is configured to generate a second signal and transmit the second signal to the navigation system; 
 the flexible instrument has a predetermined parameterized energy between the first tracking device and the second tracking device and a predetermined energy functional based on the parameterized energy of the instrument between the first tracking device and the second tracking device; and 
 a determined minimization of the energy functional is operable to determine a probable location and orientation of the instrument. 
   
     
     
         11 . The system of  claim 10 , further comprising:
 a memory system having stored thereon at least one instrument physical constraint based on a physical characteristic of the flexible instrument at least between a first instrument position and a second instrument position.   
     
     
         12 . The system of  claim 11 , further comprising:
 the navigation system having a processor configured to:
 access the stored at least one instrument physical constraint stored on the memory system; and 
 execute an algorithm to determine an energy of bending of the flexible instrument based on the accessed stored at least one instrument physical constraint of the flexible instrument. 
   
     
     
         13 . The system of  claim 12 , wherein the processor is further configured to deem improper navigation if a relative location and orientation of the first tracking device and the second tracking device is determined to be improbable based on the recalled at least one instrument physical constraint. 
     
     
         14 . The system of  claim 10 , wherein the navigation of the instrument is able to be deemed improper if the relative location and orientation of the first tracking device and the second tracking device is determined to be improbable based on the recalled at least one instrument constraint. 
     
     
         15 . The system of  claim 10 , wherein the instrument is able to flex to change at least one of a relative distance or orientation between the first portion and the second portion. 
     
     
         16 . The system of  claim 10 , wherein the predetermined parameterized energy is operable to identify an energy threshold and forbidden energies of the instrument. 
     
     
         17 . A system to determine proper navigation of a flexible instrument in a navigation field, comprising:
 a localizer to generate an electromagnetic field as the navigation field;   a navigation processor configured for:
 receiving a first signal from a first tracking device; 
 receiving a second signal from a second tracking device; 
 determining a relative position of the first tracking device and the second tracking device based on the respective received first signal and second signal; and 
 determining whether the determined relative position of the first tracking device and the second tracking device is probable based on a predetermined physical parameterized energy of the flexible instrument between the first tracking device and the second tracking device and a predetermined energy functional based on the physical parameterized energy of the instrument between the first tracking device and the second tracking device, wherein the determination includes an evaluation of the predetermined energy functional. 
   
     
     
         18 . The system of  claim 17 , further comprising:
 the flexible instrument configured to be moved relative to the navigation field;   the first tracking device fixed to the flexible instrument at a first position; and   the second tracking device fixed to the flexible instrument at a second position spaced apart from the first position.   
     
     
         19 . The system of  claim 17 , further comprising:
 a notification system configured to notify a user that the evaluation of the predetermined energy functional is at least one of expected, unlikely, or forbidden.   
     
     
         20 . The system of  claim 17 , further comprising:
 a display device configured to illustrate a model of the flexible instrument;
 wherein the model of the flexible instrument is based on the determined relative position of the first tracking device and the second tracking device and the predetermined physical parameterizable energy.