A medical instrument system with integrated axial force sensor

Abstract

The present invention relates to a delivery catheter system for delivering an implantable object to a target site in a patient's body. The delivery catheter system according to embodiments of the present invention comprises a catheter body, a delivery cable disposed within the catheter body, the delivery cable being configured to releasably hold the implantable object, and an integrated force sensor, integrated near a distal end of the delivery cable, the force sensor being configured for measuring an axial force between the implantable object to be delivered at the one hand, and the environment, e.g. the bodily tissue, on the other hand.

Description

[0001] A medical instrument system with integrated Axial Force Sensor

[0002] Technical field of the invention

[0003] The present invention relates to systems and methods for assisting in catheter assisted procedures, such as for example catheter assisted implant procedures, like e.g. (left) atrial appendage closure procedures.

[0004] Summary of the invention

[0005] The present invention relates to medical instrument system for performing an action at a target site in a patient’s body, the instrument system comprising a longitudinal instrument and an integrated force sensor, integrated near a distal end of the longitudinal instrument, the force sensor being configured for measuring an axial force between the longitudinal instrument on the one hand and the environment of the patient’s body on the other hand. The force sensor furthermore comprises a calibration means for filtering out the influences of the lateral forces. Near a distal end of the longitudinal instrument may be defined as within 20cm from the distal end, e.g. within 10cm from the distal end, e.g. within 5cm from the distal end. The sensor system may be configured for use in cardiovascular, neurovascular, gastrointestinal, or urological procedures requiring minimally invasive force-controlled navigation or deployment.

[0006] The system may comprise a body and the longitudinal instrument may be at least partly positioned in the body.

[0007] The calibration means may be configured for filtering out lateral forces without quantification of the lateral forces, based on a plurality of applied lateral forces applied from different directions to the force sensor. The plurality of applied lateral forces applied from different directions typically are performed during the calibration procedure.

[0008] Off-center positioning of the sensor may e.g. be present due to fabrication misalignments or can also be intended by design. As a consequence, the sensorthat is intended for measuring axial forces only will also be influenced by lateral forces as these can result into bending induced strain on the fiber cores which are not in the neutral axis of the force sensor. The off- center compensating calibration method may be used to decouple strain in a core induced by external axial forces acting on the flexure structure, from strain caused by the bending of the flexure structure.

[0009] The force sensor may be based on optical sensing elements such as Fiber Bragg Gratings. Strain detection may be based on these Bragg gratings in combination with wavelength division multiplexing or code division multiplexing. Nevertheless, optical measurementsbased on other principles, such as for example making use of Optical Frequency Domain Reflectometry (OFDR) based on Rayleigh backscattering without FBG’s, or other FBG or non-FBG measurement technologies also are envisaged in the present invention. Embodiments describing the use of Bragg gratings may hence be equally implemented using such other optical sensing elements and corresponding optical sensing techniques.

[0010] The force sensor may comprise a deformable support structure and a multi-core optical fiber, having a plurality of optical cores or a set of linked single-core optical fibers, the optical fiber(s) being fixedly positioned with respect to the deformable support structure. The optical fiber can e.g. be fixed inside the deformable support structure. The optical fiber can, in another example, be fixed before and after the deformable support structure. The force sensor may have a Fibre Bragg Grating sensor at this position.

[0011] The force sensor advantageously comprises at least three optical cores. The plurality of cores may in some embodiments correspond with a central core and at least two surrounding cores, although embodiments are not limited thereto. Alternatively, the cores may all be clearly distinct from the center of the multi-core optical fiber. In some embodiments, the multi-core optical fiber may comprise exactly three surrounding cores disposed symmetrically around a central core. In some embodiments, the surrounding cores may be positioned equidistant from each other at angular intervals of 120 degrees around the central core. Each core may comprise one optical sensing element or a plurality of optical sensing elements written in the core. In the latter case, the optical sensing elements typically are spaced from each other along the axial direction of the core. The FBGs thus may be inscribed along the length of each core.

[0012] The calibration means may be configured for compensating for off-center positioning of the optical fiber with respect to the deformable support structure. Optionally, the calibration means further could be configured for filtering out temperature effects.

[0013] The sensor may be configured for performing a calibration procedure, whereby predominantly lateral forces are applied on the sensor from different directions. It may be configured for recording wavelength shifts of two sets of gratings in the optical fiber during the application of the lateral forces. It may be configured for calculating measured strain in the cores, e.g. the central core and surrounding cores, under combined axial and lateral forces. It may be configured for formulating and / or solving an optimization problem by minimizing a cost function based on the measured strains to determine the radial offset and angular offset of the optical fiber within the flexure structure. It may be configured for compensating for the off- center positioning by using the determined offsets to calculate axial strain thereby enabling accurate measurement of axial forces applied to the sensor. The optimization problem maybe solved using a least squares method. The cost function minimized in the optimization problem may be based on the difference between measured strains and estimated strains from lateral forces applied at different directions.

[0014] The deformable support structure may be designed to transmit forces to the multi-core optical fiber, and the calibration means may be configured for deriving, based on optical signals from the optical fiber in reply to lateral forces applied from different directions, radial and / or angular offsets of the optical fiber with respect to the deformable structure.

[0015] The calibration means may be configured for inducing predominantly lateral forces from different directions, recording optical signals originating from at least 2 cores of the optical fiber(s) during the application of the lateral forces, calculating the strain in the cores from these measured optical signals under these lateral forces, and solving an optimization problem by minimizing a cost function based on the measured strains to determine the radial offset and angular offset of the optical fiber with respect to the deformable support structure. The deformable support structure may be any of a lumen like structure such as a spring, a coil, a plain tube with a given wall thickness, a tube processed to be locally weakened by a regular or irregular pattern of holes or cutouts, a sleeve or a sheet.

[0016] The force sensor may be configured to measure axial forces up to a predetermined force at least up to 5 N applied to the sensor.

[0017] The force sensor may be configured for measuring an axial force by detecting strain in at least two cores of the optical fiber.

[0018] The force sensor may comprise a set of optical sensors located in parallel in different cores at a position within the deformable support structure hence being sensitive to both mechanical strain and temperature and at least one optical sensor located in parallel in at least one of the cores at a position outside the deformable support structure and hence being sensitive to temperature, the system being configured for determining based on measurements from both sets of optical sensors a temperature compensated force value. The optical sensors may be Fibre Bragg Gratings.

[0019] The medical instrument system may be a catheter delivery system for positioning an implantable object at the target site, wherein the longitudinal instrument is a delivery cable disposed within a catheter body, the delivery cable being configured with a release mechanism to releasably hold the implantable object and the force sensor being positioned on the longitudinal instrument, near the release mechanism, opposite the implantable object. It is to be noted that the system may be a delivery catheter system hence may be configured to deliver the implantable objects directly to a specific site, target site, within the body, facilitating targeted treatment or interventions. Examples of objects that typically can bepositioned with an object delivery catheter include stents, occluders, embolic coils, valve implants, etc. As indicated above, the delivery catheter system typically may comprise a delivery cable to which the implantable object is temporarily attached, for transferring the implantable object, advancing and positioning it accurately at the target site in the body after which the implantable object is released from the delivery cable. The delivery cable can be guided through the catheter body operating as a sheath to reduce the friction forces between the implantable object and the environment when navigating to the target site in the body. The force sensor may be configured to generate a signal indicative of the axial force on the implantable object, the signal being usable by an operator to assess whether the implantable object is properly positioned prior to releasing the implantable object from the delivery cable. The delivery cable may comprise a release mechanism such as for example a threaded or twist-lock mechanism positioned between the force sensor and the implantable object, in order to release the implantable object from the delivery cable. The medical instrument system may comprise a mobile or desktop application configured to visualize the force and to provide procedural guidance or alerts, and / or the system may comprise a robotic or teleoperated actuator system configured to respond to force data to adjust operation.

[0020] In one aspect, the present invention also relates to a method for using a medical instrument system for performing an action at a target side in a patient’s body, the method comprising operating a longitudinal instrument, and

[0021] measuring an axial force between the longitudinal instrument on the one hand and the patient’s body on the other hand using an integrated force sensor,

[0022] whereby the force sensor comprises a calibration means to filter out the influences of the lateral forces.

[0023] The force sensor thereby may comprise a deformable support structure and a multicore optical fiber having a plurality of cores or a set of linked single-core optical fibers, the optical fiber(s) being fixedly positioned with respect to the deformable support structure.

[0024] Filtering out lateral forces may be performed without quantification of the lateral forces, based on a plurality of applied lateral forces applied from different directions to the force sensor. The method may comprise compensating for radial and / or angular offsets of the optical fiber with respect to the deformable support structure.

[0025] The method may comprises clamping the force sensor horizontally. The method may comprise applying predominantly lateral forces at the sensor from different directions. The method may comprise recording wavelength shifts of one or two sets of gratings in the optical fiber during the application of the lateral forces. The method may comprise calculating measured strain in the cores under lateral forces. The method may comprise formulating anoptimization problem by minimizing a cost function based on the measured strains to determine the radial offset and angular offset of the optical fiber within the flexure structure. The method may comprise compensating for the off-center positioning by using the determined offsets to calculate axial strain thereby enabling accurate measurement of axial forces applied to the sensor. The optimization problem may be solved using a least squares method.

[0026] The cost function minimized in the optimization problem may be based on the difference between measured strains and estimated strains from lateral forces applied at different directions.

[0027] The method may further comprise recording the temperature variations during the calibration process and compensating for temperature effects on the measured strains. It is an advantage of embodiments that the size of the applied forces do not need to be known for performing the calibration.

[0028] The method may further comprise verifying the calibration by applying known axial forces and comparing the measured strains to expected values.

[0029] The above described system and method may furthermore additionally comprise features respectively steps of the system and method described below, wherein axial force and / or axial force related data is used for delivery of an implantable object.

[0030] The present invention also relates to a medical instrument system for delivery an implantable object at a target site in a patient’s body, the instrument system comprising a longitudinal instrument configured with a release mechanism for releasably holding an implantable object for implanting at the target site, and an integrated force sensor, integrated near a distal end of the longitudinal instrument before the implantable object, the force sensor being configured for measuring a force between the implantable object on the one hand and the environment on the other hand. The sensor system may be configured for use in cardiovascular, neurovascular, gastrointestinal, or urological procedures requiring minimally invasive force- controlled navigation or deployment.

[0031] The system may be configured for obtaining information regarding a force-displacement relationship at the position or at the level of the force sensor and / or the implantable object. The information regarding the force as function of displacement, may be used to identify characteristic phases or events e.g. during deployment of a device in a catheter-based procedure or e.g. during interaction with tissue. A signal processing unit may be configured for generating time-resolved force-displacement information, e.g. a force-displacement profile. In some embodiments, the force and displacement data may be wirelessly transmitted to an external interface or clinical display in real time. The system furthermore may beconfigured for detecting deviations from a reference force-displacement profile, i.e. detecting deviations from an expected procedural behavior. Such deviations may be used for indicating a deviation of the standard procedure. The system may be configured for performing an algorithm or procedure for classifying the medical procedure outcome, e.g. deployment of a device, or procedural quality, using the force-displacement information, e.g. forcedisplacement profile. The system may be configured to characterize mechanical interactions between, on the one hand, a deployed medical device or a medical system used to introduce the medical device, and, on the other hand, the surrounding tissue. For example, the system may be configured to interpret force, displacement and / or force-displacement profiles to assess the correct placement of a WATCHMAN™, of an Amplatzer™ Amulet™ or a LAmbre™ or any other implant in the left atrial appendage. As another example the system may be configured to assess the success of a transseptal puncture made by a transseptal needle by interpreting force, displacement and / or force displacement profiles. The system may be configured for enabling characterization of properties of the anatomic structure including but not limited to the quality of the tissue, based on the collected displacement, force, and / or force-displacement information.

[0032] The system may be configured for detecting deviations from a reference force-displacement relationship corresponding with an expected procedural behavior, and for identifying a deviation from a standard procedure based thereon.

[0033] The system may comprise one or more electromagnetic sensors for providing position and / or orientation information regarding the force sensor and / or the implantable object.

[0034] Such one or more electromagnetic sensors can be integrated in the force sensor. Such one or more electromagnetic sensors may also be positioned nearby the force sensor or in the delivery cable. The one or more EM sensors typically may be configured for providing realtime spatial localization, hence allowing to track displacement in real time relative to an external electromagnetic field generator. Such information may be used for gathering forcedisplacement information as described above.

[0035] An imaging technique alternatively or also may be used for providing position and / or orientation information, also referred to as displacement information, regarding the force sensor and / or the implantable object.

[0036] One or more regions of the sensor or in the vicinity of the sensor may have specific features making them radio-opaque for fluoroscopy detection.

[0037] One or more regions of the sensor may be echogenic making them ultrasound detectable. One or more regions may be made of a material detectable by magnetic resonance imaging (MRI), or by Computed Tomography (CT) imaging, or by Positron Emission Tomography(PET) imaging.

[0038] The force sensor may comprise a multi-core optical fiber, having a plurality of optical cores or a set of linked single-core optical fibers.

[0039] The force sensor may comprise a deformable support structure and the optical fiber may be fixedly mounted with respect to the deformable support structure. The optical fiber can e.g. be fixed inside the deformable support structure. The optical fiber can, in another example, be fixed before and after the deformable support structure. The force sensor may have a Fibre Bragg Grating sensor at this position. The system may comprise shape-sensing capability through the optical fiber(s) for providing position and / or orientation information regarding the force sensor and / or the implantable object.

[0040] The force sensor advantageously comprises at least three optical cores. The plurality of cores may in some embodiments correspond with a central core and at least two surrounding cores, although embodiments are not limited thereto. Alternatively, the cores may all be clearly distinct from the center of the multi-core optical fiber. In some embodiments, the multi-core optical fiber may comprise exactly three surrounding cores disposed symmetrically around a central core. In some embodiments, the surrounding cores may be positioned equidistant from each other at angular intervals of 120 degrees around the central core.

[0041] Each core may comprise one optical sensing element or a plurality of optical sensing elements written in the core. In the latter case, the optical sensing elements typically are spaced from each other along the axial direction of the core. The FBGs thus may be inscribed along the length of each core.

[0042] The force sensor may thus be based on optical sensors, such as Fiber Bragg Gratings. Alternatively, the force sensor may be based on optical frequency domain reflectometry (OFDR).

[0043] The system may comprise shape-sensing means configured for deriving the displacement information regarding the force sensor and / or the implantable object from said shape sensing capability.

[0044] The force sensor may be configured to generate a signal indicative of the force, the signal being usable by an operator to assess whether the implantable object is properly positioned prior to releasing the implantable object.

[0045] The release mechanism may comprise a threaded or twist-lock mechanism and may be positioned between the force sensor and the implantable object, in order to release the implantable object from the delivery cable.

[0046] The longitudinal instrument may comprise a Nitinol tube with a central lumen.

[0047] The system may comprise a mobile or desktop application configured to visualize the force-displacement curve and to provide procedural guidance or alerts, and / or

[0048] The system may comprise a robotic or teleoperated actuator system configured to respond to force-displacement data to adjust operation.

[0049] The medical instrument system may be a catheter delivery system for positioning the implantable object, wherein the longitudinal instrument is a delivery cable disposed within the catheter body.

[0050] In one aspect, the present invention also relates to a method for using a medical instrument system, the method comprising

[0051] - operating a longitudinal instrument configured with a release mechanism for releasably holding an implantable object for implanting at the target site, and

[0052] - measuring an axial force between the implantable object on the one hand and the environment on the other hand using an integrated force sensor, integrated near a distal end of the longitudinal instrument.

[0053] The method furthermore may comprise obtaining information regarding a force-displacement relationship at the level of the force sensor and / or implantable object, for operating the longitudinal instrument.

[0054] The method may comprise adjusting the deployment force based on the measured axial forces to ensure proper engagement with the environment where the implantable object needs to be implanted, e.g. the left atrial appendage walls for the occluder.

[0055] The method may comprise checking the fixation force of the implantable object in the body after installation of the implantable object in the body and before releasing the implantable object from the delivery cable. This can be done by applying forces to the implantable object using the delivery cable until a certain force level is reached (e.g. applying force on the implantable object by pulling the delivery cable, resulting into an axial force on the force sensor)

[0056] The method may comprise checking the propre installation on the implantable object by analysing the displacement of the implantable object as function of the applied force to the implantable object using the delivery cable.

[0057] The method may comprise thereby improving precision, minimizing procedural risks, and enhancing patient safety during an object delivery procedure, such as the LAAO procedure. The above described system and method may furthermore additionally comprise features respectively steps of the system and method described above, wherein calibration is performed for filtering out the influences of the lateral forces

[0058] In the above aspects, the force sensor is configured to generate a signal indicative of the force detected. Such a signal may be usable by an operator to perform an action at a target site ina patient’s body. The latter may for example be assessing whether the implantable object is properly positioned prior to releasing the implantable object from the delivery cable, but may for example also be positioning or moving a cable or needle in a patient’s body. By putting the force sensor close to e.g. the implantable object or the end of the longitudinal instrument, forces coming from friction between the longitudinal instrument and the environment are neglected and only the interaction forces between e.g. the end of the longitudinal instrument or the implantable object and the environment are measured.

[0059] The deformable support structure may be a plain tube with a given wall thickness, the deformable support structure may be a tube that is processed to be locally weakened e.g. by a regular or irregular pattern of holes, cutouts or any other means that material can be removed from the tube. The deformable support structure may be a spring, a coil such as a torque coil, or any other flexure structure. The deformable support structure may be a sleeve, a sheath, a coating or any other structure surrounding the optical fiber.

[0060] The force sensor may be configured to measure axial forces up to a predetermined force, such as for example at least up to 5 N applied to the sensor, or at least upto 10N, by detecting strain in a given core of the optical fiber, e.g. the central core.

[0061] The system may use measurements for obtaining temperature information and hence to perform temperature compensation. Nevertheless, alternative temperature compensation or no temperature compensation may be performed, and the system may in some embodiments have only optical sensing elements located within the deformable structure.

[0062] The sensor may be selected so that a resolution of at least 25mN for force measurement is obtained. The system may be configured for resolving the displacement to sub-millimeter accuracy. It is an advantage of embodiments of the present invention that the force sensor can be compact. The force sensor may especially be useful for integration within the delivery cable. The sensor may have an outer diameter less than 1.2 mm.

[0063] The sensor may be capable of estimating triaxial forces by decoupling axial and lateral forces through calibration.

[0064] It is an advantage of embodiments of the present invention that an axial force sensor based on multi-core FBG technology is provided to enhance the precision, safety, efficiency, reliability or any of the combinations of those properties of applying a predominantly axial force on the anatomy whereby information related to lateral forces acting on the force sensor or information of the shape of the instrument in the vicinity can be used to adjust the pose of the instrument such that predominantly forces along the longitudinal direction of the instrument can be exerted on the anatomy. It is an advantage that the information of the radial forces or of the instrument shape can be used to adjust the pose of the instrument such thatthe orientation of the instrument at the location where it contacts the environment is predominantly perpendicular to the surface of the anatomy or in any other desirable angle relative to the anatomy. It is an advantage of embodiments of the present invention that this feature could be used to align for example a transseptal needle perpendicular to the interatrial septum at the level of the fossa ovalis and that the axial force information can be used to guide and ease the creation of a transseptal puncture.

[0065] The sensor may reduce reliance on subjective tactile feedback during deployment of an occluder device. The sensor may be specifically designed for use with an Amplatzer Amulet Left Atrial Appendage Occluder. In other embodiments the sensed information is employed to help pierce through a blood clot, to predict the likelihood that the instrument may buckle given a certain axial external force and a given unsupported length of the corresponding longitudinal instrument. The limit for buckling may be determined by any combination of knowledge on the material properties of the instrument and / or knowledge of the properties of the anatomy and / or knowledge or an estimation of the contact locations between the instrument and the anatomy from which then e.g. an unsupported length can be derived. The knowledge on the buckling force and the current force levels can be exploited to determine the strategy for steering the instrument to induce buckling or to rather avoid buckling of the longitudinal instrument.

[0066] The system may further comprise a user interface configured to present real-time feedback to an operator based on the measured forces and catheter shape, facilitating precise control during catheterization procedures.

[0067] Whereas above, the invention has been described with respect to the full medical instrument system, the present invention in one aspect also relates to the longitudinal instrument with integrated force sensor as such or to the corresponding integrated force sensor.

[0068] The present invention also relates to a kit for performing delivery of an implantable object, e.g. a left atrial appendage occlusion (LAAO) procedure. The kit may comprise a force sensor as described above. The kit also may comprise an implantable device, e.g. occluder device, for sealing the left atrial appendage. The kit may comprise a delivery catheter adapted to accommodate the force sensor within its lumen, the delivery catheter having an outer diameter not exceeding 1.25 mm. The kit may comprise instructions for use detailing the calibration and operation of the force sensor during the positioning procedure, e.g. LAAO procedure. The kit may further comprise a signal processing unit configured to receive and process signals from the force sensor. In some embodiments, the occluder device may be an Amplatzer Amulet Left Atrial Appendage Occluder. The kit may further comprise a display unit for providing real-time visualization of the measured axial forces and catheter shapeduring the procedure. The delivery catheter may include markings or features to facilitate alignment with the force sensor. The signal processing unit may include software for processing the detected strains, performing temperature compensation, and may provide force and shape measurements. It is an advantage of embodiments of the present invention that an axial force sensor based on multi-core FBG technology is provided to enhance the precision and safety of implantable object positioning procedures like the LAAO procedure. The off-center calibration process decouples axial and lateral forces, compensating for off- center positioning of the optical fiber within the flexure structure. Experimental validation confirmed the sensor’s ability to measure axial forces up to 5 N with a resolution of 25 mN, enhancing deployment precision and reducing reliance on subjective feedback.

[0069] Although there has been constant improvement, change and evolution of devices in this field, the present concepts are believed to represent substantial new and novel improvements, including departures from prior practices, resulting in the provision of more efficient - including more cost efficient -, stable and reliable devices of this nature.

[0070] The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.

[0071] Short description of the drawings

[0072] FIG. 1 shows a cross-sectional view of the flexure and multi-core FBG fiber. The multi-core FBG is at a radial offset df from the flexure’s center and an angular offset 0fwith respect to the reference axis.

[0073] FIG. 2 illustrates the off-center calibration setup in (a), wherein to identify the two offset parameters, the developed axial tip force sensor is clamped horizontally and lateral forces are applied in different directions. The strain measured by the central core of the first set of grating emiand the estimated axial strain e Axial during the off-center calibration process (only lateral forces applied) are plotted in blue and orange, respectively in. It also illustrates in (b) the first force sensor sample and in (c) the second force sensor sample.

[0074] FIG. 3 illustrates an experimental setup (a) used for axial force calibration and validation comprising a linear stage with a tip force sensor clamp fixed on top, a 6-DOF force sensor and a 3D printed clamp and also illustrates an example (b) of data collected during the axial force calibration process.

[0075] FIG. 4 illustrates relationships between the axial force experienced by the developed tip forcesensor (measured by 6-DOF force sensor) and the calculated strain (including axial strain and bend-induced strain) of the first sample and the second sample.

[0076] FIG. 5 illustrates axial tip force sensor validation results for the first and second sample. FIG. 6 illustrates the result of the decoupling of lateral force and axial force experiment. FIG. 7 shows a cross-sectional view of the multi-core FBG fiber, wherein the distance between the central and the surrounding core is defined as r, the angle of the bending plane and the angle of the second core with respect to the x-axis of the multi-core fiber are denoted as 0b and 02, respectively, and the unit vectors along the x- and y-axes of the fiber crosssection are denoted as i and j, respectively.

[0077] FIG. 8 illustrates a scheme (a) of the proposed optical fiber-based axial tip force sensor features a multi-core FBG fiber rigidly fixed at both ends of a flexure, with a set of FBGs positioned in the middle for force measurement, and (b) a possible integration of the developed axial tip force sensor with an Amplatzer Amulet LAA Occluder via a connection capillary.

[0078] FIG. 9 illustrates (a) the strain measured by the FBG at the central core (emi) and the calculated axial (eAxiai) during the off-center calibration process (under lateral forces application), plotted in blue and orange, respectively, (b) the experimental setup for performance validation, and (c) the axial fip force sensor validation results wherein the estimated axial force, the ground truth force measured by the 6-DOF force sensor, and the absolute error are shown.

[0079] FIG. 10 illustrates a force sensing-based classifier, wherein (a) represents the outcomes of teleoperated occlude deployment in the left atrial appendage (LAA) illustrating from top to bottom the deployment with excessive intrusion of the disk (bad in), optimal deployment with the disk adherent to the ostium (good) and deployment with excessive extrusion (bad out), wherein (b) represents the force-displacement curves collected during teleoperated deployment illustrating training data shown in semi-transparent lines and validation data shown as dashed lines, and the dataset provided to the classifier being shown as a semitransparent yellow line, and wherein (c) represents decision boundaries of the Naive Bayes classifier, with corresponding training and validation data points indicated.

[0080] FIG. 11 illustrates a boxplot and 3D plot of the path tracking errors during insertion (I) and deployment (D).

[0081] FIG. 12 illustrates force profiles and classification of autonomous occlude deployments wherein (a) shows force-displacement curves recorded during occlude extraction following autonomous deployment, mean force profiles of the training data shown in semi-transparent lines, curves from autonomous (robotic) deployments in dashed lines and the datasetprovided to the classifier in semitransparent yellow and wherein (b) shows the decision boundaries of the Naive Bayes classifier, with corresponding training and validation data points indicated.

[0082] Description of illustrative embodiments

[0083] The present invention will be described with respect to particular embodiments and with reference to certain drawings, but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

[0084] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

[0085] It is to be noticed that the term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. The term “comprising” therefore covers the situation where only the stated features are present and the situation where these features and one or more other features are present. The word “comprising” according to the invention therefore also includes as one embodiment that no further components are present. Thus, the scope of the expression “a device comprising means A and B” should not be interpreted as being limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

[0086] Similarly, it is to be noticed that the term “coupled”, also used in the claims, should not be interpreted as being restricted to direct connections only. The terms “coupled” and “connected”, along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Thus, the scope of the expression “a device A coupled to a device B” should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a pathbetween an output of A and an input of B which may be a path including other devices or means. “Coupled” may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other.

[0087] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

[0088] Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

[0089] Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art.

[0090] By way of illustration, embodiments of the present invention not being limited thereto, an exemplary system, method, controller and kit of parts is further discussed below, including advantages that result thereof.

[0091] In a first example, a particular embodiment of a calibration procedure is described, according to at least some embodiments of the present invention. In this example, principles are explained, resulting in advantages according to embodiments of the present invention. The off-center calibration process of the first example helps identifying the spatial position of the multi-core FBG fiber corresponding to the center-line of the flexure. Through the axial force calibration process, the flexure axial rigidity Ctotcdthat relates the axial strain eAxiaitothe axial force Fiongcan be calculated.

[0092] Assuming that due to the fabrication error, the multi-core FBG fiber is placed at a radial offset dffrom the flexure’s center and at an angular offset efwith respect to a reference axis (see FIG. 1). The reference axis of the flexure structure is selected to be in alignment with the reference axis of the multi-core optical fiber. Assuming that during the calibration process, the environmental temperature is constant. In this case, the measured strain in each core of the multi-core FBG fiber when both axial force and lateral force are applied can be given as follows:

[0093]

[0094] The bend-induced strain of each outer core can be calculated by subtractingemifrom em., where em., is the strain measured at core i.

[0095]

[0096] The curvature K and the angle of the bending plane 6bof the flexure caused by the lateral force can be calculated as below :

[0097] >

[0098]

[0099] 9bctTi^lc( capp'). (3)

[0100] The off-center calibration procedure starts first by clamping the developed axial tip force sensor horizontally. After that, predominantly lateral forces are applied at the tip from different directions, as shown in FIG. 2 part (a). The wavelength shifts of the two sets of gratings are measured by the interrogator (FBG-scan 915-EP) at 100 Hz during the off-center calibration procedure. To find the two parameters dfand 0f, an optimization problem is formulated by minimizing the following cost function

[0101] &

[0102]

[0103] where the subscript t indicates the data recorded at time step tthduring the calibration procedure. The total number of recorded sample is denoted as q. The curvature K and the angle of bending plane 9bcan be calculated as shown in Equations (2) and

[0104] (3). Once the two parameters dfand 9fare identified, the axial strain eAxialcan be calculated as

[0105]

[0106] The strain measured by the central core of the first set of grating emiand the estimated axial strain eAxiai(Using Equation (5)) during the off-center calibration process of the first and second force sensor sample are shown in FIG. 2 part (b) and FIG. 2 part (c), respectively . It is apparent that when the multi-core FBG fiber is positioned off-center, the application of lateral force alone can induce strain in the central core of the multi-core fiber. Therefore, the spatial position of the multi-core FBG fiber should be taken into account when estimating the axial strain eAxial.

[0107] In the case of the first sample, the calculated axial strain fluctuates when lateral force is applied. During the off-center calibration process for the first sample, the mean calculated axial strain is 13.8 microstrain with a standard deviation of 8.3 microstrain. This clearly indicates that the multi-core optical fiber is not aligned parallel to the center-line of the flexure structure. This can be further demonstrated during the axial force calibration process. In contrast, the mean and the standard deviation of calculated axial strain during the off-center calibration process of the second sample is 4.6 microstrain and 3.6 microstrain, respectively, Figure 2c. However, given that lateral forces are applied manually, there is a potential for the applied force to not perfectly perpendicular with the tip force sensor, resulting in a minor axial force component and consequently inducing a slight axial strain. The low value of calculated axial strain for the second sample during this calibration process indicates that the multi-core fiber in the second sample is positioned more parallel to the center-line of the flexure.

[0108] The axial force calibration procedure targets at identifying the axial rigidity Ctotalthat helps relate the calculated axial eAxiaito the axiall force Faxica. An experimental setup has been built as shown in FIG. 3 part (a). The built experimental setup includes a linear stage with a sensor clamp fixed on top, a 6-degree-of-freedom (DOF) force sensor (ATI Nano17 force / torque sensor, ATI Industrial Automation, United States) and a 3D-printed clamp. The 6-DOF force sensor has a resolution of 1 / 160 N. The 3D printed clamp is attached to the surface of the 6-DOF force sensor and is able to firmly hold the tip of the developed axial tip force sensor. This allows the 6-DOF force sensor to measure both the compressive force and tensile force.

[0109] During the axial force calibration process, the linear stage is controlled manually allowing the developed tip force sensor move back and forth to apply both compressive and tensile force on the 6-DOF force sensor. Both the force measured by the 6-DOF force sensor and wavelength shifts of the first and the second set of grating are recorded. The FBG interrogator and the 6-DOF force sensor operates at 100Hz. The sensor data are recorded and synchronized using ROS. An example of data collected during the axial force calibrationprocess is shown in FIG. 3 part (b) including measured force in x, y and z directions by the 6-DOF force sensor and the calculated axial strain eAxiai. Given that the axial tip force sensor exerts a force perpendicular to the surface of the 6-DOF force sensor, the axial force experienced by the axial tip force sensor corresponds to the force acting along the z-axis of the 6-DOF force sensor. It can be seen in FIG. 3 part (b) that the force along the x- and y-axis of the 6-DOF force sensor is approximately 0. The 6-DOF force sensor measures forces along the z-axis within the range of -5 N to +5 N. A negative value on the z-axis indicates a compressive force, whereas a positive value indicates a tensile force.

[0110] FIG. 4 shows the axial strain eAxiaiand the bend-induced strain eBend. of the outer core (calculated by Equation (2)) versus the force along the z-axis of the 6-DOF force sensor of both developed samples. In FIG. 4, a clear correlation between the axial force encountered by the developed tip force sensors and the calculated axial strain eAxicdcan be seen. It's worth highlighting that the axial force applied to the second sample does not impact the bend-induced strain of the outer cores. This observation strongly indicates that in sample 2, the multi-core fiber is indeed aligned parallel to the center-line of the flexure. In contrast, when axial force is applied to the first sample, a certain level of bend-induced strain is detected in the surrounding cores. This occurrence arises from the fact that the fiber is not aligned parallel to the center-line of the flexure. When the first tip force sensor experiences compressive force, it results in the bending of the segment of fiber between the two fixation points.

[0111] Assuming that, n samples of eAxicdand Fzduring the calibration process, the axial rigidityctotaicanbe calculated as

[0112] < (®)

[0113]

[0114] FZn] and eAxiai= [^xia^ ■■■eAxiain] . The sign (. )+denotes the Moore-Penrose inverse operator.

[0115] To validate the performance of the developed axial tip force sensors (the axial force estimation), a separate dataset is measured with the experimental setup as described. The data is measured at a sampling rate of 100 Hz and synchronized by ROS. Three different experiments have been done for each sample. Different patterns of compressive and tensile force are applied on the developed tip force sensor. The axial force estimated by the calibrated tip force sensors is compared to the ground truth force recorded by the 6-DOF force sensor (see FIG. 5). A summary of the corresponding absolute force errors between the ground truth and the calibrated forces for each experiment is provided in Table 1.Table 1 : Validation results of the second sample. The percentages are with respect to the testing range.

[0116]

[0117] The validation results show that the first sample can sense the axial force with an average mean absolute error of 0.18 N (corresponds to 2.56% of the full measuring range) while the second sample shows an average mean absoluter error of 0.16 N (corresponds to 1.50% of the full measuring range). The absolute error increases when there is abrupt change in the measured force as can be seen in the third experiment of the second sample (for example, at t = 140 s and 170 s). This phenomenon can be attributed to potential synchronization issues between the wavelength data and the data from the 6-DOF force sensor. The resulting linearity of the response, given as the R2value between the calculated axial strain and the experienced axial force, of both samples are found to be approximately 0.99. The sensor’s repeatability, given as the standard deviation of the difference between the ground truth and estimated forces of both sample is approximately 0.14 N. These results clearly indicate the high linearity and repeatable behavior of both samples.

[0118] An extra experiment has been done to validate the decoupling between the estimated axial force and the applied lateral force. In this experiment, only a lateral force is applied to the developed sensors. The wavelength shifts of the FBGs are recorded and used to estimate the axial force. The experimental results are shown in FIG. 6. In this experiment, the second sample exhibited a mean absolute error of 0.078 N, accompanied by a standard deviation of0.052 N in estimating the axial force. Meanwhile, the first sample displayed a slightly higher mean absolute error compared to the second sample, with a value of 0.112 N and a standard deviation of 0.086 N. This discrepancy is attributed to the misalignment of the multi-core fiber in the first sample, impacting the sensor's capacity to differentiate between lateral and axial forces. The remarkably low mean absolute error observed in the second sample underscores the capability of the developed tip force sensor to effectively distinguish axial forces from lateral forces.

[0119] The calculated values for experimental and theoretical axial rigidity, resolution, and mean absolute error of the two developed FBGs-based tip force sensors are summarized in Table 2. The experimental axial rigidity and force resolution exhibit comparable orders of magnitude when compared to the theoretical calculations. Variations between the theoretical and empirical values may arise due to disparities in the separation distance between the two fixation points. Given that adhesive is introduced through the two fixation holes, precise determination of the distance between these points is challenging. Furthermore, during the fabrication process, the multi-core fiber is inserted into a PTFE tube to increase its 450, reducing the likelihood of fiber misalignment during integration into the flexure structure. However, the additional axial rigidity contributed by this extra PTFE tube is not factored into the calculation of the theoretical axial rigidity.

[0120] Table 2: Validated sensor performance.

[0121] &<

[0122]

[0123] The validation process conducted has underscored the significance of aligning the multi-core fiber correctly during the fabrication of the force sensor. Both of the developed sensors can effectively measure tensile forces of up to +5 N, meeting the required technical specifications. However, there is difference in their ability to measure compressive forces. The first sample can accurately measure compressive forces within the range of 0 to -2.5 N, whereas thesecond sample offers a broader range from 0 to -5 N for compressive force measurement. This discrepancy is primarily due to difference in the pre-strain applied to the multi-core fiber. In the first sample, the multi-core fiber is subjected to less pre-strain, causing the multi-core fiber to experience buckling when a compressive force of approximately -2.5 N is applied. This issue can be addressed by increasing the pre-strain during the integration of the multicore fiber to the flexure structure. The experimental results presented underscore the critical importance of precise alignment of the multi-core fiber, specifically ensuring it is parallel to the center-line of the flexure. Misalignment directly impacts the sensor's ability to differentiate between axial and lateral forces in the FBG-based tip force sensor.

[0124] The axial force resolution of the FBG-based tip force sensor is primarily determined by the axial rigidity of the flexure structure. While both sensors meet the necessary technical requirements, the first sample of the tip force sensor provides a resolution roughly four times higher than the second sample (niOnflftex= 0.0056 N compared to

[0125]

[0126] 0.0248 N). While higher resolution is advantageous, it's essential to note that the perforated flexure structure of the first sample is more susceptible to failure when subjected to lateral forces compared to a solid Nitinol tube flexure structure (second sample). The presence of perforations in the flexure structure weakens its overall structural integrity by creating stress concentration points, making it more susceptible to deformation or fracturing under lateral forces. In contrast, a regular Nitinol tube flexure typically boasts a continuous, uninterrupted structure with a larger cross-sectional area compared to a perforated structure, providing superior resistance against lateral forces. Hence, when deciding between a perforated flexure structure and a solid Nitinol tube for the tip force sensor, it is essential to conduct a thorough assessment of the potential bending and forces that the sensor may encounter during the procedure. This evaluation helps strike a balance between the FBG-based tip force sensor's resolution and its ability to withstand external forces.

[0127] In a second example, optional features and characteristics of embodiments of the present invention are further illustrated.

[0128] The left atrial appendage occlusion (LAAO) procedure is a minimally invasive method to reduce stroke risk in atrial fibrillation (AF) patients who cannot tolerate long-term anticoagulation. By sealing off the left atrial appendage (LAA) — a common site for blood clot formation — this procedure effectively lowers the risk of stroke. However, LAAO is complex, requiring specialized expertise and precise occluder device deployment to ensure a secure seal. A critical challenge in LAAO is assessing the deployment force of the occluder device. This step ensures proper engagement with the LAA walls, as insufficient force can lead toincomplete sealing and residual leakage. Currently, this process relies on the physician’s tactile feedback, making it subjective. Integrating a catheter tip force sensor could improve precision, reduce errors, and enhance patient safety.

[0129] Several catheter tip force sensors have been developed for cardiac applications. A triaxial catheter tip force sensor using reflective light-intensity modulation exists, with a working range of approximately 0.5 N. Similarly, Fiber Bragg Grating (FBG)-based triaxial catheter tip force sensors have been proposed, demonstrating promising results in resolution and accuracy. However, the larger outer diameters of these sensors (ranging from 2 to 4 mm) make them unsuitable for the LAAO procedure, where size constraints are critical. For example, the Amplatzer Amulet Left Atrial Appendage Occluder (Abbott Laboratories) features a delivery catheter with an outer diameter of just 1.25 mm. To meet these stringent size requirements, a tip force sensor for LAAO must not exceed 1.25 mm in diameter and should support an axial force measurement range of up to 5 N.

[0130] In this example, an axial catheter tip force sensor is presented specifically designed for the LAAO procedure, but also usable in other applications. The sensor leverages optical fiber sensing technology, utilizing multi-core Fiber Bragg Gratings (FBGs) to achieve a compact design with an outer diameter of 1.25 mm. This optical fiber-based sensor eliminates the need for additional components, simplifying the design while offering simultaneous shape sensing capabilities. Although the sensor can measure both axial forces and the 3D shape of the catheter, the focus of this example is on its axial force-sensing functionality. The example will now further be described by introducing the working principle and calibration of the multi-core FBG-based force sensor, the details the sensor design, calibration results, and a performance evaluation. Finally, conclusions for this example are made.

[0131] The developed fiber optic-based axial tip force sensor is based on the strain sensing capability of a multi-core FBG fiber. A multi-core FBG fiber typically contains a central core and multiple surrounding cores (at least two) circumferentially distributed at a given radial distance from the center. Each core features several FBGs inscribed along its length. Thus, strain can be measured at discrete locations along the multi-core FBG fiber. The FBGs distributed along the surrounding cores are normally sensitive to the bend-induced strain EBend, axial force-induced strain eAxiai, and temperature variations while the ones in the central core are only sensitive to the axial strain and temperature variations. In this example, a multicore FBG fiber features one central core and three surrounding cores is used. The cross-sectional view of the used multi-core fiber is described in FIG. 7.

[0132] The relations between the wavelength shifts AAJ, the environment temperature variation AT, the measured strain emi, the bend-induced strain eBendi and the axial-induced strain eAxiai ofthe FBG in the central core and the surrounding core is given by equation (7). The Bragg wavelengths of the cores measured in the unstrained state are denoted as ABOI while the current measured wavelengths are denoted as ABI where ie{1 ,2,3,4}. The constant Seand ST are the strain and temperature coefficients, respectively.

[0133] "" " <

[0134]

[0135] The FBGs-based axial tip force sensor configuration typically includes a multi-core FBG fiber integrated into a force-transmitting flexure, as illustrated in FIG. 8 part (a). The fiber is centrally positioned with two-point fixation and includes two sets of gratings: one within the flexure exposed to mechanical strain (axial and bend-induced) and temperature fluctuations, and the other beyond the flexure, exposed only to temperature variations. Measuring the wavelength shift of the second set allows temperature compensation, isolating mechanical strain for accurate axial force measurements.

[0136] Once the temperature has been compensated, the axial strain can be calculated thanks to the central core of the first set of grating. The axial strain measured by the central core of the first set of gratings has a linear relationship with the longitudinal force applying on the flexure. The relation between the applied longitudinal force Fiongand the axial strain is given as below: "

[0137]

[0138] The axial rigidity of the flexure structure, Ctotaz, is calculated as the sum of the axial rigidity of the flexure structure, denoted as Cfiexure, and the axial rigidity of the multi-core FBG fiber, referred to as Cfiber, due to their parallel alignment along the center-line of the flexure structure. Ideally, the multi-core fiber is in the neutral axis of the flexure making the FBG at the central core only sensitive to the longitudinal force applied on the flexure. However, in practice due to fabrication errors, it is difficult to position the multi-core fiber in the central axis of the flexure segment. In case the multi-core optical fiber is position off-center, the central core of the fiber is not only sensitive to longitudinal force but also lateral force. To address this, an off-center calibration procedure needs to be done to compensate for the off-center distance of the multi-core fiber. Due to fabrication errors, the multi-core FBG fiber is placed at a radial offset df from the flexure’s center and at an angular offset 0f with respect to a reference axis. The reference axis of the flexure structure is selected to be in alignment with the reference axis of the multi-core optical fiber. Assuming constant environmental temperature during the calibration process, the measured strain in each core of the multicore FBG fiber under combined longitudinal and lateral forces can be expressed as follows: + Kdf COS(0b- 7T - 0f),

[0139] Kdf COs(0b— TT — 0f) + ^Bendf '

[0140]

[0141] (9) The bend-induced strain of each outer core eBendi can be calculated by subtracting emifrom emi. The curvature K and angle of the bending plane 0b of the flexure caused by the lateral force can be calculated from EBendi- The off-center calibration procedure starts first by clamping the developed axial tip force sensor horizontally. After that, predominantly lateral forces are applied at the tip from different directions. The wavelength shifts of the two sets of gratings are recorded during the off-center calibration procedure. To find the two parameters df and 0f, an optimization problem is formulated by minimizing the following cost function

[0142]

[0143] where the subscript t indicates the data recorded at time step tthduring the calibration procedure and q is the total number of recorded samples. Once the two parameters df and 0f are identified, the axial strain eAxiai can be calculated as

[0144]

[0145] To enable axial tip force sensing, a flexural section with high elastic yield strength and low modulus is required to exhibit spring-like behavior. This structure transforms externally applied forces into detectable strain, measured by the integrated multi-core FBG fiber. The flexure's mechanical properties, dimensions, and shape significantly affect the sensor's sensitivity, precision, and directional response. While helical and perforated flexures are common, neither is ideal for LAAO. Helical flexures lack sufficient torsional stiffness, necessary for disengaging the delivery catheter, while perforated flexures are prone to stress fractures under lateral forces, risking sensor damage during navigation.

[0146] To address these issues, in the present example, a Nitinol tube with an outer diameter of 1.25 mm and an inner diameter of 1.05 mm is used as the flexure. Since body temperature remains relatively stable during occluder deployment, the FBG set for temperature compensation is unnecessary, allowing the last grating set on the multi-core FBG fiber to be used for axial force measurement, simplifying the fabrication process. A multi-core FBG fiber with 37 grating sets (FBGS International NV, Belgium) is glued to the inner surface, with the distal grating set measuring axial force and the proximal sets reserved for 3D shape sensing. To prevent the multi-core FBG fiber from buckling during operation, pre-straining should be applied while fixing the fiber to the flexure. The axial tip force sensor is designed to integrate seamlessly with the Amplatzer Amulet LAA Occluder via a connection capillary, as shown inFIG. 8 part (b).

[0147] The off-center calibration as explained has been done with the developed sensor. The strain measured by the central core emiand the calculated eAxiai during the off-center calibration process are shown in FIG. 9 part (a). It was observed that when the multi-core FBG fiber is positioned off-center, lateral forces alone can induce strain in the central core. By employing a multi-core fiber and the off-center calibration steps, the strain caused by axial and lateral forces can be effectively decoupled. Ideally, the calculated axial strain eAxiai should remain zero during the calibration. However, fluctuations of eAxiai (mean value of 4.6 microstrain and standard deviation of 3.6 microstrain) were observed. These variations can be attributed to minor misalignments during the manual application of lateral forces, introducing a longitudinal force component and consequently inducing slight axial strain.

[0148] To validate the sensor’s performance, an experimental setup (FIG. 9 part (b)) was built, consisting of a linear stage, a 6-DOF force sensor (ATI Nano17, ATI Industrial Automation, United States, resolution: 1 / 160 N), and a 3D-printed clamp to securely hold the sensor tip. This allows the 6-DOF force sensor to measure both the compressive force and tensile force. The data is measured at 100 Hz by an interrogator FBG-scan 915-EP (FBGS International NV, Geel, Belgium) and synchronized by ROS. The sensor was tested under different compressive and tensile force patterns and compared to ground truth data from the 6-DOF sensor. Experimental results (FIG. 9 part (c)) show the sensor accurately measures force up to 5 N, with a mean absolute error of 0.16 N (1.50% of the full range) and a standard deviation of 0.14 N. The axial rigidity Ctotai of the developed sensor is 28521 N. Given that the resolution of the measured strain (Qstram) of FBG-scan 915-EP interrogator is 0.87 microstrain. Thus, the designed sensor can exhibit an axial force sensing resolution of QFiong=Ctotai.Qstrain=25 mN. The present example shows a novel axial tip force sensor based on multi-core FBG technology to enhance the precision and safety of the LAAO procedure. Designed to meet the stringent size requirements of the Amplatzer Amulet LAA Occluder (outer diameter of 1.25 mm), the Nitinol-based flexure and multi-core FBG fiber enable precise axial force measurement with 3D shape sensing capabilities. The off-center calibration process decouples axial and lateral forces, compensating for fabrication misalignments. Experimental validation confirmed the sensor’s ability to measure forces up to 5 N with a resolution of 25 mN, enhancing deployment precision and reducing reliance on subjective feedback. Notably, the integrated multi-core fiber is capable of measuring bend-induced strain, which directly correlates with lateral forces acting on the force sensor. This capability highlights the potential for accurate lateral force measurement, providing critical feedback during procedures where the catheter navigates through vessels.Further by way of illustration, embodiments not being limited thereto, a further study of the use of an exemplary embodiment of the present invention is discussed, illustrating optional features and advantages of embodiments of the present invention. The context of the example given here is also the Left Atrial Appendage Closure procedure, although embodiments are not limited by the specific medical procedure.

[0149] The left atrial appendage closure (LAAC) procedure is an interventional therapy designed to reduce the risk of thromboembolic events in patients with atrial fibrillation (AF) who are unable to tolerate long-term oral anticoagulation. AF is a common cardiac arrhythmia associated with an increased risk of stroke due to the formation of blood clots in the left atrial appendage (LAA). The procedure is typically performed under general anesthesia or conscious sedation and begins with femoral venous access. A catheter is advanced through the venous system to the right atrium, followed by a transseptal puncture to access the left atrium. Using fluoroscopic and echocardiographic guidance, an occluder is carefully positioned and deployed within the LAA, ensuring a secure seal. Once the correct placement is confirmed, the occluder is released, effectively occluding the appendage. Post-procedural imaging is performed to assess for potential complications such as pericardial effusion, occluder embolization, or leaks. Robot-assisted systems for endovascular catheterization have been extensively explored, particularly in teleoperated configurations that incorporate haptic feedback to enhance operator control and safety. For example, known systems use magnetorheological fluids for haptic feedback, enabling remote catheter manipulation while providing tactile cues related to vessel contact. Similarly, a compact master-slave robotic system with strain-based force sensing was developed and demonstrated significant reductions in contact force during catheterization in a vascular phantom. While these systems highlight the maturity of teleoperated catheter technologies, comparatively fewer works have addressed autonomous navigation in the context of intracardiac procedures. As interest grows in augmenting such procedures with sensing and automation, new technologies are being explored to support navigation and device delivery in dynamic, blood-filled environments. One such approach was demonstrated whereby an autonomous robotic catheter system equipped with a novel haptic vision sensor that combines visual and contactbased sensing was developed. The method enabled biologically inspired wall-following behavior and showed safe, accurate catheter navigation inside the beating heart. In vivo experiments demonstrated success rates comparable to those of experienced clinicians, suggesting the potential of such systems to contribute to intracardiac interventions.

[0150] Assessment of Left Atrial Appendage Closure (LAAC) occluder deployment commonly involves evaluating the occluder’s engagement with the LAA wall to confirm appropriatesealing. Techniques such as tactile feedback, contrast injection, and Doppler ultrasound are typically used during the procedure for this purpose. One potential approach to support deployment assessment is the integration of a tip-mounted force sensor on the delivery system, providing quantitative feedback on contact forces during implantation. Several force sensors have been proposed for cardiac applications. These include triaxial sensors based on reflective light-intensity modulation, and fiber Bragg grating (FBG)-based designs. While these sensors offer high resolution and accuracy, their diameters - typically between 2 and 4 mm - exceed the size constraints of LAAC delivery system. For example, the Amplatzer Amulet occluder employs a delivery catheter with an outer diameter of approximately 1.25 mm. Sensors intended for integration into such systems must meet comparable dimensional constraints while enabling axial force measurements in the range of up to 5 N. These requirements motivate the development of miniaturized force sensors tailored for LAAC applications.

[0151] In this example, an autonomous robotic approach for LAA occluder implantation, combined with a force sensor designed to support quantitative assessment of occluder deployment is illustrated. Specifically, a novel steerable and sensorized guiding catheter, and robotic system for the LAAC procedure are described, as well as automatic robotic deployment of a LAA occlude and FBG-based force measurement for assessment of LAA occluder implantation. In the following, first the automated deployment force assessment of the implant deployment is described, then experimental setup and results are discussed, followed by findings and conclusions of the example.

[0152] For force sensing for deployment assessment, first an evaluation strategy is developed to intra-operatively assess the outcome of the autonomous implantation without relying on ionizing radiation. To this end, the delivery sheath is equipped with a distal FBG-based force sensor. Following deployment, a pull-back motion is performed using the sheath leveraging the RACS-only motion, and the resulting resistance from the occluder is measured as a force response. Simultaneously, the EM sensor at the catheter tip tracks the displacement during the pull, enabling the acquisition of force-displacement curves that characterize the occluder’s anchoring performance. A Naive Bayes classifier is then employed to evaluate the anchoring performance based on these curves. The force sensing and classification strategies are described hereby.

[0153] The use of an FBG-based force sensing sheath is now discussed. To enable quantitative assessment of occluder deployment, a miniaturised axial force sensor based on multi-core Fiber Bragg Grating (FBG) technology was integrated into the distal end of the delivery sheath. The sensor features a Nitinol flexure housing a multi-core optical fiber with one1

[0154] central and three peripheral cores. The central core primarily senses axial strain, while the surrounding cores detect bending-induced strain. Although FBG sensors are sensitive to temperature, no dedicated thermal compensation was used, as the temperature inside the body remains sufficiently stable during deployment. This simplification reduces sensor complexity and allows all distal gratings to be used for force measurement.

[0155] The fiber is fixed at both ends of the flexure using epoxy, and axial strain is measured through the distal grating sets. To account for minor fabrication misalignments, an off-centre calibration method was applied, enabling the decoupling of axial and lateral forces. Experimental validation with a 6-DOF force sensor confirmed a measurement range up to 5 N, with a resolution of 25 mN and a mean error of 0.16 N. With a compact 1.25 mm diameter, the sensor integrates seamlessly into the Amplatzer Amulet catheter and offers reliable realtime feedback for improving deployment precision and anchoring safety.

[0156] The deployment assessment is now discussed.

[0157] The assessment of occluder deployment outcomes in the LAA relies on the hypothesis that proper and improper seating of the occluder produces distinct pulling force profiles, as perceived by the clinician through the delivery sheath. By combining data from the distal force sensor with the absolute position of the catheter tip from the EM sensor, forcedisplacement curves are generated during occluder retraction following occluder deployment. These curves are used to train a Naive Bayes classifier to distinguish among three possible conditions: successful implantation (labeled as class 0, good), excessive protrusion of the occluder outside the LAA leading to inadequate wall engagement (class 1, bad out), and excessive insertion resulting in poor adherence of the occluder disk to the ostium (class 2, bad in). The Naive Bayes classifier is selected for its simplicity and robustness to small training datasets. The classifier is trained on pulling force measurements sampled every 0.1 mm from 1 mm to 10 mm, yielding T = 100 features for each of the N curves (i.e, per occluder deployment). This results in a matrix of features X e RWxrused to train the classifier. A small upper displacement limit (10 mm) is selected to ensure that the occluder remains engaged regardless of the deployment quality, thus avoiding unwanted dislodgement. This enables the classifier to deliver intraoperative feedback, allowing the clinician to make an informed decision on whether to detach or reposition the occluder. The classification process can be formalized as follows. In training, each sample is assigned a label y e {0,1,2}, corresponding to its class k e {0,1,2}. The class label is assigned based on expert clinical evaluation after visual assessment of the deployment. The prior probability of each class is given by

[0158]

[0159] where Nk is the number of curves assigned to class k, and N is the total number of training curves. For each feature j e {1,..., 7} across all curves / e {1,..., / V}, the feature valuesx^ are assumed to be normally distributed. The parameters of the Gaussian distribution for class k and feature j, mean,fc-’

[0160]

[0161] and variance,

[0162]

[0163] =' i:yi=k(xij - Wy)2, are estimated.

[0164] Given a new curve, its feature vector x e Rris extracted, and the predicted class label y is obtained by selecting the class with the maximum posterior probability:

[0165] y = arg max [logP( logN(xj / C G {0,1,2}

[0166]

[0167]

[0168] where N(xy| / Jkj^k ) denotes the probability density of a Gaussian distribution with mean / jkj and variance okj2, evaluated at the feature xj. The classifier was trained on 18 occluder extraction profiles obtained following teleoperative deployments and successfully validated on 6 additional profiles acquired using the same procedure. FIG. 10 illustrates representative deployments from the three classes (bad out, good, bad in), along with the training and validation profiles and the classifier’s decision boundaries. The confusion matrix, shown in Table 3, reports an accuracy of 83.3%, with only one misclassified curve — belonging to the bad in class — which was incorrectly labeled as bad out.

[0169] Table 3 : CONFUSION MATRIX ON VALIDATION SET

[0170]

[0171] To validate the automatic deployment and force-based assessment of the LAA occluder implantation quality, experiments were conducted on a simulator phantom designed for LAAC procedures (Simulands, Zurich, Switzerland). This phantom replicates the anatomical structures involved in the LAAC procedure, such as the vena cava, the interatrial septum and the LAA. The phantom was positioned on top of an EM field generator (Northern Digital AURORA Tabletop FG). A registration between the EM data and preoperative plan was gathered before the start of the experiments through registration pillars, which were placed at a known location in relation to the phantom. The starting point was after crossing septum. Catheter was automatically navigated to the deployment position following the preoperatively planned path. Upon reaching the deployment position, the automatic deployment procedure was initiated. During deployment, the catheter was automatically controlled to maintain the centerline with the bending degrees of freedom, while the insertion was controlled by the deployment process. The experiment was repeated 5 times. After each deployment, theimplant was pulled while gathering the force data from the FBG-based implant force sensor and the displacement data of the tip EM sensor for implantation quality assessment.

[0172] The controller was validated by considering the Euclidean distance between the appendage centerline and catheter tip both during insertion of the catheter into the appendage and the deployment of the implant. The paths and error distributions for all 5 runs are shown in FIG.

[0173] 11. Over all 5 runs, position errors of 0.84 ± 0.59 mm and 1.32 ± 1.06 mm were obtained during insertion and deployment respectively. All 5 runs resulted in a successful implant deployment. Success was assessed visually based on the following clinically relevant criteria [8]: i) the lobe was fully deployed within the appendage, ii) the disk sealed the appendage ostium, without folding into the appendage or leaving a gap, and Hi) the waist remained aligned along the appendage centerline, with no visible buckling or distortion.

[0174] After each deployment, the implantation was assessed by extracting the occluder using the robotic system in RAGS motion mode and by feeding the force and catheter tip displacement measurements into the classifier described. At a displacement of 10 mm, the classifier evaluated all five implantations, categorizing each as a successful implantation (i.e., within the good class), thereby confirming the results of the visual assessment. The complete occluder extraction profiles, along with the positioning of each implantation within the classifier’s decision boundaries, are presented in FIG. 12.

[0175] In the present example, an autonomous robotic approach for LAA occluder implantation and deployment assessment is presented. The system leverages a sensorized, steerable catheter actuated by a robotic platform to autonomously navigate from the interatrial septum to the appendage, where it performs occluder deployment and assesses the quality of its positioning with FBG-based force sensing feedback. The robotic system controls both the catheter and the occluder leveraging three motion modalities and enabling an optimized deployment strategy.

[0176] The controller was evaluated on the LAA centerline tracking. Across five runs, average errors of 0.84 ± 0.59 mm during insertion and 1.32 ± 1.06 mm during deployment were observed. The increased error during deployment is likely due to mechanical interaction with the appendage introduced by the occluder as it is released. The deployment path is generated from preoperative imaging. In a clinical context, this approach depends on accurate registration between imaging and the EMtracked catheter. Additionally, physiological motion would affect positioning. These issues could be addressed using intraoperative imaging such as EM-tracked 3D TEE, which could improve registration or replace preoperative planning altogether. Automatic occluder deployments performed by the robotic system were evaluated using a Naive Bayes classifier. Ground-truth labels for the training data were establishedthrough visual assessment by a clinical expert. The classifier was trained on 100 force values extracted from each of 18 force-displacement curves. These profiles were obtained during occluder extraction following teleoperated deployment. Subsequently, the classifier was validated on 6 curves obtained in the same manner. A classification accuracy of 83.3% was achieved. This was considered adequate, as no false positives (i.e., unsuccessful deployments classified as successful) were observed. When tested on the autonomously executed deployments, all cases were classified as successful, which was in accordance with the assessment of the clinical expert, thus validating the autonomous deployment strategies, as well as the force-based deployment assessment. The Amplatzer occluder, originally designed for single-use clinical applications, was subjected to repeated mechanical stress during experimental trials. Signs of mechanical wear were observed after multiple deployments, potentially influencing the mechanical response during extraction and thus affecting the force measurements. To mitigate this, the study was limited to a total of 29 occluder deployment-extraction cycles. This constraint, however, resulted in a limited dataset size for classifier training and validation. Despite this, distinct force-displacement profiles were identifiable across different deployment outcomes. In particular, a generally increasing slope within the first 10 mm of extraction was observed for bad out, good, and bad in curves. Anomalous profiles in the bad in validation set, as for profile valid. #1 shown in FIG. 10, are attributed to mechanical degradation of the occluder. This aspect is also expected to be the reason underlying the misclassification of the same force profile. Nonetheless, the results demonstrate that a simple probabilistic model can be employed for classification of LAA occluder deployment outcomes with satisfactory results. A limitation of the present study lies in the use of a static silicone phantom model, which simplifies the anatomical complexity of the LAA. In vivo conditions are characterized by significant inter-patient variability in LAA geometry, resulting in corresponding variability in the mechanical response during occluder extraction. Future work will investigate the feasibility of simulating the interaction forces between the seated occluder and the LAA using preoperative imaging data within a virtual environment. This approach would aim at defining reliable force profile thresholds to enhance intraoperative force-based deployment assessment.

[0177] In conclusion, the robotic system of the example offers a novel solution for automating LAA occluder deployment, integrating preoperative planning, real-time control, and force-based assessment. While the current results in a phantom environment are encouraging, future work will focus on incorporating intraoperative 3D TEE imaging, addressing physiological variability, and validating performance in more realistic anatomical scenarios.

Claims

1. Claims1. A medical instrument system for performing an action at a target site in a patient’s body, the instrument system comprising- a longitudinal instrument, and- an integrated force sensor, integrated near a distal end of the longitudinal instrument, the force sensor being configured for measuring an axial force between the longitudinal instrument on the one hand and the environment of the patient’s body on the other hand,wherein the force sensor furthermore comprises a calibration means for filtering out the influences of lateral forces.

2. The medical instrument system according to claim 1, wherein the calibration means is configured for filtering out lateral forces without quantification of the lateral forces, based on a plurality of applied lateral forces applied from different directions to the force sensor.

3. The medical instrument system according to any of the previous claims, wherein the force sensor comprises a deformable support structure and a multi-core optical fiber having a plurality of optical cores, or a set of linked single-core optical fibers, the optical fiber(s) being fixedly positioned with respect to the deformable support structure.

4. The medical instrument system according claim 3, wherein the calibration means is configured for compensating for off-center positioning of the optical fiber with respect to the deformable support structure.

5. The medical instrument system according to any of the previous claims in as far as dependent on claim 3, whereinthe deformable support structure is designed to transmit forces to the multi-core optical fiber, andwherein the calibration means is configured for deriving, based on optical signals from the optical fiber in reply to lateral forces applied from different directions, radial and / or angular offsets of the optical fiber with respect to the deformable support structure.

6. The medical instrument system according to claim 5, wherein the calibration means is configured forinducing predominantly lateral forces from different directionsrecording optical signals originating from at least 2 cores of the optical fiber(s) during the application of the lateral forces,calculating the strain in the cores from these measured optical signals under these lateral forces,solving an optimization problem by minimizing a cost function based on the measured strains to determine the radial offset and angular offset of the optical fiber with respect to the deformable support structure7. The medical instrument system according to any of the previous claims in as far as dependent on claim 3, wherein the deformable support structure is any of a lumen like structure such as a spring, a coil, a plain tube with a given wall thickness, a tube processed to be locally weakened by a regular or irregular pattern of holes or cutouts, a sleeve, or a sheet.

8. The medical instrument system according to any of the previous claims, wherein the force sensor is configured to measure axial forces up to a predetermined force at least up to 5 N applied to the sensor.

9. The medical instrument system according to any of the previous claims, wherein the force sensor is configured for measuring an axial force by detecting strain in at least two cores of the optical fiber(s).

10. The medical instrument system according to any of the previous claims in as far as dependent on claim 3 wherein the force sensor comprises a set of optical sensors located in parallel in different cores at a position within the deformable support structure hence being sensitive to both mechanical strain and temperature and at least one optical sensor located in parallel in at least one of the cores at a position outside the deformable support structure and hence being sensitive to temperature, the system being configured for determining based on measurements from both sets of optical sensors a temperature compensated force value.

11. The medical instrument system according to any of the previous claims, the medical instrument system being a catheter delivery system for positioning an implantable object at the target site, wherein the longitudinal instrument is a delivery cable disposed within a catheter body, the delivery cable being configured with a release mechanism to releasably hold the implantable object and the force sensor being positioned on the longitudinal instrument, near the release mechanism, opposite to the implantable object.

12. The medical instrument system according to claim 11, wherein the force sensor is configured to generate a signal indicative of the axial force on the implantable object, the signal being usable by an operator to assess whether the implantable object is properly positioned prior to releasing the implantable object from the delivery cable.

13. The medical instrument system according to any of claims 11 or 12, wherein the delivery cable comprises a release mechanism such as for example a threaded or twist-lock mechanism positioned between the force sensor and the implantable object, in order to release the implantable object from the delivery cable.

14. The medical instrument system according to any of the previous claims,the system comprising a mobile or desktop application configured to visualize the force and to provide procedural guidance or alerts, and / orthe system comprising a robotic or teleoperated actuator system configured to respond to force data to adjust operation.

15. A method for using a medical instrument system for performing an action at a target side in a patient’s body, the method comprisingoperating a longitudinal instrument, andmeasuring an axial force between the longitudinal instrument on the one hand and the patient’s body on the other hand using an integrated force sensor comprising a deformable support structure and a multi-core optical fiber having a plurality of optical cores, or a set of linked single-core optical fibers, the optical fiber(s) being fixedly positioned with respect to he deformable support structure,whereby the force sensor comprises a calibration means to filter out the influences of the lateral forces.

16. The method according to claim 15, wherein filtering out lateral forces is performed without quantification of the lateral forces, based on a plurality of applied lateral forces applied from different directions to the force sensor.

17. The method according to any of claims 15 to 16, wherein the method comprises compensating for radial and / or angular offsets of the optical fiber with respect to the deformable support structure.

18. A medical instrument system for delivery an implantable object at a target site in a patient’s body, the instrument system comprising- a longitudinal instrument configured with a release mechanism for releasably holding an implantable object for implanting at the target site, and- an integrated force sensor, integrated near a distal end of the longitudinal instrument before the implantable object, the force sensor being configured for measuring a force between the implantable object on the one hand and the environment on the other hand.

19. The medical instrument system according to the previous claim, wherein the system is configured for obtaining information regarding a force-displacement relationship at the position or at the level of the force sensor and / or the implantable object.

20. The medical instrument system according to claim 19, wherein the system is configuredfor detecting deviations from a reference force-displacement relationship corresponding with an expected procedural behavior, and for identifying a deviation from a standard procedure based thereon.

21. The medical instrument system according to any of claims 18 to 20, the system comprising one or more electromagnetic sensors for providing position and / or orientation information regarding the force sensor and / or the implantable object.

22. The medical instrument system according to any of claims 18 to 21, wherein an imaging technique is used for providing position and / or orientation information regarding the force sensor and / or the implantable object and wherein- one or more regions of the sensor or in the vicinity of the force sensor and / or the implantable object have specific features making them radio-opaque for fluoroscopy detection, or- one or more regions of the sensor are echogenic making them ultrasound detectable, - one or more regions are made of a material detectable by magnetic resonance imaging (MRI), or by Computed Tomography (CT) imaging, or by Positron Emission Tomography (PET) imaging,23. The medical instrument system according to any of claims 18 to 22, wherein the force sensor comprises a multi-core optical fiber, having a plurality of optical cores, or a set of linked single-core optical fibers.

24. The medical instrument system according to claim 23, wherein the force sensor comprises a deformable support structure and where the optical fiber is fixedly mounted with respect to the deformable support structure.

25. The medical instrument system according to any of claims 23 or 24, wherein the system comprises shape-sensing capability through the optical fiber(s) for providing position and / or orientation information regarding the force sensor and / or implantable object.

26. The medical instrument system according to claim 25, wherein the system comprises shape-sensing means configured for deriving the displacement of the force sensor and / or the implantable object from said shape sensing capability.

27. The medical instrument system according to any of claims 18 to 26, wherein the force sensor is configured to generate a signal indicative of the force, the signal being usable by an operator to assess whether the implantable object is properly positioned prior to releasing the implantable object.

28. The medical instrument system according to any of claims 18 to 27, wherein the release mechanism is positioned between the force sensor and the implantable object, in order to release the implantable object from the delivery cable.

29. The medical instrument system according to any of claims 18 to 28,the system comprising a mobile or desktop application configured to visualize the force-displacement curve and to provide procedural guidance or alerts, and / or the system comprising a robotic or teleoperated actuator system configured to respond to force-displacement data to adjust operation.

30. The medical instrument system according to any of claims 18 to 29, the medical instrument system being a catheter delivery system for positioning the implantable object, wherein the longitudinal instrument is a delivery cable disposed within the catheter body.

31. A method for using a medical instrument system, the method comprising- operating a longitudinal instrument configured with a release mechanism for releasably holding an implantable object for implanting at the target site, and- measuring a force between the implantable object on the one hand and the environment on the other hand using an integrated force sensor, integrated near a distal end of the longitudinal instrument.

32. The method according to claim 31, wherein the method furthermore comprises obtaining information regarding a force-displacement relationship at the level of the force sensor and / or implantable object, for operating the longitudinal instrument.

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