Patent Description:
<CIT> discloses a method that includes, in a processor, receiving position signals that are indicative of positions of (i) multiple electrodes disposed on an inflatable balloon fitted at a distal end of a catheter, and (ii) first and second electrodes fitted on a shaft of the catheter, on either side of the balloon. The positions of the multiple electrodes disposed on the balloon are calculated based on the received position signals and based on a known distance between the first and second electrodes.

Ablation of body tissue, such as cardiac tissue is known. Reference is made to <FIG> showing an exemplary catheter-based electro-anatomical (EA) mapping and ablation system <NUM>. System <NUM> includes multiple catheters, which are percutaneously inserted by a physician <NUM> through the patient's vascular system into a chamber or vascular structure of a heart <NUM>. Typically, a delivery sheath catheter is inserted into the left or right atrium near a desired location in heart <NUM>. Thereafter, one or more catheters may be inserted into delivery sheath catheter(s) so as to arrive at the desired location in heart <NUM>. The plurality of catheters may include catheters dedicated for sensing Intracardiac Electrogram (IEGM) signals, catheters dedicated for ablating and/or catheters dedicated for both sensing and ablating. An exemplary catheter <NUM> that is configured for ablating is illustrated herein. Physician <NUM> may place a distal end of an ablation catheter in contact with a target site for ablating tissue.

Catheter <NUM> is an exemplary basket catheter that includes a basket distal assembly <NUM> having one and preferably multiple electrodes <NUM> optionally distributed over a plurality of splines <NUM>. Other ablating catheters include balloon catheters having balloon distal assemblies. Basket catheter <NUM> may additionally include a position sensor <NUM> embedded in a shaft <NUM> to which basket distal assembly <NUM> is attached, for tracking position and orientation of a distal tip <NUM> of basket distal assembly <NUM>. Optionally and preferably, position sensor <NUM> is a magnetic based position sensor including three magnetic coils for sensing three-dimensional (3D) position and orientation.

Magnetic based position sensor <NUM> may be operated together with a location pad <NUM> including a plurality of magnetic coils <NUM> configured to generate magnetic fields in a predefined working volume. Real time position of distal tip <NUM> of catheter <NUM> may be tracked based on magnetic fields generated with location pad <NUM> and sensed by magnetic based position sensor <NUM>. Details of the magnetic based position sensing technology are described in <CIT>; <CIT>;<CIT>;<CIT>;<CIT>; <CIT>; <CIT>; <CIT>; <CIT>;<CIT>;<CIT>.

System <NUM> includes one or more electrode patches <NUM> positioned for skin contact on patient <NUM> to establish location reference for location pad <NUM> as well as impedance-based tracking of electrodes <NUM>. Impedance based tracking of electrodes <NUM> is also referred to as Active Current Location (ACL) tracking. The ACL method is implemented in various medical applications, for example, in the CARTO™ system, produced by Biosense-Webster Inc. (Irvine, California).

For impedance-based tracking, electrical current is directed to electrodes <NUM> and sensed at electrode skin patches <NUM> so that the location of each electrode can be triangulated via the electrode patches <NUM>. Details of the impedance-based location tracking technology (ACL tracking) are described in <CIT>; <CIT>;<CIT>;<CIT>; and <CIT>.

System <NUM> may include an ablation energy generator <NUM> that is adapted to conduct ablative energy to one or more of electrodes <NUM>. Energy produced by ablation energy generator <NUM> may include, but is not limited to, radiofrequency (RF) energy or pulsed-field ablation (PFA) energy, including monopolar or bipolar high-voltage DC pulses as may be used to effect irreversible electroporation (IRE), or combinations thereof.

Patient interface unit (PIU) <NUM> is an interface configured to establish electrical communication between catheters, other electrophysiological equipment, power supply and a workstation <NUM> for controlling operation of system <NUM>. Optionally and preferably, PIU <NUM> additionally includes processing capability for implementing real-time computations of location of the catheters and for performing ECG calculations.

Workstation <NUM> includes a memory, a processor unit with memory or storage with appropriate operating software stored therein, and a user interface capability. Workstation <NUM> may provide multiple functions, optionally including (<NUM>) modeling the endocardial anatomy in three-dimensions (3D) and rendering the model or anatomical map <NUM> for display on a display device <NUM>, (<NUM>) displaying on display device <NUM> activation sequences (or other data) compiled from recorded electrograms <NUM> in representative visual indicia or imagery superimposed on the rendered anatomical map <NUM>, (<NUM>) displaying real-time location and orientation of multiple catheters within the heart chamber (<FIG> shows an icon of catheter <NUM> and its recent ablation area <NUM> positioned in relation to EA map <NUM>), and (<NUM>) displaying on display device <NUM> sites of interest such as places where ablation energy has been applied. One commercial product embodying elements of system <NUM> is available as the CARTO™ <NUM> System, available from Biosense Webster, Inc. , <NUM> Technology Drive, Suite <NUM>, Irvine, CA <NUM> USA.

Reference is made to <FIG>, which illustrates an exemplary basket catheter <NUM> in an expanded form in which splines <NUM> bow radially outwardly. In a collapsed form, not shown, splines <NUM> are arranged generally along a longitudinal axis <NUM> of tubular shaft <NUM>. Basket distal assembly <NUM> expands to a spherical or near spherical shape with a diameter of <NUM> or more. Basket catheter <NUM> is typically deflectable at a vicinity of an interface between shaft <NUM> and distal assembly <NUM> where, in <FIG>, there is a joint connection. In the embodiment of <FIG>, basket catheter <NUM> includes a contact force sensor assembly <NUM> at the vicinity of the interface to determine contact force of splines <NUM> against cardiac tissues. The force sensing capability may be added to ablation catheters to provide indication that sufficient contact with the tissue has been established before delivering the ablation energy.

Contact force sensor assembly <NUM> includes a helical spring <NUM> integrated as part of shaft <NUM> and/or disposed inside shaft <NUM>. Typically, helical spring <NUM> is positioned as close as possible to a distal assembly, which may be basket distal assembly <NUM> or a balloon assembly. Contact force applied on cardiac tissue by the electrodes <NUM> actuate compression and/or bending of helical spring <NUM>. Compression and/or bending is sensed by a transmitting circuit and sensing circuit located on opposite ends of helical spring <NUM> (e.g., opposite ends along longitudinal axis <NUM>) and related to contact force. The transmitting circuit and sensing circuit are not shown here for simplicity purposes. An example contact-force sensor assembly <NUM> is described for example in <CIT> entitled "Calibration of a force measuring system for large bend angles of a catheter" and/or <CIT> entitled "Catheter with multiple irrigated electrodes and a force sensor. " Typically, helical spring <NUM> may bend up to <NUM> degrees in one or more directions depending on the force applied or optionally up to <NUM> degrees in one or more directions.

In accordance with the present invention there is provided a method implemented by a processor of an electro-anatomical mapping system as claimed in claim <NUM> and an electrode location determiner for an electro-anatomical mapping system as claimed in claim <NUM>. Embodiments of the present invention are provided in the dependent claims.

Applicant has realized that for catheters with large distal assemblies, such as basket assemblies and balloon assemblies, bending at a distal end of the shaft due to pressing as the catheter against the body tissue may lead to significant deflection of the distal assembly with respect to the shaft.

Applicant has further realized that the significant deflection is at least partially due to the relatively large size of the distal end assembly. Due to its size, the distal assembly may have a moment arm of <NUM> or more, e.g., <NUM> - <NUM>. The bend angle of the distal assembly may be especially significant for catheters that include a helical spring on its shaft.

In known systems, when displaying visual indicia of a catheter on an EA map displayed on display <NUM> (<FIG>) in real time, the visual indicia is positioned at the location determined based on the output of the position sensor mounted on the shaft proximal to the bending point. This location is selected since it includes a magnetic based position sensor that can track location with high accuracy, e.g., +/- <NUM> accuracy. However, Applicant has realized that for relatively large distal assemblies mounted on a shaft that accommodates bending, such as for basket catheter <NUM> of <FIG>, there may be a significant discrepancy between a location of position sensor on the shaft and a distal end of distal assembly and/or locations of electrodes on the distal assembly.

Applicant has realized that ACL tracking of the electrodes on the distal assembly may be used for improving the ability to track the location of the distal assembly when bending is expected. Although ACL tracking is known to have limited accuracy, Applicant has realized that this may be due to its use of individual ACL determined locations of each of a plurality of electrodes on the distal assembly. Applicant has further realized that since basket and balloon catheters may be assumed to have a rigid assembly, combining the individual ACL determined locations to compute a center of mass of the distal assembly may provide significantly better accuracy for the center of mass location, which may then be utilized to infer the location of each of the electrodes on the distal assembly.

An example deflection is shown in <FIG>, to which reference is now made. <FIG> shows basket catheter <NUM> of <FIG>, along with its multiple electrodes <NUM>, shaft <NUM> and helical spring <NUM> and magnetic sensor <NUM>, known as a triaxial sensor (TAS). Magnetic sensor <NUM> is longitudinally mounted on shaft <NUM>, next to contact force assembly <NUM>. <FIG> shows basket distal assembly <NUM> against a tissue surface <NUM> to be ablated and the resulting bend in spring <NUM> with a tilt angle α.

Applicant has further realized that, even though basket catheter <NUM> may be an ablation catheter, it has the capability to provide the ACL locations of its electrodes <NUM>, using an active current location (ACL) method of determining electrode location.

As mentioned hereinabove, while the 3D location and orientation of shaft <NUM> may be determined with relatively high accuracy, e.g., +/- <NUM> accuracy, 3D location of each of electrodes <NUM> based on the ACL tracking is significantly less accurate. As a result, ACL tracking may not be utilized to visually indicate on display <NUM> the location of basket distal assembly <NUM> or other distal assembly on the rendered EA map <NUM> (<FIG>) and/or visually indicating on display <NUM> places where ablation energy has been applied by one or more electrodes <NUM>. The locations cannot be easily inferred from the output of position sensor <NUM> due to the ability of basket catheter <NUM> or other type of catheter to bend in different directions with respect to the orientation of shaft <NUM> on which position sensor <NUM> is mounted.

Applicant has realized that the ACL locations may be sufficiently accurate when averaging the ACL locations of multiple electrodes <NUM>, and has further realized that such an average may provide a simple and sufficiently accurate method for determining a location of a center Cm of mass of basket distal assembly <NUM>. Based on the determined center of mass and assuming that basket distal assembly <NUM> or other distal assembly maintains its shape during contact with the tissue, 3D position of each of the electrodes on basket distal assembly <NUM> or other distal assembly may be computed.

In accordance with a preferred embodiment of the present invention and in reference to <FIG>, processor <NUM> comprises an electrode location determiner <NUM> which utilizes the center Cm of mass of basket distal assembly <NUM> and known geometry of basket distal assembly <NUM> to track the 3D location of each of electrodes <NUM>, e.g., to update or correct the three-dimensional ACL locations (xi,yi,zi) of electrodes <NUM>. Electrode location determiner <NUM> comprises a center of mass calculator <NUM>, a tilt angle calculator <NUM> and an electrode position updater <NUM>. Reference is also made to <FIG>, which illustrates a method implemented by electrode location determiner <NUM>.

Center of mass calculator <NUM> receives the ACL locations (xi,yi,zi), defined in a coordinate system of location pad <NUM>. Center of mass calculator <NUM> computes (step <NUM> of <FIG>) the location of center Cm of mass of basket distal assembly <NUM> therefrom. For example, since electrodes <NUM> are generally spread symmetrically around center Cm, and since basket distal assembly <NUM> may be considered to maintain its shape when pressed against tissue <NUM>, the location of center Cm may be determined by the average of the ACL locations of electrodes <NUM>. Alternatively, for a basket assembly including an electrode arrangement that is not symmetrical, location of center Cm may be determined based on the known positioning of the electrodes on that basket assembly.

Reference is now made to <FIG> which illustrate the operation of tilt angle calculator <NUM>. Tilt angle calculator <NUM> utilizes center Cm of mass together with the output of position sensor <NUM> to determine tilt angle α. Position sensor <NUM> generates a position of shaft <NUM> in six degrees of freedom, e.g., three-dimensional position (x,y,z) as well as its three-dimensional rotation (ϕ, θ, Ψ) in the coordinate system defined by location pad <NUM>.

<FIG> shows shaft <NUM> with distal assembly <NUM> fixed at its distal end thereof, aligned with shaft <NUM>. As a result, a line <NUM> drawn through the location of position sensor <NUM>, along a longitudinal axis <NUM>, extends to center Cm of mass of basket distal assembly <NUM>. Thus, tilt angle calculator <NUM> initially checks (in step <NUM> of <FIG>) whether longitudinal axis <NUM> extends through center Cm of mass as computed by center of mass calculator <NUM>. If there is little error, then tilt angle α is minimal or <NUM> and electrode location determiner <NUM> may display (step <NUM>) basket distal assembly <NUM> at its location on map <NUM> (<FIG>).

Otherwise, the situation of <FIG> applies, in which center Cm of mass is deflected from longitudinal axis <NUM>. To determine tilt angle α, tilt angle calculator <NUM> extends (step <NUM>) a line <NUM> from the location (x,y,z)SHAFT of position sensor <NUM>, here acting as a shaft sensor, to the computed center Cm of mass and then determines (step <NUM>) the angle therebetween in the 3D coordinate system of location pad <NUM>. Tilt angle calculator <NUM> may implement vector angle calculations, as is known in the art, to determine the angle. As can be seen from <FIG>, that angle is angle β, which is the supplementary angle of tilt angle α defining the deflection of basket catheter <NUM>.

Electrode position updater <NUM> may then combine tilt angle α with the three-dimensional position (x,y,z)SHAFT of sensor <NUM> as well as its three-dimensional rotation (ϕ, θ, Ψ) around its longitudinal axis <NUM> to determine (step <NUM>) the locations (xi,yi,zi) of electrodes <NUM>. Electrode position updater <NUM> may assume that splines <NUM> will not bend significantly when pressed against tissue <NUM>, giving basket catheter <NUM> a rigid construction. Optionally, electrode position updater <NUM> may first update the ACL location of distal end <NUM>. Since the other ACL locations are defined with respect to distal end <NUM>, updater <NUM> may determine the ACL locations and/or may update the ACL locations of electrodes <NUM> from the computed location of distal end <NUM>.

Electrode position updater <NUM> may then display (step <NUM>) basket distal assembly <NUM> on the anatomical map <NUM> displayed on display device <NUM> with improved accuracy. During a mapping procedure, this may lead to a more accurate map. Furthermore, during an ablation procedure when one or more of electrodes <NUM> delivers ablation energy, the electrode position updater <NUM> may more accurately display the locations at which an ablation event took place. It will be appreciated that, although each ACL location (xi, yi, zi) is not particularly accurate, the present invention, using the accumulated output from all or most of electrodes <NUM>, may provide a sufficiently accurate estimation of the location and angular deflection of center Cm of mass with respect to the location and angular positioning of position sensor <NUM>.

Moreover, it will be appreciated that electrode location determiner <NUM> may operate on each set of ACL electrode locations which may be received. Since these ACL electrode locations may be received in real-time, electrode location determiner <NUM> may operate in real-time in order to display center Cm of mass of basket distal assembly <NUM> and/or the updated locations of electrodes <NUM> on electro-anatomical map <NUM> (<FIG>). Further, the output of electrode location determiner <NUM> may be utilized for real-time tracking of electrodes <NUM>.

It will be appreciated that, although most of the embodiments have been described herein with reference to a basket type catheter, the system and methods described herein may also be applied to balloon type catheters.

It will also be appreciated that, although most of the embodiments have been described in reference to an ablation catheter including a force sensing device at a distal end of the shaft, the system and methods described herein may also be applied to catheters that otherwise bend without a force sensing device and/or may be applied to diagnostic based catheters with or without force sensing devices on their shaft.

Unless specifically stated otherwise, as apparent from the preceding discussions, it is appreciated that, throughout the specification, discussions utilizing terms such as "processing," "computing," "calculating," "determining," or the like, refer to the action and/or processes of a general purpose computer of any type, such as a client/server system, mobile computing devices, smart appliances, cloud computing units or similar electronic computing devices that manipulate and/or transform data within the computing system's registers and/or memories into other data within the computing system's memories, registers or other such information storage, transmission or display devices.

Embodiments of the present disclosure may include apparatus for performing the operations herein. This apparatus may be specially constructed for the desired purposes, or it may comprise a computing device or system typically having at least one processor and at least one memory, selectively activated or reconfigured by a computer program stored in the computer. The resultant apparatus when instructed by software may turn the general-purpose computer into elements as discussed herein. The instructions may define the device in operation with the computer platform for which it is desired. Such a computer program may be stored in a computer readable storage medium, such as, but not limited to, any type of disk, including optical disks, magnetic-optical disks, read-only memories (ROMs), volatile and non-volatile memories, random access memories (RAMs), electrically programmable read-only memories (EPROMs), electrically erasable and programmable read only memories (EEPROMs), magnetic or optical cards, Flash memory, disk-on-key or any other type of media suitable for storing electronic instructions and capable of being coupled to a computer system bus. The computer readable storage medium may also be implemented in cloud storage.

Some general-purpose computers may comprise at least one communication element to enable communication with a data network and/or a mobile communications network.

Claim 1:
A method implemented by a processor (<NUM>) of an electro-anatomical mapping system (<NUM>) utilizing a catheter (<NUM>) having a basket distal assembly comprising a plurality of splines and having multiple electrodes (<NUM>) distributed over the splines, the method comprising:
receiving active current locations, ACL, of said electrodes (<NUM>);
calculating (<NUM>) a center of mass of said distal assembly from the ACL locations of said electrodes (<NUM>) by generating an average value of said ACL locations;
using a sensor (<NUM>) having a sensor longitudinal axis (<NUM>) aligned along a shaft longitudinal axis (<NUM>) of a shaft (<NUM>) to which said distal assembly is attached and configured to generate a position of the shaft in six degrees of freedom, checking whether or not said shaft longitudinal axis extends through said center of mass;
if not, calculating (<NUM>) a tilt angle of said center of mass from said sensor longitudinal axis and a line (<NUM>) extending from a position of said sensor and said center of mass; and
correcting said ACL locations according to said tilt angle.