Tracking catheters based on a model of an impedance tracking field

1. A system for tracking a catheter in a patient comprising:

a plurality of surface electrodes attached to the patient;

a surface patch attached to the patient;

a stylus including a magnetic tracking system for a location of the stylus within a magnetic field; and

a processor coupled to the stylus, the plurality of surface electrodes and the surface patch, the processor configured to:

determine a location of at least one of the plurality of surface electrodes based on the location of the stylus;

store a location of the surface patch and the location of the at least one of the plurality of surface electrodes;

determine a three-dimensional shell shape that corresponds to a portion of the patient;

determine a model of an impedance tracking field in at least a portion of the three-dimensional shell shape;

inject current through one or more of the plurality of surface electrodes to create an electric field in the patient;

fit measured voltages from the catheter to the model of the impedance tracking field to determine locations of the catheter in the patient; and

provide therapy to the patient based on the locations of the catheter.

2. The system of claim 1 , wherein the plurality of surface electrodes is a plurality of electro-cardiogram electrodes attached to the patient.

3. The system of claim 1 , wherein the processor is configured to determine the three-dimensional shell shape based on one or more of an ovoid shape, the location of the surface patch and the location of the at least one of the plurality of surface electrodes, locations of multiple points on surfaces of the patient, and anatomical landmarks in the patient.

4. The system of claim 1 , wherein the processor is configured to determine the model of the impedance tracking field based on estimates of electromagnetic tissue properties of the patient.

5. The system of claim 4 , wherein the estimates of electromagnetic tissue properties of the patient are based on at least one of constant gradients across the patient, estimates of locations of organs in the patient, and electrical impedance tomography imaging of the patient.

6. The system of claim 4 , wherein the processor is configured to refine the model of the impedance tracking field based on at least one of measured voltages from a tracking catheter and magnetically obtained locations of the tracking catheter in the patient.

7. The system of claim 1 , wherein the processor is configured to receive a system reference voltage that is used to obtain the measured voltages from the catheter, the system reference voltage received from at least one of a reference catheter in the patient, a reference patch attached to the patient, one or more of the plurality of surface electrodes, and the surface patch.

8. The system of claim 1 , wherein the processor is configured to provide respiration gating to fit the measured voltages from the catheter to the model of the impedance tracking field to determine the locations of the catheter in the patient.

9. A system for tracking a catheter in a patient comprising:

a plurality of electro-cardiogram electrodes attached to the patient;

a surface back patch that includes a magnetic tracking system that provides location information about a location of the surface back patch on the back of the patient;

a stylus that is enabled for tracking a location of the stylus; and

a processor coupled to the plurality of surface electrodes, the surface back patch, and the stylus, the processor configured to:

determine locations of the plurality of electro-cardiogram electrodes from location information obtained from the stylus;

determine the location of the surface back patch from the location information from the surface back patch;

store the locations of the plurality of electro-cardiogram electrodes and the location of the surface back patch;

determine a three-dimensional shell shape that corresponds to a portion of the patient based on the locations of the plurality of electro-cardiogram electrodes and the location of the surface back patch;

determine a model of an impedance tracking field in at least a portion of the three-dimensional shell shape;

inject current through one or more of the plurality of electro-cardiogram electrodes to create an electric field in the patient;

fit measured voltages from the catheter to the model of the impedance tracking field to determine locations of the catheter in the patient; and

provide therapy to the patient based on the locations of the catheter.

10. The system of claim 9 , wherein the processor is configured to determine the three-dimensional shell shape based on one or more of an ovoid shape, locations of multiple points on surfaces of the patient, and anatomical landmarks in the patient.

11. The system of claim 9 , wherein the processor is configured to determine the model of the impedance tracking field based on estimates of electromagnetic tissue properties of the patient including one or more of constant gradients across the patient, estimates of locations of organs in the patient, and electrical impedance tomography imaging of the patient.

12. The system of claim 9 , wherein the processor is configured to receive a system reference voltage obtained from one or more of a reference catheter in the patient, a reference patch attached to the patient, one or more of the plurality of surface electrodes, and the surface patch.

13. A method of tracking a catheter in a patient comprising:

receiving, by a processor, a signal transmitted from a stylus indicating a location of the stylus;

determining, by a processor and based on the signal received from the stylus, a location of at least one of a plurality of surface electrodes attached to the patient;

storing, by the processor, the location of the at least one of the plurality of surface electrodes;

storing, by the processor, a location of a surface patch attached to the patient;

determining, by the processor, a three-dimensional shell shape that corresponds to a portion of the patient;

determining, by the processor, a model of an impedance tracking field in at least a portion of the three-dimensional shell shape;

injecting, by the processor, current to one or more of the plurality of surface electrodes to create an electric field in the patient;

fitting, by the processor, measured voltages from the catheter to the model of the impedance tracking field to track locations of the catheter in the patient; and

providing, by the processor, therapy to the patient based on the locations of the catheter.

14. The method of claim 13 , wherein storing the location of the surface patch includes obtaining location information from a tracking system in a surface back patch, and wherein determining the location of the at least one of a plurality of surface electrodes includes determining, by the processor, a location of at least one of a plurality of electro-cardiogram electrodes attached to the patient.

15. The method of claim 13 , wherein determining, by the processor, the three-dimensional shell shape includes determining the three-dimensional shell shape based on one or more of an ovoid shape, the location of the surface patch and the location of the at least one of the plurality of surface electrodes, locations of multiple points on surfaces of the patient, and anatomical landmarks in the patient.

16. The method of claim 13 , wherein determining, by the processor, the model of the impedance tracking field in at least a portion of the three-dimensional shell shape, includes determining the model based on estimates of electromagnetic tissue properties of the patient that include one or more of constant gradients across the patient, estimates of locations of organs in the patient, electrical impedance tomography imaging of the patient, measured voltages from a tracking catheter and magnetically obtained locations of the tracking catheter in the patient.

17. The method of claim 13 , wherein the processor 26 is configured to provide respiration gating while obtaining the measured voltages from the catheter.