Patent Description:
<CIT> describes determining wall thickness of a cavity by inserting a catheter into contact with a wall of a cavity in a body of a subject. The distal segment of the catheter is provided with a contact force sensor and an ultrasound transducer. The transducer is actuated to acquire ultrasound reflection data from the wall of the cavity, and while the transducer is actuated, the catheter is reciprocated against the wall of the cavity and the contact force measured between the catheter and the wall of the cavity. The reflection data is correlated with the contact force. A set of the correlated reflection data having the highest correlation with the contact force is identified. The tissue thickness between the inner surface and the identified set of the reflection data is calculated according to the time-of-flight therebetween.

<CIT> describes a medical probe that includes a flexible insertion tube, having a distal end for insertion into a body cavity of a patient, and a distal tip, which is disposed at the distal end of the insertion tube and is configured to be brought into contact with tissue in the body cavity. A resilient member couples the distal tip to the distal end of the insertion tube and is configured to deform in response to pressure exerted on the distal tip when the distal tip engages the tissue. A position sensor within the probe senses a position of the distal tip relative to the distal end of the insertion tube, which changes in response to deformation of the resilient member.

<CIT> describes a device for measuring a spatial location of a tissue surface, such as the interface between different types of tissues or between tissue and body fluids, which generally includes an elongate catheter body having a distal end portion, a plurality of localization elements carried by the distal end portion, and at least one pulse-echo acoustic element carried by the distal end portion. The localization elements allow the catheter to be localized (e.g., position and/or orientation) within a localization field, while the acoustic element allows for the detection of tissue surfaces where incoming acoustic energy will reflect towards the acoustic element. A suitable controller can determine the location of the detected tissue surface from the localization of the distal end portion of the catheter body. Tissue thicknesses can be derived from the detected locations of multiple (e.g., near and far) tissue surfaces. Maps and models of tissue thickness can also be generated.

<CIT> describes various embodiments that concern delivering an ablation therapy to different areas of the cardiac tissue and, for each of the areas, sensing an ultrasound signal with at least one ultrasound sensor, the ultrasound signal responsive to the ultrasound energy reflected from the area of cardiac tissue. Such embodiments can further include for each of the plurality of different areas of the cardiac tissue, associating with each area an indication of the degree to which the area of cardiac tissue was lesioned by the delivery of the ablation therapy based on the ultrasound signal and representing a map of the different areas on a display. A user input can select one of the different areas and the indication associated with the selected one area can be represented on the map.

<CIT> describes a dynamic ultrasound image catheter that includes a catheter body with an acoustic window on the distal end, an ultrasound phased array transducer assembly configured to rotate within the acoustic window through an angle of rotation, an acoustic coupling fluid filling a gap between the transducer array and the acoustic window, and a drive motor at the proximal end of the catheter body that is configured to rotate the transducer array. The drive motor may transmit a rotational force to the ultrasound phased array transducer by a drive wire or by tension wires coupled to drive spools. A system processor coupled to the drive motor controls rotation of the transducer array and estimates the angular orientation of the transducer array. By taking ultrasound images at increments through the angle of rotation, the dynamic ultrasound image catheter can obtain images spanning a volume which can be processed to generate three-dimensional composite images.

<CIT> describes a tracking, and point-of-view-based imaging, device that is configured for deriving a position of, and a direction from, a location at a distal tip of an elongated instrument, for performing coordinate system transformation in accordance with the position and direction, and for forming, from the location and based on a result of the transformation, a local view that moves with the tip. The device can keep, with the movement, a field of view of the local view fixed but the local view otherwise in synchrony with the position and the direction. From real-time ultrasound imaging, the local view and a more overall view that includes the tip but which does not move with said tip can be displayed. The distal tip can be that of a catheter and can be outfitted with a micromanipulator for surgery aided interactively by the combination of dynamic local and overall imaging.

<CIT> describes a sensor system for measuring an elastic modulus and a shear modulus and a method for using the sensor system to evaluate a tissue by determining the presence of and/or characterizing abnormal growths. The method involves applying a set of forces of different magnitudes to one or more locations of tissue, detecting the corresponding displacements due to said applied forces, determining the forces acting on those locations of tissue which are a combination of forces from the applied voltages and the countering forces from tissue deformation, obtaining the elastic modulus and/or shear modulus for a plurality of locations, and determining abnormal growth invasiveness, malignancy or the presence of a tumor from said elastic and/or shear moduli.

In <CIT> wall thickness of a cavity is determined by inserting a catheter into contact with a wall of a cavity in a body of a subject. The distal segment of the catheter is provided with a contact force sensor and an ultrasound transducer. The transducer is actuated to acquire ultrasound reflection data from the wall of the cavity, and while the transducer is actuated, the catheter is reciprocated against the wall of the cavity and the contact force measured between the catheter and the wall of the cavity. The reflection data is correlated with the contact force. A set of the correlated reflection data having the highest correlation with the contact force is identified. The tissue thickness between the inner surface and the identified set of the reflection data is calculated according to the time-of-flight therebetween.

<CIT> provides an ultrasound device and a method of assessing a bone of a subject. The ultrasound device assesses a bone of a subject in at least two modes comprising a first mode and a second mode. The ultrasound device comprises: a selecting unit configured to select a mode from the at least two modes; a first ultrasound probe configured to transmit an ultrasound signal to the bone; a second ultrasound probe configured to receive the ultrasound signal from the bone; an assessing unit configured to derive a first parameter indicating one or more characteristics of the bone based on the selected mode and the ultrasound signal received by the second ultrasound probe; and a coupler for coupling the first ultrasound probe and the second ultrasound probe, the coupler being configured to be switched to a first configuration in the first mode and to a second configuration in the second mode.

<CIT> discloses An ultrasonic measuring device including: an ultrasonic transducer device; a force sensor that measures pressing force; an emission unit that performs processing for emitting an ultrasonic beam; a reception unit that performs processing for receiving an ultrasonic echo obtained from the ultrasonic beam being reflected by a test subject; and a processing unit that performs analysis processing based on a reception signal from the reception unit and detection information from the force sensor, wherein the processing unit obtains elasticity information of a biological tissue layer of the test subject based on thickness information and pressing force information, the thickness information being thickness information of the biological tissue layer acquired based on the reception signal from the reception unit, and the pressing force information being pressing force information regarding the pressing force applied to the test subject from the force sensor.

There is provided, an apparatus according to independent claim <NUM>.

Optional features of the apparatus are disclosed in dependent claims <NUM> - <NUM>.

When performing an ablation of tissue, it is often helpful to know the thickness of the tissue, such that the parameters of the ablating signal may be appropriately set. One option for measuring tissue thickness is to use ultrasound imaging. For example, to prepare for a cardiac ablation, an ultrasound transducer inside the heart may transmit ultrasound signals into the cardiac tissue, and the tissue thickness may be ascertained from the times-of-flight of the reflections of these signals.

A challenge with the above-described method, not claimed, is that the thickness of the cardiac tissue may vary with the mechanical force (or equivalently, mechanical pressure) that is applied to the tissue by the ablation electrode. Embodiments of the present invention address this challenge, by using a signal from a force sensor to learn the dependency of the tissue thickness on the force that is applied to the tissue. In other words, the signal from the force sensor is used to express the tissue thickness as a function of the applied force. Subsequently, the tissue thickness that would result from the desired ablation contact force is estimated, and the other ablation parameters are then set accordingly.

In embodiments not claimed, a catheter is inserted into the heart of a subject. The distal end of the catheter comprises an ablation electrode for ablating cardiac tissue, a force sensor, and an ultrasound transducer. As the physician moves the distal end of the catheter along the tissue of the heart, the force sensor measures the force applied to the tissue by the distal end, and the ultrasound transducer records ultrasound reflections from the tissue. A processor receives signals from the force sensor and the ultrasound transducer, and, using the signals, learns the dependency of the tissue thickness on the applied force.

Reference is initially made to <FIG>, which is a schematic illustration of a system <NUM> for performing a cardiac ablation, in accordance with some embodiments of the present invention.

System <NUM> comprises a catheter <NUM>, a proximal end of which is connected, via an electrical interface <NUM> (e.g., any suitable type of connector, jack, port, or plug), to a console <NUM>, which comprises a processor <NUM>. As described in detail hereinbelow, processor <NUM> receives, via electrical interface <NUM>, electrical signals from catheter <NUM>, processes these signals, and generates appropriate output in response thereto.

During a cardiac ablation procedure, catheter <NUM> is inserted by a physician <NUM> into the heart of a subject <NUM>. The distal end <NUM> of catheter <NUM> comprises an ablation electrode <NUM>, which is used to apply an ablating signal to cardiac tissue of subject <NUM>. An ultrasound transducer <NUM>, disposed at distal end <NUM> (e.g., inside ablation electrode <NUM>), is used to transmit ultrasound signals, and receive reflections of the signals from the tissue. In response to the received reflections, ultrasound transducer <NUM> generates signals, which are received by processor <NUM>. The ultrasound transducer is used for both (i) measuring tissue thickness prior to the ablation, in order to properly set the ablation parameters, and (ii) evaluate echogenic changes to the tissue caused by the ablation, in order to assess the outcome of the ablation.

In some embodiments, catheter <NUM> comprises a plurality of ultrasound transducers, which may be arranged within the ablation electrode in any suitable arrangement. For example, the ultrasound transducers may be distributed around the circumference of the ablation electrode, at the distal tip of the ablation electrode and/or proximally to the distal tip. Such a plurality of ultrasound transducers may be used to transmit ultrasound signals from multiple locations, and/or in multiple directions, thus facilitating the performance of the techniques described herein.

In some embodiments, distal end <NUM> further comprises one or more temperature sensors <NUM>, which may be used to record the temperature of the tissue during the ablation. Temperature sensors <NUM> generate signals indicative of the recorded temperatures, and communicate these signals to processor <NUM>.

Catheter <NUM> further comprises a force sensor <NUM>, which may alternatively be referred to as a pressure sensor, at the distal end of the catheter. In some embodiments, force sensor <NUM> operates as described in <CIT>. Force sensor <NUM> is configured to generate a signal that indicates both the magnitude and the direction of the mechanical force that is applied to the tissue by the distal end of the catheter.

Typically, system <NUM> further comprises an electromagnetic tracking system, which tracks the position and orientation of the distal end of the catheter during the procedure, as described, for example, in <CIT>.

Typically, console <NUM> further comprises a display <NUM>, which displays appropriate output for the physician during the procedure. For example, display <NUM> may show an electroanatomical map of the subject's heart, constructed, for example, using techniques described in <CIT>. Alternatively or additionally, display <NUM> may be driven by processor <NUM> to show output from the processing of signals received from ultrasound transducer <NUM> and force sensor <NUM>, as described in detail hereinbelow.

One commercial product embodying elements of system <NUM> is the CARTO® <NUM> System, available from Biosense Webster, Inc. , <NUM> Diamond Canyon Road, Diamond Bar, CA <NUM>. This system may be modified by those skilled in the art to embody the principles of embodiments described herein.

In general, processor <NUM> may be embodied as a single processor, or a cooperatively networked or clustered set of processors. Processor <NUM> is typically a programmed digital computing device comprising a central processing unit (CPU), random access memory (RAM), non-volatile secondary storage, such as a hard drive or CD ROM drive, network interfaces, and/or peripheral devices. Program code, including software programs, and/or data are loaded into the RAM for execution and processing by the CPU and results are generated for display, output, transmittal, or storage, as is known in the art. The program code and/or data may be downloaded to the computer in electronic form, over a network, for example, or it may, alternatively or additionally, be provided and/or stored on non-transitory tangible media, such as magnetic, optical, or electronic memory. Such program code and/or data, when provided to the processor, produce a machine or special-purpose computer, configured to perform the tasks described herein.

Reference is now made to <FIG>, which is a schematic illustration of a visual output <NUM> that includes a force signal <NUM> and an m-mode ultrasound image <NUM>, which may be displayed on display <NUM> (e.g., overlaid over a displayed electroanatomical map) in accordance with some embodiments of the present invention.

Upon inserting the catheter into the subject's heart, the physician presses the distal end of the catheter against the cardiac tissue. Typically, due to movement of the tissue over the course of the cardiac cycle, the force with which the catheter presses against the tissue varies. Alternatively or additionally, the physician may manually vary the contact force, and/or a linear actuator (not shown) incorporated into the distal end of the catheter may vary the contact force, as described, for example, in <CIT>. While the contact force varies, the ultrasound transducer transmits ultrasound signals into the tissue, and receives reflections of the signals from the tissue.

Processor <NUM> receives, from force sensor <NUM>, a force signal <NUM>, which indicates the time-varying contact force "F" applied to the tissue. Processor <NUM> further receives, from the ultrasound transducer, one or more signals that are derived from ultrasound reflections received by the ultrasound transducer. Such signals from the ultrasound transducer may be used to generate an m-mode ultrasound image <NUM> of the tissue, which shows the portion <NUM> of tissue that is in front of the ultrasound transducer. Assuming a large-enough contrast between tissue portion <NUM> and the adjacent anatomical portion <NUM> of the subject, image <NUM> allows the thickness T of tissue portion <NUM> to be visualized. In particular, it may be seen that T is a function of the contact force F. As the contact force increases, the tissue becomes more compressed, and hence, the thickness decreases; conversely, as the force decreases, the tissue thickness increases.

In some embodiments, at least some tissue thicknesses may be measured manually (e.g., by the physician) from image <NUM>, and/or from the displayed electroanatomical map of the subject's heart. Typically, however, the thicknesses are obtained automatically by the processor, based on the times-of-flight of the ultrasound reflections received from the tissue. In cases in which reflections are received from multiple tissue interfaces, the processor may use techniques described in <CIT> to identify the reflections from the tissue interface <NUM> of interest. In brief, the aforementioned '<NUM> publication describes correlating force signal <NUM> with the time-varying times-of-flight of the received reflections. The times-of-flight from tissue interface <NUM> will be highly correlated with force signal <NUM>, while those from other tissue interfaces will be less correlated. That is, as the applied force increases, thus causing the distance from the ultrasound transducer to tissue interface <NUM> to decrease, the times-of-flight from tissue interface <NUM> will decrease, and vice versa, whereas other times-of-flight will be less correlated with force signal <NUM>. Consequently, the processor may obtain the time-varying distance from the ultrasound transducer to tissue interface <NUM>, which is the desired tissue thickness.

Subsequently, given the time-varying contact force and the time-varying tissue thickness, the dependency of the thickness on the contact force is learned. That is, processor <NUM> learns "T=f (F)," which is the tissue thickness expressed as a function of the contact force. This dependency - as learned, stored, and subsequently used by the processor - may be embodied in any suitable form, such as in the form of a lookup table of corresponding "T" and "F" values, and/or in the form of parameters derived by fitting a function to the acquired "T" and "F" values.

Typically, the dependency of the tissue thickness on the contact force is learned for each of a plurality of portions of tissue. That is, as the physician moves the catheter along the tissue, force signal <NUM>, and the signals based on the ultrasound reflections, are received, and are used to learn the dependency for each of the portions of tissue over which the catheter moves. Typically, the dependencies are first learned for a local area of an intended ablation site, an ablation is then performed at the local area, and then the catheter is moved to the next intended ablation site. In other embodiments, the learning is first performed for all of the intended ablation sites, and only afterwards are each of the sites ablated.

As indicated in <FIG> and described above, force signal <NUM> and image <NUM> are typically displayed on display <NUM>. (Although, as described above, force signal <NUM> typically includes both the magnitude and direction of the force, the display of force signal <NUM> may indicate only the magnitude of the force, expressed, for example, in units of weight, such as grams. ) Alternatively, processor <NUM> may learn the dependency of the tissue thickness on the contact force, even without any signals or images being displayed on the display.

Reference is now made to <FIG>, which is a schematic illustration of a method for ascertaining thickness of tissue, in accordance with some embodiments of the present invention.

If distal end <NUM> of the catheter is perpendicular to the tissue during the acquisition of the force signal and the ultrasound reflections, the ultrasound reflections will be received from the portion of tissue to which force is being applied. On the other hand, if, as depicted in <FIG>, the distal end of the catheter is not perpendicular to the tissue, the ultrasound transducer will face away from the portion of tissue that the catheter is pressing against, and consequently, the force signal and the ultrasound-reflection signals may not correspond to the same portion of tissue. For example, in <FIG>, the catheter contacts a first portion <NUM> of tissue, but ultrasound reflections are received from a second portion <NUM> of tissue.

Hence, typically, the processor is configured to determine, based on the directionality of the force signal, the portion of the tissue from which the ultrasound signals were received. (The directionality of the force signal is captured by the bending of force sensor <NUM>, as depicted in <FIG>. ) If the portion of tissue from which the ultrasound signals were received is not the currently-contacted portion of tissue, the processor selects, as the one or more ultrasound-reflection-based signals, signals derived from ultrasound reflections received during a different period of time.

For example, in the case depicted in <FIG>, the ultrasound-reflection-based signals correspond to tissue portion <NUM>, rather than to portion <NUM>. Therefore, to learn the dependency for tissue portion <NUM>, the processor selects ultrasound-reflection-based signals that correspond to tissue portion <NUM>, these signals being acquired prior to or following the acquisition of the force signal for tissue portion <NUM>. The processor similarly uses the correct set of signals to learn the dependency for tissue portion <NUM>. <FIG> thus shows two learned dependencies: T_52=f(F_52) for tissue portion <NUM>, and T_54=f(F_54) for tissue portion <NUM>. (Although, in <FIG>, ablation electrode <NUM> is not perpendicular to tissue portion <NUM>, a suitable estimation technique may be used to estimate, based on the received ultrasound-reflection-based signals, the thickness of tissue portion <NUM>. For example, T_54 may be calculated by multiplying the tissue thickness T_54', which is estimated based on the received ultrasound reflections, by the cosine of the appropriate angle theta (θ), which may be ascertained from the force sensor.

The above description assumes that ultrasound signals transmitted from ablation electrode <NUM> are generally transmitted from the ablation electrode in the direction of the central longitudinal axis <NUM> of the ablation electrode. As noted above, in some embodiments, a plurality of ultrasound transducers may be used to transmit ultrasound signals from multiple locations, and/or in multiple directions, such that, in the scenario depicted in <FIG>, T_52 may be measured, despite the ablation electrode not being perpendicular to the tissue.

Subsequently to learning the dependency of the tissue thickness on the contact force for a particular portion of tissue, the learned dependency is used to set one or more ablation parameters for the ablation of the portion of tissue. In some embodiments, processor <NUM> first estimates, using the learned dependency, the thickness of the portion of tissue that would result from the desired ablation contact force (which is typically in the range of <NUM>-<NUM> grams) being applied to the portion of tissue. Then, in response to the estimated thickness, the processor generates an output indicating at least one recommended parameter for the ablation. For example, the output may indicate a recommended power, and/or a recommended duration, of the ablating signal. Typically, the processor displays such an output on display <NUM>, and the physician, in response to viewing the output on the display, then sets the ablation parameters accordingly.

In other embodiments, the processor does not explicitly estimate the thickness of the portion of tissue; rather, the processor ascertains the recommended parameter directly from the desired ablation contact force. For example, given the learned dependency T = f(F), and another function A = g(T) that specifies the dependency of the recommended ablating-signal amplitude "A" on the tissue thickness, the processor may, for a particular contact force F0, ascertain the recommended amplitude A0 in either one of the following two ways:.

In some embodiments, alternatively or additionally to generating the output that indicates the recommended ablation parameter(s), the processor generates an output - e.g., a control signal directed to the generator that supplies the ablating signal - that automatically sets the parameter(s).

Claim 1:
An apparatus comprising:
an electrical interface (<NUM>);
a console (<NUM>) comprising a processor (<NUM>); and a catheter (<NUM>) comprising an ablation electrode (<NUM>), an ultrasound transducer (<NUM>), and a force sensor (<NUM>) at its distal end (<NUM>);
wherein the proximal end of the catheter (<NUM>) is connected via the electrical interface (<NUM>) to the console (<NUM>),
wherein the processor (<NUM>) is configured to receive via the electrical interface (<NUM>):
a first signal, from the force sensor (<NUM>), that indicates a time-varying contact force that is applied to a portion of tissue (<NUM>,<NUM>), and
one or more second signals, from the ultrasound transducer (<NUM>), that are derived from ultrasound reflections received from the portion of tissue (<NUM>,<NUM>); and
the processor (<NUM>) being further configured to obtain a thickness of the portion of the tissue (<NUM>,<NUM>) based on the times of flights of the ultrasound reflections received from the portion of tissue (<NUM>,<NUM>), characterised in that the processor (<NUM>) is configured to learn, using the first signal and the second signals, the thickness of the portion of tissue (<NUM>,<NUM>) as a function of the contact force applied to the portion of tissue (<NUM>,<NUM>).