Patent Description:
The present disclosure relates to systems and methods for tracking catheters in a patient and, more particularly, to systems and methods for tracking catheters without first mapping a region of interest in the patient. The disclosure further relates to systems and methods for tracking catheters based on fitting measured voltages to a model of an impedance tracking field in the region of interest in the patient.

Some mapping systems provide impedance tracking functionality for navigating catheters in a patient's body. Typically, in these systems, impedance tracking functionality relies on injecting current into electrodes, such that an electric field is generated in the patient. To determine a catheter's location, the electric field distribution in a region of interest, such as inside the heart, is mapped with a dedicated mapping catheter. This mapping catheter may be a magnetically tracked mapping catheter that measures the impedance tracking field in the region of interest. Magnetically tracked locations of the catheter and field voltages measured by the catheter are used to create a map of the region of interest. The system stores the collected data in a map that may include one or more look-up tables of the measured field voltages. To navigate a catheter in the region of interest, field voltages are measured by the catheter and compared to the one or more look-up tables.

Rather than using mapped impedance tracking field information, some systems rely on pairs of electrodes, each placed on opposing sides of the patient's body. The electrode pairs are positioned to generate fields that are approximately orthogonal to each other, such that catheter tracking assumes orthogonal fields.

In other systems, x-ray fluoroscopy is used to navigate catheters in a patient. In x-ray fluoroscopy, a continuous x-ray image is produced and displayed on a monitor by passing x-ray beams through the body. In some procedures, fluoroscopy may be combined with an impedance tracking method, such as the impedance tracking method described above, to navigate the catheter in the patient's body.

The need to first create a map of the impedance tracking field in the region of interest and/or using x-ray fluoroscopy presents disadvantages. One disadvantage is navigating catheters in patients in less complex procedures, where the less complex procedures do not justify the time or money needed for mapping the region of interest. Another disadvantage is exposing patients to excessive x-rays in fluoroscopy procedures, where physicians and/or medical personnel want to reduce exposure to x-rays.

Also, systems employing orthogonal electrode pairs increase cost and complexity of the procedure and equipment, since additional electrode surface patches and corresponding system connectivity are needed. Moreover, assumptions of field orthogonality provide only limited accuracy since the exact electrode locations remains unknown.

<CIT> discusses an improved method for the calibration and tracking of an electromagnetic or acoustic based catheter within a catheter tracking space for use in cardiac intervention for a specific patient, utilizing prior-acquired medical imaging data for the patient.

<CIT> discusses a system and method for determining a position of a medical device within a body. The system includes an electronic control unit that receives position signals from position sensors of a first type and a second type disposed on the device and applies a filter to each of the position signals to obtain filtered estimated positions for each sensor.

<CIT> discloses a method for facilitating catheterization for performing diagnostic treatment on patient by doctor, which involves tracking actual path of probe in model using coordinates, and determining whether actual path corresponds to intended path.

<CIT> a method for providing electrode localization of lead for e.g. placement during cardiac resynchronization therapy, involves determining lead roll about longitudinal axis of lead based on measuring and offset of electrical center.

In an Example <NUM>, a system for tracking a catheter in a patient including 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 location of at least one of the plurality of surface electrodes; 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.

In an Example <NUM>, the system of Example <NUM>, wherein the plurality of surface electrodes is a plurality of electro-cardiogram electrodes attached to the patient.

In an Example <NUM>, the system of any of Examples <NUM> and <NUM>, wherein the surface patch is a surface back patch that includes a magnetic tracking system that provides location information about the location of the surface back patch attached to the back of the patient.

In an Example <NUM>, the system of any of Examples <NUM> - <NUM>, including a stylus that is enabled for tracking a location of the stylus, wherein the processor is coupled to the stylus and configured to determine the location of the at least one of the plurality of surface electrodes by receiving location information from the stylus when the stylus is touching the electrode.

In an Example <NUM>, the system of any of Examples <NUM> - <NUM>, 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.

In an Example <NUM>, the system of any of Examples <NUM> - <NUM>, wherein the processor is configured to determine the model of the impedance tracking field based on estimates of electromagnetic tissue properties of the patient that 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.

In an Example <NUM>, the system of any of Examples <NUM> - <NUM>, 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.

In an Example <NUM>, the system of any of Examples <NUM> - <NUM>, 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.

In an Example <NUM>, a method of tracking a catheter including: determining, by a processor, a location of at least one of a plurality of surface electrodes attached to a 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.

In an Example <NUM>, the method of Example <NUM>, 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.

In an Example <NUM>, the method of any of Examples <NUM> and <NUM>, including receiving location information from a stylus that is enabled for tracking a location of the stylus, in determining the location of the at least one of a plurality of surface electrodes.

In an Example <NUM>, the method of Example <NUM>, wherein determining, by the processor, the three-dimensional shell shape includes determining the three-dimensional shell shape based on one or more of the location of the surface patch and the location of the at least one of the plurality of surface electrodes determined from location information received from the stylus, locations of multiple points on surfaces of the patient determined from location information received from the stylus, and locations of anatomical landmarks in the patient determined from location information received from the stylus.

In an Example <NUM>, the method of any of Examples <NUM> - <NUM>, 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.

In an Example <NUM>, the method of any of Examples <NUM> - <NUM>, 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, such as electrical impedance tomography imaging of the patient based on sensing impedances among electrodes, measured voltages from a tracking catheter and magnetically obtained locations of the tracking catheter in the patient.

In an Example <NUM>, the method of any of Examples <NUM> - <NUM>, wherein fitting, by the processor, measured voltages from the catheter to the model of the impedance tracking field includes respiration gating.

In an Example <NUM>, a system for tracking a catheter in a patient including 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 configured to: determine a location of at least one of the plurality of surface electrodes; 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.

In an Example <NUM>, the system of Example <NUM>, wherein the surface patch is a surface back patch that includes a magnetic tracking system that provides location information about the location of the surface back patch attached to the back of the patient.

In an Example <NUM>, the system of Example <NUM>, including a stylus that is enabled for tracking a location of the stylus, wherein the processor is coupled to the stylus and configured to determine the location of the at least one of the plurality of surface electrodes by receiving location information from the stylus.

In an Example <NUM>, the system of Example <NUM>, 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.

In an Example <NUM>, the system of Example <NUM>, wherein the processor is configured to determine the model of the impedance tracking field based on estimates of electromagnetic tissue properties of the patient.

In an Example <NUM>, the system of Example <NUM>, 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.

In an Example <NUM>, the system of Example <NUM>, 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.

In an Example <NUM>, the system of Example <NUM>, 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.

In an Example <NUM>, the system of Example <NUM>, 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.

In an Example <NUM>, a system for tracking a catheter in a patient including 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.

In an Example <NUM>, the system of Example <NUM>, 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.

In an Example <NUM>, the system of Example <NUM>, 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, such as electrical impedance tomography imaging of the patient using impedance information measured with the plurality of surface electrodes and the surface patch.

In an Example <NUM>, the system of Example <NUM>, 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.

In an Example <NUM>, a method of tracking a catheter in a patient including: determining, by a processor, 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.

In an Example <NUM>, the method of Example <NUM>, including receiving location information from a stylus that is enabled for tracking a location of the stylus, in determining the location of the at least one of a plurality of surface electrodes.

In an Example <NUM>, the method of Example <NUM>, 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.

In an Example <NUM>, the method of Example <NUM>, 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.

In an Example <NUM>, the method of Example <NUM>, wherein the processor is configured to provide respiration gating while obtaining the measured voltages from the catheter.

While multiple embodiments are disclosed, still 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 disclosure.

<FIG> is a diagram illustrating a system <NUM> for tracking a catheter <NUM> (or multiple catheters <NUM>) in a patient <NUM>, according to embodiments of the disclosure. The system <NUM> is configured to track the catheter <NUM> in a region of interest, such as the heart, in the patient <NUM> without first mapping the region of interest. The system <NUM> is configured to track the catheter <NUM> based on measuring field voltages in the patient <NUM> with the catheter <NUM> and fitting the measured field voltages to a model of an impedance tracking field in the region of interest in the patient <NUM>. In embodiments, the system <NUM> is used to insert catheters, such as catheter <NUM>, into the heart or a heart cavity of the patient <NUM>.

The system <NUM> includes a processor <NUM>, a pointer or stylus <NUM>, a plurality of surface electrodes <NUM>, a surface patch <NUM>, the catheter <NUM> and, in at least some embodiments, a magnet <NUM>. In embodiments, the plurality of surface electrodes <NUM> are a plurality of electro-cardiogram (ECG) electrodes attached to the patient <NUM>. In some embodiments, the surface patch <NUM> is a surface back patch attached to the back of the patient <NUM>.

The plurality of surface electrodes <NUM> and the surface patch <NUM> are attached to the patient <NUM> and coupled to the processor <NUM> by conductive paths (not shown for clarity). The stylus <NUM> is coupled to the processor <NUM> by conductive path <NUM>, and the magnet <NUM> is coupled to the processor <NUM> by conductive path <NUM>. The catheter <NUM> is coupled to the processor <NUM> by conductive path <NUM>. In embodiments, one or more of the processor <NUM>, the stylus <NUM>, the plurality of surface electrodes <NUM>, the surface patch <NUM>, the catheter <NUM>, and the magnet <NUM> can be coupled to the processor <NUM> by wireless communications.

The stylus <NUM> is enabled for tracking a location of the stylus <NUM> in the system <NUM>. In embodiments, the stylus <NUM> is enabled for tracking the location of the stylus <NUM> in relation to one or more of a table the patient <NUM> is lying on and the magnet <NUM>, or another part of the system <NUM>. In some embodiments, the stylus <NUM> includes a magnet field tracking system, such that the stylus <NUM> is enabled for magnetically tracking the location of the stylus <NUM> in the magnetic field of the magnet <NUM>. In some embodiments, the magnet <NUM> is an electromagnet and, in some embodiments, the magnet <NUM> is controlled by the processor <NUM>.

The processor <NUM> is configured to receive location information from the stylus <NUM> to determine the location of the plurality of surface electrodes <NUM>. In embodiments, the processor <NUM> is configured to activate the magnet <NUM> and the stylus <NUM> is configured to provide location information to the processor <NUM>. In some embodiments, each of the plurality of surface electrodes <NUM> is touched by the stylus <NUM> and the stylus <NUM> provides the location information of the stylus <NUM> to the processor as the stylus <NUM> is touched to each of the plurality of surface electrodes <NUM>. In embodiments, the processor <NUM> determines the location of the stylus <NUM> and the touched surface electrode <NUM> and stores the location of the touched surface electrode <NUM>.

The processor <NUM> is further configured to store the location of the surface patch <NUM>. In embodiments, the surface patch <NUM> is enabled for tracking a location of the surface patch <NUM> in the system <NUM>. In embodiments, the surface patch <NUM> is enabled for tracking the location of the surface patch <NUM> in relation to one or more of a table the patient <NUM> is lying on and the magnet <NUM>, or another part of the system <NUM>. In some embodiments, the surface patch <NUM> includes a magnet field tracking system, such that the surface patch <NUM> is enabled for magnetically tracking the location of the surface patch <NUM> in the magnetic field of the magnet <NUM>. In embodiments, the processor <NUM> is configured to activate the magnet <NUM> and the surface patch <NUM> is configured to provide location information to the processor <NUM>. In some embodiments, the surface patch <NUM> is a surface back patch that includes a magnetic tracking system that provides location information about the location of the surface back patch, attached to the back of the patient <NUM>, to the processor <NUM>.

In some embodiments, the stylus <NUM> is used as described above in relation to the plurality of surface electrodes <NUM> to obtain the location of the surface patch <NUM>. In embodiments, the stylus <NUM> touches the surface patch <NUM> and the processor <NUM> receives location information from the stylus <NUM> as it touches the surface patch <NUM>, where the processor <NUM> determines and stores the location of the surface patch <NUM>.

The processor <NUM> determines a three-dimensional shell shape that corresponds to a portion of the patient <NUM>. In some embodiments, the processor <NUM> determines a three-dimensional shell shape that corresponds to the region of interest in the patient <NUM>. In some embodiments, the processor <NUM> determines a three-dimensional shell shape that corresponds to the thorax region in the patient <NUM>. In embodiments, the processor <NUM> is configured to determine the three-dimensional shell shape based on one or more of an ovoid shape, the locations of the surface patch <NUM> and the plurality of surface electrodes <NUM> on the patient <NUM>, the locations of multiple other points on the surfaces of the patient <NUM>, and anatomical landmarks in the patient <NUM>.

The processor <NUM> determines a model of an impedance tracking field in at least a portion of this three-dimensional shell shape, based on estimates of electromagnetic tissue properties of the patient <NUM>. In embodiments, these estimates of electromagnetic tissue properties of the patient <NUM> are based on at least one of constant gradients across the patient <NUM>, estimates of the locations of organs in the patient <NUM>, and electrical impedance tomography (EIT) imaging of the patient <NUM>.

In some embodiments, the processor <NUM> is configured to refine the model of the impedance tracking field based on location information and measured field voltages received from a tracking catheter in the patient <NUM>. The tracking catheter measures the field voltages of an impedance tracking field that is generated in the patient <NUM>, such as by injecting currents though the plurality of surface electrodes <NUM> and the patient <NUM> to the surface patch <NUM>. The processor <NUM> fits the model of the impedance tracking field to the measured voltages to refine the model. In some embodiments, the tracking catheter is catheter <NUM>. In some embodiments, the tracking catheter includes a magnetic tracking system that provides the location information about the location of the tracking catheter to the processor <NUM> along with the measured field voltages.

To track a catheter, such as catheter <NUM>, in the region of interest in the patient <NUM>, the processor <NUM> is configured to inject current through one or more of the plurality of surface electrodes <NUM> to create an electric field in the patient <NUM>. This electric field is an impedance tracking field that is used to track the location of the catheter <NUM>. In operation, the catheter <NUM> measures field voltages of the impedance tracking field and the processor <NUM> fits the measured field voltages from the catheter <NUM> to the model of the impedance tracking field and determines the location of the catheter <NUM> in the patient <NUM>.

Also, the processor <NUM> receives a system reference voltage that is used to obtain the measured field voltages from the catheter <NUM>. In embodiments, the system reference voltage is received from at least one of a reference catheter in the patient <NUM>, a reference patch attached to the patient <NUM>, one or more of the plurality of surface electrodes <NUM>, and the surface patch <NUM>. Also, in some embodiments, the processor <NUM> is configured to provide respiration gating to fit the measured field voltages from the catheter <NUM> to the model of the impedance tracking field to determine the locations of the catheter <NUM> in the patient <NUM>.

The catheter <NUM> is a moveable catheter <NUM> having one or more spatially distributed electrodes. The catheter <NUM> can be used to perform various medical procedures, such as cardiac mapping and/or medical therapeutic treatments including ablation, such as radio frequency (RF) ablation and/or cryogenic ablation. The catheter <NUM> is used by medical personnel and/or a physician based on the location of the catheter <NUM> in the patient <NUM>, which was determined by the processor <NUM>.

In some embodiments, the catheter <NUM> is fitted with various types of electrodes that are configured to perform various functions. For example, the catheter <NUM> can include at least one pair of current injection electrodes (CIEs) configured to inject electrical current into the medium in which the catheter <NUM> is disposed. The catheter <NUM> may also include multiple potential measuring electrodes (PMEs) configured to measure the potentials resulting from the current injected by the current injection electrodes. In some embodiments, the PMEs are used for cardiac mapping. In some embodiments, the relative positions of multiple catheters <NUM> disposed in the heart of the patient <NUM> or a cardiac chamber of the heart are determined based on measured field voltages obtained by the PMEs on the catheters <NUM>. In some embodiments, the positions of the catheters <NUM> can be determined with respect to a surface of the organ, such as the heart of the patient <NUM>.

Further, as to the system <NUM>, the processor <NUM> is configured to provide and does provide the functions of the system <NUM>. The processor <NUM> is a processor-based device that includes one or more computers, micro-processors, and/or other types of processor-based devices suitable for multiple applications. The processor <NUM> can include volatile and/or nonvolatile memory elements <NUM>, and peripheral devices to enable input/output functionality. The peripheral devices can include, for example, a CD-ROM drive, a floppy drive, and/or a network connection for downloading related content to the processor <NUM>. Such peripheral devices may also be used for downloading software containing computer instructions to enable operation of the processor <NUM>, and for downloading software implemented programs to perform the operations of the system <NUM>. The processor <NUM> may be implemented on a single or multiple processor-based platform capable of performing the functions of the system <NUM>. Additionally, one or more of the procedures performed by the processor <NUM> may be implemented using processing hardware such as digital signal processors (DSPs), field programmable gate arrays (FPGAs), mixed-signal integrated circuits, and application specific integrated circuits (ASICs).

In embodiments, the processor <NUM> includes an electronics module <NUM> that is coupled to one or more of the stylus <NUM>, the plurality of surface electrodes <NUM>, the surface patch <NUM>, and the catheter <NUM>, to receive signals from and provide signals to the one or more of the stylus <NUM>, the plurality of surface electrodes <NUM>, the surface patch <NUM>, and the catheter <NUM>. The electronics module <NUM> can include a signal generation module for injecting current into the region of interest, such as the heart cavity, through the surface electrodes <NUM>. The electronics module <NUM> can also include a signal acquisition module for measuring potentials through the surface electrodes <NUM> and/or through the electrodes of the catheter <NUM>, such as the PMEs. The electronics module <NUM> may further include a signal acquisition module for receiving the location information from the stylus <NUM> and/or the location information from the surface patch <NUM>. In embodiments, the electronics module <NUM> is used for one or more of sampling, sensing, filtering, and amplifying received signals.

The electronics module <NUM> can be implemented using analog or digital electronics, or a combination of both. In some embodiments, the electronics module <NUM> is implemented by use of 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 electronics module <NUM> is implemented using analog hardware augmented with signal processing capabilities provided by CPU, FPGA and DSP devices.

As illustrated in <FIG>, the system <NUM> further includes input/output devices <NUM>, such as a mouse and a keyboard, a printer <NUM>, and a display device <NUM> that may include a touch screen. Also, the system <NUM> includes a storage device <NUM> that is used to store data acquired by the processor <NUM>. The input/output devices <NUM>, the printer <NUM>, the display device <NUM>, and the storage device <NUM> are each communicatively coupled to the processor <NUM>, such as by a wired connection or wirelessly.

The processor <NUM> can access one or more input devices to obtain input data, and one or more output devices to communicate output data. In embodiments, the input/output devices <NUM> include one or more of the following: random access memory (RAM), a redundant array of independent disks (RAID), a floppy drive, a compact disc (CD) drive, a DVD drive, a magnetic disk, an internal hard drive, an external hard drive, a memory stick, and other storage devices capable of being accessed by the processor <NUM>, where such aforementioned examples are not exhaustive, and are for illustration and not limitation.

The systems and methods described herein are not limited to one hardware/software configuration. The systems and methods can be implemented in hardware, or a combination of hardware and software, and/or can be implemented from commercially available modules, applications, and devices. Where the systems and methods described herein are at least partly based on the use of computers, micro-processors and/or other computing devices, the systems and methods can be implemented in one or more computer programs, where a computer program can be understood to include one or more processor executable instructions. The computer programs can execute on processor <NUM>, and can be stored on one or more storage mediums, such as the memory elements <NUM> and the storage device <NUM>, which are readable by the processor <NUM>.

In addition, the computer programs can be implemented using one or more high level procedural or object-oriented programming languages to communicate with a computer system and/or the computer programs can be implemented in assembly or machine language. The language can be compiled or interpreted. Devices and/or computer systems that integrate with the processor <NUM> can include, for example, a personal computer, a workstation (e.g., Sun, HP), a personal digital assistant (PDA), a handheld device such as cellular telephone, laptop, handheld, or another device capable of being integrated with a processor. Accordingly, the devices provided herein are not exhaustive and are provided for illustration and not limitation.

Also, throughout this disclosure references to "a micro-processor" and "a processor", or "the micro-processor" and "the processor," can be understood to include one or more micro-processors and/or processors that can communicate in a stand-alone and/or a distributed environment and can thus be configured to communicate via wired or wireless communications with other processors. Furthermore, references to memory, unless otherwise specified, can include one or more processor-readable and accessible memory elements and/or components that can be internal to the processor device, and/or external to the processor device, and accessed via a wired or wireless network using a variety of communications protocols, and unless otherwise specified, can be arranged to include a combination of external and internal memory devices, where such memory can be contiguous and/or partitioned based on the application. Accordingly, references to a database can be understood to include one or more memory associations, where such references can 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, with such structures provided for illustration and not limitation.

<FIG> is a diagram illustrating one example of a stylus <NUM> that is enabled for tracking the location of the stylus <NUM> in the system <NUM>, according to embodiments of the disclosure. In embodiments, the stylus <NUM> is configured for determining six degrees of freedom in a six degrees of freedom electromagnetic tracking system. Also, in embodiments, the stylus <NUM> is at least one of non-sterile and reusable.

In the example embodiments described herein, the stylus <NUM> includes three magnetic tracking coils 60a-60c for determining the location of the stylus <NUM> in the magnetic tracking field (or fields) generated by the magnet <NUM>. In other example embodiments, the stylus <NUM> includes only two magnetic coils for determining six degrees of freedom. In some example embodiments, the stylus <NUM> includes only two magnetic coils for determining six degrees of freedom, where the two magnetic coils are not orthogonal or parallel to one another.

In the present example, the three magnetic coils 60a-60c are situated at the distal end <NUM> or toward the distal end <NUM> of the stylus <NUM>. The three magnetic coils 60a-60c are oriented orthogonal to one another, such that one coil is situated in each of the three x-y-z axis directions. Each of the three magnetic tracking coils 60a-60c is electrically coupled to the processor <NUM>, such as by a separate wire, in conductive path <NUM>. The stylus <NUM> and the connecting conductive path <NUM> are long enough to reach each of the surface electrodes <NUM> while the magnetic tracking coils 60a-60c are maintained inside the magnetic tracking field created by the magnet <NUM>. In some embodiments, the three magnetic coils 60a-60c are not oriented orthogonal to one another. Also, in other embodiments, the stylus <NUM> includes less than three magnetic coils 60a-60c or more than three magnetic coils 60a-60c, where the less than three magnetic coils and the more than three magnetic coils can be orthogonal or not orthogonal to one another.

In operation, the processor <NUM> activates the magnet <NUM> to generate a magnetic tracking field (or fields) and each of the three magnetic tracking coils 60a-60c transmits a signal that corresponds to the magnetic tracking field(s) back to the processor <NUM>. The processor <NUM> receives the signals and determines the location of the stylus <NUM> in the magnetic tracking field and in relation to the system <NUM>, such as in relation to one or more of the table the patient <NUM> is lying on and the magnet <NUM>, or another part of the system <NUM>.

In some embodiments, the stylus <NUM> includes a distal tip <NUM> that can be depressed, such as by touching an electrode, and the stylus <NUM> transmits a signal to the processor <NUM> in response to the distal tip <NUM> being depressed. This signal can be used, by the processor <NUM>, to indicate that the signals currently being transmitted by the magnetic tracking coils 60a-60c are to be used to determine the location of the stylus <NUM>. Also, in some embodiments, the distal tip <NUM> of the stylus <NUM> can be depressed and the stylus <NUM> transmits one or more of a separate signal to the processor <NUM> in response to the distal tip <NUM> being depressed and the signals from the magnetic tracking coils 60a-60c to be used to determine the location of the stylus <NUM>. In other embodiments, the stylus <NUM> can be otherwise configured, such as by using capacitance or inductance, to indicate that the stylus <NUM> has been touched to an object, such as an electrode.

<FIG> are diagrams illustrating the plurality of surface electrodes <NUM> and the surface patch <NUM> attached to the patient <NUM>, according to embodiments of the disclosure.

<FIG> is a diagram illustrating the plurality of surface electrodes <NUM> attached to the patient <NUM> and a three-dimensional shell shape <NUM>, depicted in dashed lines, that corresponds to a portion of the patient <NUM>, according to embodiments of the disclosure. In this example, the plurality of surface electrodes <NUM> are a plurality of ECG electrodes <NUM> attached to the patient <NUM>. In embodiments, the plurality of ECG electrodes <NUM> includes <NUM> electrodes. In other embodiments, the plurality of ECG electrodes <NUM> includes more than <NUM> electrodes, such as <NUM> or more electrodes. In some embodiments, the plurality of ECG electrodes <NUM> includes less than <NUM> electrodes.

To obtain the locations of the plurality of ECG electrodes <NUM> attached to the patient <NUM>, at least one of the plurality of ECG electrodes <NUM> is touched by the stylus <NUM> and the stylus <NUM> provides the signals from the three magnetic tracking coils 60a-60c to the processor <NUM>. The stylus <NUM> is touched to the at least one of the plurality of ECG electrodes <NUM> by one or more medical personnel, such as a physician, a nurse, and/or a mapping specialist. In embodiments, the stylus <NUM> also provides the separate signal that indicates the stylus <NUM> has been touched to one of the plurality of ECG electrodes <NUM> and the processor <NUM> uses this signal to indicate that the signals transmitted by the magnetic tracking coils 60a-60c are to be used to determine the location of the stylus <NUM>. In some embodiments, the locations of other electrodes of the plurality of ECG electrodes <NUM> are calculated or determined from the location of the at least one of the plurality of ECG electrodes <NUM> as determined above.

In embodiments, to obtain the location of each of the plurality of ECG electrodes <NUM> attached to the patient <NUM>, each of the plurality of ECG electrodes <NUM> is touched by the stylus <NUM> and the stylus <NUM> provides the signals from the three magnetic tracking coils 60a-60c to the processor <NUM> as each of the plurality of ECG electrodes <NUM> is touched. In embodiments, the stylus <NUM> provides the separate signal that indicates the stylus <NUM> is being touched to one of the plurality of ECG electrodes <NUM>, as each of the plurality of ECG electrodes <NUM> is touched.

The processor <NUM> receives the signals from the stylus <NUM> and determines the location of the stylus <NUM> and the touched ECG electrode <NUM>. The processor <NUM> then stores the location of the stylus <NUM> and the touched ECG electrode <NUM>.

<FIG> is a diagram illustrating the surface patch <NUM> attached to the patient <NUM>, according to embodiments of the disclosure. In this example, the surface patch <NUM> is a back patch <NUM> attached to the back of the patient <NUM>. The back patch <NUM> is configured for magnetically tracking the location of the back patch <NUM> in the magnetic tracking field of the magnet <NUM>. In embodiments, the back patch <NUM> is configured for magnetically tracking <NUM> or <NUM> degrees of freedom in the magnetic tracking field of the magnet <NUM>. In some embodiments, the back patch <NUM> includes one magnetic tracking coil for determining five degrees of freedom. In some embodiments, the back patch <NUM> includes two magnetic tracking coils for determining six degrees of freedom. In some embodiments, the back patch <NUM> includes three magnetic tracking coils for determining six degrees of freedom. In some embodiments, the back patch <NUM> includes two magnetic coils for determining six degrees of freedom, where the two magnetic coils are not orthogonal or parallel to one another. In some embodiments, the back patch <NUM> includes three magnetic tracking coils like the three magnetic tracking coils 60a-60c described above for the stylus <NUM>.

The back patch <NUM> is enabled for tracking the location of the back patch <NUM> in relation to one or more of the table the patient <NUM> is lying on and the magnet <NUM>, or another part of the system <NUM>. In some embodiments, the two or three magnetic coils are not oriented orthogonal to one another. Also, in other embodiments, the back patch <NUM> includes less than three magnetic coils or more than three magnetic coils.

To obtain the location of the back patch <NUM>, the processor <NUM> activates the magnet <NUM> and the back patch <NUM> provides signals from the magnetic coils to provide location information to the processor <NUM>. The processor <NUM> receives the signals from the back patch <NUM> and determines the location of the back patch <NUM>. The processor <NUM> then stores the location of the back patch <NUM>.

Also, in some embodiments, shifts in the position and/or orientation of the back patch <NUM> represent shifts in the position of the patient <NUM>. These shifts in the position of the patient <NUM> are detected using the back patch <NUM> and used by the processor <NUM> to compensate the tracked positions or locations of, for example, the catheter <NUM>. Where, the back patch <NUM> is used as the impedance tracking space reference. Thus, if the patient <NUM> moves with respect to the magnetic tracking reference frame, the movement is detected, and a mathematical correction is applied, such that the impedance tracked and/or magnetically tracked catheter <NUM> remains in the same coordinate frame.

In some embodiments, the stylus <NUM> is used as described above in relation to the plurality of ECG electrodes <NUM> to obtain the location of the back patch <NUM>. In embodiments, the stylus <NUM> is touched to the back patch <NUM> and the processor <NUM> receives location information from the stylus <NUM> as it touches the back patch <NUM>. The processor <NUM> then determines the location of the stylus <NUM> and the back patch <NUM> and stores the location of the stylus <NUM> and the back patch <NUM>.

After the locations of the at least one or all of the plurality of ECG electrodes <NUM> and the back patch <NUM> are known and recorded, the processor <NUM> determines the three-dimensional shell shape <NUM> and a mathematical model of an electric field through the three-dimensional shell shape <NUM>. In the current example, the three-dimensional shell shape <NUM> corresponds to the thorax region in the patient <NUM>, which includes the heart of the patient <NUM>.

The processor <NUM> determines the three-dimensional shell shape <NUM>. In some embodiments, the processor <NUM> determines the three-dimensional shell shape <NUM> to be a simple ovoid shape, with little or no scaling of the ovoid shape. In some embodiments, the processor <NUM> determines the three-dimensional shell shape <NUM> using an optimization algorithm to scale the ovoid shape to a best fit inside the locations of the at least one or all of the plurality of ECG electrodes <NUM> and the back patch <NUM>.

In some embodiments, the processor <NUM> fits the three-dimensional shell shape <NUM> to the locations of the at least one or all of the plurality of ECG electrodes <NUM> and the back patch <NUM>. In some embodiments, the processor <NUM> determines the three-dimensional shell shape <NUM> using an optimization algorithm to obtain a best fit to the locations of the at least one or all of the plurality of ECG electrodes <NUM> and the back patch <NUM>. In some embodiments, the processor <NUM> determines the three-dimensional shell shape <NUM> using a three-dimensional fitting algorithm to fit the three-dimensional shell shape <NUM> to the locations of the at least one or all of the plurality of ECG electrodes <NUM> and the back patch <NUM>.

In some embodiments, the stylus <NUM> is used to scribe points along the surface of the patient <NUM>, where the processor <NUM> records the locations of the scribed points and fits the three-dimensional shell shape <NUM> to the locations of the scribed points and the locations of the at least one or all of the plurality of ECG electrodes <NUM> and the back patch <NUM>. In some embodiments, the processor <NUM> fits the three-dimensional shell shape <NUM> to the locations of the scribed points and the locations of the at least one or all of the plurality of ECG electrodes <NUM> and the back patch <NUM>, using one or more of an optimization algorithm to obtain a best fit and a three-dimensional fitting algorithm.

In some embodiments, anatomical landmarks are identified in or on the patient <NUM>, such as by EIT or using the stylus <NUM>, and the processor <NUM> fits the three-dimensional shell shape <NUM> to the anatomical landmarks and the locations of the at least one or all of the plurality of ECG electrodes <NUM> and the back patch <NUM>. In some embodiments, the stylus <NUM> is used to identify anatomical landmarks in the patient <NUM>, where the processor <NUM> records the locations of the anatomical landmarks and fits the three-dimensional shell shape <NUM> to the locations of the anatomical landmarks and the locations of the at least one or all of the plurality of ECG electrodes <NUM> and the back patch <NUM>. In some embodiments, the processor <NUM> fits the three-dimensional shell shape <NUM> to the anatomical landmarks and the locations of the at least one or all of the plurality of ECG electrodes <NUM> and the back patch <NUM>, using one or more of an optimization algorithm to obtain a best fit and a three-dimensional fitting algorithm.

Next, the processor <NUM> records the locations of the plurality of ECG electrodes <NUM> as current injection points and determines the model of the impedance tracking field in the three-dimensional shell shape <NUM>, which corresponds to the thorax region of the patient <NUM> including the heart of the patient <NUM>. The processor <NUM> determines the model of the impedance tracking field based on estimates of the electromagnetic tissue properties in the region of interest, in this example the thorax, of the patient <NUM>.

The electromagnetic tissue properties have an impact on the voltage distribution inside the body. Parameters such as conductivity σ (r) and permittivity ε (r) are different among tissue types, see Table <NUM>.

Depending on the tracking field model accuracy needs, an assumption of uniform tissue properties can be used. Alternatively, the model can contain different tissue regions based on a shape atlas of common human anatomical data. This atlas is then scaled based on the approximated thorax shape. In a further refinement, a dedicated driving pattern of available surface electrodes <NUM> can provide input data to an optimization routine to adjust tissue type distribution, in a method akin to EIT.

Also, a related parameter to include in the model is the impedance of the electrode-skin interface. This impedance can be determined by driving a current from one ECG electrode <NUM> and sinking it to an adjacent ECG electrode <NUM>. Analyzing the resulting voltage drop can provide an estimate of skin-to-electrode interface and underlying tissue impedance.

In embodiments, the estimates of the electromagnetic tissue properties of the patient <NUM> are based on constant gradients across the thorax of the patient <NUM>, without considering different tissue properties. In some embodiments, the estimates of the electromagnetic tissue properties of the patient <NUM> are based on estimates of the locations of organs, such as the heart and lungs, in the thorax of the patient <NUM>, where the organs are scaled internally as the three-dimensional shell shape <NUM> is scaled externally. In some embodiments, the estimates of the electromagnetic tissue properties of the patient <NUM> are based on EIT imaging of the patient <NUM>.

In embodiments, the distal tip <NUM> of the stylus <NUM> includes a stylus tip electrode that makes electrical contact with the skin of the patient <NUM>. The stylus tip electrode is configured as a voltage sensing and a current driving electrode. In embodiments, the stylus <NUM> transmits one or more separate signals to the processor <NUM> in response to the stylus tip electrode touching the skin of the patient <NUM>. The signals are used to determine the location of the stylus <NUM>.

In embodiments, the user touches a number of skin surface points of the patient <NUM> around an anatomical region of interest and the system records the locations of the stylus tip electrode and the impedances between the stylus tip electrode and electrodes, such as the ECG electrodes <NUM> and/or the back patch <NUM>. The stylus tip electrode location information and the impedance information complement the location and impedance information of the electrodes, such as the ECG electrodes <NUM> and the back patch <NUM>. This results in a better posed mathematical problem, when solving for the anatomical distribution of heterogeneous complex permittivity, such as when using an EIT algorithm.

In embodiments, to facilitate electrical contact between the stylus tip electrode and the skin of the patient <NUM>, the stylus tip electrode is configured with an absorbent material saturated with an electrically conductive gel. Also, in some embodiments, additional surface electrodes are attached to the patient <NUM> in locations that are favorable to solving for the anatomical distribution of heterogeneous complex permittivity by, for example, the EIT algorithm. The additional surface electrodes are not permanently connected to the system. Instead, impedance measurements with these additional electrodes are only performed when they are touched by the stylus <NUM>, such that when touched, the system acquires the additional electrode locations based on the magnetically tracked position of the stylus <NUM>, and electrical impedance measurements are acquired at the same time.

The processor <NUM> determines the model of the impedance tracking field in the three-dimensional shell shape <NUM>, which corresponds to the thorax region of the patient <NUM>, as follows:.

The Poisson Equation establishes a relationship between local voltage (V (r)) and charge density. Since, the impedance tracking field frequency is low enough to assume quasi static model behavior, magnetic induction effects are neglected. Under these assumptions, the Poisson Equation in its generalized form is given as: <MAT>
where ρ denotes complex valued charge density and εc is the complex permittivity according to: <MAT>.

Since we expect permittivity and current density to be non-uniform throughout the chest cavity, EC (r) is a function of location r.

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: <MAT>.

In the forward solution, a relatively simple method to solve (<NUM>) and (<NUM>) is the Finite-Difference Method. As its name suggests, it approximates derivatives by finite differences in a discretized model.

Using homogeneous tissue properties, to implement (<NUM>), a three-point approximation of the second derivative of V (r) with respect to the x coordinate is: <MAT>
where n, m, and k are the indices of the discretized computation domain, and h is the grid spacing. Applied to equation (<NUM>), and assuming equal grid spacing in all three directions provides: <MAT>.

Solving for V (n, m, k) results in <MAT>.

Approximations using a larger number of neighboring points are available as well.

In the Generalized Poisson Equation, in case of a varying electromagnetic tissue properties, the representation of equation (<NUM>) has to account for the local εc (r) distribution. In this scenario, the solution evaluates the finite differences between 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 solution of the Generalized Poisson Distribution for V (r) is (compare to <FIG>): <MAT>
where <MAT> <MAT> <MAT> <MAT> <MAT> <MAT> <MAT>.

Note that the grids for Cc and V are offset by half the grid spacing, (<FIG>) i.e. εc (n, m, k) =εc (xn + h/<NUM>, zm + h/<NUM>, zk. + h/<NUM>). This coordinate offset simplifies the mathematical solution and allows for computing electric fields along the boundaries of Cc.

The boundary conditions of the numerical optimization problem are the voltages measured at the ECG electrodes <NUM> and the back patch <NUM>, as well as the fact that conductivity outside the body is zero. These scalar measurements and values are referred to as Dirichlet boundary conditions (see <FIG>).

If an inferior vena cava (IVC) catheter is used, a further boundary condition could be applied to its measurements. However, IVC catheter location is not known a-priori. To apply its measurements as a boundary condition, catheter location can be fixed to a 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 true only with respect to its atlas-based model.

In some embodiments, the processor <NUM> is configured to refine the model of the impedance tracking field based on location information and measured field voltages received from a tracking catheter in the patient <NUM>. An impedance tracking field is generated in the patient <NUM> by injecting currents through the plurality of ECG electrodes <NUM> to the back patch <NUM>. The tracking catheter measures the field voltages of the impedance tracking field and provides the measured voltages to the processor <NUM>. The processor <NUM> fits the model of the impedance tracking field to the measured voltages to refine the model. In some embodiments, the tracking catheter is catheter <NUM>. 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 location information about the location of the tracking catheter to the processor <NUM> along with the measured field voltages.

<FIG> is a diagram illustrating catheter <NUM> in the heart <NUM> of the patient <NUM> and the three-dimensional shell shape <NUM> superimposed on the patient <NUM>, according to embodiments of the disclosure. The ECG electrodes <NUM> and the back patch <NUM> (not shown in <FIG> for clarity) are attached to the patient <NUM>, as illustrated in <FIG>. Also, a reference patch <NUM> is attached to the patient <NUM> to provide a reference voltage for taking measurements of the impedance tracking field in the patient <NUM> with electrodes <NUM> on the catheter <NUM>.

The catheter <NUM> is a moveable catheter having one or more spatially distributed electrodes <NUM> at the distal end or near the distal end of the catheter <NUM>. In some embodiments, the catheter <NUM> is used to perform therapeutic treatments. In some embodiments, the catheter <NUM> is used to perform ablation, such as RF ablation and/or cryogenic ablation. In some embodiments, the catheter <NUM> is used to perform diagnostics. In some embodiments, the catheter <NUM> is used to perform cardiac mapping. In some embodiments, the catheter <NUM> is inserted into the coronary sinus of the patient <NUM>. In some embodiments, the catheter <NUM> is used to refine the model of the impedance tracking field based on the location of the catheter <NUM> and the measured field voltages received from the electrodes <NUM> of the catheter <NUM>.

The catheter <NUM> can be fitted with various types of electrodes <NUM>. In some embodiments, the catheter <NUM> includes one or more ablation electrodes <NUM> for performing ablation. In some embodiments, the catheter <NUM> includes at least one pair of CIEs configured to inject electrical current into the medium in which the catheter <NUM> is disposed. In some embodiments, the catheter <NUM> includes PMEs to measure the voltages or potentials of the impedance tracking field in the patient <NUM>. In some embodiments, the catheter <NUM> includes PMEs to measure voltages or potentials resulting from the current injected by the CIEs. In some embodiments, the PMEs are used for cardiac mapping.

The reference patch <NUM> provides a reference voltage to the processor <NUM>, which is used by the processor <NUM> as a reference to the measured voltages from the catheter <NUM>. In other embodiments, the processor <NUM> receives the reference voltage from another source. In some embodiments, the processor <NUM> receives a system reference voltage from a reference catheter in the patient <NUM>, such as a reference catheter situated in the IVC or the SVC. In some embodiments, the processor <NUM> receives a system reference voltage from one or more of the plurality of surface electrodes <NUM>. In some embodiments, the processor <NUM> receives a system reference voltage from the surface patch <NUM>.

In operation, the processor <NUM> injects current through one or more of the plurality of ECG electrodes <NUM> to the back patch <NUM>. This creates an electric field in the patient <NUM>, which is the impedance tracking field used to track the location of the catheter <NUM>. With the catheter <NUM> inserted in the patient <NUM>, such as in the heart <NUM>, electrodes <NUM> on the catheter <NUM> measure the field voltages of the impedance tracking field and provide the measured voltages or potentials to the processor <NUM>. The processor <NUM> receives the measured field voltages, referenced to the reference voltage from the reference patch <NUM>, and performs signal conditioning on the measured voltages as needed.

In some embodiments, the processor <NUM> performs pre-processing of the measured voltage signals, where the pre-processing includes one or more of noise reduction and filtering.

The processor <NUM> then fits the measured field voltages from the catheter <NUM> to the model of the impedance tracking field. In embodiments, the processor <NUM> matches the measured field voltages to the model of the impedance tracking field. In some embodiments, the processor <NUM> uses an optimization algorithm to match the measured field voltages to the model of the impedance tracking field and the processor <NUM> obtains a best fit of the measured field voltages to the model.

After fitting the measured field voltages from the catheter <NUM> to the model of the impedance tracking field, the processor <NUM> determines the location of the catheter <NUM> in the patient <NUM>, such as in the heart <NUM> of the patient <NUM>. Based on the location of the catheter <NUM> in the patient <NUM>, determined by the processor <NUM>, medical personnel and/or a physician use the catheter <NUM> to perform procedures, such as diagnostic, mapping or therapeutic procedures, including ablation.

In embodiments, the processor <NUM> is configured to detect artifacts and reduce artifacts in the measured field voltages. In some embodiments, the processor <NUM> is configured to provide noise reduction on the measured field voltages. In some embodiments, the processor <NUM> is configured to provide respiration gating to obtain the measured field voltages. In respiration gating, as the patient <NUM> breathes air in and out, the processor <NUM> measures the field voltages of the impedance tracking filed using the catheter <NUM> during the same period of the respiratory cycle. In some embodiments, the processor <NUM> measures the field voltages when the air is out of the patient, since there is more time for measurement when the air is out of the patient <NUM>.

<FIG> is a method of tracking a catheter, such as catheter <NUM>, in the patient <NUM>, according to embodiments of the disclosure. The method is performed by system <NUM>. In other embodiments, the method can be or is performed by a different system.

The method, at <NUM>, includes determining, by the processor <NUM>, a location of at least one of a plurality of surface electrodes <NUM> attached to the patient <NUM>. Where, in some embodiments, the plurality of surface electrodes <NUM> is a plurality of ECG electrodes <NUM>. Also, in some embodiments, the method includes determining, by the processor <NUM>, a location of each of the plurality of surface electrodes <NUM> attached to the patient <NUM>. In some embodiments, the processor <NUM> determines the locations of other electrodes of the plurality of surface electrodes <NUM> based on the location(s) of the at least one of the plurality of surface electrodes <NUM>.

Further, in some embodiments, the method includes receiving location information from a stylus, such as stylus <NUM>. The stylus is enabled for tracking a location of the stylus and provides location information to the processor <NUM> as it is touched to an electrode of the plurality of surface electrodes <NUM>, a surface patch <NUM>, and/or another point on the patient <NUM>.

At <NUM>, the method includes storing, by the processor <NUM>, the location of the at least one of the plurality of surface electrodes <NUM>, and at <NUM>, the method includes storing, by the processor <NUM>, the location of the surface patch <NUM> attached to the patient <NUM>. The locations can be stored in internal memory of the processor <NUM> or in memory that is external to the processor <NUM>. In some embodiments, the method includes storing, by the processor <NUM>, the location of each of the plurality of surface electrodes <NUM>. In some embodiments, the method includes storing, by the processor <NUM>, the location of each of the plurality of ECG electrodes <NUM>. Also, in some embodiments, the method includes storing the location of the back patch <NUM>.

Next, the method includes, at <NUM>, determining, by the processor <NUM>, a three-dimensional shell shape <NUM> that corresponds to a portion of the patient <NUM>. In some embodiments, determining the three-dimensional shell shape <NUM> includes determining the three-dimensional shell shape <NUM> based on an ovoid shape, which can include scaling the ovoid shape to fit the locations of the surface electrodes <NUM> and the back patch <NUM>. In some embodiments, determining the three-dimensional shell shape <NUM> includes determining the three-dimensional shell shape <NUM> based on the location of the surface patch <NUM> and the locations of one or more of the plurality of surface electrodes <NUM>. In some embodiments, determining the three-dimensional shell shape <NUM> includes determining the three-dimensional shell shape <NUM> based on locations of other points on the patient <NUM>. In some embodiments, determining the three-dimensional shell shape <NUM> includes determining the three-dimensional shell shape <NUM> based on anatomical landmarks in the patient <NUM>, such as anatomical landmarks obtained from an atlas model or from imaging, such as EIT imaging or the like.

At <NUM>, the method includes determining, by the processor <NUM>, a model of an impedance tracking field in a portion of the three-dimensional shell shape <NUM>. In some embodiments, the method includes determining the model based on estimates of electromagnetic tissue properties of the patient <NUM>. In some embodiments, the method includes determining the model based on estimates of electromagnetic tissue properties of the patient <NUM> that include constant gradients across the patient <NUM>. In some embodiments, the method includes determining the model based on estimates of electromagnetic tissue properties of the patient <NUM> including estimates of the locations of organs in the patient <NUM>. In some embodiments, the method includes determining the model based on estimates of electromagnetic tissue properties of the patient <NUM> based on EIT imaging or the like. In some embodiments, the method includes determining the model based on estimates of electromagnetic tissue properties of the patient <NUM> including measured field voltages from a tracking catheter and magnetically obtained locations of the tracking catheter in the patient <NUM>.

In tracking the catheter, at <NUM>, the method includes injecting current, by the processor <NUM>, through one or more of the plurality of surface electrodes <NUM> to the surface patch <NUM> to create an electric field in the patient <NUM>. This electric field is the impedance tracking field that is subsequently detected and measured by electrodes on the catheter, such as electrodes <NUM> on the catheter <NUM>, inserted into the patient <NUM>.

At <NUM>, the method includes fitting, by the processor <NUM>, the field voltages measured by the catheter to the model of the impedance tracking field to track locations of the catheter in the patient <NUM>. In some embodiments, the processor <NUM> matches the measured field voltages to the model of the impedance tracking field. In some embodiments, the processor <NUM> uses an optimization algorithm to match the measured field voltages to the model of the impedance tracking field and the processor <NUM> obtains a best fit of the measured field voltages to the model.

In embodiments, after fitting the measured field voltages from the catheter to the model of the impedance tracking field, the processor <NUM> determines the location of the catheter in the patient <NUM>, such as in the heart <NUM> of the patient <NUM>. Based on the location of the catheter in the patient <NUM>, medical personnel and/or a physician use the catheter to perform procedures, such as diagnostic, mapping and/or therapeutic procedures, such as therapeutic procedures that include ablation.

At <NUM>, the method includes providing, by the processor <NUM>, therapy to the patient based on the locations of the catheter determined by the processor <NUM>.

Also, in some embodiments, the method includes detecting and reducing artifacts in the measured voltages, such as by providing noise reduction to the measured field voltages and/or providing respiration gating while obtaining the measured field voltages.

Claim 1:
A system (<NUM>) for tracking a catheter (<NUM>) in a patient (<NUM>) comprising:
a plurality of surface electrodes configured to be attached to the patient;
a surface patch configured to be attached to the patient;
stylus (<NUM>) enabled for tracking a location of the stylus (<NUM>) within a magnetic field; and a processor (<NUM>) coupled to the stylus (<NUM>), the plurality of surface electrodes (<NUM>) and the surface patch (<NUM>), the processor (<NUM>) configured to:
determine a location of at least one of the plurality of surface electrodes (<NUM>)based on the location of the stylus (<NUM>);
store a location of the surface patch (<NUM>) and the location of the at least one of the plurality of surface electrodes (<NUM>);
determine a three-dimensional shell shape that corresponds to a portion of the patient (<NUM>) using a three-dimensional fitting algorithm;
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 (<NUM>) to create an electric field in the patient (<NUM>);
fit measured voltages from the catheter (<NUM>) to the model of the impedance tracking field to determine locations of the catheter (<NUM>) in the patient (<NUM>); and
provide therapy to the patient (<NUM>) based on the locations of the catheter (<NUM>).