Patent Publication Number: US-2023147259-A1

Title: Estimating contact force applied between catheter and tissue using transmitter and receivers of the catheter

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to medical devices, and particularly to methods and systems for estimating contact force applied between catheter and tissue. 
     BACKGROUND OF THE INVENTION 
     Various techniques for measuring and/or estimating contact force between a medical device and tissue and relative positions thereof are known in the art. 
     For example, U.S. Pat. Application Publication 2020/0206461 describes a system that includes an expandable distal-end assembly, a proximal position sensor, a distal position sensor, and a processor. The expandable distal-end assembly is coupled to a distal end of a shaft for insertion into a cavity of an organ of a patient. The proximal and distal position sensors are located at a proximal end and a distal end of the distal-end assembly, respectively. The processor is configured to estimate a position and a longitudinal direction of the proximal sensor, and a position of the distal sensor, all in a coordinate system used by the processor. The processor is further configured to project the estimated position of the distal sensor on an axis defined by the estimated longitudinal direction, and calculate an elongation of the distal-end assembly by calculating a distance between the estimated position of the proximal sensor and the projected position of the distal sensor. 
     U.S. Pat. Application Publication 2018/0076336 describes systems, devices and methods that integrate stretchable or flexible circuitry, including arrays of active devices for enhanced sensing, diagnostic, and therapeutic capabilities. The invention enables conformal sensing contact with tissues of interest, such as the inner wall of a lumen, the brain, or the surface of the heart. Such direct, conformal contact increases accuracy of measurement and delivery of therapy. Further, the invention enables the incorporation of both sensing and therapeutic devices on the same substrate allowing for faster treatment of diseased tissue and fewer devices to perform the same procedure. 
     SUMMARY OF THE INVENTION 
     An embodiment of the present invention that is described herein provides a system including a catheter and a processor. The catheter includes an expandable distal-end assembly (EDEA) having: (i) a transmitter, which is coupled to the EDEA and is configured to transmit a first signal, and (ii) one or more receivers, which are coupled to an elastic component of the EDEA, and are configured to produce one or more respective second signals in response to receiving the first signal. The processor is configured to estimate, based on the one or more respective second signals, a force applied to the elastic component. 
     In some embodiments, the EDEA includes a basket, the elastic component includes one or more splines of the basket, the force includes a contact force applied between the EDEA and tissue of an organ, and in response to applying the contact force, at least one of the splines is configured to deform for conforming with a shape of the tissue. In other embodiments, the transmitter is coupled to a rigid component of the EDEA. In yet other embodiments, the rigid component includes an irrigation apparatus or a shaft of the catheter. 
     In an embodiment, the processor is configured to: (i) hold a calibration dataset for quantifying a relation between at least one of the respective second signals and a level of deformation of at least one of the splines, and (ii) estimate the contact force based on at least one of the respective second signals and the calibration set. In another embodiment, the processor is configured to produce the calibration set before insertion of the EDEA into the organ, and to estimate the contact force when the EDEA is placed in contact with the tissue. In yet another embodiment, when the EDEA is in an expanded position, the one or more respective second signals include: (i) a first given signal received from a given receiver of the one or more receivers without applying the contact force, and (ii) a second given signal received from the given receiver when the contact force is applied, and the processor is configured to estimate the contact force based on the first and second given signals. 
     In some embodiments, the EDEA includes a balloon, and the elastic component includes a member of the balloon. In other embodiments, the force includes a contact force applied between the member and tissue of an organ, and in response to applying the contact force, the member is configured to deform for conforming with a shape of the tissue, and the processor is configured to: (i) hold a calibration dataset for quantifying a relation between at least one of the respective second signals and a level of deformation of at least a section of the member, and (ii) estimate the contact force based on at least one of the respective second signals and the calibration set. 
     There is additionally provided, in accordance with an embodiment of the present invention, a method including inserting into an organ of a patient a catheter including an expandable distal-end assembly (EDEA) having: (i) a transmitter, which is coupled to the EDEA for transmitting a first signal, and (ii) one or more receivers, which are coupled to an elastic component of the EDEA for producing one or more respective second signals in response to receiving the first signal. The first signal is applied to the transmitter and the one or more respective second signals are received. Based on the one or more respective second signals, a force applied to the elastic component is estimated. 
     There is further provided, in accordance with an embodiment of the present invention, a method for producing a catheter, the method includes coupling, to an expandable distal-end assembly (EDEA) of a catheter, a transmitter for transmitting a first signal. One or more receivers for producing one or more respective second signals in response to receiving the first signal, are coupled to an elastic component of the EDEA. At least the one or more receivers are electrically coupled to a processor for receiving the one or more respective second signals and for estimating, based on the one or more respective second signals, a force applied to the elastic component. 
     In some embodiments, the EDEA includes a basket, the elastic component includes one or more splines of the basket, the force includes a contact force applied between the EDEA and tissue of an organ, and in response to applying the contact force, at least one of the splines is configured to deform for conforming with a shape of the tissue. In other embodiments, the transmitter is coupled to a rigid component of the EDEA, and the rigid component includes a shaft or an irrigation apparatus of the catheter. In yet other embodiments, coupling the one or more receivers includes coupling a given receiver to a given spline of the basket. 
     In an embodiment, the EDEA includes a balloon, and the elastic component includes a member of the balloon. In another embodiment, the force includes a contact force applied between the member and tissue of an organ, in response to applying the contact force, the member is configured to deform for conforming with a shape of the tissue. 
     The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic, pictorial illustration of a catheter-based position-tracking and ablation system, in accordance with an embodiment of the present invention; 
         FIG.  2    is a schematic, pictorial illustration of a distal-end assembly of a catheter of the system depicted in  FIG.  1   , in accordance with an embodiment of the present invention; 
         FIG.  3    is a flow chart that schematically illustrates a method for estimating a contact force applied between the distal-end assembly and tissue of a patient heart, in accordance with an embodiment of the present invention; and 
         FIG.  4    is a flow chart that schematically illustrates a method for producing the distal-end assembly depicted in  FIG.  2   , in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Overview 
     Some medical procedures, such as radiofrequency (RF) ablation of tissue in a patient heart, require controlled contact force between ablation electrodes of an ablation catheter inserted into a patient heart and the heart tissue intended to be ablated by applying RF signals to the ablation electrodes. The ablation electrodes may be coupled to flexible splines of a basket-shaped expandable distal-end assembly. During the ablation procedure the distal-end assembly is inserted into the heart and expanded to an expanded position for exposing the ablation electrodes to the tissue. Some of the splines are placed in contact with the tissue and are deformed in order to conform with the tissue and for placing the electrodes in contact with the tissue intended to be ablated. The controlled contact force between the respective splines and the tissue is important for properly ablating the tissue and for producing, in the tissue in question, a lesion having specified properties. 
     In principle, it is possible to couple to the distal-end assembly, a device for measuring the contact force. For example, the device may include one or more piezoelectric crystals that output voltage in response to sensing contact force applied to the splines. However, the piezoelectric crystals may increase the complexity of the catheter and may provide insufficient accuracy of the measured or estimated contact force, inter alia, due to the flexibility of the splines. 
     Embodiments of the present invention that are described hereinbelow provide improved techniques for estimating the contact force applied, during an ablation procedure, between tissue in question (e.g., of a patient heart) and an expandable distal-end assembly (EDEA) of a catheter. Note that the improved techniques rely on quantifying and using the elastic properties of a flexible component of the distal-end assembly. 
     In some embodiments, a system for performing RF ablation to tissue in question comprises a catheter and a processor. The catheter comprises an EDEA having a transmitter and one or more receivers, typically implemented in electrical coils. The transmitter is coupled to a rigid component of the EDEA, e.g., a shaft or an irrigation apparatus of the catheter. The one or more receivers are coupled to respective elastic component(s) of the EDEA. For example, (i) in an EDEA comprising a basket, one or more receiver(s) may be coupled to each spline of the basket, and (ii) in an EDEA comprising a balloon, the one or more receivers may be disposed and fitted at several positions on the outer surface of the balloon. 
     In some embodiments, the one or more receivers are electrically connected to the processor and the transmitter is electrically connected to the processor or to a pulse generator controlled by the processor. In some embodiments, the electrical connection may be carried out using (i) electrical wires or traces running between the proximal and distal ends of the catheter, e.g., between the EDEA and an operating console of the system that comprises the processor, or (ii) wirelessly, using wireless devices coupled to the proximal and distal ends of the catheter. 
     In some embodiments, the processor is configured to apply to the transmitter a transmission signal, referred to herein as a first signal, and at least one of the receivers is configured to produce a receiving signal, referred to herein as a second signal, in response to receiving the first signal. 
     In some embodiments, during the ablation procedure, a physician inserts the EDEA into the patient heart, expands the EDEA to an expanded position, places the EDEA in contact with the tissue and applies contact force to the elastic component (e.g., splines) for performing the ablation. The processor is configured to estimate, based on the second signal received from the receiver, the contact force applied to the respective one or more splines. Note that the intensity of the first signal sensed by the receiver is proportional to the distance between the transmitter and the respective receiver. In some embodiments, in response to the contact force applied by the physician, a given spline of the splines deforms, and the deformation is sensed by the altered intensity of the first signal sensed by the respective receiver. 
     In some embodiments, the processor is configured to hold a calibration dataset (e.g., a calibration table) for quantifying the relation between the one or more second signals and the level of deformation of the one or more respective splines. The calibration process may be carried out as part of the manufacturing process of the EDEA, or before inserting the catheter into the patient heart. 
     In other embodiments, after expanding the EDEA and before placing the EDEA in contact with the heart tissue, the physician may control the processor to: (i) apply the first signal using the transmitter, and (ii) receive the one or more second signal(s) for obtaining a reference before applying the contact force to the splines. In such embodiments, after placing the EDEA in contact with the tissue and applying the contact force to the splines, the processor is configured to reapply the first signal and to receive an additional second signal. The processor is configured to estimate the contact force applied to the respective splines using the received second signals before and after applying the contact force to the splines. 
     The disclosed techniques improve the quality of RF ablation procedures by improving the accuracy and reducing the complexity of sensing contact force applied between ablation electrodes and tissue intended to be ablated during the RF ablation procedure. The disclosed techniques are also applicable, mutatis mutandis, to any other medical procedure that requires accurate sensing of contact force between a medical device pressed against tissue. 
     System Description 
       FIG.  1    is a schematic, pictorial illustration of a catheter-based position-tracking and ablation system  20 , in accordance with an embodiment of the present invention. In some embodiments, system  20  comprises a catheter  22 , in the present example an expandable cardiac catheter, and a control console  24 . In the embodiment described herein, catheter  22  may be used for any suitable therapeutic and/or diagnostic purposes, such as ablation of tissue in a heart  26  and for mapping cardiac arrhythmias by sensing intra-cardiac electrical signals. 
     In some embodiments, console  24  comprises a processor  42 , typically a general-purpose computer, with suitable front end and interface circuits for receiving signals from catheter  22  and for controlling other components of system  20  described herein. Processor  42  may be programmed in software to carry out the functions that are used by the system, and is configured to store data for the software in a memory  50 . The software may be downloaded to console  24  in electronic form, over a network, for example, or it may be provided on non-transitory tangible media, such as optical, magnetic or electronic memory media. Alternatively, some or all of the functions of processor  42  may be carried out using an application-specific integrated circuit (ASIC) or any suitable type of programmable digital hardware components. 
     Reference is now made to an inset  25 . In some embodiments, catheter  22  comprises an expandable distal-end assembly  40  having multiple splines (shown in detail in  FIG.  2    below), and a shaft  23  for inserting distal-end assembly  40  to a target location for ablating tissue in heart  26 . During an ablation procedure, physician  30  inserts catheter  22  through the vasculature system of a patient  28  lying on a table  29 . Physician  30  moves distal-end assembly  40  to the target location in heart  26  using a manipulator  32  near a proximal end of catheter  22 , which is connected to interface circuitry of processor  42 . 
     In some embodiments, catheter  22  comprises a position sensor  39  of a position tracking system, which is coupled to the distal end of catheter  22 , e.g., in close proximity to distal-end assembly  40 . In the present example, position sensor  39  comprises a magnetic position sensor, but in other embodiments, any other suitable type of position sensor (e.g., other than magnetic-based) may be used. 
     Reference is now made back to the general view of  FIG.  1   . In some embodiments, during the navigation of distal-end assembly  40  in heart  26 , processor  42  receives signals from magnetic position sensor  39  in response to magnetic fields from external field generators  36 , for example, for the purpose of measuring the position of distal-end assembly  40  in heart  26 . In some embodiments, console  24  comprises a driver circuit  34 , configured to drive magnetic field generators  36 . Magnetic field generators  36  are placed at known positions external to patient  28 , e.g., below table  29 . 
     In some embodiments, processor  42  is configured to display, e.g., on a display  46  of console  24 , the tracked position of distal-end assembly  40  overlaid on an image  44  of heart  26 . 
     The method of position sensing using external magnetic fields is implemented in various medical applications, for example, in the CARTO™ system, produced by Biosense Webster Inc. (Irvine, Calif.) and is described in detail in U.S. Pats. 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612 and 6,332,089, in PCT Patent Publication WO 96/05768, and in U.S. Pat. Application Publications 2002/0065455 A1, 2003/0120150 A1 and 2004/0068178 A1. 
     This particular configuration of system  20  is shown by way of example, in order to illustrate certain problems that are addressed by embodiments of the present invention and to demonstrate the application of these embodiments in enhancing the performance of such a system. Embodiments of the present invention, however, are by no means limited to this specific sort of example system, and the principles described herein may similarly be applied to other sorts of medical systems and procedures. 
     Distal-End Assembly Having Transmitter and Receivers For Measuring Contact Force 
       FIG.  2    is a schematic, pictorial illustration of distal-end assembly  40  in an expanded position, in accordance with an embodiment of the present invention. 
     In some embodiments, distal-end assembly  40  comprises multiple splines  55  of a basket-shaped assembly. Each spline  55  comprises a flexible arm  77  made from a suitable elastic substance, such as but not limited to a flexible printed circuit board (PCB), or a suitable biocompatible and flexible metal alloy (e.g., nickel-titanium based, such as nitinol) that may be partially coated with one or more electrically insulating layer(s) to prevent electrical shorts between splines  55 . 
     In some embodiments, one or more ablation electrodes  66  are coupled to each spline  55  and are configured to apply ablation pulse(s) to tissue of heart  26 . The ablation pulse(s) are intended to kill cells of the tissue in question and to produce, instead of the tissue, a lesion that prevents or reduces the propagation of electrophysiological (EP) waves through the ablated tissue. 
     In some embodiments, distal-end assembly  40  comprises a transmitter  88  and one or more receivers  99 . Transmitter  88  is coupled to a rigid component of distal-end assembly  40 , in the present example, transmitter  88  is coupled to an irrigation apparatus, also referred to herein as an irrigator  60 , which is configured to apply irrigation fluid when applying the ablation signals to tissue of heart  26 , or at any other suitable time interval of the ablation procedure. In other embodiments, transmitter  88  may be coupled to any other suitable rigid component of distal-end assembly  40 , such as shaft  23 . In the context of the present disclosure and in the claims, the term “rigid” refers to a component of catheter  22  that moves together with the catheter and whose location is not affected by any force, such as contact force, applied to distal-end assembly  40 , as will be described in detail below. In other words, transmitter  88  has the same angular velocity and the same angular acceleration of the distal end of shaft  23 . 
     In some embodiments, one or more receivers  99  are coupled to respective elastic components of distal-end assembly  40 . In the present example, distal-end assembly  40  comprises a basket having multiple splines  55 , and one receiver  99  is coupled to each spline  55  of the basket. In alternative embodiments, distal-end assembly  40  may comprise a balloon (not shown) having a flexible member, or any other suitable type of expandable distal-end assembly. In case of a balloon, receivers  99  may be disposed at several positions on the outer surface of the balloon. Note that in the example of  FIG.  2   , only three receivers  99  are shown, but a receiver  99  is coupled to each spline  55  even though some of receivers  99  are hidden by the isometric perspective of distal-end assembly  40 , and therefore, are not shown in the example configuration of  FIG.  2   . 
     In some embodiments, transmitter  88  and receivers  99  may be implemented using electrical coils that are coupled to irrigator  60  and splines  55 , respectively. The coils of transmitter  88  and receivers  99  are electrically connected to console  24 , and more particularly, to processor  42  using any suitable connection techniques described in detail below. 
     In some embodiments, receivers  99  are electrically connected (e.g., via traces of the aforementioned flexible PCB, and via catheter  22 ) to processor  42 . Moreover, transmitter  88  is electrically connected to processor  42  (e.g., via wires running between (i) the distal end of shaft  23  or irrigator  60 , and (ii) the proximal end of catheter  22 ). Additionally, or alternatively, transmitter  88  may be electrically connected to a pulse generator (not shown) controlled by processor  42  and configured to apply one or more pulses using transmitter  88  as will be described below. 
     In other embodiments, the electrical connection between (i) transmitter  88  and/or receivers  99  and (ii) processor  42 , may be carried out using wireless devices (not shown) coupled to the proximal and distal ends of catheter  22 . 
     In some embodiments, processor  42  is configured to control transmitter  88  to apply a transmission signal, also referred to herein as a first signal. In response to receiving the first signal, at least one of and typically all receivers  99 , are configured to produce a receiving signal, also referred to herein as a second signal. 
     In some embodiments, the second signal produced by a given receiver  99  is indicative of the distance between transmitter  88  and given receiver  99 , as will be described below. 
     In some embodiments, during the ablation procedure, physician  30  inserts distal-end assembly  40  into a cavity of heart  26 . Subsequently, physician  30  expands distal-end assembly  40  to an expanded position (as shown in the example of  FIG.  2   ), places distal-end assembly  40  in contact with the tissue intended to be ablated, and applies contact force to splines  55  (or any elastic component of another sort of expandable distal-end assembly) for performing the ablation of the tissue in heart  26 . 
     In some embodiments, processor  42  is configured to receive the second signals from receivers  99  and to estimate, based on the second signals, the contact force applied to the respective one or more splines  55 . Note that the intensity of the first signal sensed by a given receiver  99  is indicative of (e.g., proportional to) the distance between transmitter  88  and given receiver  99 , the smaller the distance the larger the intensity of the first signal sensed by given receiver  99 . In the present example, the sensitivity of the estimated change in distance between transmitter  88  and given receiver  99  is about 0.01 mm, whereas when applying the contact force to distal-end assembly  40  the change in distance between transmitter  88  and given receiver  99  is typically larger than about 0.1 mm. 
     In the context of the present disclosure and in the claims, the terms “about” or “approximately” for any numerical values or ranges indicate a suitable dimensional tolerance that allows the part or collection of components to function for its intended purpose as described herein. 
     In some embodiments, in response to the contact force applied to distal-end assembly  40  by physician  30 , arm  77  of a given spline  55  having given receiver  99  coupled thereto is deformed, and the deformation is sensed by the altered intensity of the first signal sensed by the given receiver  99 . 
     In some embodiments, processor  42  is configured to hold a calibration dataset (e.g., a calibration table) for quantifying the relation between the one or more second signals and the level of deformation of the one or more respective splines  55 . The calibration process may be carried out as part of the manufacturing process of distal-end assembly  40 , or at any other time interval before inserting distal-end assembly  40  into heart  26  of patient  28 . 
     In some embodiments, processor  42  is configured to translate the change in distance between transmitter  88  and given receiver  99  to the contact force applied to the spline having the given receiver coupled thereto (e.g., using the calibration dataset. As described above, the sensitivity of estimating the change in distance is higher than the typical deformation of the spline. Therefore, processor  42  is configured to estimate the contact force applied to the spline with a typical sensitivity of about 5 grams also referred to herein as gram-force (GF), whereas a typical value of contact force applied in such procedures is between about 0 grams and 100 grams. 
     In other embodiments, after expanding distal-end assembly  40  and before placing distal-end assembly  40  in contact with the tissue in question of heart  26 , physician  30  may control processor  42  to: (i) apply the first signal using transmitter  88 , and (ii) receive the one or more second signal(s) from one or more respective receivers  99  for obtaining a reference before applying the contact force to splines  55 . In such embodiments, after placing distal-end assembly  40  in contact with the tissue intended to be ablated, and applying the contact force to splines  55 , processor  42  is configured to control transmitter  88  to reapply the first signal. Subsequently, processor  42  is configured to receive from one or more receivers  99 , additional second signals. 
     In some embodiments, processor  42  is configured to estimate the contact force applied to the respective splines  55  using the received second signals before and after applying the contact force to the respective splines  55 . 
     In some embodiments, processor  42  holds a threshold indicative of the minimal level of contact force, which is applicable for applying the ablation pulse(s) to the tissue in question of heart  26 . In some embodiments, processor  42  controls a RF pulse generator (not shown) of system  20  to apply the RF ablation signal(s) to a given ablation electrode  66 , only when the contact force estimated by processor  42  using the techniques described above, is larger than the threshold. Thus, the disclosed techniques improve the quality of RF ablation procedures by improving the accuracy of the estimated contact force applied between ablation electrodes  66  and the tissue of heart  26 , which is intended to be ablated during the RF ablation procedure described above. The disclosed techniques are also applicable, mutatis mutandis, to any other medical procedure that requires accurate and stable sensing of contact force between a medical device pressed against tissue. 
     The configuration of distal-end assembly  40  is provided in  FIG.  2    by way of example, in order to illustrate certain problems that are addressed by embodiments of the present invention and to demonstrate the application of these embodiments in enhancing the performance of such a distal end for treating arrhythmias in patient heart. Embodiments of the present invention, however, are by no means limited to this specific sort of example distal-end assembly, and the principles described herein may similarly be applied to other sorts of catheters used in any suitable sort of medical systems and procedures that require measurement or estimation of contact force applied to any suitable type of medical device pressed against any suitable tissue of a patient. 
       FIG.  3    is a flow chart that schematically illustrates a method for estimating contact force applied between distal-end assembly  40  and tissue of heart  26 , in accordance with an embodiment of the present invention. 
     The method begins at a catheter insertion step  100 , with physician  30  inserting distal-end assembly  40  of catheter  22  into a cavity of heart  26 . In some embodiments, distal-end assembly  40  comprises a basket having splines  55  and ablation electrodes  66  coupled to arms  77  of splines  55 . 
     In some embodiments, distal-end assembly  40  has transmitter  88  coupled to a rigid component of distal-end assembly  40 , in the present example, irrigator  60  or the distal end of shaft  23 . Distal-end assembly  40  further comprises one or more receivers  99  coupled to at least one of and typically all splines  55 , which are elastic components of distal-end assembly  40  and are configured to deform in response to applying contact force between the tissue and the respective spline(s)  55 , as described in  FIG.  2    above. 
     In some embodiments, transmitter  88  is controlled by processor  42  and is configured to apply a transmitted signal, also referred to herein as the first signal, as described in  FIG.  2    above. Receivers  99  are configured to produce respective second signals in response to sensing/receiving the first signal applied by transmitter  88 , as also described in  FIG.  2    above. 
     At a signal application step  102 , processor  42  controls transmitter  88  to apply the first signal, and, in response to applying the first signal, processor  42  receives one or more second signals from respective receivers  99 , as described in  FIG.  2    above. 
     At a contact force estimation step  104  that concludes the method, processor  42  estimates the contact force applied to the respective one or more splines  55 , based on the one or more second signals received from the one or more respective receivers  99  coupled to the one or more respective splines  55  of distal-end assembly  40 . 
     In some embodiments, a calibration process is carried out before estimating the contact force. In the calibration process, the applied contact force and resulting deformation of splines  55  are quantified relative to the second signal produced by one or more receivers  99  coupled to one or more splines  55 . In other words, after the calibration, processor  42  is configured to receive from a given receiver  99  that is coupled to a given spline  55 , a given second signal, and based on the given second signal, processor  42  is configured to provide physician  30  with an estimated change in the contact force applied to given spline  55  pressed against tissue of heart  26 . The calibration may be carried out in the production of distal-end assembly  40 , or at any other suitable time interval before applying the contact force to one or more splines  55  of distal-end assembly  40 . 
       FIG.  4    is a flow chart that schematically illustrates a method for producing distal-end assembly  40  depicted in  FIG.  2    above, in accordance with an embodiment of the present invention. 
     The method begins at a transmitter coupling step  200 , with coupling transmitter  88  to a rigid component of catheter  22  and/or distal-end assembly  40 . In the example of  FIG.  2    above, the rigid component comprises an irrigation apparatus, referred to herein as irrigator  60 , or the distal end of shaft  23 . In other embodiments, transmitter  88  may be coupled to any other suitable rigid component of catheter  22 . 
     In some embodiments, transmitter  88  is controlled by processor  42  and is configured to produce a first signal, as described in  FIG.  2    above. 
     At a receiver coupling step  202 , one or more receivers  99  are coupled to one or more respective elastic components (e.g., splines  55 ) of distal-end assembly  40 . In some embodiments, in response to receiving or sensing the first signal applied by transmitter  88 , receivers  99  are configured to produce a second signal indicative of the distance between transmitter  88  and the respective receiver  99 . 
     In some embodiments, any suitable number of receivers  99  may be coupled along each spline  55 , the number of coupled receivers  99  may be similar among all splines  55  or may differ between different splines  55 . In one example implementation of distal-end assembly  40 , one receiver  99  may be coupled to each spline  55 . In another example implementation of distal-end assembly  40 , multiple receivers  55  are coupled to a first spline  55 , only one receiver  99  is coupled to a second spline  55 , and a third spline  55  may not have any receiver  99 . 
     At a connecting step  204  that concludes the method, transmitter  88  and receivers  99  are electrically connected to processor  42  for estimating, based on the first and second signals, the contact force applied to each spline  55  of distal-end assembly  40 . The electrical connectors may comprise electrical leads or wires coupled between the distal and proximal ends of catheter  22 , or electrical traces of the flexible PCB, or wireless devices coupled to the distal and proximal ends of catheter  22 , as described in  FIG.  2    above. 
     In some embodiments, after the production method may comprise additional steps, such as but not limited to: (i) coupling ablation electrodes to arms  77  of splines  55 , (ii) coating one or more sections of one or more splines  55  using one or more electrically insulating layer(s), and (iii) coupling distal-end assembly  40  to catheter  22 , for example by coupling splines  55  to the distal end of shaft  23  or to any other suitable component of catheter  22 . 
     Although the embodiments described herein mainly address estimation of contact force applied between an expandable distal-end assembly of an RF ablation catheter and tissue intended to be ablated, the methods and systems described herein can also be used in other applications, such as in any application that requires accurate measurement of contact force applied between any suitable medical device and any suitable tissue of an organ of a patient. For example, in organs of an ear-nose-throat (ENT) system of a patient. 
     It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.