Tracking catheter based on impedance tracking field model

Abstract

A system for tracking a catheter in a patient. The system includes a plurality of surface electrodes and a surface patch attached to the patient, and a processor coupled to the plurality of surface electrodes and the surface patch. The processor determines a position of at least one of the plurality of surface electrodes; stores the position of the surface patch and at least one of the plurality of surface electrodes; determines a three-dimensional shell shape corresponding to a portion of the patient; determines a model of an impedance tracking field in at least a portion of the three-dimensional shell shape; injects a current through one or more of the plurality of surface electrodes; fits a measured voltage from the catheter to the model of the impedance tracking field to determine the position of the catheter; and provides therapy to the patient based on the position of the catheter.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Provisional Patent Application No. 62 / 822,351 filed on March 22, 2019, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to systems and methods for tracking a catheter within a patient, and more particularly, to systems and methods for tracking a catheter without first mapping a region of interest within the patient. The present disclosure also relates to systems and methods for tracking a catheter based on fitting measured voltages to a model of an impedance tracking field in a region of interest within the patient. Background Art

[0004] Some mapping systems provide impedance tracking functionality for navigating a catheter within a patient's body. Typically, in these systems, the impedance tracking functionality relies on injecting current into electrodes so that an electric field is generated within the patient's body. In order to determine the position of the catheter, a dedicated mapping catheter is used to map the electric field distribution in a region of interest (e.g., inside the heart). This mapping catheter can be a magnetic tracking mapping catheter that measures the impedance tracking field in the region of interest. The magnetically tracked position of the catheter and the field voltage measured by the catheter are used to create a map of the region of interest. The system stores the collected data in a map, which may include one or more lookup tables of the measured field voltages. In order to navigate the catheter in the region of interest, the field voltage is measured by the catheter and compared to one or more lookup tables.

[0005] Some systems do not use mapped impedance tracking field information, but instead rely on pairs of electrodes, each placed on opposite sides of the patient's body. The electrode pairs are positioned to generate fields that are approximately orthogonal to each other, so that catheter tracking employs orthogonal fields.

[0006] In other systems, x-ray fluoroscopy is used to navigate catheters within a patient. In x-ray fluoroscopy, by passing an x-ray beam through the body, a continuous x-ray image is produced and displayed on a monitor. In some procedures, fluoroscopy can be combined with an impedance tracking method (such as the impedance tracking method described above) to navigate a catheter within a patient.

[0007] The need to first create a map of the impedance tracking field in the region of interest and / or use x-ray fluoroscopy presents disadvantages. One disadvantage is navigating the catheter within the patient during less complex procedures where it is not worth the time and money to map the region of interest. Another disadvantage is exposing the patient to excessive x-rays during fluoroscopic procedures where the physician and / or medical staff wish to reduce exposure to x-rays.

[0008] Furthermore, systems employing orthogonal electrode pairs increase the cost and complexity of the procedure and equipment, since additional electrode surface patches and corresponding system connections are required. Furthermore, employing field orthogonality provides only limited accuracy, since the exact electrode locations remain unknown. Summary of the invention

[0009] In Example 1, a system for tracking a catheter in a patient includes a plurality of surface electrodes attached to the patient, a surface patch attached to the patient, and a processor coupled to the plurality of surface electrodes and the surface patch. The processor is configured to: determine a position of at least one of the plurality of surface electrodes; store the position of the surface patch and the position of at least one of the plurality of surface electrodes; determine a three-dimensional shell shape corresponding 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 a measured voltage from the catheter to the model of the impedance tracking field to determine the position of the catheter in the patient; and provide therapy to the patient based on the position of the catheter.

[0010] In Example 2, the system of Example 1, wherein the plurality of surface electrodes is a plurality of electrocardiogram electrodes attached to the patient.

[0011] In Example 3, the system according to any of Examples 1 and 2, wherein the surface patch is a surface back patch including a magnetic tracking system that provides position information about the position of the surface back patch attached to the patient's back.

[0012] In Example 4, the system according to any one of Examples 1 to 3 includes a stylus capable of tracking the position of the stylus, wherein the processor is coupled to the stylus and is configured to determine the position of at least one of the plurality of surface electrodes by receiving position information from the stylus when the stylus contacts the electrode.

[0013] In Example 5, a system according to any of Examples 1 to 4, wherein the processor is configured to determine the three-dimensional shell shape based on one or more of: an oval shape, a location of a surface patch and a location of at least one of a plurality of surface electrodes, a location of a plurality of points on a surface of the patient, and anatomical landmarks within the patient.

[0014] In Example 6, a system according to any one of Examples 1 to 5, wherein the processor is configured to determine a model of the impedance tracking field based on an estimate of electromagnetic tissue properties of the patient, the estimate of the electromagnetic tissue properties of the patient being based on at least one of: a constant gradient across the patient, an estimate of the position of an organ within the patient, and electrical impedance tomography of the patient.

[0015] In Example 7, according to any one of Examples 1 to 6, the processor is configured to refine the model of the impedance tracking field based on at least one of a measured voltage from the tracking catheter and a magnetically obtained position of the tracking catheter within the patient.

[0016] In Example 8, the system according to any one of Examples 1 to 7, wherein the processor is configured to provide respiration gating to fit the measured voltage from the catheter to a model of the impedance tracking field to determine the position of the catheter within the patient.

[0017] In Example 9, a method for tracking a catheter includes: determining, by a processor, a position of at least one of a plurality of surface electrodes attached to a patient; storing, by the processor, the position of at least one of the plurality of surface electrodes; storing, by the processor, a position of a surface patch attached to the patient; determining, by the processor, a three-dimensional shell shape corresponding 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 into one or more of the plurality of surface electrodes to create an electric field in the patient; fitting, by the processor, a measured voltage from the catheter to the model of the impedance tracking field to track the position of the catheter in the patient; and providing, by the processor, treatment to the patient based on the position of the catheter.

[0018] In Example 10, according to the method of Example 9, wherein storing the position of the surface patch includes obtaining position information from a tracking system in the surface back patch, and wherein determining the position of at least one of the plurality of surface electrodes includes determining, by a processor, the position of at least one of the plurality of electrocardiogram electrodes attached to the patient.

[0019] In Example 11, the method of any one of Examples 9 and 10 includes, in determining the position of at least one of the plurality of surface electrodes, receiving position information from a stylus capable of tracking a position of the stylus.

[0020] In Example 12, according to the method of Example 11, determining, by the processor, the three-dimensional shell shape includes determining the three-dimensional shell shape based on one or more of: a position of a surface patch and a position of at least one of a plurality of surface electrodes determined based on position information received from a stylus, positions of a plurality of points on a surface of a patient determined based on position information received from the stylus, and positions of anatomical landmarks within the patient's body determined based on position information received from the stylus.

[0021] In Example 13, according to the method of any one of Examples 9 to 12, determining, by the processor, the three-dimensional shell shape includes determining the three-dimensional shell shape based on one or more of: an oval shape, a position of a surface patch and a position of at least one of a plurality of surface electrodes, a position of a plurality of points on the surface of the patient, and anatomical landmarks within the patient.

[0022] In Example 14, according to the method of any one of Examples 9 to 13, determining by the processor a model of the impedance tracking field in at least a portion of the three-dimensional shell shape includes determining the model based on an estimate of electromagnetic tissue properties of the patient, the estimate of the electromagnetic tissue properties including one or more of: a constant gradient across the patient, an estimate of the position of an organ within the patient, electrical impedance tomography of the patient (such as electrical impedance tomography of the patient based on sensed impedance between electrodes), a measured voltage from a tracking catheter, and a magnetically obtained position of the tracking catheter within the patient.

[0023] In Example 15, according to the method of any one of Examples 9 to 14, wherein fitting, by the processor, the measured voltage from the catheter to the model of the impedance tracking field comprises respiratory gating.

[0024] In Example 16, a system for tracking a catheter in a patient includes a plurality of surface electrodes attached to the patient, a surface patch attached to the patient, and a processor coupled to the plurality of surface electrodes and the surface patch. The processor is configured to: determine a position of at least one of the plurality of surface electrodes; store the position of the surface patch and the position of at least one of the plurality of surface electrodes; determine a three-dimensional shell shape corresponding 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 a measured voltage from the catheter to the model of the impedance tracking field to determine the position of the catheter in the patient; and provide therapy to the patient based on the position of the catheter.

[0025] In Example 17, the system of Example 16, wherein the plurality of surface electrodes are a plurality of electrocardiogram electrodes attached to the patient.

[0026] In Example 18, the system of Example 16, wherein the surface patch is a surface back patch comprising a magnetic tracking system that provides position information about the position of the surface back patch attached to the patient's back.

[0027] In Example 19, the system according to Example 16 includes a stylus operable to track a position of the stylus, wherein the processor is coupled to the stylus and configured to determine a position of at least one of the plurality of surface electrodes by receiving position information from the stylus.

[0028] In Example 20, a system according to Example 16, wherein the processor is configured to determine the three-dimensional shell shape based on one or more of: an oval shape, a location of a surface patch and a location of at least one of a plurality of surface electrodes, a location of a plurality of points on the surface of the patient, and anatomical landmarks within the patient.

[0029] In Example 21, the system of Example 16, wherein the processor is configured to determine the model of the impedance tracking field based on an estimate of electromagnetic tissue properties of the patient.

[0030] In Example 22, the system according to Example 21, wherein the estimate of the electromagnetic tissue property of the patient is based on at least one of: a constant gradient across the patient, an estimate of the position of an organ within the patient, and electrical impedance tomography of the patient.

[0031] In Example 23, the system according to Example 21, wherein the processor is configured to refine the model of the impedance tracking field based on at least one of a measured voltage from the tracking catheter and a magnetically obtained position of the tracking catheter within the patient.

[0032] In Example 24, according to the system of Example 16, the processor is configured to receive a system reference voltage for obtaining a measured voltage from the catheter, the system reference voltage being received from at least one of: a reference catheter within the patient, a reference patch attached to the patient, one or more of a plurality of surface electrodes, and a surface patch.

[0033] In Example 25, the system of Example 16, wherein the processor is configured to provide respiratory gating to fit the measured voltage from the catheter to a model of the impedance tracking field to determine the position of the catheter within the patient.

[0034] In Example 26, a system for tracking a catheter in a patient includes: a plurality of electrocardiogram electrodes attached to the patient; a surface back patch including a magnetic tracking system that provides position information about the position of the surface back patch on the patient's back; a stylus that enables the stylus to track the position of the stylus; and a processor coupled to the plurality of surface electrodes, the surface back patch, and the stylus. The processor is configured to: determine the positions of multiple ECG electrodes based on position information obtained from the stylus; determine the position of the surface back patch based on position information from the surface back patch; store the positions of the multiple ECG electrodes and the position of the surface back patch; determine a three-dimensional shell shape corresponding to a portion of the patient based on the positions of the multiple ECG electrodes and the position of the surface back patch; determine a model of the impedance tracking field in at least a portion of the three-dimensional shell shape; inject current through one or more of the multiple ECG electrodes to create an electric field in the patient; fit the measured voltage from the catheter to the model of the impedance tracking field to determine the position of the catheter in the patient; and provide treatment to the patient based on the position of the catheter.

[0035] In Example 27, the system according to Example 26, wherein the processor is configured to determine the three-dimensional shell shape based on one or more of: an oval shape, locations of multiple points on the surface of the patient, and anatomical landmarks within the patient.

[0036] In Example 28, according to Example 26, the processor is configured to determine a model of the impedance tracking field based on an estimate of the patient's electromagnetic tissue properties, the estimate of the electromagnetic tissue properties including one or more of: a constant gradient across the patient, an estimate of the location of organs within the patient, and electrical impedance tomography of the patient (such as electrical impedance tomography of the patient using impedance information measured using multiple surface electrodes and surface patches).

[0037] In Example 29, the system of Example 26, wherein the processor is configured to receive a system reference voltage obtained from one or more of: a reference catheter within the patient, a reference patch attached to the patient, one or more of a plurality of surface electrodes, and a surface patch.

[0038] In Example 30, a method for tracking a catheter within a patient includes: determining, by a processor, a position of at least one of a plurality of surface electrodes attached to the patient; storing, by the processor, the position of at least one of the plurality of surface electrodes; storing, by the processor, a position of a surface patch attached to the patient; determining, by the processor, a three-dimensional shell shape corresponding 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 into one or more of the plurality of surface electrodes to create an electric field within the patient; fitting, by the processor, a measured voltage from the catheter to the model of the impedance tracking field to track the position of the catheter within the patient; and providing, by the processor, treatment to the patient based on the position of the catheter.

[0039] In Example 31, according to the method of Example 30, wherein storing the position of the surface patch includes obtaining position information from a tracking system in the surface back patch, and wherein determining the position of at least one of the plurality of surface electrodes includes determining, by a processor, the position of at least one of the plurality of electrocardiogram electrodes attached to the patient.

[0040] In Example 32, the method of Example 30 includes, in determining the position of at least one of the plurality of surface electrodes, receiving position information from a stylus capable of tracking the position of the stylus.

[0041] In Example 33, according to the method of Example 30, determining, by the processor, the three-dimensional shell shape includes determining the three-dimensional shell shape based on one or more of: an oval shape, a position of a surface patch and a position of at least one of a plurality of surface electrodes, a position of a plurality of points on the surface of the patient, and anatomical landmarks within the patient.

[0042] In Example 34, according to the method of Example 30, determining by the processor a model of the impedance tracking field in at least a portion of the three-dimensional shell shape includes determining the model based on an estimate of electromagnetic tissue properties of the patient, the estimate of the electromagnetic tissue properties including one or more of: a constant gradient across the patient, an estimate of the position of an organ within the patient, electrical impedance tomography of the patient, a measured voltage from a tracking catheter, and a magnetically obtained position of the tracking catheter within the patient.

[0043] In Example 35, according to the method of Example 30, the processor is configured to provide respiratory gating while obtaining the measured voltage from the catheter.

[0044] Although multiple embodiments are disclosed, other embodiments of the present disclosure will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the present disclosure. Therefore, the drawings and detailed description are to be regarded as illustrative in nature, rather than restrictive. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a schematic diagram illustrating a system for tracking a catheter (or multiple catheters) within a patient according to an embodiment of the present disclosure.

[0046] Figure 2 is a diagram illustrating one example of a stylus that can be used to track the position of the stylus in a system according to an embodiment of the present disclosure.

[0047] Figure 3A is a diagram showing a plurality of surface electrodes attached to a patient and a three-dimensional housing shape depicted in dashed lines corresponding to a portion of the patient according to an embodiment of the present disclosure.

[0048] Figure 3B is a diagram showing a surface patch attached to a patient according to an embodiment of the present disclosure.

[0049] Figure 4 is a diagram showing a calculation grid for voltage and complex permittivity according to an embodiment of the present disclosure.

[0050] Figure 5 is a diagram illustrating a finite difference model at a body surface (two-dimensional) according to an embodiment of the present disclosure.

[0051] Figure 6 is a diagram showing a catheter in a patient's heart and a three-dimensional housing shape attached to the patient according to an embodiment of the present disclosure.

[0052] Figure 7 A method of tracking a catheter within a patient according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0053] Figure 1 is a diagram showing a system 20 for tracking a catheter 22 (or multiple catheters 22) within a patient 24 according to an embodiment of the present disclosure. The system 20 is configured to track the catheter 22 in a region of interest (e.g., a heart) within the patient 24 without first mapping the region of interest. The system 20 is configured to track the catheter 22 based on measuring field voltages within the patient 24 using the catheter 22 and fitting the measured field voltages to a model of impedance tracking fields in the region of interest of the patient 24. In an embodiment, the system 20 is used to insert a catheter (such as the catheter 22) into the heart or heart chamber of the patient 24.

[0054] System 20 includes a processor 26, an indicator or stylus 28, a plurality of surface electrodes 30, a surface patch 32, catheter 22, and in at least some embodiments, a magnet 34. In embodiments, the plurality of surface electrodes 30 are a plurality of electrocardiogram (ECG) electrodes attached to patient 24. In some embodiments, the surface patch 32 is a surface back patch attached to the back of patient 24.

[0055] A plurality of surface electrodes 30 and a surface patch 32 are attached to the patient 24 and are coupled to the processor 26 via conductive paths (not shown for clarity). The stylus 28 is coupled to the processor 26 via conductive paths 38, and the magnet 34 is coupled to the processor 26 via conductive paths 40. The catheter 22 is coupled to the processor 26 via conductive paths 42. In an embodiment, one or more of the processor 26, the stylus 28, the plurality of surface electrodes 30, the surface patch 32, the catheter 22, and the magnet 34 may be coupled to the processor 26 via wireless communications.

[0056] The stylus 28 is enabled to be used to track the position of the stylus 28 in the system 20. In an embodiment, the stylus 28 is enabled to track the position of the stylus 28 relative to one or more of: a table on which the patient 24 lies and a magnet 34 or another portion of the system 20. In some embodiments, the stylus 28 includes a magnetic field tracking system that enables the stylus 28 to be used to magnetically track the position of the stylus 28 in the magnetic field of the magnet 34. In some embodiments, the magnet 34 is an electromagnet, and in some embodiments, the magnet 34 is controlled by the processor 26.

[0057] The processor 26 is configured to receive position information from the stylus 28 to determine the positions of the plurality of surface electrodes 30. In an embodiment, the processor 26 is configured to activate the magnet 34, and the stylus 28 is configured to provide the position information to the processor 26. In some embodiments, each of the plurality of surface electrodes 30 is contacted by the stylus 28, and when the stylus 28 is brought into contact with each of the plurality of surface electrodes 30, the stylus 28 provides the processor with position information of the stylus 28. In an embodiment, the processor 26 determines the positions of the stylus 28 and the contacted surface electrodes 30, and stores the positions of the contacted surface electrodes 30.

[0058] The processor 26 is also configured to store the position of the surface patch 32. In an embodiment, the surface patch 32 is enabled to be used to track the position of the surface patch 32 in the system 20. In an embodiment, the surface patch 32 is enabled to be used to track the position of the surface patch 32 relative to one or more of: a table on which the patient 24 lies and a magnet 34 or another part of the system 20. In some embodiments, the surface patch 32 includes a magnetic field tracking system, so that the surface patch 32 can be used to magnetically track the position of the surface patch 32 in the magnetic field of the magnet 34. In an embodiment, the processor 26 is configured to activate the magnet 34, and the surface patch 32 is configured to provide position information to the processor 26. In some embodiments, the surface patch 32 is a surface back patch that includes a magnetic tracking system that provides position information to the processor 26 about the position of the surface back patch attached to the back of the patient 24.

[0059] In some embodiments, the position of the surface patch 32 is obtained using the stylus 28 as described above with respect to the plurality of surface electrodes 30. In an embodiment, the stylus 28 contacts the surface patch 32, and the processor 26 receives position information from the stylus 28 when the stylus contacts the surface patch 32, wherein the processor 26 determines and stores the position of the surface patch 32.

[0060] Processor 26 determines a three-dimensional shell shape corresponding to a portion of patient 24. In some embodiments, processor 26 determines a three-dimensional shell shape corresponding to a region of interest within patient 24. In some embodiments, processor 26 determines a three-dimensional shell shape corresponding to a chest region within patient 24. In an embodiment, processor 26 is configured to determine the three-dimensional shell shape based on one or more of an oval shape, a location of a surface patch 32 and a plurality of surface electrodes 30 on patient 24, a location of a plurality of other points on the surface of patient 24, and anatomical landmarks within patient 24.

[0061] Processor 26 determines a model of the impedance tracking field in at least a portion of the three-dimensional shell shape based on an estimate of electromagnetic tissue properties of patient 24. In an embodiment, the estimate of electromagnetic tissue properties of patient 24 is based on at least one of: a constant gradient across patient 24, an estimate of the location of an organ within patient 24, and electrical impedance tomography (EIT) imaging of patient 24.

[0062] In some embodiments, processor 26 is configured to refine the model of the impedance tracking field based on the position information and the measured field voltage received from the tracking catheter in the patient 24. The tracking catheter measures the field voltage of the impedance tracking field generated in the patient 24, such as by injecting current into the surface patch 32 through multiple surface electrodes 30 and the patient 24. Processor 32 fits the model of the impedance tracking field to the measured voltage to refine the model. In some embodiments, the tracking catheter is catheter 22. In some embodiments, the tracking catheter includes a magnetic tracking system that provides position information about the tracking catheter position and the measured field voltage to processor 26.

[0063] To track a catheter, such as catheter 22, in a region of interest within patient 24, processor 26 is configured to inject current through one or more of plurality of surface electrodes 30 to create an electric field in patient 24. This electric field is an impedance tracking field that is used to track the position of catheter 22. In operation, catheter 22 measures the field voltage of the impedance tracking field, and processor 26 fits the measured field voltage from catheter 22 to a model of the impedance tracking field and determines the position of catheter 22 in patient 24.

[0064] Furthermore, processor 26 receives a system reference voltage for obtaining the measured field voltage from catheter 22. In an embodiment, the system reference voltage is received from a reference catheter within patient 24, a reference patch attached to patient 24, one or more of the plurality of surface electrodes 30, and at least one of the surface patches 32. Furthermore, in some embodiments, processor 26 is configured to provide respiratory gating to fit the measured field voltage from catheter 22 to a model of the impedance tracking field to determine the position of catheter 22 within patient 24.

[0065] The catheter 22 is a movable catheter 22 having one or more spatially distributed electrodes. The catheter 22 can be used to perform various medical procedures, such as cardiac mapping and / or medical treatments including ablation (such as radiofrequency (RF) ablation and / or cryoablation). The catheter 22 is used by medical personnel and / or doctors based on the position of the catheter 22 in the patient 24 determined by the processor 26.

[0066] In some embodiments, the catheter 22 is equipped with various types of electrodes configured to perform various functions. For example, the catheter 22 may include at least one pair of current injection electrodes (CIE) configured to inject current into a medium in which the catheter 22 is disposed. The catheter 22 may also include a plurality of potential measuring electrodes (PEM) configured to measure the potential generated by the current injected by the current injection electrodes. In some embodiments, PME is used for cardiac mapping. In some embodiments, the relative positions of a plurality of catheters 22 disposed in the heart or a cardiac chamber of the heart of the patient 24 are determined based on the measured field voltage obtained by the PME on the catheter 22. In some embodiments, the position of the catheter 22 may be determined relative to the surface of an organ (such as the heart of the patient 24).

[0067] Further, with respect to the system 20, the processor 26 is configured to provide and actually provide the functions of the system 20. The processor 26 is a processor-based device, which includes one or more computers, microprocessors and / or other types of processor-based devices suitable for a variety of applications. The processor 26 may include volatile and / or non-volatile memory elements 44 and peripheral devices to implement input / output functions. The peripheral devices may include, for example, a CD-ROM drive, a floppy disk drive and / or a network connection for downloading relevant content to the processor 26. Such peripheral devices may also be used to download software containing computer instructions to implement the operation of the processor 26, and to download software-implemented programs to perform the operation of the system 20. The processor 26 may be implemented on a single or multiple processor-based platforms capable of performing the functions of the system 20. Additionally, one or more of the processes performed by the processor 26 may be implemented using processing hardware, such as a digital signal processor (DSP), a field programmable gate array (FPGA), a mixed signal integrated circuit, and an application specific integrated circuit (ASIC).

[0068] In an embodiment, the processor 26 includes an electronic module 46 coupled to one or more of the stylus 28, the plurality of surface electrodes 30, the surface patch 32, and the catheter 22 to receive signals from and provide signals to one or more of the stylus 28, the plurality of surface electrodes 30, the surface patch 32, and the catheter 22. The electronic module 46 may include a signal generation module for injecting current into a region of interest, such as a heart chamber, through the surface electrodes 30. The electronic module 46 may also include a signal acquisition module for measuring electrical potentials through the surface electrodes 30 and / or through electrodes (e.g., PMEs) of the catheter 22. The electronic module 46 may also include a signal acquisition module for receiving position information from the stylus 28 and / or receiving position information from the surface patch 32. In an embodiment, the electronic module 46 is used to sample, sense, filter, and amplify one or more of the received signals.

[0069] The electronic module 46 can be implemented using analog or digital electronics or a combination of both. In some embodiments, the electronic module 46 is implemented using integrated components on a dedicated printed circuit board. In some embodiments, at least some of the signal conditioning tasks are implemented by one or more of a central processing unit (CPU), an FPGA, and a DSP. In some embodiments, the electronic module 46 is implemented using analog hardware enhanced with signal processing capabilities provided by the CPU, FPGA, and DSP devices.

[0070] like Figure 1 As shown, the system 20 also includes input / output devices 48, such as a mouse and keyboard, a printer 50, and a display device 52, which may include a touch screen. In addition, the system 20 includes a storage device 54 for storing data collected by the processor 26. The input / output device 48, the printer 50, the display device 52, and the storage device 54 are each communicatively coupled to the processor 26, such as by a wired connection or wirelessly.

[0071] The processor 26 may access one or more input devices for obtaining input data, and one or more output devices for communicating output data. In an embodiment, the input / output devices 48 include one or more of the following: random access memory (RAM), redundant array of independent disks (RAID), floppy disk drive, compact disc (CD) drive, DVD drive, disk, internal hard drive, external hard drive, memory stick, and other storage devices that can be accessed by the processor 26, wherein such foregoing examples are not exhaustive and are for illustration rather than limitation.

[0072] The systems and methods described herein are not limited to a hardware / software configuration. The systems and methods may be implemented in hardware or a combination of hardware and software, and / or may be implemented by commercially available modules, applications, and devices. In the case where the systems and methods described herein are at least partially based on the use of computers, microprocessors, and / or other computing devices, the systems and methods may be implemented with one or more computer programs, wherein a computer program may be understood to include one or more processor executable instructions. The computer program may be executed on processor 26 and may be stored on one or more storage media that may be read by processor 26, such as memory element 44 and storage device 54.

[0073] In addition, the computer program can be implemented using one or more high-level processes or object-oriented programming languages ​​to communicate with the computer system, and / or the computer program can be implemented in assembly or machine language. The language can be compiled or interpreted. The device and / or computer system integrated with the processor 26 can include, for example, a personal computer, a workstation (e.g., Sun, HP), a personal digital assistant (PDA), a handheld device such as a cellular phone, a laptop, a handheld device, or another device that can be integrated with the processor. Therefore, the device provided herein is not exhaustive, and is provided for illustration rather than limitation.

[0074] Moreover, throughout this disclosure, references to "microprocessor" and "processor" or "the microprocessor" and "the processor" may be understood to include one or more microprocessors and / or processors that may communicate in an independent and / or distributed environment and may therefore be configured to communicate with other processors via wired or wireless communications. Additionally, unless otherwise specified, references to memory may include one or more processor-readable and accessible memory elements and / or components that may be internal to a processor device, and / or external to a processor device, and may be accessed via a wired or wireless network using various communication protocols, and may be arranged to include a combination of external and internal memory devices, unless otherwise specified, wherein such memory may be contiguous and / or partitioned based on application. Thus, references to a database may be understood to include one or more memory associations, wherein such references may include commercially available database products (e.g., SQL, Informix, Oracle) and / or proprietary databases, and may also include other structures for associating memory such as links, queues, graphs, trees, wherein such structures are provided for illustration and not limitation.

[0075] Figure 2is a diagram showing one example of a stylus 28 that can be used to track the position of the stylus 28 in the system 20 according to an embodiment of the present disclosure. In an embodiment, the stylus 28 is configured to determine six degrees of freedom in a six-degree-of-freedom electromagnetic tracking system. Moreover, in an embodiment, the stylus 28 is at least one of non-sterile and reusable.

[0076] In the example embodiments described herein, the stylus 28 includes three magnetic tracking coils 60a-60c for determining the position of the stylus 28 in the magnetic tracking field generated by the magnet 34. In other example embodiments, the stylus 28 includes only two magnetic coils for determining six degrees of freedom. In some example embodiments, the stylus 28 includes only two magnetic coils for determining six degrees of freedom, wherein the two magnetic coils are not orthogonal or parallel to each other.

[0077] In the present example, three magnetic coils 60a-60c are disposed at or toward the distal end 62 of the stylus 28. The three magnetic coils 60a-60c are oriented orthogonally to one another, such that one coil is disposed in each of the three xyz axis directions. Each of the three magnetic tracking coils 60a-60c is electrically coupled to the processor 26 in the conductive path 38, such as by a separate line. The stylus 28 and the connecting conductive path 38 are long enough to reach each of the surface electrodes 30 while the magnetic tracking coils 60a-60c remain within the magnetic tracking field created by the magnet 34. In some embodiments, the three magnetic coils 60a-60c are not oriented orthogonally to one another. Moreover, in other embodiments, the stylus 28 includes less than three magnetic coils 60a-60c or more than three magnetic coils 60a-60c, wherein the less than three magnetic coils and the more than three magnetic coils may be orthogonal or non-orthogonal to one another.

[0078] In operation, processor 26 activates magnet 34 to generate magnetic tracking field(s), and each of the three magnetic tracking coils 60a-60c transmits a signal corresponding to the magnetic tracking field(s) back to processor 26. Processor 26 receives the signals and determines the position of stylus 28 in the magnetic tracking field and relative to system 20, such as relative to one or more of: the table on which patient 24 lies and magnet 34 or another portion of system 20.

[0079] In some embodiments, stylus 28 includes a distal tip 64 that can be depressed, such as by contacting electrodes, and stylus 28 transmits a signal to processor 26 in response to distal tip 64 being depressed. The signal can be used by processor 26 to indicate that the signals currently transmitted by magnetic tracking coils 60a-60c are to be used to determine the position of stylus 28. Also, in some embodiments, distal tip 64 of stylus 28 can be depressed, and stylus 28 transmits one or more separate signals to processor 26 in response to distal tip 64 being depressed and the signals from magnetic tracking coils 60a-60c to be used to determine the position of stylus 28. In other embodiments, stylus 28 can be otherwise configured to indicate that stylus 28 has been brought into contact with an object, such as an electrode, such as by using capacitance or inductance.

[0080] Figure 3A and Figure 3B is a diagram showing a plurality of surface electrodes 30 and a surface patch 32 attached to a patient 24 according to an embodiment of the present disclosure.

[0081] Figure 3A is a diagram showing a plurality of surface electrodes 30 attached to a patient 24 and a three-dimensional housing shape 66 depicted in dashed lines corresponding to a portion of the patient 24 according to an embodiment of the present disclosure. In this example, the plurality of surface electrodes 30 are a plurality of ECG electrodes 30 attached to the patient 24. In an embodiment, the plurality of ECG electrodes 30 includes 10 electrodes. In other embodiments, the plurality of ECG electrodes 30 includes more than 10 electrodes, such as 12 or more electrodes. In some embodiments, the plurality of ECG electrodes 30 includes less than 10 electrodes.

[0082] To obtain the position of the plurality of ECG electrodes 30 attached to the patient 24, at least one of the plurality of ECG electrodes 30 is contacted by the stylus 28, and the stylus 28 provides signals from the three magnetic tracking coils 60a-60c to the processor 26. The stylus 28 is contacted to at least one of the plurality of ECG electrodes 30 by one or more medical personnel, such as a doctor, a nurse, and / or a mapping specialist. In an embodiment, the stylus 28 also provides a separate signal to one of the plurality of ECG electrodes 30 indicating that the stylus 28 has been contacted, and the processor 26 uses this signal to indicate that the signals transmitted by the magnetic tracking coils 60a-60c are to be used to determine the position of the stylus 28. In some embodiments, the positions of other electrodes in the plurality of ECG electrodes 30 are calculated or determined based on the position of at least one of the plurality of ECG electrodes 30 determined as above.

[0083] In an embodiment, to obtain the position of each of the plurality of ECG electrodes 30 attached to the patient 24, each of the plurality of ECG electrodes 30 is contacted by the stylus 28, and when each of the plurality of ECG electrodes 30 is contacted, the stylus 28 provides signals from the three magnetic tracking coils 60a-60c to the processor 26. In an embodiment, when each of the plurality of ECG electrodes 30 is contacted, the stylus 28 provides a separate signal to one of the plurality of ECG electrodes 30 indicating that the stylus 28 is being contacted.

[0084] Processor 26 receives signals from stylus 28 and determines the position of stylus 28 and contacted ECG electrodes 30. Processor 26 then stores the position of stylus 28 and contacted ECG electrodes 30.

[0085] Figure 3B is a diagram showing a surface patch 32 attached to a patient 24 according to an embodiment of the present disclosure. In this example, the surface patch 32 is a back patch 32 attached to the back of the patient 24. The back patch 32 is configured to magnetically track the position of the back patch 32 in the magnetic tracking field of the magnet 34. In an embodiment, the back patch 32 is configured to magnetically track 5 or 6 degrees of freedom in the magnetic tracking field of the magnet 34. In some embodiments, the back patch 32 includes one magnetic tracking coil for determining five degrees of freedom. In some embodiments, the back patch 32 includes two magnetic tracking coils for determining six degrees of freedom. In some embodiments, the back patch 32 includes three magnetic tracking coils for determining six degrees of freedom. In some embodiments, the back patch 32 includes two magnetic coils for determining six degrees of freedom, wherein the two magnetic coils are not orthogonal or parallel to each other. In some embodiments, the back patch 32 includes three magnetic tracking coils similar to the three magnetic tracking coils 60a-60c described above for the stylus 28.

[0086] The back patch 32 is enabled to be used to track the position of the back patch 32 relative to one or more of: the table on which the patient 24 lies and the magnet 34 or another part of the system 20. In some embodiments, the two or three magnetic coils are not oriented orthogonally to each other. Moreover, in other embodiments, the back patch 32 includes less than three magnetic coils or more than three magnetic coils.

[0087] To obtain the position of the back patch 32, the processor 26 activates the magnet 34, and the back patch 32 provides a signal from the magnetic coil to provide position information to the processor 26. The processor 26 receives the signal from the back patch 32 and determines the position of the back patch 32. The processor 26 then stores the position of the back patch 32.

[0088] Moreover, in some embodiments, changes in the position and / or orientation of the back patch 32 represent shifts in the position of the patient 24. These shifts in the position of the patient 24 are detected using the back patch 32 and used by the processor 26 to compensate for, for example, the tracked position or orientation of the catheter 22. Among other things, the back patch 32 is used as an impedance tracking spatial reference. Thus, if the patient 24 moves relative to the magnetic tracking reference frame, the movement is detected and a mathematical correction is applied so that the impedance tracked and / or magnetically tracked catheter 22 remains in the same coordinate system.

[0089] In some embodiments, the position of the back patch 32 is obtained using the stylus 28 as described above with respect to the plurality of ECG electrodes 30. In an embodiment, the stylus 28 is brought into contact with the back plate 32, and the processor 26 receives position information from the stylus 28 when the stylus contacts the back plate 32. The processor 26 then determines the position of the stylus 28 and the back patch 32 and stores the position of the stylus 28 and the back patch 32.

[0090] After the locations of at least one or all of the plurality of ECG electrodes 30 and back patch 32 are known and recorded, processor 26 determines a three-dimensional shell shape 66 and a mathematical model of the electric field passing through the three-dimensional shell shape 66. In the current example, the three-dimensional shell shape 66 corresponds to a chest region within patient 24 that includes the heart of patient 24.

[0091] The processor 26 determines a three-dimensional shell shape 66. In some embodiments, the processor 26 determines the three-dimensional shell shape 66 as a simple oval shape with little or no scaling. In some embodiments, the processor 26 determines the three-dimensional shell shape 66 using an optimization algorithm to scale the oval shape to a best fit within the location of at least one or all of the plurality of ECG electrodes 30 and the back patch 32.

[0092] In some embodiments, the processor 26 fits the three-dimensional shell shape 66 to the location of at least one or all of the plurality of ECG electrodes 30 and the back patch 32. In some embodiments, the processor 26 determines the three-dimensional shell shape 66 using an optimization algorithm to obtain the best fit with the location of at least one or all of the plurality of ECG electrodes 30 and the back patch 32. In some embodiments, the processor 26 determines the three-dimensional shell shape 66 using a three-dimensional fitting algorithm to fit the three-dimensional shell shape 66 to the location of at least one or all of the plurality of ECG electrodes 30 and the back patch 32.

[0093] In some embodiments, stylus 28 is used to scribble points along the surface of patient 24, wherein processor 26 records the locations of the scribble points and fits three-dimensional housing shape 66 to the locations of the scribble points and the locations of at least one or all of the plurality of ECG electrodes 30 and back patch 32. In some embodiments, processor 26 fits three-dimensional housing shape 66 to the locations of the scribble points and the locations of at least one or all of the plurality of ECG electrodes 30 and back patch 32 using one or more of an optimization algorithm and a three-dimensional fitting algorithm for obtaining a best fit.

[0094] In some embodiments, anatomical landmarks are identified in or on the patient 24, such as by EIT or using the stylus 28, and the processor 26 fits the three-dimensional shell shape 66 to the anatomical landmarks and the locations of at least one or all of the plurality of ECG electrodes 30 and the back patch 32. In some embodiments, the stylus 28 is used to identify anatomical landmarks within the patient 24, wherein the processor 26 records the locations of the anatomical landmarks and fits the three-dimensional shell shape 66 to the locations of the anatomical landmarks and the locations of at least one or all of the plurality of ECG electrodes 30 and the back patch 32. In some embodiments, the processor 26 fits the three-dimensional shell shape 66 to the anatomical landmarks and the locations of at least one or all of the plurality of ECG electrodes 30 and the back patch 32 using one or more of an optimization algorithm and a three-dimensional fitting algorithm for obtaining a best fit.

[0095] Next, processor 26 records the locations of multiple ECG electrodes 30 as current injection points and determines a model of the impedance tracking field in a three-dimensional shell shape 66 that corresponds to the chest region of patient 24, including the heart of patient 24. Processor 26 determines the model of the impedance tracking field based on an estimate of electromagnetic tissue properties in the region of interest of patient 24, in this example, the chest.

[0096] Electromagnetic tissue properties have an impact on the voltage distribution inside the body. Parameters such as conductivity σ(r) and dielectric constant ∈(r) differ between tissue types, see Table 1.

[0097] Table 1: Electromagnetic tissue properties at 13027 Hz [4].

[0098]

[0099] Depending on the tracking field model accuracy requirements, an assumption of uniform tissue properties may be used. Alternatively, the model may contain different tissue regions based on a shape atlas of common human anatomy data. The atlas is then scaled based on the approximate chest shape. In further limitations, a dedicated drive pattern for the available surface electrodes 30 may provide input data to the optimization routine in a manner similar to EIT to adjust the tissue type distribution.

[0100] Furthermore, a relevant parameter to include in the model is the impedance of the electrode-skin interface. This impedance can be determined by driving current from one ECG electrode 30 and sinking it to an adjacent ECG electrode 30. Analysis of the resulting voltage drop can provide an estimate of the impedance of the skin-electrode interface and the underlying tissue.

[0101] In an embodiment, the estimation of electromagnetic tissue properties of patient 24 is based on a constant gradient across the chest of patient 24 without taking into account different tissue properties. In some embodiments, the estimation of electromagnetic tissue properties of patient 24 is based on an estimation of the location of organs, such as the heart and lungs, in the chest of patient 24, where the organs scale inside as the three-dimensional shell shape 66 scales outside. In some embodiments, the estimation of electromagnetic tissue properties of patient 24 is based on EIT imaging of patient 24.

[0102] In an embodiment, the distal tip 64 of the stylus 28 includes a stylus tip electrode that is in electrical contact with the skin of the patient 24. The stylus tip electrode is configured as a voltage sensing and current driving electrode. In an embodiment, in response to the stylus tip electrode contacting the skin of the patient 24, the stylus 28 transmits one or more separate signals to the processor 26. These signals are used to determine the position of the stylus 28.

[0103] In an embodiment, the user contacts multiple skin surface points of the patient 24 around the anatomical region of interest, and the system records the location of the stylus tip electrode and the impedance between the stylus tip electrode and various electrodes, such as the ECG electrodes 30 and / or the back patch 32. The stylus tip electrode location information and impedance information supplements the location and impedance information of the electrodes, such as the ECG electrodes 30 and the back patch 32. This results in a better-posed mathematical problem when solving for anatomical distributions of non-uniform complex permittivity, such as when using the EIT algorithm.

[0104] In an embodiment, to facilitate electrical contact between the stylus tip electrode and the skin of the patient 24, the stylus tip electrode is configured with an absorbent material impregnated with a conductive gel. Also, in some embodiments, additional surface electrodes are attached to the patient 24 at locations that facilitate addressing the anatomical distribution of the inhomogeneous complex permittivity, for example, by the EIT algorithm. The additional surface electrodes are not permanently connected to the system. Instead, impedance measurements made with these additional electrodes are performed only when they are contacted by the stylus 28, such that when contacted, the system acquires the additional electrode locations based on the magnetically tracked position of the stylus 28, and simultaneously acquires electrical impedance measurements.

[0105] Processor 26 determines a model of the impedance tracking field in three-dimensional shell shape 66, which corresponds to the chest region of patient 24, as follows:

[0106] Poisson's equation establishes the relationship between the local voltage (V(r)) and the charge density. Since the impedance tracking field frequency is low enough to assume a quasi-static model behavior, the magnetic induction effect is neglected. Under these assumptions, the Poisson's equation in generalized form is given as follows:

[0107]

[0108] where ρ represents the complex-valued charge density and ∈c is the complex dielectric constant according to:

[0109]

[0110] Since we expect the dielectric constant and current density to be non-uniform throughout the thoracic cavity, Ec(r) is a function of position r.

[0111] Alternatively, if model accuracy requirements are less stringent, a simpler approximation is a uniform distribution of Ec(r). In this case, the generalized Poisson equation simplifies to:

[0112]

[0113] In the forward solution, a relatively simple method for solving (1) and (3) is the finite difference method. As the name suggests, it approximates the derivatives in the discretized model by finite differences.

[0114] Using the homogeneous tissue properties, to implement (3), the three-point approximation of the second-order derivative of V(r) with respect to the x-coordinate is:

[0115]

[0116] where n, m and k are indices of the discretized computational domain, and h is the grid spacing. Applying equation (3) and assuming equal grid spacing in all three directions provides:

[0117]

[0118] Solving for V(n,m,k) yields

[0119]

[0120] Approximations using a large number of neighboring points are also available.

[0121] In the case of varying electromagnetic tissue properties in the generalized Poisson equation, the representation of equation (6) must take into account the local ∈c(r) distribution. In this scenario, the solution evaluates the finite differences between the voltage samples weighted by the average complex permittivity between them. Following a mathematical derivation similar to the two-dimensional case, the three-dimensional finite difference decomposition of the generalized Poisson distribution for V(r) is (with Figure 4 compared to):

[0122]

[0123] in

[0124]

[0125]

[0126]

[0127]

[0128]

[0129]

[0130]

[0131] Note that the grids of ∈c and V are offset by half the grid spacing ( Figure 4 ), that is, ∈c(n,m,k)=∈c(xn+h / 2,zm+h / 2,zk+h / 2). This shift simplifies the mathematical solution and allows the calculation of the electric field along the boundary of ∈c.

[0132] The boundary conditions of the numerical optimization problem are the voltages measured at the ECG electrodes 30 and the back patch 32, and the fact that the in vitro conductivity is zero. These scalar measurements and values ​​are called Dirichlet boundary conditions (see Figure 5 ).

[0133] If an inferior vena cava (IVC) catheter is used, further boundary conditions can be applied to its measurements. However, the IVC catheter position is not known a priori. To apply its measurements as boundary conditions, the catheter position can be fixed to a certain point in the atlas-based anatomical model. This approach is acceptable, as long as it is understood that the impedance field approximation provides tracking information that is strictly valid only with respect to its atlas-based model.

[0134] In some embodiments, processor 26 is configured to refine a model of an impedance tracking field based on position information and measured field voltages received from a tracking catheter in patient 24. An impedance tracking field is generated in patient 24 by injecting current into back patch 32 through multiple ECG electrodes 30. The tracking catheter measures the field voltage of the impedance tracking field and provides the measured voltage to processor 26. Processor 26 fits the model of the impedance tracking field to the measured voltage to refine the model. In some embodiments, the tracking catheter is catheter 22. In some embodiments, the tracking catheter is inserted into one of the IVC and the superior vena cava (SVC). In some embodiments, the tracking catheter includes a magnetic tracking system that provides position information about the position of the tracking catheter and the measured field voltage to processor 26.

[0135] Figure 6 is a diagram showing a catheter 22 in a heart 68 of a patient 24 and a three-dimensional housing shape 66 attached to the patient 24 according to an embodiment of the present disclosure. Figure 3A and Figure 3B As shown, ECG electrodes 30 and back patch 32 (for clarity, in Figure 6 Attached to the patient 24 (not shown). Also, a reference patch 70 is attached to the patient 24 to provide a reference voltage for measurement of the impedance tracking field within the patient 24 using electrodes 72 on the catheter 22.

[0136] Catheter 22 is a movable catheter having one or more spatially distributed electrodes 72 at or near the distal end of catheter 22. In some embodiments, catheter 22 is used to perform therapy. In some embodiments, catheter 22 is used to perform ablation, such as RF ablation and / or cryoablation. In some embodiments, catheter 22 is used to perform diagnosis. In some embodiments, catheter 22 is used to perform cardiac mapping. In some embodiments, catheter 22 is inserted into the coronary sinus of patient 24. In some embodiments, catheter 22 is used to refine a model of an impedance tracking field based on the position of catheter 22 and the measured field voltage received from electrodes 72 of catheter 22.

[0137] The catheter 22 can be equipped with various types of electrodes 72. In some embodiments, the catheter 22 includes one or more ablation electrodes 72 for performing ablation. In some embodiments, the catheter 22 includes at least one pair of CIEs configured to inject current into a medium in which the catheter 22 is disposed. In some embodiments, the catheter 22 includes a PME for measuring the voltage or potential of an impedance tracking field within the patient 24. In some embodiments, the catheter 22 includes a PME for measuring the voltage or potential generated by the current injected by the CIE. In some embodiments, the PME is used for cardiac mapping.

[0138] Reference patch 70 provides a reference voltage to processor 26, which is used by processor 26 as a reference for the measured voltage from catheter 22. In other embodiments, processor 26 receives the reference voltage from another source. In some embodiments, processor 26 receives the system reference voltage from a reference catheter within patient 24, such as a reference catheter placed in the IVC or SVC. In some embodiments, processor 26 receives the system reference voltage from one or more of the plurality of surface electrodes 30. In some embodiments, processor 26 receives the system reference voltage from surface patch 32.

[0139] In operation, the processor 26 injects current into the back patch 32 through one or more of the plurality of ECG electrodes 30. This creates an electric field in the patient 24, which is an impedance tracking field used to track the position of the catheter 22. With the catheter 22 inserted into the patient 24, such as into the heart 68, the electrodes 72 on the catheter 22 measure the field voltage of the impedance tracking field and provide the measured voltage or potential to the processor 26. The processor 26 receives the measured field voltage referenced to the reference voltage from the reference patch 70 and performs signal conditioning on the measured voltage as needed.

[0140] In some embodiments, the processor 26 performs pre-processing on the measured voltage signal, wherein the pre-processing includes one or more of noise reduction and filtering.

[0141] Processor 26 then fits the measured field voltage from catheter 22 to the model of the impedance tracking field. In an embodiment, processor 26 matches the measured field voltage to the model of the impedance tracking field. In some embodiments, processor 26 uses an optimization algorithm to match the measured field voltage to the model of the impedance tracking field, and processor 26 obtains the best fit of the measured field voltage to the model.

[0142] After fitting the measured field voltage from catheter 22 to a model of the impedance tracking field, processor 26 determines the location of catheter 22 within patient 24, such as within heart 68 of patient 24. Based on the location of catheter 22 within patient 24 determined by processor 26, medical personnel and / or physicians use catheter 26 to perform a procedure, such as a diagnostic, mapping, or therapeutic procedure, including ablation.

[0143] In an embodiment, processor 26 is configured to detect artifacts and reduce artifacts in the measured field voltage. In some embodiments, processor 26 is configured to provide noise reduction to the measured field voltage. In some embodiments, processor 26 is configured to provide respiratory gating to obtain the measured field voltage. In respiratory gating, processor 26 measures the field voltage of the impedance tracking field using catheter 22 during the same period of the breathing cycle as patient 24 inhales and exhales air. In some embodiments, processor 26 measures the field voltage when air leaves the patient because there is more time to measure when air leaves the patient 24.

[0144] Figure 7 is a method of tracking a catheter, such as catheter 22, within a patient 24 according to an embodiment of the present disclosure. The method is performed by system 20. In other embodiments, the method may be performed by or by a different system.

[0145] The method includes determining, by the processor 26, at 100, a position of at least one of a plurality of surface electrodes 30 attached to the patient 24. In some embodiments, the plurality of surface electrodes 30 are a plurality of ECG electrodes 30. In addition, in some embodiments, the method includes determining, by the processor 26, a position of each of the plurality of surface electrodes 30 attached to the patient 24. In some embodiments, the processor 26 determines positions of other electrodes in the plurality of surface electrodes 30 based on one or more positions of at least one of the plurality of surface electrodes 30.

[0146] Further, in some embodiments, the method includes receiving position information from a stylus, such as stylus 28. The stylus is enabled to track the position of the stylus and provide the position information to processor 26 when the stylus is brought into contact with electrodes of the plurality of surface electrodes 30, surface patch 32, and / or another point on patient 24.

[0147] The method includes storing, by the processor 26 at 102, the position of at least one of the plurality of surface electrodes 30, and the method includes storing, by the processor 26 at 104, the position of the surface patch 32 attached to the patient 24. These positions may be stored in an internal memory of the processor 26 or in a memory external to the processor 26. In some embodiments, the method includes storing, by the processor 26, the position of each of the plurality of surface electrodes 30. In some embodiments, the method includes storing, by the processor 26, the position of each of the plurality of ECG electrodes 30. Also, in some embodiments, the method includes storing the position of the back patch 32.

[0148] Next, the method includes determining, by the processor 26, at 106, a three-dimensional shell shape 66 corresponding to a portion of the patient 26. In some embodiments, determining the three-dimensional shell shape 66 includes determining the three-dimensional shell shape 66 based on an oval shape, which may include scaling the oval shape to fit the locations of the surface electrodes 30 and the back patch 32. In some embodiments, determining the three-dimensional shell shape 66 includes determining the three-dimensional shell shape 66 based on the location of the surface patch 32 and the location of one or more of the plurality of surface electrodes 30. In some embodiments, determining the three-dimensional shell shape 66 includes determining the three-dimensional shell shape 66 based on the locations of other points on the patient 24. In some embodiments, determining the three-dimensional shell shape 66 includes determining the three-dimensional shell shape 66 based on anatomical landmarks within the patient 24, such as anatomical landmarks obtained from an atlas model or from imaging, such as EIT imaging, etc.

[0149] The method includes determining, by the processor 26 at 108, a model of the impedance tracking field in a portion of the three-dimensional shell shape 66. In some embodiments, the method includes determining the model based on estimates of electromagnetic tissue properties of the patient 24. In some embodiments, the method includes determining the model based on estimates of electromagnetic tissue properties of the patient 24, the estimates including a constant gradient across the patient 24. In some embodiments, the method includes determining the model based on estimates of electromagnetic tissue properties of the patient 24, the estimates including estimates of the locations of organs in the patient 24. In some embodiments, the method includes determining the model based on estimates of electromagnetic tissue properties of the patient 24, the estimates based on EIT imaging, etc. In some embodiments, the method includes determining the model based on estimates of electromagnetic tissue properties of the patient 24, the estimates including measured field voltages from a tracking catheter and a magnetically obtained location of the tracking catheter within the patient 24.

[0150] While tracking the catheter, at 110, the method includes injecting, by the processor 26, current into the surface patch 32 through one or more of the plurality of surface electrodes 30 to create an electric field within the patient 24. This electric field is an impedance tracking field that is subsequently detected and measured by electrodes on a catheter inserted into the patient 24, such as the electrodes 72 on the catheter 22.

[0151] At 112, the method includes fitting, by processor 26, the field voltage measured by the catheter to a model of the impedance tracking field to track the position of the catheter within patient 24. In some embodiments, processor 26 matches the measured field voltage to the model of the impedance tracking field. In some embodiments, processor 26 uses an optimization algorithm to match the measured field voltage to the model of the impedance tracking field, and processor 26 obtains a best fit of the measured field voltage to the model.

[0152] In an embodiment, after fitting the measured field voltage from the catheter to a model of the impedance tracking field, processor 26 determines the location of the catheter within patient 24, such as within heart 68 of patient 24. Based on the location of the catheter within patient 24, medical personnel and / or physicians use the catheter to perform a procedure, such as a diagnostic, mapping, and / or therapeutic procedure, such as a therapeutic procedure including ablation.

[0153] At 114 , the method includes providing, by processor 26 , therapy to the patient based on the catheter position determined by processor 26 .

[0154] Moreover, in some embodiments, the method includes detecting and reducing artifacts in the measured voltage, such as by providing noise reduction on the measured field voltage and / or providing respiratory gating while obtaining the measured field voltage.

[0155] The systems and methods described herein reduce or eliminate the need to first create a map of the impedance tracking field in the region of interest within the patient 24. This reduces the cost of performing the procedure, allowing for a less complex procedure that does not require the time or money required to map the region of interest. Furthermore, the systems and methods described herein do not use fluoroscopy, resulting in reduced exposure to excess x-rays.

[0156] Various modifications and additions may be made to the exemplary embodiments discussed without departing from the scope of the present disclosure. For example, although the above embodiments refer to particular features, the scope of the present disclosure also includes embodiments with different combinations of features and embodiments that do not include all of the features described above.

Claims

1. A system for tracking a catheter in a patient, comprising: a plurality of surface electrodes attached to the patient; a surface patch that is attached to the patient; a stylus including a magnetic tracking system for tracking the position of the stylus in a magnetic field; as well as a processor coupled to the stylus, the plurality of surface electrodes, and the surface patch, the processor being configured to: determining a position of at least one surface electrode of the plurality of surface electrodes based on the position of the stylus; storing a position of the surface patch and a position of at least one surface electrode of the plurality of surface electrodes; determining a three-dimensional shell shape corresponding to a portion of the patient; determining a model of an impedance tracking field in at least a portion of the three-dimensional shell shape; injecting current through one or more of the plurality of surface electrodes to create an electric field in the patient; fitting a measured voltage from the catheter to a model of the impedance tracking field to determine a position of the catheter within the patient; as well as Treatment is provided to the patient based on the position of the catheter.

2. The system of claim 1, wherein the plurality of surface electrodes are a plurality of electrocardiogram electrodes attached to the patient.

3. A system according to claim 1 or 2, wherein the processor is configured to determine the three-dimensional shell shape based on one or more of: an oval shape, a position of the surface patch and a position of at least one of the plurality of surface electrodes, a position of a plurality of points on the surface of the patient, and anatomical landmarks within the patient.

4. A system according to claim 1 or 2, wherein the processor is configured to determine a model of the impedance tracking field based on an estimate of electromagnetic tissue properties of the patient, wherein the estimate of electromagnetic tissue properties of the patient is based on at least one of: a constant gradient across the patient, an estimate of the location of an organ within the patient, and electrical impedance tomography of the patient.

5. A system according to claim 1 or 2, wherein the processor is configured to refine the model of the impedance tracking field based on at least one of a measured voltage from a tracking catheter and a magnetically obtained position of the tracking catheter within the patient's body.

6. A system according to claim 1 or 2, wherein the processor is configured to provide respiratory gating to fit the measured voltage from the catheter to a model of the impedance tracking field to determine the position of the catheter within the patient.

7. A method for tracking a catheter, comprising: receiving, by a processor, a signal sent from a stylus indicating a position of the stylus; determining, by the processor, a position of at least one surface electrode of a plurality of surface electrodes attached to a patient based on the signal received from the stylus; storing, by the processor, a position of at least one surface electrode 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 corresponding 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 into one or more of the plurality of surface electrodes to create an electric field within the patient; as well as The measured voltage from the catheter is fit, by the processor, to a model of the impedance tracking field to track the position of the catheter within the patient.

8. A method according to claim 7, wherein storing the position of the surface patch includes obtaining position information from a tracking system in the surface back patch, and wherein determining the position of at least one of the multiple surface electrodes includes determining, by the processor, the position of at least one of the multiple electrocardiogram electrodes attached to the patient.

9. The method of claim 7 or 8, comprising receiving position information from a stylus capable of tracking the position of the stylus when determining the position of at least one of the plurality of surface electrodes.

10. The method of claim 9, wherein determining, by the processor, the three-dimensional shell shape comprises determining the three-dimensional shell shape based on one or more of: a position of the surface patch and a position of at least one of the plurality of surface electrodes determined based on position information received from the stylus, positions of a plurality of points on the surface of the patient determined based on position information received from the stylus, and positions of anatomical landmarks within the patient determined based on position information received from the stylus.

11. A method according to claim 7 or 8, wherein determining the three-dimensional shell shape by the processor includes determining the three-dimensional shell shape based on one or more of the following: an oval shape, a position of the surface patch and a position of at least one of the multiple surface electrodes, a position of multiple points on the surface of the patient, and anatomical landmarks within the patient's body.

12. A method according to claim 7 or 8, wherein determining by the processor a model of the impedance tracking field in at least a portion of the three-dimensional shell shape includes determining the model based on an estimate of electromagnetic tissue properties of the patient, the estimate of electromagnetic tissue properties of the patient including one or more of the following: a constant gradient across the patient, an estimate of the position of an organ within the patient, electrical impedance tomography of the patient, a measured voltage from a tracking catheter, and a magnetically obtained position of the tracking catheter within the patient.

13. The method of claim 7 or 8, wherein fitting by the processor the measured voltage from the catheter to a model of the impedance tracking field comprises respiratory gating.

Images