Efficient surface generation for anatomical mapping

Abstract

An example computer-implemented method includes receiving tracking data representative of a cardiac chamber location of a medical device that includes a plurality of electrodes. The method includes measuring a voltage between at least one pair of the electrodes responsive to an applied electrical current. The method includes calculating an impedance based on the measured voltage and the applied electrical current. The method includes determining a size for a volume element to be filled based on the calculated impedance and determining a position for the volume element to be filled based on the location of the medical device. The method includes generating a representation including the volume element in a spatial domain based on the size and the position determined for the volume element.

Description

Docket No. A0013362W001EFFICIENT SURFACE GENERATION FOR ANATOMICAL MAPPING CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of and priority to U.S. provisional patent application no. 63 / 749287, filed on January 24, 2025, which is incorporated herein by reference in its entirety.TECHNICAL FIELD

[0001] This disclosure relates to expeditiously generating a representation of an anatomical structure.BACKGROUND

[0002] In many electrophysiology procedures, mapping and navigation systems use invasive devices (e.g., catheters, probes, and the like) to probe around cardiac chambers and create representations of endocardial surface structures. The surface structures provide user intuitive three-dimensional views of one or more of the cardiac chambers, which can provide guidance to assist users in moving the invasive medical device. For example, a catheter inserted into the heart or other anatomic structure and used to further map and / or treat certain regions of the anatomic structure. Many existing processes for generating a representation of a surface structure tend to be time consuming, especially at the beginning of a procedure when little or no portion of the surface structure yet has been generated.SUMMARY

[0003] This disclosure relates to generating a representation of an anatomical structure.

[0004] As one example, a computer-implemented method includes receiving tracking data representative of a cardiac chamber location of a medical device that includes a plurality of electrodes. The method includes measuring a voltage between at least one pair of the electrodes responsive to an applied electrical current. The method includes calculating an impedance based on the measured voltage and the applied electrical current. The method includes determining a size for a volume element to be filled based on the calculated impedance and determining a position for the volume element to be filled based on the location of the medical device. The method includes generating a representation including the volume element in a spatial domain based on the size and the position determined for the volume element.

[0005] As another example, a non-transitory memory can store data and instructions that, when executed by a processor, cause the processor to perform the method.Docket No. A0013362WG01

[0006] As another example, a system includes a medical device including a plurality of electrodes. An interface circuit is coupled to each of the electrodes, in which the interface circuit is configured to apply an electrical signal to and / or measure an electrical signal from each the plurality of electrodes. A tracking system can be configured to provide tracking data representative of an anatomical location of at least a portion of the medical device. Non-transitory memory can store instructions and data, in which the data comprises electrical data representative of an electrical characteristic between at least one pair of the electrodes responsive to an applied electric field. A processor is coupled to the memory to access the data and instructions stored in the memory, the instructions, when executed by the processor, cause the processor to at least:determine an impedance between the at least one pair of the electrodes based on the electrical data;determine a size for a volume element to be filled based on the impedance between the at least one pair of the electrodes; anddetermine a position for the volume element to be filled based on the location of the medical device.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is a block diagram depicting an example system to facilitate creation of anatomic structures for use in mapping procedures.

[0008] FIG. 2 is a block diagram depicting an example impedance calculator.

[0009] FIG. 3 is a block diagram depicting an example volume element generator.

[0010] FIG. 4 is a block diagram depicting an example volume calculator.

[0011] FIG. 5 is a graph showing an example of volume size plotted as a function of impedance.

[0012] FIG. 6 is a graph showing another example volume size plotted as a function of impedance.

[0013] FIGS. 7 and 8 depict a first example catheter being used to fill a volume within an anatomic structure.

[0014] FIGS. 9 and 10 depict a second example catheter being used to fill a volume within an anatomic structure.

[0015] FIGS. 11 and 12 depict a second example catheter being used to fill a volume within an anatomic structure.Docket No. A0013362WG01

[0016] FIG. 13 depicts an example of a 3D geometry generated for a portion of an anatomic structure.

[0017] FIG. 14 is a flow diagram of an example method for generating a surface for a portion of an anatomic structure.DETAILED DESCRIPTION

[0018] This disclosure relates systems and methods to facilitate creating a surface or a portion of a surface for an anatomic structure.

[0019] The systems and methods described herein can be used as part of an anatomic mapping process, such as for mapping at least a portion of a surface of an anatomic structure. For example, the systems and methods can be used in a cardiac mapping process for generating at least a portion of an endocardial surface for one or more cardiac chambers, or an endocardial surface, or a combination of endocardial and epicardial surfaces. While examples described herein generally describe the systems and methods in the context of cardiac mapping, the systems and methods described herein can be used for mapping one or more surfaces of other anatomical structures.

[0020] As an example, a medical device includes a plurality of electrodes. The electrodes can be in a fixed or variable (e.g., movable) configuration. Each of the electrodes can be coupled to an interface circuit. The interface circuit can be configured to apply an electrical signal (e.g., an AC electrical current) to one or more of the electrodes, such as to generate an electric field between one or more pairs of the electrodes. For example, the electric field can be generated responsive to electrical current applied between a respective pair of electrodes (e.g., at subthreshold level). Also, or alternatively, the electrical interface can be configured to measure an electrical characteristic from at least some of the plurality of electrodes. The measured electrical characteristic can be one or more of a voltage, a current, an impedance, an electric field or other electrical characteristic measured between one or more pairs of the electrodes. In an example, the electrical interface is configured to measure a voltage potential between one or more respective pairs of the electrodes responsive to an electric field. The electric field can be induced responsive to an electrical current applied between a pair or multiple pairs of the electrodes. The measured electrical characteristic between each pair of the respective electrodes can be provided as (or define) electrical data.

[0021] The system can also include a tracking system configured to provide tracking data representative of a spatial location (e.g., an anatomical location such as a cardiac chamber) ofDocket No. A0013362W001at least a portion of the medical device during the measurements. The tracking data can be provided in real-time (or near real-time) during a procedure in which the electrical characteristic(s) are measured to provide the electrical data. As described herein, various types of tracking system can be used to provide the tracking data. The tracking data can be used to determine a location of the electrodes for which the electrical signals are measured. The tracking data and / or location information can be stored with and / or linked to the measurement data so a location of the electrodes is known or can be determined for each of the electrodes at the time when respective measurements are made.

[0022] Non-transitory memory can store instructions and data, including the tracking data, the measurement data, and / or other data, which can be accessed by one or more processors and cause the one or more processors to execute the instructions for performing functions described herein. For example, the instructions can cause the processor to determine an electrical impedance between the at least one pair of the electrodes based on the electrical data. For example, the impedance associated with a respective pair of the electrodes (e.g., impedance of the surrounding material, tissue and / or blood) can be calculated based on the voltage potential between the respective pair of electrodes and an applied electrical current. The applied current (e.g., applied between a pair of electrodes) induces an electric field for which the voltage potential is measured by one or more respective pairs of electrodes. The processor can also determine a size for a volume element, which is associated with the respective pair of electrodes, based on the impedance determined for the respective pair of electrodes. The processor can also determine a position (e.g., spatial coordinates) for the volume element that is to be filled based on the location of the medical device, which can be defined or determined based on the tracking data at the time of measuring the electrical characteristics. In an example, the size and position of a number of volume elements can be determined as the medical device is moved within a volume (e.g., the volume of an anatomic structure) and a corresponding 3D surface can be generated based on the volume elements. For example, as the medical device is moved within the volume during a procedure (e.g., a mapping procedure) a size and position are determined for each respective volume element to be filled based on respective impedance values. The collection of volume elements generated during the procedure defines an outer boundary around the volume elements. Concurrently, or subsequently, a graphical representation of a 3D surface geometry for the anatomic structure (e.g., cardiac chamber wall and cardiac landmarks) can be constructed and rendered on a display based on the size and position of the volume elements that have been (and are being) generated. The display can thus show a 3D surface geometry being constructed according to the boundary defined by theDocket No. A0013362W001arrangement of volume elements, which can have different sizes according to the impedance measurements across the volume and reflecting locations visited by the electrodes of the medical device. At least some of the volume elements can define the 3D boundary (e.g., or shell) of at least a portion of the 3D volume (e.g., a boundary of the anatomical structure), and a graphical representation for at least a portion of the anatomical surface geometry can be generated based on the 3D boundary thereof. In the example of an electrophysiology (EP) mapping procedure (e.g., where the volume is a cardiac chamber), the determination of volume elements will facilitate (e.g., expedite) the mapping process and creation of the boundary of the cardiac chamber because the larger volume elements will be filled at locations in the volume spaced apart from the chamber wall more expeditiously than smaller volume elements that are provided at or near locations on the chamber wall. As a result, the time required to construct the 3D geometry (e.g., or shell) for the chambers of the heart can be reduced compared to many existing approaches.

[0023] FIG. 1 depicts an example of a system 10 for performing mapping and related functions. The system 10 includes a medical device 12 that includes a plurality of (e.g., two or more) electrodes 14. The medical device 12 or a portion thereof can be configured to be positioned with an anatomical structure of a patient’s body. For example, the medical device 12 is a catheter or other type of probe having a distal body portion that includes arrangement of electrodes 14, and the distal body portion and electrodes carried thereby are moveable within a patient’s body. The distal body portion of catheter or other type of probe can be implemented in a variety of shapes, such as a linear (e.g., a fixed or deflectable rod or tube), a loop, a spiral, basket, sphere, or combinations thereof. The shape of the distal body portion can be fixed or variable. For example, the distal body portion of the medical device 12 can be expandable (e.g., self-expanding or expandable responsive to an external applied force) between a compressed condition and an expanded condition. The electrodes 14 can be located on or within a substrate structure of the distal body portion of the catheter or other type of probe. Each of the electrodes 14 can have shapes, such as rings, spirals, coils, discs, rectangles or the like, and the electrodes can have the same shape or some can have different shapes. The particular shape of a given electrode 14 can depend on how and where the electrode is located on the distal end portion of the medical device 12. Also, or as an alternative example, the medical device 12 can be an implantable medical device, which can be implanted at a fixed location within the anatomic structure 16, and the electrodes 14 (or at least some of the electrodes) form part of the implantable medical device. Useful examples of the implantableDocket No. A0013362W001type of medical device 12 include an implantable cardioverter-defibrillator, a pacemaker, or a ventricular assist device.

[0024] During the use of the system 12, such as part of a medical procedure, the medical device 12 or a portion thereof carrying the electrodes 14 (e.g., a portion of catheter extending proximally from the distal body portion) can be located within an anatomical structure 16 (e.g., heart) of a patient’s body. While the following examples are described in the context of performing procedures (e.g., mapping procedures) with respect to chambers of the heart, the systems and methods described herein are applicable to other anatomic structures.

[0025] The system also includes an interface circuit 18 and a computing apparatus 20. The interface circuit 18 can include input / output (I / O) ports (or terminals) coupled to the electrodes 14, such as through respective electrically conductive traces or wires. The interface circuit 18 can also be coupled to the computing apparatus 20 through respective electrically conductive traces or wires. Alternatively, in some examples, the coupling between the interface circuit 18 and the medical device 12 and / or between the interface circuit 18 and the computing apparatus 20 can be implemented as by wireless communications links. Each electrode and its corresponding trace, wire, or other communications link can define a channel that can send and / or receive electrical signals. While the example of FIG. 1 shows the interface circuit 18 and a computing apparatus 20 as separate structures, in other examples, the interface circuit 18 and computing apparatus 20 can be implemented in a single structure (e.g., a special purpose computing apparatus containing both hardware and software components).

[0026] The interface circuit 18 can include signal measurement circuit 24 and a signal generator circuit 26. The signal measurement circuit 24 is configured to measure electrical signals from one or more of the electrodes 14 and provide corresponding electrical data 28 that is representative of the electrical signals measured by the respective electrodes 14. For example, the electrophysiological data includes a value representative of a measured voltage potential between one or more pairs of the electrodes 14 and other related information (e.g., a channel identifier for each electrode and a timestamp). The electrical data 28 can be stored in memory (e.g., non-transitory memory) that is part of or coupled to the computing apparatus 20.

[0027] The signal generator circuit 26 is configured to provide one or more electrical signals to one or more of the respective electrodes 14. The signal generator circuit 26 can include circuitry configured to apply one or more electric fields (e.g., by injecting electrical energy in the form of electrical current) between a pair of the electrodes 14 (e.g., a source electrode and a sink electrode). In an example, the signal generator circuitry 26 can include an instance of a current source (e.g., a controllable AC current source) coupled to some to each ofDocket No. A0013362WG01the electrodes 14. Alternatively, an instance of a respective current source can be coupled to more than one of the electrodes 14 as to be configured to apply electrical current to multiple electrodes 14, consecutively or concurrently. The electrical current applied by the signal generator circuit 26 can be a subthreshold AC current having an amplitude insufficient to cause an action potential in surrounding myocardial tissue. The signal measurement circuit 24 can measure a voltage potential between one or more other respective pairs of the electrodes 14 responsive to the applied electrical field(s). The interface circuit 18 can also be configured to provide information characterizing features of each of the applied electrical signals, such as electrical parameters (e.g., amplitude, frequency, pulse duration, etc.) and timing information (e.g., a timestamp). The information characterizing the features of the applied signal(s) can be stored as part of the electrical data 28 in combination with the electrical data provided by the signal measurement circuit responsive to the applied field(s).

[0028] The computing apparatus 20 includes one or more non-transitory memory (not shown), which may be resident in the computing apparatus 20 or remotely located from the computing apparatus (e.g., cloud memory). The memory can include data and instructions executable by one or more processors (not shown) of the computing apparatus 20. The processor can be coupled to the memory to access the data and instructions (e.g., program code) stored in the memory. The instructions, when executed by the processor, cause the processor to perform respective control logic, functions, and / or methods described herein. The processor may include any one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or equivalent discrete or integrated logic circuitry. In some examples, the processor may include multiple components, such as any combination of one or more microprocessors, one or more controllers, one or more DSPs, one or more ASICs, or one or more FPGAs, as well as other discrete or integrated logic circuitry. The term “processor” may generally refer to any of the foregoing logic circuitry, alone or in combination with other logic circuitry, or any other equivalent circuitry.

[0029] The computing apparatus 20 includes an interface control function 30 (e.g., code executable by one or more processors of the computing apparatus) configured to control the signal generator circuit 26. For example, the interface control function 30 can be configured to control (e.g., by providing control instructions or commands to) the signal generator circuit 24 to provide an electrical current between a selected pair (or more than one pairs) of the electrodes, in which one electrode of the pair of electrodes defines a source electrode and the other electrode of the pair of electrodes defines a sink electrode. As described herein, theDocket No. A0013362W001current provided between each source and sink electrode provides an electric field in the volume around each pair of electrodes. In an example, the interface control function is configured to control the signal generator circuit 26 to provide AC electrical current between multiple pairs of the electrodes 14 at different frequencies concurrently.

[0030] In another example, the interface control function 30 is configured to control the signal generator circuit 26 to provide AC electrical current between each of two or more pairs of the electrodes 14 consecutively, which can be at the same or different frequencies. By injecting current with multiple frequencies between different pairs of the electrodes 14 concurrently, the time for spatially mapping the volume of the anatomical structure 16 can be reduced. The interface control function 30 thus can control which one or more pairs of the plurality of electrodes 14 are used for generating electric fields and which one or more pairs of the plurality of electrodes are used for measuring voltage potentials during a mapping process in which a volume of the anatomical structure 16 is spatially mapped. The interface control function 30 can be preprogrammed to control the current injection by the signal generator circuit 26 and voltage measurement by the signal measurement circuit 24. Also, or instead, the interface control function 30 can be programmed to control the signal generator circuit 26 and the signal measurement circuit 24 responsive to a user input provided at an input device 31 through a user interface 32 to control which electrode pairs inject current and which electrode pairs measure electrical signals. The interface control function 30 (or another function - not shown) can also be configured to control the signal measurement circuit 24 to measure a voltage potential between one or more pairs of the electrodes responsive to the electrical current provided by the signal generator circuit 26 (e.g., based on the interface control function 30).

[0031] The interface circuit 18 can include an analog-to-digital converter (not shown) to convert analog signals to respective digital signals, which can be stored as the electrical data 28 described herein. The electrical data 28 thus can include digital information representing each applied electrical signal (e.g., current) and each electrical signal measurement (e.g., measured voltage potentials) for each phase of the mapping process. The electrical data 28 further can include channel information (e.g., for each electrode), timestamps, and other parameters associated with each applied and / or measured signal.

[0032] The interface circuit 18 and / or the computing apparatus 20 can be configured to perform analog or digital signal processing on the measured signals. In examples where the signal generator 26 is controlled to drive the input electrodes with one or more AC signals, the signal measurement circuit 24 can include hardware configured to demodulate the measured signals to enable the amplitude and phase (e.g., the in-phase [real] and quadrature [imaginary]Docket No. A0013362W001components) of the measured signals to be determined. Also, or as an alternative, the signal measurement circuit and / or the computing apparatus 20 can include digital signal processing components (e.g., digital signal processor and / or signal processing code) configured to demodulate the AC signals provided in the electrical data for determining the amplitude and phase for the measured signals. As a further example, where the signal generator 26 is controlled to drive the input current to one or more electrode pair at multiple frequencies, the signal measurement circuit 24 and / or the computing apparatus 20 can be configured to demodulate the measured signals at the respective frequencies. The frequency demodulation can be implemented in the analog domain (e.g., by circuitry) or the digital domain (e.g., by a digital signal processor and / or signal processing code).

[0033] The system 10 also includes a tracking system 34 configured to provide tracking data 36. The tracking data 36 can be representative of a spatial position of at least a portion of the medical device 12 (e.g., one or more points on or within the distal end portion). Also, or as an alternative, the spatial position of at least a portion of the medical device 12 can be determined based on the tracking data 36, individually or in combination with other information. The tracking data 36 can define spatial coordinates of one or more portions of the medical device 12 in a spatial coordinate system of the tracking system 34 or in another spatial coordinate system. In some examples, the tracking data 36 can be converted (e.g., spatially registered) from the tracking coordinate system into another spatial coordinate system using a corresponding spatial transform. The tracking data 36 can be acquired at a sample rate defined by tracking system 34, which rate can be sufficient to enable real-time (or near-real-time) position tracking of one or parts of the medical device. The tracking data further can include a timestamp to enable temporal coordination of the electrical data 28 and the tracking data 36. In some examples, a plurality of samples of the tracking data 36 and the electrical data 28 are acquired at each location throughout the volume of the anatomical structure 16 to provide multiple measures of impedance at each of a plurality of locations, which can be filtered (e.g., via high-pass and / or low-pass filtering) to provide a respective filtered impedance measurement at each of the plurality of locations.

[0034] As a further example, the computing apparatus 20 includes a location calculator 38 configured to compute the location of one or more (e.g., each of the plurality) of electrodes 14 based on the tracking data. In an example, the tracking data 36 is representative of a spatial position of one or more parts of the medical device 12 having a known spatial position relative to one or more of the electrodes 14. Geometry data (e.g., stored in the memory) can define a spatial relationship (e.g., a distance and orientation in 3D space) between one or more parts ofDocket No. A0013362W001the medical device 12 and the one or more electrodes 14. The location calculator 38 thus can be configured to compute the location of the one or more electrodes 14 based on the tracking data 36 and the geometry data.

[0035] As a further example, the tracking system 34 can be an electromagnetic tracking system, a magnetic tracking system, an optical tracking system, or other navigation system, which is configured to provide the tracking data 36. Useful examples of the tracking system 34 include the STEALTHSTATION navigation system (commercially available from Medtronic Inc.), the CARTO XP EP navigation system (commercially available from Biosense Webster, Inc.) and the ENSITE NAVX visualization and navigation technology (commercially available from St. Jude Medical); although other types of tracking systems could be used to provide the tracking data 36 representative of the spatial position for the medical device 12 and / or one or more of the electrodes 14. Examples of other tracking systems include an electromagnetic tracking system, a magnetic tracking system, an optical tracking system, and the like.

[0036] As one example, the tracking system 34 includes one or more tracking sensors 40, which can be carried by (e.g., attached to) the medical device 12. The tracking sensor 40 can communicate (e.g., send or receive) a tracking signal with respect to the tracking system, in response to which the tracking system provides the tracking data, in which the tracking data represents a spatial position of the one or more tracking sensors. Each tracking sensor 40 can have a known spatial relationship relative to one or more of the electrodes 14, which can be defined by electrode geometry data.

[0037] As an example, the tracking system includes a field generator configured to provide an electromagnetic field, and the sensor 40 provides a tracking sensor signal in response to the electromagnetic field provided by a field generator. For example, the distal end portion of the medical device, which also includes one or more electrodes 14, includes one or more tracking sensors, each including a conductive sensor coil around a magnetic core. A conductive link (e.g., a twisted pair of wires) extends from the coil to carry a respective sensor signal to processing electronics of the tracking system 34. The tracking sensor(s) 40 can be a five degree of freedom (5DOF) or six degree of freedom (6DOF) sensor (e.g., commercially available from Northern Digital Inc. of Ontario, Canada). The electrode location calculator 38 thus can be configured to determine the spatial position and orientation of the electrodes 14 based on the tracking data 36 and geometry data representing the spatial relationship between the electrodes and the one or more tracking sensors 40. As mentioned, other types of sensors and tracking systems can be used to implement the tracking system 34 in the system 10.Docket No. A0013362W001

[0038] The computing apparatus 20 can also include an impedance calculator 42 (e.g., instructions executable by one or more processors of the computing apparatus) to calculate electrical impedance values for one or more pairs of the electrodes 14 based on the electrical data 28. The impedance values can represent the electrical impedance (e.g., a measure of the electrical impedance spectra) at respective locations throughout a volume within the anatomical structure 16 based on the tracking data 36. For example, the volume within the anatomical structure 16 defines a cardiac chamber of an individual’s heart, and the locations (e.g., determined based on the tracking data 36) correspond to locations within the cardiac chamber where the distal portion of the medical device 12 is located when the electrical signals are measured. A higher impedance implies a closer distance to a wall of the anatomical structure 16 and a lower impedance value implies a greater distance to the wall of the anatomical structure. That is, the impedance value for a given pair of electrodes provides a surrogate estimate for the distance between the given pair of electrodes to the wall of the anatomical structure that does not require imaging or other information. The accuracy of the distance estimate can be improved based on impedance calibration, as described herein. The impedance calculator 42 can compute impedance values continually based on electrical data 28 acquired over time (e.g., over a number of acquisition cycles) for one or more electrode pairs, such as to provide real-time (or near real-time) electrical impedance values at respective locations within the anatomical structure 16 (e.g., cardiac chamber). A location or region for the impedance value computed for a given electrode pair can be determined based on the locations of each respective electrode in the given electrode pair. For example, the location of the impedance value can be computed as a centroid or geometric center (e.g., in 3D spatial coordinates) between the respective electrodes in the given electrode pair. A respective impedance measurement location or region can be computed for each pair of electrodes for which a voltage potential is determined based on the electrical data 28. The computed electrical impedance value and associated location can be stored as impedance data in memory, such as part of the electrical data 28.

[0039] As described herein, the electrical data 28 can represent the electrical current signal applied (e.g., by the signal generator circuit 26) between one or more pairs of the electrodes 14 and the electrical signal measurements (e.g., voltage potentials) between respective pairs of the electrodes 14. The applied electrical current can be an AC current having magnitude and phase and the electrical signals (e.g., voltage potential) measured between respective pairs of electrodes 14 likewise can include a magnitude and phase. Thus, the impedance calculator 42 can compute a value of electrical impedance having magnitude and phase components as aDocket No. A0013362W001function of the AC current and measured voltage values (e.g., Z=V / I) for respective pairs of the electrodes 14. Also, or as an alternative, the impedance calculator 44 can compute the impedance values for one or more respective pairs of the measurement electrodes having only magnitude based on the electrical data 28. The position for each computed impedance value can be determined based on the tracking data 36 as described herein.

[0040] In some examples, the computing apparatus includes an impedance calibration function 44 (e.g., instructions executable by one or more processors of the computing apparatus) to calibrate the impedance calculator 42 according to range of impedance values within the volume of the anatomical structure 16. The calibration further can depend on the configuration of the device 12 and spatial arrangement of the electrodes on the device. For example, electrical signal measurements can be made (e.g., by signal measurement circuit 24) responsive to moving the distal portion of the device 12, which includes the electrodes, along one or more substantially orthogonal paths between opposing sides of the anatomical structure. The location of the electrodes 14 can be determined for each measurement location to provide corresponding locations for the impedance values across the anatomical structure. A range of impedance values at locations across one or more diametrically opposed sides of the anatomical structure 16 can provide calibration data for scaling the impedance values within the volume of the anatomical structure that provide the calibrated impedance data for locations within the anatomical structure. In an example, the impedance can be measured at a first location with electrodes in contact with the anatomical structure and at one or more second locations with the electrodes not contacting the anatomical structure. The impedance measurements at the first and second locations can provide the calibration data.

[0041] The computing apparatus 20 can also include a volume element generator 46 (e.g., instructions executable by one or more processors of the computing apparatus) to provide a volume element to be filled based on the impedance data (e.g., the impedance value and associated location thereof). For example, the volume element generator 46 determines a size for the volume element to be filled based on the impedance value for a location between a respective pair of the electrodes 14. The size of a given volume element can be inversely proportional to the impedance value determined for a respective electrode pair. Thus, larger volume elements will be determined for electrode locations closer to the center of the volume defined by the anatomical structure 16 (e.g., heart chamber) than locations at or near the wall of the anatomical structure. In an example, each volume element can be generated as a sphere having a diameter or radius that is inversely proportional to the impedance value determinedDocket No. A0013362W001for each respective pair of electrodes. Other volumetric shapes can be used for volume elements in other examples.

[0042] The volume element generator 46 also determines a position for the volume element to be filled based on the computed location of the electrodes of the medical device 12 (e.g., based on the tracking data 36). The location for a given volume element is based on the location of the respective electrode pair 14 that made the electrical signal measurements from which the impedance value has been derived. The volume element generator 46 can determine the size and location of a number of respective volume elements based on the electrical data 28 for any number of electrode pairs (or other groupings of multiple electrodes) on the medical device.

[0043] The computing apparatus 20 can also include an output generator 48 (e.g., instructions executable by one or more processors of the computing apparatus) configured to provide output data 50 to a display 52 for providing a graphical representation 54 that includes rendering of one or more volume elements. The output data 50 can be stored in memory of the computing apparatus 20. The output data 50 thus can include data describing graphical representation of one or more volume elements (e.g., sphere(s)) based on the size and the spatial position determined (e.g., by the volume element generator 46 and location calculator 38) for each respective volume element. As mentioned, the spatial position of the volume elements can be determined in the same 3D coordinate space as the tracking system 34 or another spatial domain into which the tracking data 36 has been registered. As described herein, the graphical representation 54 of each volume element that is generated has a size based on the impedance value (e.g., determined by the impedance calculator 42 based on the electrical data 28) and a respective location (e.g., determined by location calculator 38 based on the tracking data 36) to facilitate creating of boundary (e.g., a shell) structure for the anatomical structure 16. Over time and responsive to moving the medical device 12 and electrodes 14 thereof within the interior volume of the anatomical structure 16 a graphical representation 54 of a number of volume elements can be generated and a 3D surface (e.g., boundary) of the volume elements can be graphically rendered on the display 52. The volume elements thus can fill the interior volume and the resulting 3D surface of the volume elements be used to provide a graphical visualization the surface geometry of the anatomical structure 16 based on the electrical data 28 and tracking data that is acquired. Due to impedance differences based on measurement locations, the volume elements located near the surface of the anatomical structure 16 will generally be smaller than volume elements located away from the surface of the anatomical structure. Thus, the central region of the interior volume of the anatomical structure 16 can fill faster (e.g., more efficiently) than at or nearer the surface of the anatomical structure. A 3DDocket No. A0013362W001surface defined by outer surfaces of the volume elements can thus define a boundary or interior surface wall of the anatomical structure 16.

[0044] The computing apparatus 20 can also include a surface generator 56 (e.g., instructions executable by one or more processors of the computing apparatus) configured to generate a surface representation for at least the portion of the anatomical structure 16 based on respective volume elements. In an example, the surface generator 56 can generate a surface geometry to represent the surface of anatomical structure (e.g., a cardiac chamber). For example, the surface generator 56 includes code to execute a surface wrapping method to generate a surface geometry (e.g., a 3D shell or other 3D boundary representation) for a bounding volume that is defined by the volume elements that have been generated within at least a portion of the anatomical structure. The surface geometry can be a polygon mesh (e.g., triangles, rectangles, and / or other polygons) having vertices, edges and faces along a surface of the bounding volume. The surface generator 56 can be configured to extract the surface geometry for the surface of the anatomical structure according to other methods, such as an isosurface extraction (e.g., marching cubes) algorithm as well as other methods.

[0045] The output generator 48 further can include program code programmed to generate a graphical representation based on the surface geometry provided by the surface generator 56. The graphical representation of the surface geometry can be a 3D representation or a two-dimensional projection of the 3D surface. In an example, the 2D projection can be provided from a point-of-view that can be selected responsive to a user input entered at the input device 31 to the user interface 32 . Alternatively, the 2D projection can be provided from a point-of-view that can be determined responsive to a position and orientation of the distal end portion of the medical device 12 within the anatomical structure 16, which is based on the tracking data 36. For example, the graphical representation 54 of the surface geometry can be visualized during a mapping or electrophysiology study in which a graphical representation of the distal end (or other) portion of the medical device 12 is superimposed on the graphical representation of the surface geometry based on the tracking data 36. The interface circuit 18 further can be configured to control delivery of energy to one or more of the electrodes 14 (or other components) for applying treatment or therapy to the surface of the anatomical structure 16. The treatment can include ablation (e.g., radio-frequency ablation, cryoablation, laser ablation, pulsed field ablation, or the like), cardiac resynchronization therapy, pacing, any combination thereof, or any other treatments.

[0046] FIG. 2 is a block diagram depicting an example impedance calculator 200. The impedance calculator 200 can be used to implement the impedance calculator function 42 ofDocket No. A0013362WG01FIG. 1. Accordingly, the description of FIG. 2 can also refer to certain aspects of FIG. 1. The impedance calculator 200 includes an impedance measurement calculator 202 configured to compute a measure of impedance based on current data 204, voltage measurement data 206, and other data 208. In examples described herein, the computed measure of impedance represents an electrical impedance between a pair of electrodes within an anatomical structure (e.g., a cardiac chamber). For example, the current data (e.g., part of the electrical data 28 of FIG. 1) represents electrical current that is injected between a respective pair of electrodes (e.g., the electrodes 14 of FIG. 1) to provide an electric field based on the injected current. The current can be an AC current having a frequency and magnitude, which can be represented in the current data 204. In some examples, the current can be injected between more than one pair of electrodes at different frequencies concurrently to provide multiple concurrent electric fields at respective frequencies. The current data 204 can be measured data (e.g., a measurement of electrical current through a current sense resistor or other circuitry) or be derived from instructions specifying current that is to be applied between source and sink electrodes of a current path. The voltage measurement data 206 can include an electrical potential measured between one or more pairs of electrodes responsive to the electric field(s) that are generated. In examples where current is injected between more than one pair of electrodes at different frequencies concurrently, respective electrical potentials can be measured concurrently between one or more pairs of the electrodes at each of the different frequencies.

[0047] The other data 208 can include timing data (e.g., a timestamp from a clock - not shown) associated with each of the current data 204 and 206, which can be provided according to a sample rate. Also, or instead, the other data 208 can include channel data identifying each electrode or electrode pair that provides an instance of the current data 204 and electrical data 206. Additionally, or as an alternative, the other data can also include data describing a location of one or more of the electrodes that provide the current data and / or voltage data or other information (e.g., tracking data 36) based on which the location of the electrodes can be determined. While the other data is shown as a separate data instance, in examples, the other data 208 can be part of or linked to the current data 204 and the voltage measurement data 206. The other data can likewise be part of or linked to the computed measurement of impedance determined by the impedance measurement calculator 202.

[0048] The impedance calculator 200 also includes one or more processing functions 210, which can be applied to the computed measurement of impedance determined by the impedance measurement calculator 202 to provide the impedance data 212. For example, theDocket No. A0013362W001one or more processing functions 210 can be applied to the measurement of impedance computed over time based on the current data 204 and the voltage measurement data 206 to provide the impedance data to represent a measurement of impedance for each of a plurality of locations within the anatomical structure. The measurement of impedance for a respective location within the anatomical structure (e.g., a local impedance measurement) can be determined by the one or more processing functions 210 based on a set of computed measurements of impedance determined by the impedance measurement calculator 202. As described herein, each of the current data 204 and voltage measurement data 206 can be provided at respective sample rate. The tracking data similarly can be generated at a sample rate, which can be the same or different rate than current and voltage data.

[0049] In the example of FIG. 2, the one or more processing functions 210 include a high-pass filter 214, a low-pass filter 216, and a statistical processing function 218. Other types of processing functions can be implemented by the impedance calculator 200 in other examples to provide impedance values at respective locations for use in generating volume elements. The high-pass filter 214 can be configured to pass high-frequency impedance data (or filter out lower frequencies), such as to remove low frequency noise in the voltage and current signal measurements. The low-pass filter 216 can be configured to remove higher frequency components (e.g., due to catheter motion as reflected in the tracking data) so that the resulting impedance data represents one or more averaged values of impedance at the respective locations without artifacts due to catheter motion during mapping. The statistical processing function 218 can be configured to apply one or more statistical functions or methods, such as to compute a mean value of impedance (e.g., based on the current data 204 and voltage measurement data 206) for each respective location. The statistical processing function 218 can also be applied to the location of the electrodes and / or the tracking data used to determine such locations over time so that each value of impedance and associated location are spatially and temporally consistent. In one example, the impedance calculator 200 computes the impedance data 212 for one pair of electrodes responsive to an electric field provided based on an applied current between another pair of electrodes. In another example, the impedance calculator 200 computes the impedance data 212 for multiple pairs of electrodes responsive to an electric field provided based on an applied current between another pair of electrodes. In yet another example, the impedance calculator 200 computes the impedance data 212 for a number of electrode pairs responsive to multiple electric fields electric field provided based on current applied between more than one pair of electrodes at different frequencies. Thus, there can be various combinations of electrodes used for measurement of voltages and injectingDocket No. A0013362WG01current. The electrodes used for measurement and signal injection can depend on the configuration and arrangement of electrodes on the medical device and the manner in which the current is injected and measured over a number of cycles (e.g., by interface control 30 and / or interface circuit 18).

[0050] FIG. 3 is a block diagram depicting an example volume element generator 300. The volume element generator 300 can be used to implement the volume element generator 46 of FIG. 1. Accordingly, the description of FIG. 3 can also refer to certain aspects of FIG. 1. The volume element generator 300 is configured to provide volume element data 302 based on impedance data (e.g., the impedance data 212), electrode geometry data 306, and electrode location data 308. The volume element data 302 thus can represent a size (e.g., volume) and location (e.g., spatial coordinates) for each volume element. In the example of FIG. 3, the volume element generator 300 includes a volume calculator 310 and a location calculator 312. The volume calculator 310 can compute the volume for a given volume element to be filled based on the impedance data 304. In an example, the volume calculator 310 computes the volume value as a function of the impedance. Thus, a lower impedance value has a larger volume than a higher impedance value. The location calculator 312 can compute a location for a given volume element to be filled based on location data 308 and the electrode geometry data 306. For example, the location data 308 can represent the location of one or more electrodes on the medical device in a spatial domain, such as can be determined based on tracking data (e.g., the tracking data 36). The electrode geometry data 306 can describe the relative spatial relationship between multiple electrodes on a medical device (e.g., the medical device 12). For a given impedance measurement stored in the impedance data 304, the geometry data 306 can represent a relative spatial position of the respective electrode of each pair of electrodes and / or a distance between each respective electrode of the pair of electrodes.

[0051] Thus, the location calculator 312 can determine the spatial location of each of the electrodes on the medical device based on the location data 308 and the electrode geometry data 306. The location calculator 312 is configured to determine the location for a given volume element to be filled based on the location (e.g., spatial coordinates) of each of the electrodes used to measure the voltage potential for which the impedance is determined (e.g., by the impedance calculator 200). In some examples, the volume calculator 310 can further determine the volume for the given volume element based on a location of electrodes and / or distance between electrodes used to measure the voltage for which the impedance has been determined.Docket No. A0013362WG01

[0052] In an example where the volume element is a sphere, the location calculator 312 can compute a center of the sphere corresponding to a center (e.g., mid-point) between the locations of each of the electrodes used to measure the voltage potential for which a given impedance value is determined. As described herein, the location of the electrodes can be defined by and / or determined from the location data 308 based on tracking data (e.g., tracking data 36). The sphere also has a volume defined by a radius (or diameter) of the sphere, in which the radius (or diameter) of the sphere has a value determined based on the calculated impedance. For example, the volume calculator 310 can determine a volume of the sphere as a function of the computed impedance. In an example, the volume calculator 310 can include a set of one or more equations (e.g., linear and / or non-linear equations) to determine the volume. In another example, the volume calculator 310 can include in a look-up table (e.g., stored in memory) that is programmed to determine volume in response to the computed impedance. The volume calculator 310 (e.g., equation(s) and / or look-up table) can be ascertained during a calibration phase (e.g., implemented by impedance calibration function 44). The size of the volume element and its location can thus be stored in the volume element data 302 for each volume element.

[0053] As a further example, FIG. 4 is a block diagram depicting an example volume calculator 400, which can be used to implement the volume calculator 310 of FIG. 3. Accordingly, the description of FIG. 4 can refer to certain aspects of FIG. 3. The volume calculator 400 is configured to provide volume data 402 for one or more respective volume elements based on impedance data 406 (determined by impedance calculator 200) and electrode geometry data 408. In some examples, the volume calculator 400 further can use calibration data (e.g., generated by impedance calibration function 44 as part of a calibration process) to determine volume data. For example, the impedance calibration function can be used to ascertain a distance between opposite sides of the anatomical structure, which can provide calibration data that is used to define a range of sizes (e.g., two or more sizes) for the volume elements.

[0054] As shown in the example of FIG. 4, the volume calculator 400 can include an electrode distance calculator 412 and a size-impedance function 414. The electrode distance calculator 412 is configured to determine a distance (e.g., a Euclidean or other distance) between each pair of electrodes between which a respective measure electrical impedance has been determined (e.g., calculated by the impedance calculator 200). The electrode distance can be stored as part of or linked to the impedance data 406 (e.g., impedance data 202). In an example, the location of one or more electrodes can be represented directly in tracking data. InDocket No. A0013362W001another example, the location of one or more electrodes can be derived based on the tracking data representing a location and orientation of a known part of a medical device (e.g., device 12) and based on electrode geometry data 408. As described herein, the electrode geometry data 408 can represent a relative spatial position of each respective electrode of the pair of electrodes and / or a distance between each respective electrode of the pair of electrodes. In some examples, the electrode distance can be fixed and defined directly in the electrode geometry data 408. In other examples, the distance between electrodes can be variable over time, such as changing responsive to contact between a distal portion of the medical device carrying the electrodes and one or more parts of the anatomical structure. A distance between each of the electrodes can be determined for each of the electrode pairs that provide or are used to measure electrical signals used to determine measurements of electrical impedance.

[0055] As mentioned, the size-impedance function 414 can determine a size (e.g., volume) for a given volume element to be filled based on impedance data that has been determined (e.g., by impedance calculator 200) for the given volume element, based on the distance between respective pair of electrodes, or based on a combination of the impedance data and distance between electrodes. In an example, the size-impedance function 414 can define a minimum size and a maximum size for volume elements. In another example, the size-impedance function 414 can define a range of more than two sizes for volume elements that depends on the respective impedance measurements between electrode pairs.

[0056] In one example, the size-impedance function 414 can limit the size of a volume element for a given anatomical structure to a maximum size (e.g., a sphere having a maximum diameter) based on the impedance being at or below a low-impedance threshold. Also, or as an alternative, the size-impedance function 414 can limit the size of a volume element for a given anatomical structure to a maximum size (e.g., as sphere having a maximum diameter) based on a distance between the pair of electrodes. For instance, the size of a given volume element can be set to a maximum diameter that is set equal to (or less than) to the distance between the electrodes for which the impedance has been determined. Also, or as an alternative, the size-impedance function 414 can limit the size of a volume element size of the volume element (e.g., a sphere) to a minimum diameter based on the impedance being equal to or greater than a high impedance threshold and / or based on a distance between the pair of electrodes.

[0057] As a further example, the size-impedance function 414 can be implemented as a mathematical equation, a curve or other function. The size-impedance function 414 can be predefined or it can be determined as part of a given procedure (e.g., during a calibrationDocket No. A0013362W001process). In one example, the size-impedance function 414 can be determined based on the calibration data 410 provided responsive to a calibration function in which measurements are made for respective electrodes on a device at different positions within the anatomical structure. The calibration data 410 can be used to define the physical size of the anatomical structure and / or establish a range of different impedance measurements at different positions throughout the structure. The calibration data can be determined during a calibration process and / or based on pre-procedural medical imaging data. For example, an approximate distance between opposing sides of the anatomical structure (e.g., along an axis) can be used to limit a maximum size of the volume element. For instance, the maximum size for a volume element (e.g., a diameter or radius thereof) can be set to a fractional part of an axis extending across the anatomical structure, such as approximately 0.5, 0.25, or 0.1 times the distance between opposing sides of the anatomical structure. Other fractional values can be used in other examples to limit a maximum size of the volume elements based on the actual size of the anatomical structure. The resulting volume data 402 thus can define a size of the volume element, which can be a radius or diameter or a spherical volume element having a location (e.g., a center of the sphere) that is determined by the location calculator 312. As a further example, a maximum impedance threshold can be defined during calibration to set a minimum size for volume elements so that, regardless of spacing between electrodes, the size of the volume elements converge to a small (e.g., minimum) volume when the impedance measurement is representative a contact between an electrode and the anatomical structure.

[0058] The systems and methods described herein can provide the volume element data for locations throughout the anatomical structure based on the tracking data for each respective location of the medical device and impedance measurements determined for one or more pairs of the electrodes for the respective locations of the medical device. As described herein, the impedance measurements can be calculated based on the measured voltage potential and electrical current for each respective location of the medical device. The size of the respective volume element to be filled further can be determined based on the calculated impedance, and the position for the respective volume element based on the respective location of the medical device, such as represented as a location between each pair of electrodes for which the impedance measure has been determined. Because larger volume elements will generally be populated away from the wall of the anatomical structure, the process of creating a boundary or shell for the anatomical structure can be facilitated. Each of the volume elements, including a respective size and position thereof, thus can be determined and a surface for the volume elements can be computed and graphically represented on a display. The volume elements atDocket No. A0013362WG01or near the wall of the anatomical structure can define a boundary of at least a portion of an anatomical structure and a 3D surface representation for such portion of the anatomical structure can be generated based on the boundary thereof. The 3D surface representation can thus be used in a subsequent mapping procedure and for treatment of the anatomical structure.

[0059] FIG. 5 is a graph 500 showing an example of a size-impedance function showing volume size plotted as a function of measured impedance. In the example of FIG. 5, the graph 500 is a curve that includes asymptotic maximum and minimum sizes, respectively, shown at 502 and 504.

[0060] FIG. 6 is a graph 600 showing another example of a size-impedance function showing volume size (e.g., diameter) plotted as a function of measured impedance. In the example of FIG. 6, the graph 600 is a curve that includes an asymptotic maximum size, shown at 602, and a fixed defined minimum size, shown at 604, which occurs at any impedance that exceeds a defined impedance threshold value, shown at 606.

[0061] The example size-impedance functions of FIGS. 5 and 6 demonstrate but two examples of determining size of volume elements based on impedance measurements between electrodes within an anatomical structure. Those skilled in the art will understand various other functions or methods that can be used to determine a range of different sizes for volume elements as a function of impedance between electrode pairs, as described herein.

[0062] As described herein, various types of medical devices, such as catheters, can be used for creating an anatomical structure. By way of example, FIGS. 7-12 demonstrate examples of three different types of catheters that can be used for mapping a volume within an anatomical structure, namely for creating an endocardial surface envelope for a cardiac chamber. Other types and configurations of devices (e.g., catheters, probes, etc.) can be used to create a surface envelope for a cardiac chamber or other anatomical structures. Each of the catheters of FIGS. 7-12 also constitute examples of the device 12 that can be used in the context of the system 10 of FIG. 1 as well as FIGS. 2-4. Accordingly, the description of FIGS. 7-12 can refer to certain aspects of any one or more of FIGS. 1-4.

[0063] FIGS. 7 and 8 depict example graphical representations of a loop catheter 700 located within a cardiac chamber 702, such as demonstrating part of a procedure for creating an endocardial surface envelope for a wall 704 of the cardiac chamber 702. In the example of FIGS. 7 and 8, the loop catheter 700 includes a plurality of electrodes 706, 708, 710, 712, 714, 716, 718, 720, and 722 distributed along a loop (e.g., an annular ring) 724 that defines a distal end portion of the catheter. As one example, the catheter 700 can be the PULSESELECT™ catheter, which is available from Medtronic Inc. of Minneapolis, Minnesota, and has nineDocket No. A0013362WG01electrodes with a fixed spacing along the loop 724. Other types of catheters having other numbers and configuration of electrodes can also be used to perform mapping and ablation.

[0064] As described herein, any two of the electrodes 706, 708, 710, 712, 714, 716, 718, 720, and 722 can define a respective electrode pair and there can be a number of electrode pairs configured for measuring an electrical impedance between the electrodes of each respective electrode pair. In the example of FIGS. 7 and 8, electrodes 708 and 710 define a first electrode pair, electrodes 714 and 716 define a second electrode pair, electrodes 716 and 718 define a third electrode pair, and electrodes 718 and 722 define a fourth electrode pair. Other numbers and pairings of electrodes can be used in other examples for measuring the electrical impedance. As described herein, the electrical impedance can be computed (e.g., by impedance calculator 42, 200) based on a measured voltage potential between each electrode pair and an electrical current applied by another pair of electrodes within the cardiac chamber 702. As described herein, each voltage potential being measured by a respective electrode pair can be based on an electric field generated within the cardiac chamber responsive to the applied electrical current. The interface control 30 and / or interface circuit 18 can control which electrodes 706, 708, 710, 712, 714, 716, 718, 720, and 722 apply electrical current (e.g., a subthreshold AC current) and which electrodes are configured to sense voltage potentials responsive to the applied electrical current.

[0065] FIG. 7 also shows examples of volume elements 726, 728, 730, and 732 that are generated (e.g., by volume element generator 46, 300) based on the impedance measurements and the location of the respective electrode pairs. As described herein, each of the volume elements 726, 728, 730, and 732 has a size that is determined (e.g., by volume calculator 310, 400) based on the impedance measurement. Additionally, each of the volume elements 726, 728, 730, and 732 has a location that is determined (e.g., by location calculator 312) based on the location of the respective electrodes that measure the electrical signals (e.g., voltage potential) used to determine the impedance measurement. The location of the electrodes can be provided by or determined from tracking data (e.g., tracking data 36 provided by a tracking system 34). The volume elements 726, 728, 730, and 732 in FIG. 7 are shown as spheres, each having a center that defines a location thereof along the loop 724 and a radius defining the size / volume thereof. For example, the volume element 726 has a center 734 between electrodes 708 and 710, the volume element 728 has a center 736 between electrodes 714 and 716, the volume element 730 has a center 738 between electrodes 716 and 718, and the volume element 732 has a center 740 between electrodes 718 and 720.Docket No. A0013362WG01

[0066] FIG. 8 shows the loop catheter 724 moved to a second position within the cardiac chamber and a second set of volume elements 802, 804, 806, and 810 that are generated (e.g., by volume element generator 46, 300) in the cardiac chamber 702 based on a second set of impedance measurements and the next location of the respective electrode pairs. In FIG. 8, the volume elements 726, 728, 730, and 732 that were generated based on the location of the loop catheter 724 shown in FIG. 7 remain. Thus, a user can move the loop catheter 724 to different locations throughout the cardiac chamber to fill the chamber volume with volume elements based on impedance measurements. Because the size of the volume elements away from the chamber wall are larger (e.g., based on lower impedance measurements) compared to the volume elements at the wall, the process of filling the chamber volume with volume elements can be expedited compared to existing approaches. As a result, the approach described herein to generate a surface (e.g., by surface generator 56) representative of the chamber wall can be implemented in a reduced amount of time compared to existing approaches.

[0067] FIGS. 9 and 10 depict example graphical representations 900 and 1000 of a second example catheter 902 (e.g., generated by output generator 48) within a cardiac chamber 904, such as demonstrating part of procedure for creating an endocardial surface envelope for a wall 906 of the cardiac chamber. In the example of FIGS. 9 and 10, the catheter 902 is shown as having a spherical distal end portion 908 extending from a shaft 910. As an example, the catheter 902 can be the SPHERE-9™ mapping and ablation catheter available from Affera, Inc., which is part of Medtronic, Inc. of Minneapolis, Minnesota. Other types and configurations of catheters can also be used to implement the catheter 902.

[0068] In the example of FIGS. 9 and 10, the spherical distal end portion 908 defines a spherical lattice structure that includes a plurality of electrodes (e.g., two or more, such as 9 electrodes) 912 distributed across an outer surface of the spherical distal end portion. In some examples, one or more other electrodes (e.g., a reference or return electrode) 914 can be located within the spherical distal end portion 908, such as at or near a center of spherical distal end portion spaced radially inwardly from the spherical distal end portion 908. The other electrode 914 can be on a rod or other member 916 that extends generally axially from the shaft 910 into an interior volume of the spherical distal end portion 908. As described herein, any combination of the electrodes 914 can define an electrode pair for sensing electrical signal (e.g., a voltage potential) used for determining impedance between the respective electrodes of each respective pair. The interface control 30 and / or interface circuit 18 can control which one or more of the electrodes 912 and 914 apply an electrical current (e.g., a subthreshold AC current) and which electrodes are configured to sense voltage potentials responsive to the appliedDocket No. A0013362WG01electrical current (e.g., between one or more other electrode pairs). For example, a given electrode pair can include two electrodes 912 on the spherical distal end portion 908. Also, or as an alternative, a given electrode pair can include one electrode 912 on the spherical distal end portion 908 and another electrode 914 within the spherical distal end portion.

[0069] FIG. 9 also shows examples of volume elements 920 and 922 that are generated (e.g., by volume element generator 46, 300) based on the impedance measurements and the location of the respective electrode pairs. As described herein, each of the volume elements 920 and 922 has a size that is determined (e.g., by volume calculator 310, 400) based on the measure of impedance between respective pairs of the electrodes 912 and 914. Additionally, each of the volume elements 920 and 922 has a location that is determined (e.g., by location calculator 312) based on the location of the respective electrodes that measure the electrical signals (e.g., voltage potential) used to determine the impedance measurement. The location of the electrodes can be provided by or determined from tracking data (e.g., tracking data 36 provided by a tracking system 34). The volume elements 920 and 922 in FIG. 9 can be spheres, each having a center (e.g., a midpoint between locations of electrodes measuring the impedance) and a radius defining the size / volume thereof. For example, the volume element 920 has a center 924 between electrodes 912 and 914, and the volume element 922 has a center 926 between a pair of the electrodes 912.

[0070] The graphical representation 1000 of FIG. 10 shows the catheter 902 at a second position within the cardiac chamber 904 and a second set of volume elements 1002 and 1004 that are generated (e.g., by volume element generator 46, 300 and / or output generator 48) based on a second set of impedance measurements and the current location of the respective electrode pairs where the measurements are mad. In FIG. 10, the volume elements 920 and 924 that were generated based on the location of the catheter 902 shown in FIG. 9 are also displayed in the graphical representation 1000. Thus, a user can move the catheter 902 to different locations throughout the cardiac chamber to fill the chamber volume with volume elements based on corresponding impedance measurements. Because the size of the volume elements away from the chamber wall are larger (e.g., based on lower impedance measurements) compared to the volume elements at the wall, the process of filling the chamber volume with volume elements and generating a 3D surface geometry can be expedited compared to existing approaches. As a result, the approach described herein to generate a surface (e.g., by surface generator 56) representative of the chamber wall can be implemented in a reduced amount of time compared to existing approaches.Docket No. A0013362WG01

[0071] FIGS. 11 and 12 depict example representations 1100 and 1200 (e.g., generated by output generator 48) of a third example catheter 1102 located within a cardiac chamber 1104, such as demonstrating part of procedure for creating an endocardial surface envelope for a wall 1106 of the cardiac chamber. In the example of FIGS. 11 and 12, the catheter 1102 is shown as having a substantially linear, distal end portion 1108. The distal end portion 1108 can be steerable in response to mechanical and / or electro-mechanical controls. As an example, the catheter 1102 can be the DECANAV ™ mapping catheter available from Biosense Webster, Inc., of Irvine, California. Other types of catheters from other vendors can also be used to implement the catheter 1102.

[0072] In the example of FIGS. 11 and 12, the distal end portion 1108 includes a plurality of electrodes (e.g., two or more, such as 10 electrodes) 1112, 1114, 1116, 1118, 1120, 1122, 1124, 1126, 1128, and 1130 distributed at respective points across an outer surface of the linear distal end portion. While the electrodes 1112, 1114, 1116, 1118, 1120, 1122, 1124, 1126, 1128, and 1130 are shown as cylindrical rings around a shaft, other shapes, configurations and / or numbers of electrodes can be used. As described herein, any combination of the electrodes 1112, 1114, 1116, 1118, 1120, 1122, 1124, 1126, 1128, and 1130 can define an electrode pair for sensing electrical signals (e.g., a voltage potential) used for determining the electrical impedance between the respective electrodes of each electrode pair. The interface control 30 and / or interface circuit 18 can control which electrodes 1112, 1114, 1116, 1118, 1120, 1122, 1124, 1126, 1128, and / or 1130 apply an electrical current (e.g., a subthreshold AC current) and which electrodes sense voltage potentials responsive to the applied electrical current (e.g., between one or more other electrode pairs) throughout the mapping procedure.

[0073] FIG. 11 also shows examples of volume elements 1132, 1134, 1136, 1138, and 1140 that are generated (e.g., by volume element generator 46, 300) based on the impedance measurements and the location of the respective electrode pairs (e.g., electrode pairs 1112-1114, 1116-1118, 1120-1122, 1124-1126, and 1128-1130). As described herein, each of the volume elements 1132, 1134, 1136, 1138, and 1140 has a size that is determined (e.g., by volume calculator 310, 400) based on the measure of impedance between respective pairs of electrodes 1112-1114, 1116-1118, 1120-1122, 1124-1126, and 1128-1130. Additionally, each of the volume elements 1132, 1134, 1136, 1138, and 1140 has a location that is determined (e.g., by location calculator 312) based on the location of the respective electrodes that measure the electrical signals (e.g., voltage potential) used to determine the impedance measurement. The location of the electrodes can be provided by or determined from tracking data (e.g., tracking data 36 provided by a tracking system 34). The volume elements 1132, 1134, 1136,Docket No. A0013362WG011138, and 1140 in FIG. 11 can be spheres having center (e.g., a midpoint between locations of electrodes measuring the impedance) and a radius defining the size / volume thereof. For example, the volume elements can each have respective centers located midway between the centroids of the electrodes that measured the signals used to determine the impedance therebetween.

[0074] In FIG. 12, the graphical representation 1200 shows the catheter 1102 moved to a second position within the cardiac chamber 1104 and a second set of volume elements 1202, 1204, 1206, 1208, and 1210 that are generated (e.g., by volume element generator 46, 300) based on a second set of impedance measurements and the current location of the respective electrode pairs where the measurements are made. The graphical representation 1200 also displays the volume elements 1132, 1134, 1136, 1138, and 1140 that were generated based on the location of the catheter 1102 shown in FIG. 11. In the example of FIG. 11 volume elements 1138 and 1140 are largest based on the impedance measurements measured by electrode pairs 1124-1126, and 1128-1130. As described herein, the spacing between electrodes can further control the size of the volume elements. For examples of equal spacing, the volume element 1136 corresponding to the impedance measured between electrode pair 1116-1118 has a larger radius than volume element 1132 corresponding to the impedance between electrode pair 1112-1114. For an example of unequal spacing, volume element 1134 corresponding to the impedance between electrode pair 1114-1116 has larger radius than volume element 1136 corresponding to the impedance measured for electrode pair 1116-1118. In some examples, the size of the volume elements can be adjusted based on calibration data, which can account for the spatial arrangement of the electrodes including the relative spacing between electrode pairs.

[0075] Thus, it is shown that a user can move the catheter 1102 to different locations throughout the cardiac chamber to fill the chamber volume with volume elements based on corresponding impedance measurements. Because the size of the volume elements (e.g., 1138, 1140, 1208, 1210) further away from the chamber wall are larger (e.g., based on lower impedance measurements measured by electrode pairs 1124-1126, and 1128-1130) compared to the volume elements (e.g., 1132, 1134, 1202, 1204) located closer to the wall 1106, the process of filling the chamber volume with volume elements can be expedited compared to existing approaches. As a result, the approach described herein to generate a surface (e.g., by surface generator 56) representative of the chamber wall can be implemented in a reduced amount of time compared to existing approaches.Docket No. A0013362WG01

[0076] FIG. 13 depicts an example of a graphical representation 1300 of a surface that can be generated (e.g., by surface generator 56) for a portion of an anatomic structure based on volume elements that have been filled within the anatomic structure. In the example of FIG.13, the graphical representation 1300 depicts an interior surface (e.g., wall of a right ventricle) and includes a right ventricle outflow tract 1302 and an opening to the tricuspid valve 1304. The graphical representation 1300 of the surface geometry can be an anatomical model such as in the form of a mesh or other surface representation in 3D space based on volume elements that have been filled within the anatomic structure (e.g., right ventricle), as described herein. While the example of FIG. 13 demonstrates the entire surface of the right ventricle, in other examples, any region of interest of the anatomical structure that is less than the entire surface can be generated (e.g., by surface generator 56). Some examples of generating an anatomical model to represent surface geometry for a cardiac surface are described in U.S. Patent Nos.10,376,320 and 10,467,801, which are assigned to Affera, Inc. and incorporated herein by reference.

[0077] In view of the foregoing structural and functional features described above, example methods that can be implemented will be better appreciated with reference to the flow diagram of FIG. 14. While, for purposes of simplicity of explanation, the method 1400 of FIG. 14 is shown and described as executing serially, it is to be understood and appreciated that such methods are not limited by the illustrated order, as some aspects could, in other examples, occur in different orders and / or concurrently with other aspects from that disclosed herein. Moreover, not all illustrated features may be required to implement a method. The methods or portions thereof can be implemented as instructions stored in one or more non-transitory machine readable media and be executed by a processor of one or more computer devices, for example. The method 1400 of FIG. 14 can be implemented by the systems and methods described herein, including FIGS. 1-13. Accordingly, the method 1400 may refer to certain aspects of FIGS. 1-13.

[0078] At 1402, the method 1400 includes receiving tracking data representative of a location of a medical device that includes a plurality of electrodes. For example, the tracking system 34 can provide tracking data 36 representative of a spatial position and orientation of a catheter or other medical device 12, which can be in a 3D coordinate system of the tracking system . The tracking data 36 can remain in the tracking coordinate system or be registered into another spatial coordinate system (e.g., a 3D coordinate system of the patient).

[0079] At 1404, the method includes measuring a voltage between at least one pair of the electrodes responsive to an applied electrical current. For example, the interface circuit 18 canDocket No. A0013362W001control electric current that is applied (e.g., an AC current having a subthreshold magnitude and frequency) between one or more pairs of electrodes 14 to induce a subthreshold electric field. The interface circuit 18 can control the magnitude and / or frequency of the AC current that is applied to each one or more pairs of the electrodes. Also, or as an alternative, the interface circuit 18 can control the one or more other pairs of electrodes 14 to measure a resulting voltage potential between respective electrodes for each applied current. The tracking data and / or corresponding location information can be stored with data representing the applied current and measured voltage potential.

[0080] At 1406, an impedance can be calculated based on the measured voltage and the applied electrical current. For example, the impedance calculator 42, 200 can provide impedance data 212 representing the calculated electrical impedance between one or more pairs of electrodes based on the applied current and measured voltage between each respective electrode pair. The electrodes used for applying current and measuring voltage can be controlled by interface control 30 and / or interface circuit 18. In other examples, the interface circuit 18 can include or otherwise implement as an ohm meter, multimeter, or other device configured to provide a measure of electrical impedance between respective electrode pairs on the device 12. The impedance measurements can be stored in memory along with location and / or tracking data 36.

[0081] At 1408, the method 1400 includes determining a size for one or more volume elements based on each impedance measurement. In some examples, the volume elements can be spheres or have other shapes (e.g., ellipsoidal, cuboidal, etc.). Also, or as an alternative, the size of each volume element can be controlled (e.g., set to a predetermined maximum or minimum size) based on a distance between the pair of electrodes and a given impedance threshold.

[0082] At 1410, the method includes determining a position for the volume element to be filled based on the location of the medical device. For example, volume element generator 46, 300 is configured to provide volume element data 302. The volume element data can include information representing the size of each volume element determined based on the impedance measurement for one or more electrode pairs. Also, the volume element data can include information representing a position for the volume element based on the location of the medical device. As described herein, the location of the medical device and electrodes thereof can be determined based on the tracking data (provided at 1402) and geometry data, in which the geometry data represents a relative spatial position of each respective electrode of the pair ofDocket No. A0013362W001electrodes and / or a distance between each respective electrode of the pair of electrodes on the medical device.

[0083] At 1412, the method 1400 includes constructing a 3D geometry based on the size and the position determined for one or more volume elements that have been generated. Each of the volume elements generated by the method 1400 has a respective size and position, which collectively defines a boundary of at least a portion (e.g., target region) of an anatomical structure. For example, surface generator 56 is configured to generate a 3D surface geometry in a spatial domain based on the volume element data (e.g., describing the size and position of each volume element. The surface generator 56 can include surface wrapping code construct the 3D surface geometry such as described herein.

[0084] At 1414, the method includes generating or updating a graphical representation for at least a portion of the anatomical structure based on the 3D geometry that is generated at 1412. For example, the output generator 48 thus can generate output data 50 representing a graphical representation of the 3D surface geometry, which that can be rendered on the display 52. A viewing angle for the graphical representation of the 3D surface geometry can be adjusted in response to a user input (e.g., through user interface 32) and / or based on the position and / or orientation of the catheter (e.g., based on the tracking data received at 1402).

[0085] In some examples, the method 1400 can include a calibration function (e.g., impedance calibration function 44) to determine a set of calibration data, which can be based on tracking data and / or impedance measurements acquired during a calibration phase. For example, the impedance calibration function 44 can provide calibration data 410 that defines a function (e.g., equation(s) and / or look-up table) that determines the size of a volume element (e.g., sphere) based on the impedance measured between electrodes during a mapping phase . Also, or as an alternative, the method 1400 can include time-multiplexing the AC current applied to each of the at least two pairs of the electrodes. Also, or as an alternative, the method 1400 can include frequency multiplexing the AC current applied to each of at least two pairs of the electrodes. In examples where such multiplexing is implemented, the respective measurements at respective electrodes would be likewise multiplexed to provide corresponding measured electrical signals.

[0086] At 1416, the method can include a determination as to whether to end the method 1400 for generating the 3D geometry for the target region. As described herein, the target region can be a portion of a cardiac chamber (or other anatomical volume), a full surface of a cardiac chamber, or any desired portion of one or more chambers and interconnecting structures. The target region can be a default value for the anatomical structure or it can beDocket No. A0013362W001defined responsive to a user input (e.g., through user interface 32 and input device 31). The determination at 1416 can be automated based on the shape and / or size of the surface being generated or responsive to a user input instruction to terminate (or continue) the method 1400 of generating the 3D geometry. If the determination is negative (e.g., NO), the method 1400 returns to 1402 to repeat 1402-1412 for generating one or more volume elements based on a next location of the medical device. Thus, for each of a plurality of respective locations of the medical device, the method 1400 can repeat 1402-1414 to continue filling the volume, constructing a corresponding 3D geometry, and generating a graphical representation thereof. If the determination at 1416 is positive (e.g., YES), the method 1400 can proceed to 1418 to terminate the method 1400.EXAMPLE EMBODIMENTS:

[0087] Several aspects of the present technology are set forth in the following numbered examples.Example 1. A computer-implemented method comprising:receiving tracking data representative of a cardiac chamber location of a medical device that includes a plurality of electrodes;measuring a voltage between at least one pair of the electrodes responsive to an applied electrical current;calculating an impedance based on the measured voltage and the applied electrical current;determining a size for a volume element to be filled based on the calculated impedance;determining a position for the volume element to be filled based on the location of the medical device; andgenerating a representation including the volume element in a spatial domain based on the size and the position determined for the volume element.Example 2. The method of example 1, wherein the volume element is a sphere having a volume defined by a radius of the sphere and a center of the sphere, the radius of the sphere having a value determined based on the calculated impedance, the center of the sphere having a location based on a location of each electrode of the at least one pair of electrodes.Docket No. A0013362W001Example 3. The method of example 2, further comprising:determining the location of each electrode of the at least one pair of electrodes based on the tracking data and device geometry data, in which the device geometry data represents a relative spatial position of each respective electrode of the at least one pair of electrodes and / or a distance between each respective electrode of the at least one pair of electrodes.Example 4. The method of example 3, wherein the size of the sphere has a minimum diameter based on a distance between the at least one pair of electrodes and a high impedance threshold.Example 5. The method according to any of examples 3 or 4, wherein the size of the sphere has a maximum diameter based on at least one of a distance between the at least one pair of electrodes and a low impedance threshold.Example 6. The method according to any of the preceding examples, further comprising generating calibration data representative of the location and the calculated impedance for a plurality of different locations of the medical device, wherein the size of the sphere is determined based on the calculated impedance and the calibration data.Example 7. The method according to any of the preceding examples, wherein the applied electrical current is an alternating-current (AC) current, and the method further comprises:controlling a magnitude and frequency of the AC current to a respective pair of the electrodes to provide an electric field, and the voltage measured for the at least one pair of electrodes is responsive to the electric field.Example 8. The method of example 7, wherein the electrodes comprise multiple pairs of electrodes, and the method further comprises:controlling the AC current applied to at least one pair of the electrodes to provide at least one respective electric field; andmeasuring a voltage potential between at least one respective pair of the electrodes responsive to each of the at least one respective electric field.Docket No. A0013362W001Example 9. The method of example 8, wherein controlling the AC current comprises at least one of time-multiplexing the AC current applied to each of the at least one pair of the electrodes or frequency multiplexing the AC current applied to each of the at least one pair of the electrodes.Example 10. The method of example 1, wherein, for each of a plurality of respective locations of the medical device, the method comprises repeating each of the receiving tracking data for a respective location of the medical device, measuring a voltage between the at least one pair of the electrodes for the respective location of the medical device, calculating an electrical impedance based on the measured voltage and electrical current for the respective location of the medical device, determining a size for a respective volume element to be filled based on the calculated electrical impedance, and determining a position for the respective volume element to be filled based on the respective location of the medical device.Example 11. The method according to any of the preceding examples, further comprising:determining the size and the position for each of a plurality of volume elements, in which the plurality of volume elements defines a volume; andgenerating a graphical representation of a surface geometry based on a boundary of the volume.Example 12. The method according to any of the preceding examples, wherein a plurality of volume elements, each having a respective size and position, are determined and defines a boundary of at least a portion of an anatomical structure, and the method further comprises generating a surface representation for at least the portion of the anatomical structure based on the boundary thereof.Example 13. The method according to any of the preceding examples, wherein the medical device comprises a catheter, in which the electrodes are distributed across the catheter at respective positions, and the medical device further comprises at least one tracking sensor having a known spatial position relative to the electrodes.Docket No. A0013362W001Example 14. A non-transitory memory to store data and instructions that, when executed by a processor, cause the processor to perform a method according to any one or combination of the preceding examples.Example 15. A system comprising:a medical device including a plurality of electrodes;an interface circuit coupled to each of the electrodes, in which the interface circuit is configured to apply an electrical signal to and / or measure an electrical signal from each the plurality of electrodes;a tracking system configured to provide tracking data representative of an anatomical location of at least a portion of the medical device;non-transitory memory to store instructions and data, in which the data comprises electrical data representative of an electrical characteristic between at least one pair of the electrodes responsive to an applied electric field; anda processor coupled to the memory to access the data and instructions stored in the memory, the instructions, when executed by the processor, cause the processor to at least:determine an impedance between the at least one pair of the electrodes based on the electrical data;determine a size for a volume element to be filled based on the impedance between the at least one pair of the electrodes; anddetermine a position for the volume element to be filled based on the location of the medical device.Example 16. The system of example 15, wherein the instructions further cause the processor to:determine the size and the position for each of a plurality of volume elements, in which the plurality of volume elements defines a volume; andgenerate a graphical representation of a surface geometry based on a boundary of the volume.Example 17. The system of example 15, wherein the electrical data includes a voltage potential measured between the at least one pair of the electrodes responsive to an applied electrical current, and wherein the impedance between the at least one pair of theDocket No. A0013362W001electrodes is determined based on the measured voltage potential and the applied electrical current.Example 18. The system according to any of the examples 15-17, wherein the medical device comprises a catheter, in which the electrodes are distributed at respective positions across a distal body portion of the catheter, the medical device further comprises a tracking sensor, the tracking data represents a spatial position of the tracking sensor, and the data includes electrode geometry data representative of the respective positions of the electrodes relative to the electrodes.Example 19. The system of example 18, wherein instructions further cause the processor to determine a location of each of the electrodes of the at least one pair of the electrodes based on the tracking data and the electrode geometry data, and the position for the volume element is determined based on the location of each of the electrodes of the at least one pair of the electrodes.Example 20. The system of example 18, wherein the volume element is a sphere having a volume defined by a radius or diameter of the sphere and a center of the sphere, the radius or diameter of the sphere has a value determined based on the impedance between the at least one pair of the electrodes, the center of the sphere has a location based on a location of each electrode of the at least one pair of the electrodes.Example 21. The system of example 20, wherein the size of the sphere has a minimum diameter based on a distance between the at least one pair of the electrodes and a high impedance threshold.Example 22. The system according to any of examples 20 or 21, wherein the size of the sphere has a maximum diameter based on at least one of a distance between the at least one pair of the electrodes and a low impedance threshold.Example 23. The system according to any of examples 15 or 17, wherein the instructions further cause the processor to generate a graphical representation of a surface geometry based on a plurality of volume elements, in which each of the volume elements is associated with a respective pair of electrodes and associated location, each of theDocket No. A0013362W001volume elements has a respective size determined based on an electrical impedance determined between the respective pair of the electrodes, and the association location of each of the volume elements is determined for the respective pair of electrodes associated therewith based on the tracking data.Example 24. The system of example 23, wherein at least some of the volume elements defines a boundary of at least a portion of an anatomical structure, and the instructions further cause the processor to generate a surface representation for at least the portion of the anatomical structure based on the boundary thereof.Example 25. The system according to any of examples 15-24, the instructions further cause the processor to generate calibration data representative of the location and the determined impedance for a plurality of different locations of the medical device within an anatomic structure, wherein the size of the volume element for the at least one pair of the electrodes is determined based on the impedance between the at least one pair of the electrodes and the calibration data.Example 26. The system according to any of examples 15-26, wherein the instructions further cause the processor to provide a control signal to the interface circuit, and the interface circuit controls a magnitude and frequency of an alternating-current (AC) current to a respective pair of the electrodes to provide an electric field based on the control signal, and the electrical characteristic is a voltage potential measured between the at least one pair of the electrodes responsive to the electric field.Example 27. The system of example 26, wherein the plurality of electrodes defines multiple pairs of electrodes, and the instructions further cause the processor to:control the AC current to at least one pair of the electrodes to provide at least one respective electric field;measure a voltage potential between electrodes of at least two pairs of the electrodes responsive to one or more of the at least one respective electric field; and calculate an electrical impedance for each of the at least two pairs of the electrodes based on the AC current and the measured voltage potential.Docket No. A0013362W001Example 28. The system of example 27, wherein the AC current to the at least one pair of the electrodes is at least one of time-multiplexed to each of the at least one pair of the electrodes or frequency multiplexed to each of the at least one pair of the electrodes.Example 29. The system of example 15, wherein the instructions further cause the processor to repeatedly receive tracking data over time representing respective locations of the medical device, measure a voltage between the at least one pair of the electrodes for at least some of the respective locations of the medical device responsive to an injected electrical current, calculate an electrical impedance based on the measured voltage and the injected electrical current for each of the at least some of the respective locations of the medical device, determining a size for a respective volume element to be filled based on each calculated impedance, and determine a position for each respective volume element to be filled based on the tracking data when the voltage is measured.

[0088] In view of the foregoing structural and functional description, those skilled in the art will appreciate that portions of the invention may be embodied as a method, data processing system, or computer program product. Accordingly, these portions of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, portions of the invention may be a computer program product on a computer-usable storage medium having computer readable program code on the medium. Any suitable computer-readable medium may be utilized including, but not limited to, static and dynamic storage devices, hard disks, optical storage devices, and magnetic storage devices.

[0089] Certain embodiments of the invention have also been described herein with reference to block illustrations of methods, systems, and computer program products. It will be understood that blocks of the illustrations, and combinations of blocks in the illustrations, can be implemented by computer-executable instructions. These computer-executable instructions may be provided to one or more processors of a general purpose computer, special purpose computer, or other programmable data processing apparatus (or a combination of devices and circuits) to produce a machine, such that the instructions, which execute via the processor, implement the functions specified in the block or blocks.

[0090] These computer-executable instructions may also be stored in computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readableDocket No. A0013362W001memory result in an article of manufacture including instructions which implement the function specified in the flowchart block or blocks. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks.

[0091] What have been described above are examples. It is, of course, not possible to describe every conceivable combination of components or methods, but one of ordinary skill in the art will recognize that many further combinations and permutations are possible. Accordingly, the invention is intended to embrace all such alterations, modifications, and variations that fall within the scope of this application, including the appended claims. Where the disclosure or claims recite "a," "an," "a first," or "another" element, or the equivalent thereof, it should be interpreted to include one or more than one such element, neither requiring nor excluding two or more such elements.

[0092] Furthermore, a circuit or device that is said to include certain components may instead be configured to couple to those components to form the described circuitry, device, or system. For example, a structure described as including one or more elements A, B and C may instead include only the A elements within a single physical device and may be configured to couple to at least some of the elements B and / or C to form the described circuitry, device, or system, either at a time of manufacture or after a time of manufacture, for example, by an enduser and / or a third-party.

[0093] As used herein, the term “includes” means includes but not limited to, the term “including” means including but not limited to. The term “based on” means based at least in part on. All references, publications, and patents cited in the present application are herein incorporated by reference in their entirety.

Claims

Docket No. A0013362W001CLAIMSWhat is claimed is:

1. A computer-implemented method comprising:receiving tracking data representative of a cardiac chamber location of a medical device that includes a plurality of electrodes;measuring a voltage between at least one pair of the electrodes responsive to an applied electrical current;calculating an impedance based on the measured voltage and the applied electrical current;determining a size for a volume element to be filled based on the calculated impedance;determining a position for the volume element to be filled based on the location of the medical device; andgenerating a representation including the volume element in a spatial domain based on the size and the position determined for the volume element.

2. The method of claim 1, wherein the volume element is a sphere having a volume defined by a radius of the sphere and a center of the sphere, the radius of the sphere having a value determined based on the calculated impedance, the center of the sphere having a location based on a location of each electrode of the at least one pair of electrodes.

3. The method of claim 2, further comprising:determining the location of each electrode of the at least one pair of electrodes based on the tracking data and device geometry data, in which the device geometry data represents a relative spatial position of each respective electrode of the at least one pair of electrodes and / or a distance between each respective electrode of the at least one pair of electrodes.

4. The method of claim 3, wherein the size of the sphere has a minimum diameter based on a distance between the at least one pair of electrodes and a high impedance threshold.

5. The method according to any one of claims 3 or 4, wherein the size of the sphere has a maximum diameter based on at least one of a distance between the at least one pair of electrodes and a low impedance threshold.Docket No. A0013362W0016. The method according to any one of the preceding claims, further comprising generating calibration data representative of the location and the calculated impedance for a plurality of different locations of the medical device, wherein the size of the sphere is determined based on the calculated impedance and the calibration data.

7. The method according to any one of the preceding claims, wherein the applied electrical current is an alternating-current (AC) current, and the method further comprises: controlling a magnitude and frequency of the AC current to a respective pair of the electrodes to provide an electric field, and the voltage measured for the at least one pair of electrodes is responsive to the electric field.

8. The method of claim 7, wherein the electrodes comprise multiple pairs of electrodes, and the method further comprises:controlling the AC current applied to at least one pair of the electrodes to provide at least one respective electric field; andmeasuring a voltage potential between at least one respective pair of the electrodes responsive to each of the at least one respective electric field.

9. The method of claim 8, wherein controlling the AC current comprises at least one of time-multiplexing the AC current applied to each of the at least one pair of the electrodes or frequency multiplexing the AC current applied to each of the at least one pair of the electrodes.

10. The method of claim 1, wherein, for each of a plurality of respective locations of the medical device, the method comprises repeating each of the receiving tracking data for a respective location of the medical device, measuring a voltage between the at least one pair of the electrodes for the respective location of the medical device, calculating an electrical impedance based on the measured voltage and electrical current for the respective location of the medical device, determining a size for a respective volume element to be filled based on the calculated electrical impedance, and determining a position for the respective volume element to be filled based on the respective location of the medical device.Docket No. A0013362W00111. The method according to any one of the preceding claims, further comprising:determining the size and the position for each of a plurality of volume elements, in which the plurality of volume elements defines a volume; andgenerating a graphical representation of a surface geometry based on a boundary of the volume.

12. The method according to any one of the preceding claims, wherein a plurality of volume elements, each having a respective size and position, are determined and defines a boundary of at least a portion of an anatomical structure, and the method further comprises generating a surface representation for at least the portion of the anatomical structure based on the boundary thereof.

13. The method according to any one of the preceding claims, wherein the medical device comprises a catheter, in which the electrodes are distributed across the catheter at respective positions, and the medical device further comprises at least one tracking sensor having a known spatial position relative to the electrodes.

14. A non-transitory memory to store data and instructions that, when executed by a processor, cause the processor to perform a method according to any one of the preceding claims.

15. A system comprising:a medical device including a plurality of electrodes;an interface circuit coupled to each of the electrodes, in which the interface circuit is configured to apply an electrical signal to and / or measure an electrical signal from each the plurality of electrodes;a tracking system configured to provide tracking data representative of an anatomical location of at least a portion of the medical device;non-transitory memory to store instructions and data, in which the data comprises electrical data representative of an electrical characteristic between at least one pair of the electrodes responsive to an applied electric field; anda processor coupled to the memory to access the data and instructions stored in the memory, the instructions, when executed by the processor, cause the processor to at least:Docket No. A0013362W001determine an impedance between the at least one pair of the electrodes based on the electrical data;determine a size for a volume element to be filled based on the impedance between the at least one pair of the electrodes; anddetermine a position for the volume element to be filled based on the location of the medical device.

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