Impedance registration and catheter tracking

Abstract

Methods and systems are disclosed for determining information about a position of an object within a distribution of materials having different complex conductivities. The method includes: (i) causing current to flow in the distribution; (ii) measuring an electrical signal at each of multiple locations in the distribution of materials in response to the current flow; (iii) providing spatial information about the distribution of materials with respect to a first reference frame, the spatial information indicative of regions of different complex conductivity in the distribution of materials; and (iv) determining the position of the object with respect to the spatial information about the distribution of materials based on measured electrical signals and the spatial information. In certain embodiments, the object is a catheter inserted into a patients heart cavity for cardiac mapping.

1 . A method for determining information about a position of an object within a distribution of materials having different complex conductivities, the method comprising:
 causing current to flow in the distribution;   measuring an electrical signal at each of multiple locations in the distribution of materials in response to the current flow;   providing spatial information about the distribution of materials with respect to a first reference frame, the spatial information indicative of regions of different complex conductivity in the distribution of materials; and   determining the position of the object with respect to the spatial information about the distribution of materials based on the measured electrical signals and the spatial information.   
   
   
       2 . The method of  claim 1 , wherein determining the position of the object relative to the first reference frame comprises using an optimization algorithm that minimizes differences between the measured electrical signals and predicted signals determined from the spatial information about the distribution of materials as a function of the relative position. 
   
   
       3 . The method of  claim 2 , wherein the optimization algorithm further determines a conductivity value for each of one or more of the materials in the distribution of materials. 
   
   
       4 . The method of  claim 1 , wherein the distribution of materials comprises a patient's heart cavity and the object is a catheter inserted into the patient's heart. 
   
   
       5 . The method of  claim 4 , wherein the spatial information about the distribution of materials is based on one or more of: a computed tomography (CT) image; a magnetic resonance imaging (MRI) image; a fluoroscopic rotational angiography image; and an ultrasound image. 
   
   
       6 . The method of  claim 4 , wherein at least some of the electrodes that cause the current to flow are located on different regions of the catheter. 
   
   
       7 . The method of  claim 4 , wherein the catheter comprises spatially distributed electrodes to measure at least some of the electrical signals produced in response to the injected current. 
   
   
       8 . The method of  claim 7 , wherein the electrodes on the catheter are further used to measure electrical signals indicative of cardiac electrical activity. 
   
   
       9 . The method of  claim 8 , wherein the current is injected at frequencies spaced from those corresponding to the cardiac electrical activity and the determining comprises frequency processing the measured electrical signal to distinguish electrical signals responsive to the injected current from those corresponding to cardiac electrical activity. 
   
   
       10 . The method of  claim 4 , further comprising repeating the causing, measuring, and determining steps to track the position of the catheter in the heart with respect to the first reference frame. 
   
   
       11 . The method of  claim 4 , wherein the catheter further comprises at least one tracking element whose position in a second reference frame is detectable by an independent tracking system. 
   
   
       12 . The method of  claim 11 , wherein the method further comprises using the determined information about the position of the catheter to register the first and second reference frames. 
   
   
       13 . The method of  claim 4 , wherein the spatial information corresponds to a specific point in a cardiac cycle. 
   
   
       14 . The method of  claim 13 , further comprising synchronizing the injecting and the measuring with respect to the cardiac cycle. 
   
   
       15 . The method of  claim 4 , wherein the spatial information corresponds to an average of the geometrical configuration of the heart cavity over multiple cardiac cycles. 
   
   
       16 . A method for determining a transformation for registering first and second reference frames for a distribution of materials, the method comprising:
 causing current to flow in the distribution;   measuring an electrical signal at each of multiple locations in the distribution of materials in response to the current flow;   providing spatial information about the distribution of materials with respect to the first reference frame, the spatial information indicative of regions of different complex conductivity in the distribution of materials;   providing positions in the second reference frame for the multiple locations at which the electrical signals are measured; and   determining the transformation based on the measured electrical signals, the spatial information about the distribution of materials, and the positions in the second reference frame for the multiple locations at which the electrical signals are measured.   
   
   
       17 . The method of  claim 16 ,
 wherein the distribution of materials comprises a patient's heart cavity,   wherein at least some of the electrical signals are measured by electrodes on a catheter inserted into the heart cavity, and   wherein the second reference frame corresponds to coordinates provided by a tracking system for the catheter.   
   
   
       18 . A system for determining information about a position of an object within a distribution of materials having different complex conductivities, the system comprising:
 electronics for causing current to flow in the distribution;   electronics for measuring an electrical signal at each of multiple locations in the distribution of materials in response to the current flow; and   an electronic processor coupled to current causing and signal measuring electronics, wherein the electronic processor is configured to determine the position of the object with respect to spatial information about the distribution of materials based on the measured electrical signals and the spatial information, wherein the spatial information is indicative of regions of different complex conductivity in the distribution of materials with respect to a first reference frame.   
   
   
       19 . The system of  claim 18 , wherein the determination of the position of the object relative to the first reference frame by the electronic processor comprises using an optimization algorithm that minimizes differences between the measured electrical signals and predicted signals determined from the spatial information about the distribution of materials as a function of the relative position. 
   
   
       20 . The system of  claim 19 , wherein the optimization algorithm further determines a conductivity value for each of one or more of the materials in the distribution of materials. 
   
   
       21 . The system of  claim 18 , wherein the distribution of materials comprises a patient's heart cavity, the object is a catheter configured to be inserted into the patient's heart, and wherein the system includes the catheter. 
   
   
       22 . The system of  claim 21 , wherein the spatial information about the distribution of materials is based on one or more of: a computed tomography (CT) image; a magnetic resonance imaging (MRI) image; a fluoroscopic rotational angiography image; and an ultrasound image. 
   
   
       23 . The system of  claim 21 , wherein the catheter comprises current injecting electrodes coupled to the current causing electronics for causing the current to flow. 
   
   
       24 . The system of  claim 23 , further comprising a second catheter comprising additional current injecting electrodes coupled to the current causing electronics. 
   
   
       25 . The system of  claim 21 , wherein the catheter comprises spatially distributed electrodes coupled to the measuring electronics to measure at least some of the electrical signals produced in response to the injected current. 
   
   
       26 . The system of  claim 25 , wherein the electronic processor is further configured to use electrical signals measured by the electrodes on the catheter to determine information about cardiac electrical activity. 
   
   
       27 . The system of  claim 26 , wherein the current causing electronics causes the current to be injected at frequencies spaced from those corresponding to the cardiac electrical activity, and wherein the measuring electronics is configured to frequency process the measured electrical signal to distinguish electrical signals indicative of cardiac electrical activity from those responsive to the injected current. 
   
   
       28 . The system of  claim 23 , wherein the surface of one or more of the current injection electrode has a coating to reduce its electrical impedance with respect to blood in the heart cavity. 
   
   
       29 . The system of  claim 23 , wherein the current injection electrodes are positioned at opposite ends of a deployed configuration for the catheter with respect to each of multiple axes. 
   
   
       30 . The system of  claim 21 , wherein the electronic processor is configured to track the position of the catheter in the heart with respect to the first reference frame in response to the current injection and signal measuring. 
   
   
       31 . The system of  claim 21 , further comprising at least one tracking element coupled to the catheter and an independent tracking system coupled to the electronic processor for providing the position of the tracking element in a second reference frame. 
   
   
       32 . The system of  claim 31 , wherein the electronic processor is further configured to use the determined information about the position of the catheter to register the first and second reference frames. 
   
   
       33 . The system of  claim 21 , wherein the electronic processor is configured to process the measured signals for each of multiple catheter locations within the heart, and wherein the position of the catheter is determined based on the measured electrical signals for all of the multiple catheter locations, the spatial information about the distribution of materials, and relative changes in the position of the catheter corresponding to the multiple locations. 
   
   
       34 . The system of  claim 21 , wherein the spatial information corresponds to a specific point in a cardiac cycle. 
   
   
       35 . The system of  claim 21 , wherein the electronics are configured to synchronize the current injection and the signal measuring with respect to the cardiac cycle. 
   
   
       36 . The system of  claim 21 , wherein the spatial information corresponds to an average of the geometrical configuration of the heart cavity over multiple cardiac cycles. 
   
   
       37 . A system for determining a transformation for registering first and second reference frames for a distribution of materials, the system comprising:
 electronics for causing current to flow in the distribution;   electronics for measuring an electrical signal at each of multiple locations in the distribution of materials in response to the current flow; and   an electronic processor coupled to the current causing and signal measuring electronics and configured to determine the transformation based on the measured electrical signals, a spatial information about the distribution of materials with respect to the first reference frame, and positions in the second reference frame for the multiple locations at which the electrical signals are measured,   wherein the spatial information about the distribution of materials with respect to the first reference frame is indicative of regions of different complex conductivity in the distribution of materials.   
   
   
       38 . The system of  claim 37 , wherein the distribution of materials comprises a patient's heart cavity, and wherein the system further comprises a catheter configured for insertion into the heart cavity and an independent tracking system for the catheter, wherein at least some of the electrical signals are measured by electrodes on the catheter and wherein the second reference frame corresponds to coordinates provided by the tracking system for the catheter. 
   
   
       39 . The method of  claim 1 , wherein the spatial information comprises a conductivity value for each of the regions of different complex conductivity in the distribution of materials. 
   
   
       40 . The system of  claim 18 , wherein the spatial information comprises a conductivity value for each of the regions of different complex conductivity in the distribution of materials.