Accurate measurement of distal tip dimensions

Abstract

To provide a medical system.SOLUTION: In one embodiment, a system includes generator coils to generate respective magnetic fields, a catheter including a distal end, which includes magnetic coil sensors to output electrical signals on the basis of detection of the respective magnetic fields, and processing circuitry. The processing circuitry is configured to receive the electrical signals from the magnetic coil sensors, select at least one of magnetic fields having a magnetic field gradient as a function of at least one of the received electrical signals, compute a difference between magnetic field magnitudes of the at least one selected magnetic field detected by the first magnetic coil sensor and the second magnetic coil sensor as a function of the electrical signals, and compute a dimension of the distal end, on the basis of the difference between the magnetic field magnitudes of the at least one selected magnetic field and the magnetic field gradient of the at least one selected magnetic field.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to medical systems, particularly, but not exclusively, to catheter devices. [Background technology]

[0002] A wide range of medical procedures involve the placement of probes, such as catheters, within a patient's body. Position sensing systems have been developed to track such probes. Magnetic position sensing is one method known in the art. In magnetic position sensing, magnetic field generators are typically placed at known locations external to the patient. A magnetic field sensor in the distal end of the probe generates electrical signals in response to these magnetic fields, and these signals are processed to determine the coordinate position of the distal end of the probe. These methods and systems are described in U.S. Patent Nos. 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612, and 6,332,089, WO 1996 / 005768, and U.S. Patent Application Publication Nos. 2002 / 0065455, 2003 / 0120150, and 2004 / 0068178. Position may also be tracked using impedance or current-based systems.

[0003] One medical procedure in which these types of probes or catheters have proven extremely useful is in the treatment of cardiac arrhythmias, which, and atrial fibrillation in particular, persist as a common and dangerous condition, especially in the aging population.

[0004] Diagnosis and treatment of cardiac arrhythmias involve mapping the electrical properties of cardiac tissue, particularly the endocardium and cardiac volumes, and selectively ablating cardiac tissue through the application of energy. Such ablation can stop or modify the propagation of unwanted electrical signals from one part of the heart to another. The ablation process disrupts unwanted electrical pathways by creating non-conductive lesions. Various energy delivery modalities have been previously disclosed for creating lesions, including the use of microwave, laser, and more commonly radiofrequency energy to create conduction blocks along cardiac tissue walls. In a two-step mapping-then-ablation procedure, electrical activity at each point within the heart is typically sensed and measured by advancing a catheter containing one or more electrical sensors into the heart and acquiring data at multiple points. These data are then used to select a target region of the endocardium for this ablation.

[0005] Electrode catheters have been commonly used in medical practice for many years. They are used to stimulate and map electrical activity within the heart and to ablate sites of abnormal electrical activity. In use, an electrode catheter is inserted into a major vein or artery, such as the femoral vein, and then guided into the heart chamber of interest. A typical ablation procedure involves inserting a catheter with one or more electrodes at its distal end into a heart chamber. A reference electrode is typically taped to the patient's skin or may be provided by a second catheter placed in or near the heart. Radio frequency (RF) current is applied between the tip electrode of the ablation catheter and the reference electrode, and current flows between the electrodes, i.e., through the medium between the blood and tissue. The distribution of the current depends on the amount of electrode surface in contact with the tissue compared to blood, which has a higher electrical conductivity than tissue. Tissue heating occurs due to the electrical resistance of the tissue. Sufficient tissue heating can cause cell destruction in the cardiac tissue, resulting in lesions in the non-conductive cardiac tissue. Summary of the Invention [Means for solving the problem]

[0006] According to an embodiment of the present disclosure, a medical system is provided, including: generator coils configured to generate respective magnetic fields having respective different frequencies within a region of a body part of a living subject; a catheter configured to be inserted into the body part of the living subject, the catheter including a distal end including magnetic coil sensors configured to output electrical signals as a function of detecting the respective magnetic fields, the catheter including a first magnetic coil sensor having a first axis and a second magnetic coil sensor having a second axis, the magnetic coil sensors being disposed on the distal end with the first axis substantially parallel to the second axis; and a processing circuit configured to: receive electrical signals from the magnetic coil sensors; select at least one of the magnetic fields having a magnetic field gradient as a function of at least one of the received electrical signals; calculate a difference between magnetic field strengths of the at least one selected magnetic field detected by the first magnetic coil sensor and the second magnetic coil sensor based on the received electrical signals; and calculate a dimension of the distal end that is a function of a distance between the magnetic coil sensors based on the calculated difference between the magnetic field strengths of the at least one selected magnetic field and the magnetic field gradient of the at least one selected magnetic field.

[0007] Furthermore, according to one embodiment of the present disclosure, the calculated dimension is the distance between the magnetic coil sensors.

[0008] Still further, in accordance with one embodiment of the present disclosure, the calculated dimensions are the dimensions of the shape of the distal end of the catheter.

[0009] Additionally, according to one embodiment of the present disclosure, the processing circuitry is configured to calculate a dimension of the distal end based on the calculated difference between the magnetic field strengths of the at least one selected magnetic field divided by the magnetic field gradient of the at least one selected magnetic field.

[0010] Further, according to one embodiment of the present disclosure, the at least one selected magnetic field includes one of the magnetic fields having a highest magnetic field gradient of the magnetic fields, and the processing circuitry is configured to calculate a dimension of the distal end based on the calculated difference between the magnetic field strengths of the at least one selected magnetic field and the highest magnetic field gradient.

[0011] Further, according to one embodiment of the present disclosure, the catheter has a longitudinal axis, the distal end of the catheter includes an expandable distal tip assembly, and the magnetic field sensors are configured to move relative to each other along the longitudinal axis of the catheter when the expandable distal tip assembly is expanded and collapsed, such that when the expandable distal tip assembly is collapsed, the distance between the magnetic coil sensors increases and when the expandable distal tip assembly is deployed, the distance between the magnetic coil sensors decreases.

[0012] Still further, in accordance with an embodiment of the present disclosure, the first axis, the second axis, and the longitudinal axis are substantially coaxial.

[0013] Additionally, according to one embodiment of the present disclosure, the expandable distal tip assembly is a basket distal tip assembly including a plurality of flexible strips and electrodes disposed on the flexible strips.

[0014] Further, according to one embodiment of the present disclosure, the system includes a display, and the processing circuitry is configured to find a shape of the distal tip assembly based on at least the calculated dimensions, and to render a representation of the distal tip assembly on the display based on the found shape of the distal tip assembly.

[0015] Furthermore, according to one embodiment of the present disclosure, the calculated dimension is the distance between the magnetic coil sensors.

[0016] Still further, in accordance with an embodiment of the present disclosure, the processing circuitry is configured to calculate a relative orientation between the first axis of the first magnetic coil sensor and the second axis of the second magnetic coil sensor, and to estimate a shape of the distal tip assembly based on the calculated relative orientation.

[0017] According to another embodiment of the present disclosure, there is also provided a medical method including: generating magnetic fields having respective different frequencies within a region of a body part of a living subject; inserting a catheter into the body part of the living subject; receiving electrical signals from the magnetic coil sensors with substantially parallel axes disposed on a distal end of the catheter, the magnetic coil sensors outputting electrical signals as a function of detecting respective ones of the magnetic fields; selecting at least one of the magnetic fields having a magnetic field gradient based on at least one of the received electrical signals; calculating a difference between magnetic field strengths of the at least one selected magnetic field detected by a first magnetic coil sensor and a second magnetic coil sensor of the magnetic coil sensors based on the received electrical signals; and calculating a dimension of the distal end, the dimension being a function of a distance between the magnetic coil sensors, based on the calculated difference between the magnetic field strengths of the at least one selected magnetic field and the magnetic field gradient of the at least one selected magnetic field.

[0018] Additionally, according to one embodiment of the present disclosure, the calculated dimension is the distance between the magnetic coil sensors.

[0019] Furthermore, according to one embodiment of the present disclosure, the calculated dimensions are the dimensions of the shape of the distal end of the catheter.

[0020] Further, according to an embodiment of the present disclosure, calculating the dimension includes calculating the dimension of the distal end based on a calculated difference between the magnetic field strength of the at least one selected magnetic field divided by the magnetic field gradient of the at least one selected magnetic field.

[0021] Still further, according to one embodiment of the present disclosure, the at least one selected magnetic field includes one of the magnetic fields having a highest magnetic field gradient of the magnetic fields, and calculating the dimension includes calculating the dimension of the distal end based on a calculated difference between the magnetic field strengths of the at least one selected magnetic field and the highest magnetic field gradient.

[0022] Additionally, according to one embodiment of the present disclosure, the method includes moving the magnetic field sensors relative to one another along a longitudinal axis of the catheter as the expandable distal end assembly of the catheter expands and collapses.

[0023] Furthermore, according to one embodiment of the present disclosure, the first axis, the second axis, and the longitudinal axis are substantially coaxial.

[0024] Further, in accordance with one embodiment of the present disclosure, the method includes finding a shape of the distal tip assembly based at least on the calculated dimensions, and rendering a representation of the distal tip assembly on a display based on the found shape of the distal tip assembly.

[0025] Still further, according to one embodiment of the present disclosure, the calculated dimension is the distance between the magnetic coil sensors.

[0026] Additionally, according to an embodiment of the present disclosure, the method includes calculating a relative orientation between a first axis of the first magnetic coil sensor and a second axis of the second magnetic coil sensor, and estimating a shape of the distal tip assembly based on the calculated relative orientation. [Brief explanation of the drawings]

[0027] The present invention will be understood from the following detailed description taken in conjunction with the accompanying drawings. [Figure 1] 1 is a schematic, pictorial illustration of a system for electroanatomical mapping including a catheter, in accordance with an embodiment of the present invention; [Figure 2A] FIG. 1 is a schematic diagram of the distal end of a basket catheter in a collapsed configuration. [Figure 2B] FIG. 2B is a schematic diagram of the distal end of the basket catheter of FIG. 2A in a deployed configuration. [Figure 3] 2 is a flow chart including steps in a method of operating the system of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0028] Overview The Carto™ 3 system (manufactured by Biosense Webster, Irvine, California, USA) applies the Advanced Catheter Location (ACL) hybrid position tracking technology. In the ACL technology, the distribution of measured currents associated with probe electrodes on the catheter is correlated with a current-position matrix (CPM), which maps the current distribution to the catheter's position previously obtained from a magnetic position calibration position signal. The ACL technology uses a catheter with a magnetic coil sensor to enable localization and visualization of the catheter (even a catheter without a magnetic field sensor) as well as in the volume(s) for which the CPM is calculated. The prerequisite for constructing the CPM is to insert a catheter with a magnetic field sensor into the body and move the catheter within that volume in order to calculate the CPM for that volume.

[0029] Additionally, ACL technology can be used to track basket catheters with electrodes in the basket, however ACL technology, which measures current or impedance, may not provide sufficiently high accuracy in some situations.

[0030] One solution is to use signals from magnetic sensors disposed on the catheter to calculate the elongation of the expandable distal tip assembly (such as a basket distal tip assembly or a balloon distal tip assembly) based on the distance between the magnetic sensors. The magnetic sensors can be positioned on the catheter in a manner such that the distance between the sensors provides an indication of the elongation, and therefore the shape, of the distal tip assembly. Magnetic sensors generally provide more accurate location than using an ACL. Nevertheless, the location measured by a magnetic sensor can be subject to errors on the order of millimeters (e.g., 2 or 3 mm), and for some applications, these errors may be too large. For example, for a small basket catheter, the distance between the magnetic sensors may vary by approximately 10 or 15 millimeters between the collapsed and deployed baskets. Therefore, an error of 3 mm may be considered large. The error can be reduced by using a dual-axis sensor (DAS) or a triple-axis sensor (TAS), which generally provide more accurate position measurements. However, in many applications, a catheter may not be able to accommodate two DAS or TAS, or even one DAS or TAS.Details of magnetic location sensing are provided in commonly owned U.S. Patent Nos. 5,391,199, 5,443,489, 5,558,091, 6,172,499, 6,690963, 6,788,967, and 6,892,091, which are incorporated herein by reference, copies of which are provided in the Appendix.

[0031] Embodiments of the present invention provide systems and methods for accurately calculating the dimensions of a catheter's distal end (e.g., an expandable distal tip assembly, such as a basket or balloon distal tip assembly) using a magnetic-based tracking technique based on two magnetic coil sensors and a magnetic field generator that generate respective alternating magnetic fields (of different frequencies) for detection by the sensors. The magnetic fields detected by the sensors are indicative of the sensor's location within a given coordinate space.

[0032] The accuracy of the calculation is based on two factors, including the positioning of the two magnetic coil sensors and an accurate error cancellation calculation method.

[0033] The magnetic coil sensors are positioned along the longitudinal axis of the distal end of the catheter so that the axes of the two sensors are substantially parallel; in some embodiments, the two sensors are positioned so that they are substantially coaxial with the longitudinal axis. In this manner, both sensors sense different alternating magnetic fields in a similar manner (e.g., with respect to magnetic field gradients), so that one of the alternating magnetic fields is used for both sensors in the calculations described in more detail below, enabling error cancellation between the two sensors. As used herein and in the claims, the term "substantially parallel" is defined as parallel within a 10-degree tolerance. However, the closer the axes of the two sensors are to being exactly parallel, the more accurate the calculations performed based on the sensor outputs will be. As used herein and in the claims, the term "substantially coaxial" is defined as the region between the sensor windings where the sensor axis is within 10 degrees of the longitudinal axis and intersects the longitudinal axis.

[0034] The error cancellation calculation method includes calculating the magnetic field gradient of each of the magnetic fields (in a direction parallel to the axis of the sensor) detected at the distal end (e.g., by one or more of the sensors). As used herein and in the claims, the term "magnetic field gradient" is defined as the change in magnetic field over distance in a particular direction. In some embodiments, the approximate location of one or more of the magnetic field sensors is calculated using any suitable method, and then based on known functions of different magnetic fields in three-dimensional (3D) space, the magnetic field gradient at the distal end (in a direction parallel to the axis of the sensor) can be found for each of the magnetic fields.

[0035] One of the magnetic fields is selected (e.g., the magnetic field with the highest magnetic field gradient). In some embodiments, a subset of the magnetic fields is selected (e.g., the magnetic field with the highest magnetic field gradient), and the average magnetic field gradient of the selected magnetic fields is calculated.

[0036] The difference between the magnetic field strengths of the selected magnetic fields detected by the sensors is calculated. When a subset of the magnetic fields is selected, the average difference between the magnetic field strengths of the selected magnetic fields detected by the sensors is calculated.

[0037] The distance between the sensors may then be calculated based on the (average) difference between the (average) magnetic field gradient of the selected magnetic field(s) and the magnetic field strength of the selected magnetic field(s). In some embodiments, the distance may be calculated based on the magnetic field strength of the selected magnetic field(s) divided by the (average) magnetic field gradient of the selected magnetic field(s). Other dimensions of the distal tip assembly may be calculated from the calculated distance between the sensors. The distance and / or dimensions may then be used to find the shape of the distal tip assembly so that a representation of the distal tip assembly may be rendered on a display.

[0038] System Description Reference is now made to FIG. 1 , which is a schematic, pictorial illustration of a catheter tracking system 20 according to one embodiment of the present invention. The system 20 includes a catheter 40 configured to be inserted into a body portion of a living subject (e.g., a patient 28). A physician 30 guides the catheter 40 (e.g., a basket catheter manufactured by Biosense Webster, Inc., Irvine, CA, USA), shown in detail in inset 45, to a target location in the heart 26 of the patient 28 by manipulating a deflectable segment of the insertion tube 22 of the catheter 40 using a manipulator 32 and / or deflection from a sheath 23 near the proximal end 29 of the insertion tube 22. In the illustrated embodiment, the physician 30 uses the catheter 40 to perform electroanatomical mapping of the heart cavity.

[0039] The catheter 40 includes a distal end 33. The distal end 33 of the catheter 40 includes an assembly 35 (e.g., a basket assembly or a balloon assembly as shown in FIG. 1 ) in which a plurality of electrodes 48 (only some of which are labeled for simplicity) are disposed. The assembly 35 is disposed distal to the insertion tube 22 and may be connected to the insertion tube 22 at the distal end 33 via a coupling member of the insertion tube 22. The coupling member of the insertion tube 22 may be formed as an integral part of the remainder of the insertion tube 22 or as a separate element that connects to the remainder of the insertion tube 22.

[0040] Assembly 35 further includes a plurality of flexible strips 55 (only two are labeled for simplicity), each coupled to an electrode 48. Assembly 35 may include any suitable number of electrodes 48. In some embodiments, assembly 35 may include 10 flexible strips 55 and 120 electrodes, with 12 electrodes disposed on each flexible strip 55.

[0041] The catheter 40 includes a pusher 37. The pusher 37 is typically a tube disposed within the lumen of the insertion tube 22 and extending from the proximal end 29 to the distal end 33 of the insertion tube 22. The distal end of the pusher 37 is typically connected to a first end of the flexible strip 55 via a linking member of the pusher 37. The linking member of the pusher 37 may be formed as an integral part of the remainder of the pusher 37 or as a separate element connecting to the remainder of the pusher 37. The distal end of the insertion tube 22 is typically connected to a second end of the flexible strip 55 via a linking member of the distal end 33. The pusher 37 is generally controlled via the manipulator 32 to deploy the assembly 35 and change the ovality of the assembly 35 according to longitudinal displacement of the pusher 37 relative to the insertion tube 22.

[0042] The actual construction of the basket assembly 35 may vary. For example, the flexible strip 55 may be made of a printed circuit board (PCB) or a shape memory alloy.

[0043] The embodiments described herein, by way of example only, refer primarily to a basket distal tip assembly 35. In alternative embodiments, the disclosed techniques may be used with catheters having a balloon-based distal tip assembly or any other suitable type of distal tip assembly.

[0044] The catheter 40 is inserted through the sheath 23 in a collapsed configuration, and only after the catheter 40 exits the sheath 23 can the catheter 40 change shape by retracting the pusher 37. By housing the catheter 40 in a collapsed configuration, the sheath 23 also serves to minimize vascular trauma en route to the target location.

[0045] The distal end 33 of the catheter 40 includes magnetic coil sensors 50A and 50B. Magnetic coil sensor 50A is shown in inset 45 at the distal end of the insertion tube 22 (i.e., the proximal end of the basket assembly 35). Sensor 50A can be a Single-Axis Sensor (SAS), a DAS, or a TAS. Similarly, sensor 50B can be a SAS, a DAS, or a TAS. Magnetic coil sensors 50A and 50B, as well as electrodes 48, are connected to various drive circuits within the console 24 by wires running through the insertion tube 22.

[0046] In some embodiments, system 20 includes a magnetic sensing subsystem for estimating the ellipticity and extension / retraction state of basket assembly 35 of catheter 40 within a cardiac cavity of heart 26 by estimating the extension of basket assembly 35 from the distance between sensors 50A and 50B, as described in more detail with reference to FIGS. 2B and 3 . Patient 28 is placed within a magnetic field generated by a pad including multiple magnetic field generator coils 42 driven by unit 43. Magnetic field generator coils 42 are configured to generate respective alternating magnetic fields having respective different frequencies in a region where a body part (e.g., heart 26) of a living subject (e.g., patient 28) is located. Magnetic coil sensors 50A and 50B are configured to output electrical signals as a function of detecting the respective magnetic fields. For example, if there are nine magnetic field generator coils 42 generating nine respective different alternating magnetic fields having nine respective different frequencies, the electrical signal output by magnetic coil sensor 50 includes components of the nine different frequency alternating magnetic fields. The strength of each of the magnetic fields varies with distance from the respective field generator coil 42, so that the location of the magnetic coil sensors 50 can be determined from the magnetic fields sensed by the magnetic coil sensors 50. The transmitted alternating magnetic fields therefore generate electrical signals in the sensors 50A and 50B that in turn indicate the position and orientation of the magnetic coil sensors 50. The magnetic coil sensors 50A and 50B are described in more detail with reference to FIG. 2B.

[0047] The generated signals are transmitted to console 24 and become corresponding electrical inputs to processing circuitry 41. Processing circuitry 41 can use the signals to calculate the extension of basket assembly 35 in order to estimate basket ovality and extension / retraction state from the calculated distance between sensors 50A and 50B, as described in more detail below with reference to Figures 2B and 3, and to calculate the relative orientation between the axes of sensors 50A and 50B in order to estimate the shape of expandable distal end assembly 35 (e.g., basket shape) based on the relative orientation, as described in more detail below.

[0048] The curvature of the flexible strip 55 and / or the position of the electrodes 48 (or other features) on the flexible strip 55 relative to a fixed point on the catheter 44 (such as the distal tip of the insertion tube 22) may be measured for various distances between the magnetic sensors 50A, 50B and various relative orientation angles between the magnetic sensors 50A, 50B. For example, the position of the electrodes 48 relative to the fixed point on the catheter 44 may be measured for every 0.2 mm of movement of the pusher 37 relative to the insertion tube 22 and for every 1 degree of relative orientation between the magnetic sensors 50A, 50B (up to the maximum lateral movement of the assembly 35). At each different distance / relative orientation combination, the calculated distance and calculated relative orientation angle between the magnetic sensors 50A, 50B are recorded along with the position data of the electrodes 48. This data can then be used to estimate the curvature of the flexible strip 55 and / or the position of the electrodes 48 (or other features) on the flexible strip 55 relative to a fixed point on the catheter 40 (such as the distal tip of the insertion tube 22) based on the calculated distance and relative orientation angle between the magnetic sensors 50A, 50B.

[0049] Additionally or alternatively, the curvature of the flexible strips 55 may be estimated based on the following assumptions: (a) each of the flexible strips 55 is a fixed, known length, (b) each of the flexible strips 55 is connected to the pusher 37 via a linkage member with the distal end of the flexible strip 55 substantially perpendicular (within plus or minus 10 degrees) to the longitudinal axis 58, and (c) each of the flexible strips 55 is connected to the insertion tube 22 via a linkage member that connects the proximal end of the flexible strip 55 to the insertion tube 22 substantially parallel (within plus or minus 10 degrees) to the longitudinal axis 58 of the insertion tube 22. Based on the above assumptions (a)-(c) and based on the calculated positions of the linkage members based on the calculated positions of the magnetic sensors 50A, 50B, the curvature of each of the flexible strips 55 may be calculated using a third-order polynomial. In some embodiments, the curvature of the flexible strip 55 and / or the position of the electrodes 48 (or other features) on the flexible strip 55 relative to a fixed point on the catheter 40 (such as the distal tip of the insertion tube 22) may be calculated based on the calculated distance and orientation between the magnetic sensors 50A, 50B and a model of the catheter 40, which provides the curvature of the flexible strip 55 and / or the position of the electrodes 48 relative to a calculated distance based on the mechanical properties and dimensions of the flexible strip 55.

[0050] Methods of sensing position and / or orientation using external magnetic fields and magnetic coil sensors such as sensors 50A and 50B have been implemented in various medical applications, for example, in the CARTO® system manufactured by Biosense-Webster, and are described in detail in U.S. Pat. Nos. 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612, and 6,332,089, WO 96 / 05768, and U.S. Patent Application Publication Nos. 2002 / 0065455(A1), 2003 / 0120150(A1), and 2004 / 0068178(A1).

[0051] Processing circuitry 41, which is typically part of a general-purpose computer, is further connected via suitable front-end and interface circuitry 44 to receive signals from body surface electrodes 49. Processing circuitry 41 is connected to surface electrodes 49 by wires that extend through cable 39 to the chest of patient 28. Catheter 40 includes a connector 47 disposed at the proximal end 29 of insertion tube 22 for coupling to processing circuitry 41.

[0052] In some embodiments, the processing circuitry 41 renders a representation 31 of the catheter 40 and at least a portion of the body part on the display 27 based on calculated position coordinates of the insertion tube 22 and flexible strip 55 (e.g., from a mapping process or from a scan (e.g., CT or MRI) of the body part previously registered with the system 20), which will be described in more detail with reference to FIG. 3 .

[0053] Processing circuitry 41 is typically programmed with software to carry out the functions described herein, which software may be downloaded to a computer in electronic form, for example over a network, or alternatively or additionally may be provided and / or stored on a non-transitory tangible medium, such as magnetic, optical, or electronic memory.

[0054] The illustration of the embodiment shown in Figure 1 has been chosen solely for purposes of conceptual clarity. For simplicity and clarity, Figure 1 shows only elements relevant to the disclosed technique. System 20 typically includes additional modules and elements that are not directly related to the disclosed technology and thus have been intentionally omitted from Figure 1 and the corresponding description. The elements of system 20 and the methods described herein may be further applied, for example, to control the ablation of tissue in heart 26.

[0055] Reference is now made to Figures 2A and 2B. Figure 2A is a schematic diagram of the distal end 33 of the basket catheter 40 in a collapsed configuration. Figure 2B is a schematic diagram of the distal end 33 of the basket catheter 40 of Figure 2A in a deployed configuration.

[0056] The assembly 35 is typically an expandable distal end assembly (e.g., a basket distal end assembly) comprising a flexible strip 55 (only some of which are labeled for simplicity) circumferentially disposed around a distal portion 52 of a pusher 37, with a first end of the strip 55 connected to the distal end 33 of the insertion tube 22 (e.g., a linking member of the distal end 33) and a second end of the strip 55 connected to the distal portion 52 of the pusher 37 (e.g., a linking member of the distal portion 52). The flexible strip 55 is configured to arc radially outward when the pusher 37 is retracted. A plurality of electrodes 48 (only some of which are labeled for simplicity) are disposed on each of the flexible strips 55.

[0057] Magnetic coil sensor 50A is a coil-based position sensor disposed at the distal end 33 of insertion tube 22, for example, within a connecting member of distal end 33. Magnetic coil sensor 50A includes coil 54A having axis 56A. Magnetic coil sensor 50B is a coil-based position sensor disposed on the distal portion 52 of pusher 37, for example, within a connecting member of distal portion 52 connecting the distal end of flexible strip 55 to pusher 37. Magnetic coil sensor 50B includes coil 54B having axis 56B. Distal end 33 of catheter 40 has a longitudinal axis 58. Magnetic coil sensors 50A, 50B are disposed on distal end 33 with axis 56A substantially parallel to axis 56B. In some embodiments, axes 56A, 56B, and longitudinal axis 58 are substantially coaxial.

[0058] The pusher 37 is configured to advance and retract through the insertion tube 22. The magnetic field sensors 50A, 50B are configured to move relative to one another along the longitudinal axis 58 of the catheter 40 as the expandable distal tip assembly 35 expands and collapses. When the expandable distal tip assembly 35 collapses, the distance d between the magnetic coil sensors 50A, 50B increases, and when the expandable distal tip assembly 35 is deployed (i.e., expanded), the distance d between the magnetic coil sensors 50A, 50B decreases.

[0059] Each sensor 50A, 50B may be a SAS, DAS, or TAS. Sensors 50A, 50B may be the same type of sensor or different types of sensors. If sensors 50A, 50B are both single-axis sensors, catheter 40 typically includes another position sensor for tracking the roll of assembly 35.

[0060] Reference is now made to Figure 3, which is a flow chart 100 including steps in a method of operating the system 20 of Figure 1. See also Figure 2B.

[0061] As previously described, magnetic coil sensors 50A and 50B are configured to output electrical signals due to the inductive effect of each coil in response to its respective magnetic field. For example, if nine magnetic field generator coils 42 generate nine different alternating magnetic fields having nine different frequencies, the electrical signal output by magnetic coil sensor 50 will include components of the nine different frequency alternating magnetic fields. The strength of each of the magnetic fields varies with distance from the respective magnetic field generator coils 42, so that the location of magnetic coil sensor 50 can be determined from the magnetic field sensed by magnetic coil sensor 50. Thus, the transmitted alternating magnetic field generates electrical signals within sensors 50A and 50B, which in turn indicate the position and orientation of magnetic coil sensor 50. Processing circuitry 41 is configured to receive the electrical signals from magnetic coil sensors 50A and 50B (block 102).

[0062] Processing circuitry 41 is configured to calculate (block 104) the magnetic field gradient (e.g., parallel to the direction of axes 56A, 56B of coils 54A, 54B) of each of the magnetic fields detected by magnetic coil sensors 50A and 50B, as well as the magnetic field detected at distal end 33. That is, processing circuitry 41 calculates the magnetic fields and associated magnetic field gradients from at least one of the electrical signals received by circuitry 41 from one or more of magnetic coil sensors 54A and 54B. In some embodiments, the approximate position (location and orientation) of one or more of magnetic field sensors 50A, 50B may be calculated using any suitable method, and then based on known functions of the different magnetic fields in three-dimensional (3D) space, the magnetic field gradient at distal end 33 (e.g., parallel to the direction of axes 56A, 56B of coils 54A, 54B) may be found for each of the magnetic fields. The position of the distal end 33 may be calculated based on the average position of the magnetic coil sensors 50A, 50B, or based on the most accurate sensor of the magnetic coil sensors 50A, 50B. For example, if sensor 50B is a DAS or TAS, then the location and orientation of sensor 50B may be calculated based on all or a portion of the sensing coils of that sensor.

[0063] The processing circuitry 41 is configured to select (block 106) one of the magnetic fields having a respective one of the calculated magnetic field gradients. In some embodiments, the selected magnetic field has the highest calculated magnetic field gradient of the calculated magnetic field gradients (i.e., the magnetic field having the highest gradient is selected). The highest magnetic field gradient generally indicates that the selected magnetic field provides the highest sensitivity in a direction parallel to the axes 56A, 56B of the coils 54A, 54B of the magnetic coil sensors 50A, 50B, and therefore provides the highest accuracy in calculating the distance d between the sensors 50A, 50B.

[0064] In some embodiments, processing circuitry 41 is configured to select a subset of the magnetic fields (e.g., those with the highest magnetic field gradients among the magnetic fields) and calculate an average magnetic field gradient for the selected magnetic fields. Thus, processing circuitry 41 is configured to select at least one of the magnetic fields having a magnetic field gradient (e.g., an average calculated magnetic field gradient) as a function of at least one of the electrical signals received by circuitry 41 from the coils (used to calculate the magnetic fields and the magnetic field gradients of the respective magnetic fields). Processing circuitry 41 is also configured to calculate (block 108) a difference between the magnetic field strengths of the selected magnetic fields (e.g., the magnetic fields with the highest gradients) detected by magnetic coil sensor 50A and magnetic coil sensor 50B. For example, if the magnetic field strength of the selected magnetic field detected by magnetic coil sensor 50A is equal to B1 and the magnetic field strength of the selected magnetic field detected by magnetic coil sensor 50B is equal to B2, then the difference in the magnetic field strengths of the selected magnetic field (e.g., the magnetic field with the highest gradient) detected by magnetic coil sensor 50A and magnetic coil sensor 50B is equal to B2 minus B1.

[0065] In some embodiments, when a subset of magnetic fields is selected, processing circuitry 41 is configured to calculate a difference (which is the average difference) between the magnetic field strengths of the selected magnetic fields (e.g., the magnetic fields with the highest gradients) detected by magnetic coil sensor 50A and magnetic coil sensor 50B. For example, if the average magnetic field strength of the selected magnetic fields detected by magnetic coil sensor 50A is equal to B3 and the average magnetic field strength of the selected magnetic fields detected by magnetic coil sensor 50B is equal to B4, then the average difference in the magnetic field strengths of the selected magnetic fields (e.g., the magnetic fields with the highest gradients) detected by magnetic coil sensor 50A and magnetic coil sensor 50B is equal to B4 minus B3.

[0066] Processing circuitry 41 is configured to calculate (block 110) a dimension of distal end 33 that is a function of the distance d between magnetic field coil sensors 50A and 50B as a function of the calculated difference (e.g., average difference) between the magnetic field strengths of the selected magnetic field(s) (e.g., B2 minus B1 or B4 minus B3) and the calculated magnetic field (average) gradient (e.g., highest calculated magnetic field gradient(s)) of each of the selected magnetic fields. In some embodiments, processing circuitry 41 is configured to calculate a dimension of distal end 33 based on the calculated (average) difference between the magnetic field strengths of the selected magnetic field(s) (e.g., B2 minus B1 or B4 minus B3) divided by the calculated (average) magnetic field gradient (e.g., highest calculated magnetic field gradient(s)) of each of the selected magnetic fields. The calculated dimension may be the distance between magnetic coil sensors 50A, 50B. In some embodiments, the calculated dimension is the shape of the catheter's distal tip 33, e.g., the distance between the proximal and distal points of the distal tip assembly 35, or the dimension around the equator of the assembly 35. The processing circuitry 41 is configured to find (block 112) the shape of the distal tip assembly 35 as a derivation from the calculated dimension (e.g., by calculation or from a look-up table). The processing circuitry 41 is optionally configured to calculate a relative orientation between the axes of the sensors 50A and 50B to estimate or derive the shape (e.g., basket shape) of the expandable distal tip assembly 35 based on the relative orientation. The processing circuitry 41 is configured to render (block 114) a representation 31 ( FIG. 1 ) of the distal tip assembly 35 on the display 27 as a derivation of the found shape of the distal tip assembly 35. One technique for deriving the shape of the expandable distal tip assembly 35 based on the distance between magnetic location sensors can be found in U.S. Patent Application No. 16 / 854,538, filed April 21, 2020 (Attorney Docket No. BIO6130USNP), a copy of which is incorporated by reference in the Appendix.

[0067] As used herein, the term "about" or "approximately" with respect to any numerical value or range of values ​​indicates a suitable dimensional tolerance that enables a portion of a component or a collection of components to function in accordance with its intended purpose as described herein. More specifically, "about" or "approximately" may refer to a range of values ​​of ±20% of the recited value, for example, "about 90%" may refer to a range of values ​​of 72% to 108%.

[0068] Various features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination.

[0069] The above-described embodiments are cited by way of example, and the present invention is not limited to that particularly shown and described in the foregoing specification. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described in the foregoing specification, as well as variations and modifications thereof not disclosed in the prior art that will occur to those skilled in the art upon reading the above description.

[0070] [Embodiment] (1) A health care system: generator coils configured to generate respective magnetic fields having respective different frequencies in the region of a body-part of a biological subject; a catheter configured to be inserted into the body portion of the living subject, the catheter having a distal end including magnetic coil sensors configured to output electrical signals in response to the respective magnetic fields, the catheter including a first magnetic coil sensor having a first axis and a second magnetic coil sensor having a second axis, the magnetic coil sensors being disposed on the distal end with the first axis substantially parallel to the second axis; A processing circuit, receiving the electrical signal from the magnetic coil sensor; selecting at least one of the magnetic fields having a magnetic field gradient defined by at least one of the received electrical signals; calculating a difference between magnetic field strengths of the at least one selected magnetic field detected by the first magnetic coil sensor and the second magnetic coil sensor based on the received electrical signals; and calculating a dimension of the distal end, the dimension being a function of a distance between the magnetic coil sensors, based on the calculated difference between the magnetic field strengths of the at least one selected magnetic field and the magnetic field gradient of the at least one selected magnetic field. (2) The system of embodiment 1, wherein the calculated dimension is the distance between the magnetic coil sensors. (3) The system described in embodiment 1, wherein the calculated dimensions are the dimensions of the shape of the distal end of the catheter. (4) The system of embodiment 1, wherein the processing circuitry is configured to calculate the dimension of the distal end as a function of the calculated difference between the magnetic field strengths of the at least one selected magnetic field divided by the magnetic field gradient of the at least one selected magnetic field. (5) the at least one selected magnetic field includes one of the magnetic fields having a highest magnetic field gradient of the magnetic fields; The system of embodiment 1, wherein the processing circuit is configured to calculate the dimensions of the distal end as a function of the calculated difference between the magnetic field strengths of the at least one selected magnetic field and the highest magnetic field gradient.

[0071] (6) the catheter has a longitudinal axis; the distal end of the catheter includes an expandable distal tip assembly; the magnetic field sensors are configured to move relative to one another along the longitudinal axis of the catheter as the expandable distal tip assembly is expanded and collapsed; when the expandable distal tip assembly is collapsed, the distance between the magnetic coil sensors increases; 2. The system of claim 1, wherein the distance between the magnetic coil sensors decreases when the expandable distal end assembly is deployed. (7) The system of embodiment 6, wherein the first axis, the second axis, and the longitudinal axis are substantially coaxial. (8) The system of embodiment 6, wherein the expandable distal end assembly is a basket distal end assembly comprising a plurality of flexible strips and electrodes disposed on the flexible strips. (9) A display further comprising: finding a shape for the distal tip assembly based at least on the calculated dimensions; 7. The system of claim 6, further comprising: a display configured to display a representation of the distal end assembly based on the found shape of the distal end assembly. (10) The system of embodiment 9, wherein the calculated dimension is the distance between the magnetic coil sensors.

[0072] (11) The processing circuit calculating a relative orientation between the first axis of the first magnetic coil sensor and the second axis of the second magnetic coil sensor; and estimating a shape of the distal end assembly based on the calculated relative orientation. (12) A medical method comprising: generating magnetic fields having respective different frequencies in the region of a body part of a living subject; inserting a catheter into the body part of the living subject; detecting each one of the magnetic fields with a magnetic coil sensor having substantially parallel axes disposed on the distal end of the catheter, the magnetic coil sensor outputting an electrical signal as a function of the respective magnetic field; receiving respective electrical signals from the magnetic coil sensors; selecting at least one of the magnetic fields having a magnetic field gradient as a function of at least one of the received electrical signals; calculating a difference between a magnetic field strength of the at least one selected magnetic field detected by a first magnetic coil sensor of the magnetic coil sensors and a second magnetic coil sensor of the magnetic coil sensors as a function of the received electrical signal; and calculating a dimension of the distal end, the dimension being a function of a distance between the magnetic coil sensors, based on the calculated difference between the magnetic field strengths of the at least one selected magnetic field and the magnetic field gradient of the at least one selected magnetic field. (13) The method of claim 12, wherein the calculated dimension is the distance between the magnetic coil sensors. (14) The method of embodiment 12, wherein the calculated dimensions are the dimensions of the shape of the distal end of the catheter. (15) The method of embodiment 12, wherein calculating the dimension includes calculating the dimension of the distal end based on the calculated difference between the magnetic field strengths of the at least one selected magnetic field divided by the magnetic field gradient of the at least one selected magnetic field.

[0073] (16) The at least one selected magnetic field includes one of the magnetic fields having a highest magnetic field gradient of the magnetic fields; 13. The method of claim 12, wherein calculating the dimension includes calculating the dimension of the distal end based on the calculated difference between the magnetic field strengths of the at least one selected magnetic field and the maximum magnetic field gradient. (17) The method of embodiment 12, further comprising moving the magnetic field sensors relative to each other along the longitudinal axis of the catheter as the expandable distal end assembly of the catheter expands and collapses. (18) The method of embodiment 17, wherein the first axis, the second axis, and the longitudinal axis are substantially coaxial. (19) determining a shape of the distal tip assembly based at least on the calculated dimensions; and 18. The method of claim 17, further comprising: rendering a representation of the distal tip assembly on a display based on the found shape of the distal tip assembly. (20) The method of claim 19, wherein the calculated dimension is the distance between the magnetic coil sensors.

[0074] (21) calculating a relative orientation between the first axis of the first magnetic coil sensor and the second axis of the second magnetic coil sensor; 13. The method of claim 12, further comprising: estimating a shape of the distal tip assembly based on the calculated relative orientation.

Claims

1. 1. A healthcare system comprising: generator coils configured to generate respective magnetic fields having respective different frequencies in a heart of a living subject; a catheter configured to be inserted into the heart of the living subject, a distal end of the catheter including a first magnetic coil sensor and a second magnetic coil sensor configured to output electrical signals in response to the respective magnetic fields, the first magnetic coil sensor having a first axis that is its winding axis and the second magnetic coil sensor having a second axis that is its winding axis, the first magnetic coil sensor and the second magnetic coil sensor being disposed on the distal end with the first axis parallel to the second axis; A processing circuit, receiving the electrical signals from the first magnetic coil sensor and the second magnetic coil sensor; selecting at least one of the magnetic field having a magnetic field gradient in a direction parallel to the first axis of the first magnetic coil sensor and the magnetic field having a magnetic field gradient in a direction parallel to the second axis of the second magnetic coil sensor, defined by at least one of the received electrical signals; calculating a difference between the magnetic field strengths of the at least one selected magnetic field detected by the first magnetic coil sensor and the second magnetic coil sensor based on the received electrical signals; and calculating a dimension of the distal end in a longitudinal direction of the catheter that is a function of a distance between the first magnetic coil sensor and the second magnetic coil sensor based on the calculated difference between the magnetic field strengths of the at least one selected magnetic field and the magnetic field gradient of the at least one selected magnetic field.

2. 2. The system of claim 1, wherein the processing circuitry is configured to calculate the dimension of the distal end as a function of the calculated difference between the magnetic field strengths of the at least one selected magnetic field divided by the magnetic field gradient of the at least one selected magnetic field.

3. the at least one selected magnetic field includes one of the magnetic fields having a highest magnetic field gradient of the magnetic fields; 2. The system of claim 1, wherein the processing circuitry is configured to calculate the dimension of the distal end as a function of the calculated difference between the magnetic field strengths of the at least one selected magnetic field and the highest magnetic field gradient.

4. the catheter having a longitudinal axis; the distal end of the catheter includes an expandable distal tip assembly; the first magnetic coil sensor and the second magnetic coil sensor are configured to move relative to one another along the longitudinal axis of the catheter as the expandable distal tip assembly expands and collapses; when the expandable distal tip assembly is collapsed, the distance between the first magnetic coil sensor and the second magnetic coil sensor increases; The system of claim 1 , wherein the distance between the first and second magnetic coil sensors decreases when the expandable distal tip assembly is expanded.

5. The system of claim 4 , wherein the first axis, the second axis, and the longitudinal axis are coaxial.

6. The system of claim 4 , wherein the expandable distal tip assembly is a basket distal tip assembly comprising a plurality of flexible strips and electrodes disposed on the flexible strips.

7. a display, wherein the processing circuitry: finding a shape for the distal tip assembly based at least on the calculated dimensions; and rendering a representation of the distal tip assembly on the display based on the found shape of the distal tip assembly.

8. the processing circuitry calculating a relative orientation between the first axis of the first magnetic coil sensor and the second axis of the second magnetic coil sensor; and estimating a shape of the expandable distal tip assembly based on the calculated relative orientation.

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