Reference Structure for a Tracking System
An volume of a patient can be mapped with a system operable to identify a plurality of locations and save a plurality of locations of a mapping instrument. The mapping instrument can include one or more electrodes that can sense a voltage that can be correlated to a three dimensional location of the electrode at the time of the sensing or measurement. Therefore, a map of a volume can be determined based upon the sensing of the plurality of points without the use of other imaging devices. An implantable medical device can then be navigated relative to the mapping data.
1 . A system to determine the position of an instrument within a volume of a patient, comprising:
a first set of electrodes positioned on the patient;
a drive system operable to drive the set of electrodes to inject a current into the volume of the patient;
a processor operable to control the drive system; and
a first reference electrode fixedly positioned on a surface of the patient at a first reference location and operable to sense a voltage based on the current injected into the volume of the patient;
a processor to determine a reference electrical property at the first reference position;
wherein the first reference electrode patch is positioned on a ventral side of the patient and operable to sense an electrical property at the first fixed reference location on the patient based on the injected current.
2 . The system of claim 1 , further comprising:
a second reference electrode patch positioned at a dorsal location directly opposed to the first reference electrode patch;
wherein the second reference electrode patch is positioned on the patient and operable to sense the electrical property at a second reference position on the patient based on the injected current;
wherein the first reference electrode patch is positioned substantially over a xiphoid process of the patient.
3 . The system of claim 2 , further comprising:
an instrument operable to be positioned within the volume of the patient; and
a position element on the instrument operable to sense the electrical property at an instrument position;
wherein the processor is operable to evaluate the sensed electrical property at the first and second reference locations and the sensed electrical property at the instrument position and display an icon on a display device to show the relative position of at least one of the first and second reference electrodes and the instrument.
4 . The system of claim 3 , further comprising:
a memory system operable to store a plurality of instrument locations; and
a display device operable to display a representation of the plurality of instrument locations;
wherein at least one of a first reference electrode icon or a second reference electrode icon is displayed on the display device relative to the representation of the plurality of instrument locations.
5 . The system of claim 3 , wherein the processor is operable to be controlled to display the representation of the plurality of instrument locations relative to a selected one of either of the first reference electrode or the second reference electrode.
6 . The system of claim 5 , wherein the representation of the plurality of instrument locations represents at least a portion of a heart of the patient.
7 . The system of claim 6 , wherein the processor is operable to determine the relative position of the stored plurality of positions to generate a map of a heart of the patient;
wherein the processor is operable to determine a position of at least one of the first reference position or the second reference position relative to the map.
8 . A method of determining a position of an instrument within a volume of patient with a reference member, comprising:
connecting to the patient a set of axis electrodes;
injecting a current into the patient with the set of axis electrodes;
positioning a first reference electrode on the patient at a first reference position;
evaluating an electrical property based on input of the first reference electrode including measuring a voltage drop of a patient-to-axis electrode interface;
positioning an instrument with a position element into the patient;
evaluating the electrical property within the patient based at least in part on sensing with the position element; and
determining a position of the instrument based on the evaluated electrical property.
9 . The method of claim 8 , further comprising:
determining a plurality of positions of the instrument;
generating a map of based on the plurality of determined positions;
displaying the map; and
determining a position of the first reference electrode relative to the displayed map.
10 . The method of claim 9 , further comprising:
displaying the determined position of the first reference electrode relative to the displayed map.
11 . The method of claim 10 , further comprising:
orientating the displayed map relative to the patient by displaying the determined first reference position of the first reference electrode, including knowing the position of the first reference electrode on the patient.
12 . The method of claim 11 , further comprising:
fixing the first reference electrode to a ventral surface of the patient over a xiphoid process of the patient.
13 . The method of claim 12 , further comprising:
limiting the relative motion of a heart of the patient relative to the first reference electrode based on positioning the first reference electrode over the xiphoid process.
14 . The method of claim 13 , further comprising:
fixing a second reference electrode at a second reference position substantially opposite the first reference position on a dorsal surface of the patient.
15 . The method of claim 14 , further comprising:
displaying a position of the second reference position relative to the map.
16 . A method of determining the position of an instrument within a volume of a patient, comprising:
positioning at least three sets of electrodes on the patient;
driving the at least three sets of electrodes to inject a current along three substantially orthogonal axes into the volume of the patient;
fixedly positioning a first reference electrode on a ventral surface of the patient at a first reference position;
sensing a voltage based on the current injected into the volume of the patient; and
automatically determining a reference electrical property at the first reference position.
17 . The method of claim 16 , further comprising:
fixedly positioning a second reference electrode on a dorsal surface of the patient at a second reference position; and
determining an impedance between the first reference electrode and the second reference electrode.
18 . The method of claim 16 , further comprising:
moving an instrument having at least a first position element within the volume of the patient;
evaluating an electrical property using the first position element at a plurality of positions of the first position element;
determining a plurality of positions of the first position element at the plurality of positions based on the evaluated electrical signal; and
displaying a map based on the determined positions.
19 . The method of claim 18 , further comprising:
displaying the first reference position relative to the displayed map; and
orienting a user relative to the map and the patient based on the known first reference position of the first reference electrode.
20 . The method of claim 19 , further comprising:
selecting a location of an implantation of a lead in a heart of the patient based at least on orientating the user.