Apparatus and method for determining the status of internal body structures - Patents.com

Abstract

An intravascular device for determining the condition of a blood vessel in a body comprises an elongated wave-guiding element, such as a wire, and an actuation unit including an ultrasonic energy source for actuating the wave-guiding element and thus transmitting ultrasonic energy to an active distal portion of the wave-guiding element. A signal acquisition system acquires a feedback signal from the device for interpreting the condition of the blood vessel. The signal acquisition system comprises at least one acoustic sensor for acquiring an acoustic feedback signal generated by the device when the wave-guiding element is actuated, and / or at least one inertial sensor for acquiring information representative of the orientation of the actuation unit and / or the acceleration of the actuation unit. Data sets can be generated from the acoustic feedback signal and / or non-acoustic feedback signals (including inertial or electrical signals), and a combination of or comparison between the data sets can characterize the condition of the blood vessel, including any lesions, such as occlusions, in the blood vessel.

Description

[Technical field]

[0001] The present invention relates to techniques for determining the condition of vessels, cavities, or other structures within the body, including characterizing occlusions or blockages within such structures.

[0002] Embodiments of the present invention use active elongate elements such as wires and catheters. Some of these wires and catheters are adapted to pass through or cross an obstruction or occlusion in the body, for example to treat ischemia, and thus such elements are known in the art as crossing wires and crossing catheters. It should also be understood that crossing wires and crossing catheters may have additional functions, such as directing subsequent treatment after the obstruction has been crossed.

[0003] Although crossing wires are used herein to illustrate the concepts of the present invention, it should be understood that the concepts of the present invention are also applicable to crossing catheters. However, in other embodiments, the active elongate element, such as a wire or catheter, does not necessarily cross the occlusion. This means that the present invention is not limited to only the use of crossing wires and crossing catheters. [Background technology]

[0004] Ischemia is the insufficient supply of blood to the organs of the body. In atherosclerotic blood vessels, ischemia occurs as a result of the blood vessel being blocked by an obstruction resulting from a lesion in the vessel wall, an atherosclerotic plaque, or an embolism resulting from other causes. When a blood vessel is partially or completely blocked, the obstruction restricts the flow of blood to the tissues distal to it, causing cell death and a rapid deterioration in the health of those tissues.

[0005] Occlusions such as chronic total occlusions (CTOs) cause an ischemic response to wounds and trauma, leading to refractory ulceration of wounds and incisions, and other injuries to tissues. Because of these expected responses, surgical intervention is not preferred. Thus, the preferred method of treating such occlusions is a minimally invasive endovascular procedure such as angioplasty. In such procedures, small-diameter therapeutic devices are introduced into the vasculature via a guidewire or catheter, navigated through the lumen of veins and arteries to the occlusion, and deployed at the lesion site to restore patency. Procedures used to revascularize coronary and peripheral arterial occlusions by treating chronic atherosclerotic plaques can also be used to treat acute embolic occlusions, thrombi, or occlusive clots.

[0006] More generally, guidewires or catheters are used in other minimally invasive procedures to introduce other devices and instruments into blood vessels or other cavities within the body to allow examination, diagnosis, and different types of treatment. Other medical procedures that use guidewires or catheters include gastrointestinal, urological, and gynecological procedures, all of which may require the creation of a passageway through an obstruction to facilitate the passage of often large devices to the site of the lesion or to other target tissue distal to the lesion.

[0007] In endovascular procedures, an artery is selected and employed for use in gaining access to the vasculature based on the artery's ability to accommodate passage of a desired diagnostic or therapeutic device to the target site and the extent to which trauma to the tissue and patient can be minimized.

[0008] In peripheral arterial revascularization procedures, access is often gained through surgical cut-down and puncture of the femoral, popliteal, and foot arteries, commonly known in medical terms as the Seldinger technique. Once access is gained, an introducer wire and introducer sheath are inserted into the vessel and secured at the site. The sheath serves as a port for the introduction, withdrawal, and exchange of devices, minimizing dissection of the arterial tissue. A catheter and guidewire are then introduced into the artery to provide additional protection and aid in advancing the device to the target site.

[0009] For example, a guidewire is carefully pushed along the lumen of the vessel to avoid trauma to the vessel wall and guided to the site of the occlusion. If the procedure is successful, the guidewire is pushed across or through the occlusion and held in place to act as a guide to track a diagnostic or therapeutic device, such as a balloon catheter and / or stent, to the site of the occlusion. Visualization of the passage of the guidewire, catheter, or other diagnostic or therapeutic device through the anatomy is typically accomplished by x-ray, duplex ultrasound, or MRI.

[0010] In balloon angioplasty, a balloon catheter is introduced into the blood vessel along a guidewire and guided to the site of the blockage. The balloon is then inflated, pushing the obstructing material outward and restoring blood flow. A stent may be placed into the lesion to provide scaffolding to keep the vessel open.

[0011] Conventional intravascular wires come in a variety of configurations and designs to facilitate access to and crossing of lesions in various anatomies and to support various devices. Such wires are available in a variety of outer diameters and lengths depending on the anatomies involved and the expected working distance. These wires are made from a variety of materials, the most common being stainless steel or NiTi (nitinol). Their manufacture typically involves cold working the material into a wire and machining or polishing the wire into various shapes to obtain the desired performance. As an example, a specific taper can be ground over the length of the wire to create different degrees of flexibility along the length of the wire.

[0012] The wire must be flexible enough, especially at its distal end, to conform to the tortuosity of the vessel, yet also have sufficient axial and torsional strength to transmit forces to the distal tip and pass through the lesion. A balance is required between flexibility, expressed as "trackability," and stiffness, expressed as "pushability" or "steerability." Pushability requires longitudinal cylindrical stiffness, and steerability requires torsional stiffness.

[0013] Conventional intravascular wires are manipulated to navigate to and push through an occlusion by pushing, pulling, or torquing the proximal end, and are therefore passive in the sense that they do not transmit any energy other than that applied by the clinician.

[0014] Anatomies in which endovascular procedures may be performed include, but are not limited to, coronary arteries, neurovascular arteries, and peripheral arteries serving the lower extremities. Different anatomies are associated with different types of lesions. For example, lesions found in various peripheral blood vessels pose different challenges than lesions found in coronary arteries.

[0015] In many cases, occlusions are difficult to cross with conventional intravascular elements such as guidewires. In this regard, atherosclerotic plaques are composed of material that gradually hardens over time. For example, the iliac, femoral, popliteal, and infrapopliteal arteries are susceptible to extensive calcification, which represents a significant obstacle to successful endovascular procedures. Conventional intravascular elements are limited when attempting to cross occlusions that are nearly or completely occluded and may even be heavily calcified.

[0016] For example, in peripheral subiliac procedures, the occlusion may have a calcified proximal cap encountered in the preferred antegrade or femoral approach. Much time may be spent attempting a traditional antegrade approach to cross the lesion, and then escalating through different wires in the antegrade approach before changing to a retrograde approach. In retrograde procedures, access is gained through vessels distal to the lesion in the foot or ankle in the case of peripheral disease, or through collateral (typically septal) vessels in the coronary anatomy. In this regard, retrograde procedures take advantage of occlusions that may have softer distal caps that are easier to cross than calcified proximal caps. However, retrograde procedures are more complex than antegrade procedures, require greater skill, and take much longer to perform.

[0017] In over 50% of peripheral arterial cases, especially in the popliteal, tibial, and peroneal arteries, the vessel is completely occluded by the lesion. In approximately 30% of cases, the target lesion is heavily calcified. These calcified lesions are actually composed of hard inelastic segments that extend into much longer, widespread diffuse lesions, usually on the order of 20-25 cm in length. Selecting treatment modalities for such lesions requires insight into the length and composition of the lesion, which is not easily obtained by conventional imaging.

[0018] In the case of peripheral arteries, the blockage is often severe or composed of such resistant material that the guidewire cannot easily pass through. In such cases, the procedure may take a significant amount of time to complete and may require the use of additional devices to cross the lesion. Very often, the procedure is ultimately abandoned entirely, which prevents preferred follow-on procedures such as balloon angioplasty and stenting, thus limiting the ability to treat patients.

[0019] In view of these shortcomings, several ultrasonically actuated guidewires and catheters have been proposed for use in atherectomy or thrombectomy, where ultrasonic vibrations are transmitted along an element to a distal tip to agitate and ablate material at the occlusion. The element thus acts as a waveguide to transmit ultrasonic energy distally. Much of the prior art relevant to the concept of ultrasonic actuation in this context is described in the inventors' previous patent applications published as WO 2020 / 094747, WO 2021 / 089847, WO 2021 / 089859, and WO 2021 / 224357, the contents of which are incorporated herein by reference.

[0020] Our previous patent application, published as WO 2020 / 094747, discloses, among other concepts, a system including an ultrasound source, an active traversing wire, and a signal acquisition, processing, and communication chipset or control circuit. The chipset or circuit can generate signals to control the system and provide outputs to a user and / or an external data acquisition system. In particular, the controller monitors the frequency and amplitude of the current and voltage at the ultrasound source, as well as measurements of incident, reflected, and stationary waveforms at the wire, thereby estimating the displacement of the distal tip. Modulation of these variables is monitored as the wire passes through the anatomy and through various types of occlusions, including calcified CTOs. This allows for the determination of calcified or non-calcified lesions, and the duration or length of the calcified segments of the lesion. When a lesion determined to be calcified is encountered, the user can respond and control the system, for example by increasing the input power, or the system can self-regulate accordingly.

[0021] WO 2020 / 094747 proposes that a digital signal processor examines the measurements generated and provides feedback to interpret and compare the relative contributions of losses due to anatomical tortuosity while navigating to the site and losses incurred while passing through the occlusion. The system processes data obtained from the measurements that indicate the ultrasound waveform as the transduction of resonant vibrations occurs while passing through the vasculature and through the occlusion. An algorithm converts the raw data into an output relevant for the procedure. The system can compare and interpret the difference between the calculated values ​​from the active system and a set of predefined values ​​to characterize the nature of the material occluding the vessel.

[0022] Thus, the system of WO2020 / 094747 takes into account the typical characteristic loss variations when the active wire engages with various healthy and diseased tissue types. A distinction is made between losses in blood vessels and losses associated with lesions, and between lesions of different compositions, in particular between calcified and non-calcified lesions. The characteristic responses to the differential changes occurring in different media and when the intravascular wire is passed or guided through different anatomical structures are used to create individual algorithms that are used to 1) determine and correct the causes of losses in the system, 2) evaluate the tone of the arterial vessels, and 3) determine the compositional details of the lesions. These algorithms may, for example, provide corrections to the tip of the wire when it comes into contact with compatible, incompatible, and calcified materials, and in the latter case may amplify the energy input to the system accordingly. [Prior art documents] [Patent documents]

[0023] [Patent Document 1] International Publication No. 2020 / 094747 [Patent Document 2] International Publication No. 2021 / 089847 [Patent Document 3] International Publication No. 2021 / 089859 [Patent Document 4] International Publication No. 2021 / 224357 [Patent Document 5] International Publication No. 2022 / 129623 [Patent Document 6] International Publication No. 2019 / 152898 [Patent Document 7] U.S. Pat. No. 5,284,148 [Patent Document 8] US Patent Application Publication No. 2017 / 215837 [Patent Document 9] US Patent Application Publication No. 2004 / 260180 Summary of the Invention [Problem to be solved by the invention]

[0024] The present invention takes as its starting point WO 2020 / 094747 and further develops the concepts disclosed in the inventors' international patent application published under WO 2022 / 129623, the contents of which are also incorporated herein by reference. The present invention aims to improve the quality of feedback on the behavior of ultrasonically actuated elongated waveguiding elements, such as wires, as they traverse and interact with biological structures and occlusions or other lesions encountered therein. In this regard, it has been found that when actuated in situ, the elements generate characteristic acoustic signatures indicative of various properties characterizing the lesions, the tissue of the vessel, and possibly the flow of blood along the vessel.

[0025] WO 2019 / 152898 discloses an ultrasonically actuated tubular element advanced along a passive guidewire. The tubular element of WO 2019 / 152898 may be able to treat blood clots, but should be contrasted with wires as contemplated in preferred embodiments of the present invention, even if they can cross calcified CTOs. The wires can be configured to effectively transmit ultrasonic energy to the distal end portion and vibrate the active distal end portion with the desired characteristics. However, the tubular elements cannot be made flexible enough to track the lesion site along a tortuous and narrow path without losing the desired stiffness and uniformity to transmit signals along the element to the distal end portion and vice versa. Furthermore, there is a significant risk that the tubular or cylindrical elements will break under ultrasonic excitation due to the change in their material properties when bent. However, in the present invention, it may be advantageous for the catheter or tube surrounding the wire to support the acoustic sensor, if necessary.

[0026] WO 2019 / 152898 describes sensing ultrasonic properties such as power, frequency, amplitude, phase and / or stroke length, but does not disclose a separate acoustic sensor as contemplated by the present invention. Implicitly, these ultrasonic properties are measured in WO 2019 / 152898 directly from the transducer, not by listening to the transducer or active element, but by measuring its drive input and mechanical properties.

[0027] A wide range of different sensors and sensed parameters are proposed in WO 2019 / 152898, but no mention is made of where the sensors may be placed, or of acoustic sensors or listening. The sensors are not concerned with the interaction between the wire and the vessel wall or the surrounding tissue or occlusion, and do not allow the device to function as a diagnostic aid for the clinician. Instead, the sensors proposed by WO 2019 / 152898 are dedicated to controlling the device during the crossing procedure. No mention is made of monitoring the acoustic output independent of controlling the device, or of using the data as a clinical diagnosis as envisaged by the present invention.

[0028] U.S. Pat. No. 5,284,148 discloses an ultrasonic diagnostic probe that can scan radially but not longitudinally and cannot cross an occlusion if one is encountered.

[0029] US Patent Application Publication No. 2017 / 215837 discloses a passive guidewire in which an acoustic sensor is placed proximally relative to the guidewire. It can only hear interactions with structures immediately distal to the guidewire (e.g., the calcific cap of an occlusion) and not with the surrounding vessel wall or the internal structure of the occlusion (e.g., which may have a gel-like consistency behind a harder cap). Thus, there is no possibility to further characterize the lesion or vessel as the wire passes through and beyond its initial encounter.

[0030] US 2004 / 260180 discloses a transceiver that transmits and receives signals in a duplex fashion, where the transceiver and its supporting electronics can only detect and process reflections of the signal it itself transmits, and therefore cannot detect and process signals driven from another source, such as a transducer acting on crossed wires whose distal ends are active within a structure within the body. [Means for solving the problem]

[0031] The present invention therefore resides in an intravascular device for determining the condition of a vessel, cavity, or other structure within the body, including any lesions within such structures. The device comprises an actuation unit including an elongated waveguide element, a source of ultrasonic energy, and a coupling for coupling the source to the waveguide element to activate the waveguide element and thereby transmit ultrasonic energy from the source along the waveguide element to an active distal portion of the waveguide element, and a signal acquisition system configured to acquire a feedback signal from the device for use in interpreting the condition of the vessel. The signal acquisition system comprises at least one acoustic sensor for acquiring an acoustic feedback signal generated by the device when the waveguide element is activated. At least two acoustic sensors may be longitudinally spaced apart from each other.

[0032] At least one acoustic sensor can be mounted in or on the actuation unit, for example in longitudinal alignment with the coupling of the actuation unit, or proximal to the coupling of the actuation unit, or distal to the coupling of the actuation unit. At least one acoustic sensor can be mounted on or parallel to the waveguide element, for example proximal or distal to the length of the waveguide element.

[0033] The waveguide element may be, comprise, or be surrounded by a catheter, in which case at least one acoustic sensor may be attached to the catheter. Additionally or alternatively, the waveguide element may be, comprise, or be a wire, in which case at least one acoustic sensor may be attached to the wire. A strain gauge may be affixed to the waveguide element, such as a wire, for obtaining an operational feedback signal from the waveguide element. Such a strain gauge may function as an acoustic sensor.

[0034] The at least one acoustic sensor may be an external sensor that is placed against a part of the body, or an internal sensor that is placed for insertion into the body.

[0035] In a preferred embodiment, the signal acquisition system further comprises at least one electronic sensor configured to acquire operational feedback signals representative of operational parameters of the source of ultrasonic energy. These operational parameters may be the frequency and / or amplitude and / or phase of the current drawn by the source of ultrasonic energy or the voltage dropped across the source of ultrasonic energy. The signal acquisition system may be configured to monitor variations in the frequency or amplitude of the vibration of the wave-guiding element via the coupling.

[0036] The apparatus may further comprise a signal processing system for processing the feedback signal acquired by the signal acquisition system, such a signal processing system may be configured to employ, for example, a numerical algorithm selected for the particular type of waveguiding element.

[0037] The signal processing system can be configured to determine a characteristic of an occlusion in a blood vessel from the obtained feedback signal. The signal processing system can also be configured to compare the relative contributions of losses from anatomical tortuosity in navigating the active distal portion to the occlusion and losses caused by the active distal portion passing through the occlusion.

[0038] The signal processing system may be configured to compare the obtained feedback signal with stored data characterizing known occlusions and to characterize the occlusion with reference to the comparison.

[0039] The signal processing system may further include an output to a user interface, and / or an output to an external data acquisition system, and / or an input from a user interface, and / or an input from an external data network.

[0040] The device may further comprise a controller responsive to the signal processing system. Such a controller may be configured to modulate an excitation voltage applied to the source of ultrasonic energy or an excitation current provided to the source of ultrasonic energy. The controller may be configured to control the source of ultrasonic energy by, among other things, varying the frequency and / or amplitude of the excitation voltage applied to the source of ultrasonic energy. The controller may also be configured to drive the frequency of the excitation voltage by using the phase difference between the excitation voltage and the excitation current in conjunction with the amplitude of the excitation voltage.

[0041] The controller may include an amplitude feedback controller and may be configured to use the resonant frequency as an operating point for control. The controller may be configured to pulse or vary a drive signal to the source of ultrasonic energy.

[0042] The controller can be configured to monitor modulation of the transmitted signal and automatically control the source of ultrasonic energy to compensate for background energy loss that occurs in the waveguiding element as the active distal portion approaches the occlusion, and to distinguish between background energy loss and additional energy loss as the active distal portion passes through the occlusion and compensate for the background energy loss to maintain displacement in the active distal portion.

[0043] The controller can be configured to modify or change the control algorithm in response to variations in operating parameters of the source of ultrasonic energy resulting from interaction of the active distal section with an occlusion during use.

[0044] The inventive concept encompasses a communication system comprising an inventive device in data communication with a computer system configured to receive data from the device, optimize and update the control algorithm accordingly, and output the optimized and updated control algorithm to the device. Optimally, two or more such devices are in data communication with the computer system, such that the computer system is configured to optimize the control algorithm according to data received from a plurality of procedures performed using the device, and output the optimized and updated control algorithm to the device.

[0045] The concepts of the present invention also encompass a corresponding method for determining a condition of a blood vessel within a body, the method including directing a distal portion of an elongated waveguide element to a site within the vessel, activating the waveguide element by transmitting ultrasonic energy to the distal portion, obtaining an acoustic feedback signal generated when the waveguide element is activated, and interpreting the acoustic feedback signal to characterize the condition of the vessel.

[0046] The method of the present invention can evaluate the attenuation in amplitude, or shift in frequency, of the displacement of the waveguiding element caused by losses resulting from contact with the walls of the blood vessel or with material within the blood vessel, such as an occlusive lesion.

[0047] The distal portion of the actuated waveguide element can be brought into engagement with a lesion within a blood vessel and the resulting change in the acoustic feedback signal can be interpreted to characterize the lesion. Advantageously, the distal portion of the actuated waveguide element can also destroy the lesion.

[0048] The method may further include comparing the sensed data representative of the response of the activated waveguide element to the lesion with stored data representative of the response of a corresponding activated waveguide element to interaction with a known lesion.

[0049] The acoustic feedback signal may be obtained at an operating unit outside the body located proximal to the waveguide element, and / or at one or more locations along the waveguide element, and / or at a distal location within the body along the waveguide element, and / or at one or more locations outside the blood vessel, and / or at two or more locations spaced longitudinally from each other.

[0050] Preferably, the method further comprises obtaining a non-acoustic feedback signal representative of an operating parameter of the source of ultrasonic energy coupled to the wave-guiding element, or more generally, a non-acoustic feedback signal obtained by monitoring the variations in frequency or amplitude of the vibration of the wave-guiding element. How the source responds when the wave-guiding element encounters a blood vessel and any lesions therein can be determined from the operating parameters. For example, the non-acoustic feedback signal can be an electrical feedback signal representative of the variations in frequency and / or amplitude and / or phase of the current drawn by the source of ultrasonic energy, or the voltage dropped across the source of ultrasonic energy. Advantageously, the attenuation of the wave-guiding element can be determined by monitoring the attenuation of the current signal over time. The non-acoustic feedback signal can also be an inertial signal representative of the orientation and acceleration of the actuation unit.

[0051] Data sets can be generated from the acoustic and non-acoustic feedback signals, and a combination of the respective data sets, or a comparison between the data sets, can be used to characterize the condition of the blood vessel. The amplitude or frequency of the ultrasonic energy transmitted along the waveguide element to the distal portion can be adjusted in response to the non-acoustic feedback signal. The source can also be controlled in response to the non-acoustic feedback signal to maintain a resonant frequency in the waveguide element.

[0052] The method of the present invention may include outputting data to an external data network, receiving data from the network in response, and modifying or changing the control algorithm accordingly upon receiving the data from the network. The method also includes outputting data to an external computer system, optimizing and updating the control algorithm in the external computer system according to the data, outputting the optimized and updated control algorithm from the external computer system, and controlling the operation of the wave-guiding element using the optimized and updated control algorithm. Preferably, the computer system is capable of optimizing the control algorithm according to data received from multiple treatments.

[0053] Two or more different waveforms can be applied sequentially to a source of ultrasonic energy, the waveforms being selected from, for example, a sinusoidal waveform, a pulsed waveform, a multi-tone waveform, a chirp waveform, or a noise waveform.

[0054] To improve sensitivity, the method can include advancing a distal portion of the actuated waveguide element proximate to a lesion in a blood vessel, obtaining a baseline feedback signal, advancing the distal portion of the actuated waveguide element to engage the lesion, obtaining an operational feedback signal, and subtracting the baseline feedback signal from the operational feedback signal.

[0055] In summary, the present invention involves acoustically characterizing the effects of intraluminal elements such as ultrasonically actuated wires. In particular, the present invention employs ultrasonic waveguiding devices such as traversing wires to excavate lesions and disrupt calcified intraluminal or intramural plaques within blood vessels, as well as to determine characteristics of the vessel lumen. These characteristics may include the internal diameter of the vessel, the vascular tone of the vessel, and the mechanical characteristics and composition of any material occluding the vessel.

[0056] In WO 2020 / 094747, the inventors proposed that different wires with known characteristics, such as a particular combination of ground taper, land length and diameter, respond to lesions in a way that allows for differentiation between calcified and non-calcified lesions. The inventors determined that further analysis and processing of the spectrum could provide a more sensitive assessment of the lesion and / or other surfaces that the wire may contact within the vasculature. More specifically, the present invention aims to enable assessment of the internal diameter of the vessel and to characterize by interpolation the mechanical properties of the vessel wall and any material that may be occluding the vessel. Thus, the present invention allows for identification of whether the occlusion is composed of gelatinous plaque, calcified material, thrombus, or some other form of embolic material. Of particular interest is determining whether the occlusion is a vulnerable soft plaque or a calcified plaque, or, if the occlusion is a thrombus, characterizing what type of thrombus is present.

[0057] In the described example, the system of the present invention comprises a wire that is manufactured with a specific grinding profile toward its distal end and whose longitudinally continuous portion has a specific diameter and length. Examples of such wire characteristics are taught in our aforementioned prior patent application. These characteristics allow the distal portion of the wire to operate in a specific manner at the resonant frequency (and harmonic frequencies related to or coincident with the resonant frequency) of the piezoelectric ultrasonic transducer that actuates the wire.

[0058] A coupling mechanism allows the wire to be coupled to a transducer. The transducer is driven by an ultrasonic signal generator that can excite the transducer, and therefore the wire, at a desired frequency and amplitude. A control circuit monitors and controls the electrical load across the transducer to produce the desired actuation.

[0059] According to the present invention, at least one acoustic sensor detects and essentially listens to acoustic emissions from the wires, couplers, and / or transducers. The system can monitor and analyze the detected acoustic spectrum and present the processed information to the user in a meaningful way. The acoustic information can be used in combination with other information, such as inputs to or outputs from the control circuitry, to improve the quality of the analysis, detection, and determination. The processed information can also be stored in and shared from an external database, such as the cloud, which is more preferable for educating physicians and making the analysis algorithm more complete, along with an increasing number of samples representing the use of the present invention in actual treatments.

[0060] The present invention exploits the insight that interpretation of the acoustic spectrum emitted by a vibrating wire or other wave guide while passing through a vascular structure can provide a means of interpreting tissue characteristics. This is possible because when the wire is forced into contact with any surface, such as the inner surface of a blood vessel or a lesion obstructing the vessel, the contact modulates the frequency and / or amplitude of the acoustic waveform traveling through the wire. These modulations can be related to specific features of the vascular anatomy. Furthermore, such ultrasonic high frequencies interact with the vessel wall to disrupt calcified material within the wall, thus allowing assessment of vessel stiffness while softening plaque.

[0061] Also, by looking at the acoustic spectrum alone, and / or from other inputs from the environment, it is possible to interpret the deformation of the wire as to what structures or materials it may come into contact with as it passes through the internal morphology of the vessel lumen, including any occlusions that may be present within the lumen, or the characteristics of such occlusions if the wire is excavating or removing such occlusions.

[0062] The basis for such an assessment is that the amplitude of the axial or radial displacement associated with resonance in the system varies with the input amplitude, and the attenuation or frequency shift is associated with losses caused by the wire contacting other materials or surfaces at its ends or along its length. These changes in the acoustics detected along the wire can be used to characterize the vessel, its lumen, and occlusions. Furthermore, since the impedance of the transducer may also be modulated as a result of changes in losses in the system as the wire becomes attenuated or more or less constrained, this superposition of electrical responses can be used to more accurately analyze and describe the characteristics of the vessel, its lumen, and any occlusions.

[0063] One or more acoustic sensors can be placed, for example, on, in, or near the transducer housing, or on a wire, or on a catheter, or in or in contact with the patient's body, to detect the emitted sound and subtract ambient noise. The resulting acoustic spectrum is processed and analyzed by algorithms that recognize acoustic spectra characteristic of particular types of interference and resonant and subharmonic frequencies. As mentioned above, the sensitivity of the acoustic algorithms can be improved by examining variations in the electrical signal used to drive the transducer at its resonant frequency.

[0064] The system compares the acoustic spectrum with the ultrasound spectrum in a device employing an intravascular waveguide, such as a wire, that resonates at a frequency and amplitude that allows the distal portion of the wire to resonate with axial and radial displacements. In the case of a transverse wire, the primary purpose of the axial and radial displacements is to excavate material that is occluding the vessel. In the present invention, these displacements are used for another or additional purpose, namely to generate acoustic signals that change in different ways as they travel through the vasculature and as they encounter and engage a lesion. The acoustic signals also change in different ways as they engage different types of lesions, thus serving as acoustic signatures that characterize the lesion.

[0065] As explained in our previous patent application mentioned above, the dimensions and profile of the transverse wire allow the wire, especially at its distal end portion, to resonate at various displacement modes at harmonic and subharmonic frequencies. Modulation occurs when the wire comes into contact with various surfaces. For example, when the distal tip of the wire encounters a calcified occlusion that constrains its lateral displacement, the wire's displacement mode transitions from "fixed-free" to "fixed-fixed". "Fixed-free" can be visualized as a node at the proximal end of the wire and an antinode at the distal end of the wire, and "fixed-fixed" can be visualized as a node at both the proximal and distal ends. This modulation slightly shifts the wavelength, and therefore changes the acoustic signal transmitted by the wire.

[0066] By analyzing the change in wavelength, the system can sense what type of material has perturbed that wavelength and frequency, and can therefore determine the type of material that the distal end portion of the wire is in contact with. Thus, interpreting the acoustic spectrum emitted by the waveguide as it passes through the vasculature can provide a means of interpreting the characteristics of the tissue that the wire is in contact with. Mathematical transformations can also be used to interpolate acoustic spectra or electrical signal features that indicate how the wire is responding to the internal morphology of the lumen as it clears an occlusion in the blood vessel.

[0067] Since the system is dynamic, the manner in which the system responds must be dynamically characterized to be faithful to the comparison of electronic control and acoustically emitted variables. Dynamic interrogation and subtraction, or addition in the case of patterned excitation, of features must be monitored in time. In this regard, feedback can be examined from compared programmed inputs, such as pulses or patterns, to determine the variation of a particular feature. Feedback can also be examined from compared variations over time, such as quality factor or Q value, which represents attenuation.

[0068] Thus, the present invention embodies the principle of acoustic characterization and proposes that an active element, such as a wire in situ within a blood vessel, generates characteristic acoustics when it comes into contact with the vessel wall and with an obstruction, either a thrombus (soft or fibrous) or an atherosclerotic lesion (hard or soft) within the lumen or within the vessel wall. The acoustic signature captured is characteristic of the vessel lumen and its surrounding tissue. It is proposed that direct comparative measurements, interpolated or extrapolated, allow for the generation of reliable diagnostic outputs that relate these characteristic acoustic spectra to tissue properties and integrity using post-processing analysis and appropriate algorithms.

[0069] A preferred embodiment of the present invention employs two sensors operating simultaneously: an electrical or electronic sensor and an acoustic sensor.

[0070] The electronic sensors act on features such as the transducer generating ultrasonic energy and determine how the transducer is operating, setting the extent of its ability to sense and generate data that can be examined. The electronic sensors also detect the electrical drive frequency and the manner in which the system responds to variability or instability caused by the wire moving through the tortuous vessel to the lesion point. The electrical drive frequency is modulated by encountering occlusions in the vessel wall and lumen. The driver electronics respond to this modulation by tracking phase angle, current, and / or voltage variables. The present invention contemplates examining this dynamic control variation in key variables to provide a characteristic signature that can be correlated to the physical characteristics of the vessel and any occlusions within the vessel.

[0071] One or more acoustic sensors or microphones listen to all or part of the acoustic emissions passing through and from the biological tissue when the active wire is in vivo, whether in the wall, in the lumen, or outside the body. The acoustic sensors in particular listen to the acoustic emissions from the wire operating internally within the lumen of a blood vessel. The invention makes it possible to study the variations in acoustic emissions that are subject to the interference of the wire with the blood vessel or anything within the vessel, such as a CTO.

[0072] The data set from the acoustic sensor is much richer than the data set from the small range of operating frequencies used in actuating the wire (even though acoustic emissions are generated by that small operating range). This results in a vast amount of additional data that can be mined using various mathematical techniques to find features that can be correlated with the nature of the vessel and its contents, the behavior of the wire, and the nature of the new flow channels excavated by its use. Thus, the electronic data set can be significantly enhanced by integrating the acoustic data.

[0073] Examining the full range and spectrum of different frequencies present requires significant post-processing evaluation, and therefore a cloud-based machine learning approach is preferred for the operation, development and updating of advanced algorithms. However, a suitably programmed on-board processor facility on the local device would allow the data to be manipulated by suitable algorithms to provide at least "binary" feedback, such as whether the lesion is calcified or non-calcified, hard or soft. It is emphasized that any form of post-processing, cloud or not, is not a requirement. Such processing may be performed locally in real time.

[0074] Thus, disclosed is an ultrasound system that induces vibrations in a customized endovascular surgical wire device, examines acoustic feedback, and optionally other feedback within the system, and applies artificial intelligence that can be used to optimize the performance of the system in navigating to, crossing, and characterizing and modifying the structure and properties of the endovascular occlusion.

[0075] The programmable circuitry system for acquiring and processing data and for controlling the operation of the system may include an integrated or on-board programmable digital signal processing chipset that processes monitored, transmitted and received, or input acoustic and / or electrical or electronic signals using algorithms to examine the response, compare the effect of ultrasonic feedback to a resonant frequency standing wave, estimate the size of the opening made through the lesion by the activated tip, and modulate the power of the system via voltage amplitude and system frequency.

[0076] The device's analog and digital signal analysis and power control, as well as its communications modules, allow for wired and wireless connections of the device and its data to wider data networks and the Internet, which may, for example, facilitate the development of more intelligent algorithms to manage the system.

[0077] When ultrasonic vibrations are transmitted through the transmission member, which acts as a waveguide, the distal tip of the transmission member vibrates at a predetermined frequency and amplitude capable of advantageously destroying diseased tissue or other material. Digital signal processing and control circuitry responds to acoustic and other feedback to allow for semi-autonomous global characterization of the lesion, power control, and estimation of the size of the opening in the system.

[0078] When an ultrasonic system is activated, emitted waves travel along the wire to its distal tip where they are reflected or transmitted to nearby material. Reverberation in the wire at various transition points establishes a series of secondary and tertiary reflections. These waves are characteristic of different wire designs and features and can be optimized to accentuate differences in the signal characteristics. The reflections are determined to be composed of a particular response pattern of waveforms at any given time for a given input, the variations of which are related to perturbations or differences in the surrounding environment. The waveforms produce characteristic acoustic emissions that can be used alone or in addition to other feedback signals.

[0079] The amplitude of the displacement along the wire at a particular frequency changes during the course of the procedure as a result of attenuation due to contact with the surrounding tissue, either while being guided to the lesion site or when in contact with diseased, incompatible, or calcified tissue at the lesion. Reverberation within the system and the resulting acoustic emissions are likewise affected in characteristic ways and can be used to characterize the cause and nature of the attenuation.

[0080] To provide a constant vibration amplitude, the ultrasonic transducer is controlled by a suitable feedback controller. In the case of ultrasonic waveforms, phase feedback control and comparison can be performed by an electrical equivalent model such as the Butterworth-van Dyke model.

[0081] Ultrasonic transducers can be controlled by the frequency and amplitude of the excitation voltage. By changing the frequency, the phase between the voltage and the current can be affected. The amplitude of the excitation voltage, which controls the current, is proportional to the vibration amplitude at resonance. This allows the control algorithm to drive the frequency using only the phase and amplitude.

[0082] In a preferred embodiment, the approach is to drive the system using the resonant frequency as the control operating point in combination with an amplitude feedback controller, and manage this operation using customized programmed control algorithms specific to each wire type.

[0083] The advantage of a resonantly driven, less damped system is that it requires lower voltages and has higher available power values. This solution also offers advantages in controlling the response of the Nitinol wire to ultrasonic actuation.

[0084] Temperature effects in Nitinol and changing loading conditions during treatment due to interactions with surrounding tissue can change the resonant frequency and vibration amplitude, but for a given transducer can be compensated for within ranges.

[0085] Thus, with respect to the use of voltage and current, control and analysis through resonant frequency can be used to monitor differential changes over time and length, and this interrogation and correction can be used to characterize the properties of the intravascular biostructure. The ability to capture acoustic emissions from the interaction of the system with adjacent tissue provides an additional and separate means of inferring or characterizing the properties of the tissue, since the tissue's response to interaction with the wire depends on the tissue's structural properties.

[0086] Comparison and analysis of the primary emission signal and tertiary feedback response in the wire takes into account the variation in characteristic losses typical when the active member engages different tissue types, healthy and diseased, and distinguishes between these types of losses in blood vessels and losses associated with lesions of different composition (e.g., calcified and non-calcified lesions).

[0087] The resistive load encountered and the acoustic emissions recorded by the system vary. As the active members pass through various anatomy, the analog signals are examined and conditioned by an on-board digital signal processor, and the parametric outputs are processed by algorithms and added to data from the acoustic feedback to characterize the response, define feedback, and provide control.

[0088] The algorithms may be customized for the wire type. Using the range of change, rate of change, and differential order of change filtered by the signal processing circuitry, the algorithms can characterize the properties of the material through which the wire passes. This can be communicated to the physician as the procedure is being performed to aid in treatment decisions.

[0089] To improve performance, the algorithms can be trained on bench ex-vivo and in-vivo data. The latter possibility is made possible by a communication model that provides for data transfer to and from the device. The system can allow for wired or wireless communication of data between the device and another device or cloud service for analysis and storage.

[0090] Thus, the quality of the device's operation and interpretation can be improved over time by the interpolation of more data sets from additional procedures built on usage experience. Such data can inform the design of the iterative generation of control and interpretation algorithms. As a result, on-board, local, and / or cloud-based refinements of the algorithms can improve the design and operation interface of the treatment device, providing more detailed feedback to the physician using the device in addition to customizing the device's operation to fit various wire shapes and anatomies.

[0091] The frequency at which the transducer generates the mechanical signal may be a set short-range frequency sweep over a short frequency range to accommodate losses from collisions and interactions with various forces over the length of the wire. The speed of the microprocessor allows the device to process small variations in resonance in real time.

[0092] The signal used to drive the ultrasonic generator can be pulsed or varied to reduce heating and optimize analysis and matching of offsets in resonant frequency. For example, pulse modulation of voltage over a small frequency range can actuate the traversing wire and a digital signal processor unit can examine the measurements made and provide feedback to interpret and compare the relative contributions of losses from anatomical tortuosity in navigating to the site and losses resulting from passing through an occlusion.

[0093] The present invention employs a method of examining the feedback signal to characterize the vessel or lesion that the wire is traversing and gather data about the lesion being traversed, such as its length and composition, facets that inform the manner in which the target lesion may be treated by the physician. This data may also be provided as feedback to the physician in tactile and / or visual and / or audio form on a display to aid the physician in operating the device. For example, this feedback may allow the physician to monitor the crossing procedure while displaying and assessing the characteristics of the lesion using a simple backlit screen on a small operating unit.

[0094] In another embodiment, if the user has access to a network, data from the procedure may be captured anonymously to protect patient confidentiality and communicated from the device to a data storage and processing platform where it can be analyzed in real time or at a later time. Lesion characterization may also be presented to the user for analysis and interpretation while the procedure is being performed.

[0095] The attachment can be used to record and measure the displacement of the wire as it traverses the vasculature, and the data can be mapped to the lesion composition from the feedback to characterize the lesion properties as a function of displacement through the lesion.

[0096] Variation in the magnitude of the input and control parameters of current, voltage, and frequency with the characteristic capacitance of the transducer provides a measurement and control matrix that can be used in combination with acoustic feedback to determine power and characterize the lesion being traversed.

[0097] Monitoring electronic responses such as acoustic emissions and current flow can aid in the interpretation of the lesion, and modulating the voltage allows for power amplification and frequency recovery as the device activates the contact surface to reduce offset. A series of measurements over such a small frequency range can globally characterize the composition of the lesion, such as calcified, fibrous, gelatinous, etc., over the entire or partial length of the lesion. These interpolated characteristic components are not absolute characteristics of the lesion, but instead indicate the composition, degree of calcification, and whether the lesion is hard, compacted, or disaggregated. This can indicate the nature of the lesion and inform the physician of the optimal treatment to consider. This can be useful, for example, to determine whether the composition or consistency of the lesion is compacted calcified particles, or uncompacted fibrous, or hard or soft gelatinous.

[0098] For each standard wire type, specific algorithms can be employed to estimate the diameter that will be mapped out by the deflection of the distal tip when excited at various levels of frequency and power and device configurations under procedurally relevant conditions, thereby providing an estimate of the diameter of the resulting tunnel-like flow path through the occlusion.

[0099] The system can process data obtained from measurements of ultrasonic waveforms as they are generated, as they pass through a wire or other transmission member, as transformation of resonant vibrations occurs, and as the reflected waveform is attenuated by the transmission member while passing through vascular structures and occlusions.

[0100] By monitoring and analyzing the modulation of the delivered signal, the energy losses in the system can be automatically adjusted through voltage control to increase the power of the system to compensate for the energy losses that occur in the wire as it passes through the vasculature to the occlusion, and by monitoring and analyzing the modulation of the delivered signal, it is possible to distinguish between these losses and additional losses as the wire passes through the occlusion and to compensate for these additional losses in order to maintain displacement at the distal tip.

[0101] The measured parameters and variables can be numerically manipulated to determine rates of change relative to each other and relative to other parameters. Differences between these calculated values ​​from the active system and a set of predefined values ​​can be compared and numerically interpreted to characterize the nature of the material occluding the blood vessel.

[0102] In summary, the present invention relates to an intravascular device for determining the condition of a blood vessel in a body. The device comprises an elongated wave-guiding element, such as a wire, and an actuation unit including a source of ultrasonic energy for actuating the wave-guiding element and thus transmitting ultrasonic energy to the active distal part of the wave-guiding element. According to the present invention, a signal acquisition system acquires feedback signals from the device for interpreting the condition of a vessel, cavity or structure of the body. The signal acquisition system comprises at least one acoustic sensor for acquiring an acoustic feedback signal generated by the device when the wave-guiding element is actuated, and / or at least one inertial sensor for acquiring information representative of the orientation of the actuation unit and / or the acceleration of the actuation unit. Data sets can be generated from the acoustic and / or non-acoustic feedback signals (including inertial or electrical signals), and a combination of or comparison between the data sets can characterize the condition of the vessel, cavity or structure, including any lesions, such as occlusions, in the vessel, cavity or structure. [Brief description of the drawings]

[0103] In order that the invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings in which: [Figure 1] 1 is a perspective view of an apparatus for implementing the present invention; [Diagram 2] FIG. 2 is a schematic side view of the cross wires of the device during actuation. [Figure 3a] First, second, third and fourth harmonic waveforms are depicted, with the wavelength of the second, third and fourth waveforms each being half the wavelength of the preceding waveform. [Figure 3b] 3a depicts the fundamental composite waveform generated from the harmonic waveforms of FIG. 3a. [Figure 4] FIG. 13 is a detailed side view of the active wire of the device protruding distally from the catheter. [Diagram 5] 11A-11C are a series of images showing the wire in operation drilling a tunnel into a lesion that was occluding a blood vessel. [Figure 6] 11A-11C are a series of diagrams showing an active wire tunneling into a lesion. [Figure 7] 11A-11C are a series of diagrams showing an active wire tunneling into a lesion. [Figure 8] 11A-11C are a series of diagrams showing an active wire tunneling into a lesion. [Figure 9] 1 is a diagram of an acoustic signal over time showing the response of an active wire upon encountering a calcium sample representative of a lesion. [Figure 10] FIG. 1 is a block diagram of an embodiment of the present invention. [Figure 11] FIG. 4 is a block diagram of another embodiment of the present invention. [Figure 12] 2 shows typical oscilloscope images of voltage and current waveforms applied to a transducer of a device such as that shown in FIG. 1. [Figure 13] FIG. 13 is a side view of a longitudinal section of a transverse wire and a catheter coupled to an actuation unit, showing possible locations of an acoustic sensor within the actuation unit. [Figure 14]FIG. 1 is a side view of a traversing wire and catheter coupled to an actuation unit, showing possible acoustic sensor locations on the catheter. [Figure 15] FIG. 1 is a perspective view of a catheter including a crossing wire, showing possible acoustic sensor locations on the catheter. [Figure 16] FIG. 1 is a perspective view of a traversing wire, showing possible acoustic sensor locations on the wire. [Figure 17] 1 is a schematic cross-sectional view of a patient's leg showing an acoustic sensor of the present invention incorporated into an adhesive patch applied to the leg proximate a lesion in the patient's vasculature. [Figure 18] FIG. 17 corresponds to FIG. 17, but instead of an adhesive patch, shows an acoustic sensor unit held against the leg in proximity to the lesion. [Figure 19] FIG. 18 corresponds to FIG. 18, but shows the acoustic sensor in the form of a handheld scanner that sweeps the leg proximate to the lesion. [Figure 20] 1 is a schematic side view of a patient's leg showing an acoustic sensor of the present invention subcutaneously implanted in the leg. [Figure 21] 20 is a schematic cross-sectional view corresponding to FIG. 19, showing one of the acoustic sensors implanted near a lesion in a patient's vasculature. [Figure 22] 1 shows the acoustic signal emitted in the frequency range up to 125 kHz when the active wire traverses the chalk sample. [Diagram 23] It corresponds to FIG. 22 but focuses on the range up to 10 kHz. [Figure 24] Figure 1 shows the acoustic signal emitted in the frequency range up to 125 kHz when the active wire traverses a sample of BegoStone gypsum. [Diagram 25] It corresponds to FIG. 24 but focuses on the range up to 10 kHz. [Figure 26] 1 shows the acoustic signal emitted in the frequency range up to 125 kHz when the active wire does not cross the sample but is instead active in water. [Figure 27] It corresponds to FIG. 26 but focuses on the range up to 10 kHz. [Figure 28] FIG. 1 is a schematic diagram of a device of the present invention that engages an occlusion in a blood vessel to create an opening. [Figure 29] 1 is a flow chart of the data acquisition and processing technique of the present invention. [Diagram 30] 13 is a power spectrum plot of the actuated wire captured by an external microphone. [Diagram 31] 1 is a plot of power within a power band expressed as amplitude versus time. [Diagram 32] 1 is a plot of total power plotted against time in a particular frequency band. [Diagram 33] 1 is a spectrogram of the frequency of a current signal when the amplitude of a drive current is changed. [Diagram 34] 4 shows the impedance magnitude and impedance phase of a transducer plotted against frequency. [Diagram 35] FIG. 13 is a side view of a longitudinal section of a traversing wire and a catheter coupled to an actuation unit, showing further options for an inertial sensor within the actuation unit. [Diagram 36] FIG. 2 is a bottom perspective view of the actuation unit of the present invention showing the X, Y and Z axes along which linear acceleration can be measured, and changes in pitch, roll and yaw motion of the actuation unit can be measured by an inertial measurement system within the unit. [Figure 37] FIG. 37 is a block diagram of an embodiment of the present invention implementing inertial sensing as shown in FIGS. 35 and 36. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0104] FIG. 1 of the drawings shows the overall configuration of a system for implementing the invention, and illustrates some of the major components of such a system. This example features a handheld ultrasonic actuation unit 2 through which extends a centrally aligned flexible transmission member in the form of an intravascular waveguide or wire 4. In this example, a portion of the wire 4 extends both proximally and distally from the actuation unit 2. This arrangement is advantageous for a variety of reasons, as described in a previous patent application by the inventor, but is described here to illustrate, and not to limit, the invention. The invention may be advantageously used in combination with more conventional actuated transverse elements, which may extend only distally from the ultrasonic actuator, for example.

[0105] The wire 4 may be inserted into the patient's vasculature and traversed to move its distal end to the location of the lesion. At or before the wire 4 encounters a complex lesion that resists crossing, the actuation unit 2 may be coupled to the wire 4 at an appropriate longitudinal location. Upon actuation, the actuation unit 2 transmits ultrasonic vibrations to and along the wire 4, enhancing the ability of the wire 4 to cross the lesion via ablation and other mechanisms. This allows the wire 4 to function as a traversal wire to pass an obstruction in a vessel and then remain in situ to function as a guidewire for delivery of a subsequent therapeutic device to treat the lesion.

[0106] Typically, the length of the wire 4 can be greater than 2 m, up to 3 m. For example, accessing a lesion in or through the foot may involve the wire traveling a distance of typically 1200 mm to 2000 mm within the vasculature, depending on whether an ipsilateral, contralateral, or radial approach is selected. In this regard, the wire 4, tapering distally to become a fine wire at its tip, can be guided into the pedicle artery and around the arch of the foot between the dorsal and plantar arteries. However, the present invention is not limited to the subinguinal or peripheral vessels of the foot, and can be used, for example, in coronary applications where the ability of the wire 4 to navigate and drill within tortuous small diameter arteries is also beneficial.

[0107] The actuation unit 2 may include user controls 6 and, optionally, a display. The actuation unit 2 further comprises a distal hand toggle 8 that can be rotated by a user about a central longitudinal axis of the unit 2 and the wire 4. In particular, the actuation unit 2 can be slid over the wire 4 and can be coupled to the wire 4 at multiple longitudinally spaced positions by applying a torque to rotate the toggle 8.

[0108] To effect the coupling, the toggle 8 acts on a collet in the actuation unit 2 that surrounds and is coaxial with the wire 4, as shown in subsequent figures. When the toggle 8 is tightened, the collet grips the wire 4 to transmit ultrasonic energy from an integrated ultrasonic transducer in the actuation unit 2, optionally through an amplifier horn coupled to the transducer. The wire 4 may be coupled directly to the transducer in some embodiments, in which case the horn may be omitted.

[0109] The rotation of the toggle 8 is reversible to release the actuation unit 2 from the wire 4. This allows for the exchange of wires 4 of different sizes, configurations or materials for different purposes. There is also the possibility to exchange transducers, horns and / or collets within the actuation unit 2.

[0110] 1, the ultrasonic signal generator 10 is separate from the actuation unit 2 and is connected to the actuation unit 2 by a connector cable 12. An integrated configuration in which the ultrasonic signal generator 10 is incorporated within the housing of the actuation unit 2 is also possible.

[0111] 1 has an ultrasonic signal generator 10 that is externally powered and therefore includes a power cable 14 for connection to a source of external power. Other examples may be powered by an internal battery that may be built into the ultrasonic signal generator unit 10 or the actuation unit 2.

[0112] In general, the components of the system are preferably portable, and more preferably handheld. The components may be wireless, rechargeable, reusable, and recyclable. Any external cables 12, 14 for transmitting power or signals may be coupled through slip rings to allow free rotation of the cables 12, 14 and avoid entanglement with the wires 4.

[0113] The diameter of the distal portion of the wire 4 determines the flexibility of that distal portion and its ability to easily conform to the shape of the anatomy it is intended to pass through. For example, for a particular Nitinol with a particular thermal transition temperature, a distal portion having an appropriate length and a diameter of, for example, 0.005 inches to 0.007 inches will combine adequate flexibility with the ability to excavate occlusive material in tortuous (foot or coronary) anatomy.

[0114] When using ultrasonic energy to excite the wire 4, it is desirable to optimize the displacement amplitude at and around the distal tip of the wire to excavate and traverse the lesion. Conversely, it is desirable to minimize the displacement or movement of the proximal end portion of the wire 4, which is outside the patient's body and part of which may hang freely proximal to the working unit 2. To achieve this, the distal length of the wire 4 from the distal tip to where the working unit 2 is coupled to the wire 4 should be an odd multiple of a quarter wavelength of the ultrasound. This creates a standing wave in the wire with an oscillating antinode at the distal tip, maximizing the amplitude of vibration at the distal tip.

[0115] Referring now also to Figure 2, the wire 4 includes a region whose geometry tapers to provide a change in diameter. Specifically, the wire 4 shown in Figure 2 comprises a substantially straight proximal section 16 and a substantially straight distal tip 18 that provides a drilling section for traversing the lesion. The distal section 18 is thinner than the proximal section 16 and may be tapered or may be uniform in diameter along its length.

[0116] Distal section 18 is joined to proximal section 16 by a distally tapered transition section 20. Proximal section 16, distal section 18 and transition section 20 are coaxially aligned with one another along a central longitudinal axis of wire 4, but are substantially flexible to bend along their lengths.

[0117] The purpose of the tapered transition 20 is to provide gain and sustain the transmission of ultrasonic energy through the wire 4. For purposes of amplification, the change in cross-sectional area represents a level of gain in both lateral and longitudinal displacement amplitude in the wire 4. The length and diameter of the distal section 18 determine the mode and magnitude of displacement in the axial and radial directions. The transition 20 also affects how the lateral mode of displacement can be established in the distal section 18 of the wire.

[0118] As with all intravascular wires, a balance is required between flexibility, expressed as "trackability," and stiffness, expressed as "pushability" or "steerability." As previously mentioned, pushability requires longitudinal cylindrical stiffness, and steerability requires torsional stiffness. However, unlike passive wires, the wire 4 must also be capable of transmitting ultrasonic energy to the distal portion 18 to aid in crossing the lesion. In this way, the wire 4 functions as a driller along part of its length, not just its tip. In particular, the distal portion 18 acts radially as a lateral drilling device to drill an opening in the lesion in the vessel. The wire 4 may also have a distal portion shaped to amplify the radial drilling.

[0119] Since the goal of the actuated wire 4 is to pass through the lesion, its dimensions are optimized with the goal of drilling the largest opening possible for a given input power. Specifically, the distal portion 18 of the wire 4, when actuated by ultrasonic energy as shown in FIG. 2, moves in and out in a primary longitudinal mode, and also moves radially, mapping and drilling a larger volume at the distal end via lateral movement or radial displacement along the wire 4. It can be seen that the distal portion 18 of the wire 4 also moves through lateral and undulating motions at or near the driving frequency under secondary modes of resonant waves and differential harmonics, depending on the actuation frequency, the length of the distal portion 18, and the tortuosity of the anatomy. These waveforms can interfere with each other and can be more or less effective at drilling material at different moments.

[0120] Figures 3a and 3b show one reason for these complex movements of the distal portion 18 when the wire 4 is actuated. Figure 3a shows first, second, third and fourth harmonic waveforms 22A, 22B, 22C, 22D. Note that the wavelength of each of the second, third and fourth sub-harmonic waveforms 22B, 22C and 22D is 1 / 2 the wavelength of the preceding waveform, respectively. Figure 3b shows composite waveforms 24A, 24B, 24C that are generated from the combination or superposition of the sub-harmonic waveforms 22B, 22C, 22D with the harmonic waveform 22A of Figure 3a.

[0121] Further low frequency lateral vibrations may occur when the distal portion 18 of the wire 4 exits the surrounding sheath or catheter 26, as shown in Figure 4 of the drawings. The freedom of motion allows for lateral components to be expressed, some of which may result from a cantilever effect. In this regard, Figure 4 illustrates how sleeved wire 4 in this manner allows the desired distal length to be free to oscillate laterally as shown. The distal extent of the sleeve, and therefore the length of the free end of wire 4, controls the drilling by distal portion 18 of wire 4. Sleeved or coated wire 4 at its resonant length or harmonic wavelength such that the distal end of catheter 26 substantially matches its resonant length or harmonic wavelength, allows wire 4 to drill a larger opening.

[0122] Optionally, the catheter 26 and / or the wire 4 can be moved longitudinally relative to one another in the distal and proximal directions as shown, for example by rotating a thumbwheel on the actuation unit 2 acting on the outer sleeve of the catheter 26. The behavior of the wire 4 can also be influenced by adjusting the radial gap between the catheter 26 and the wire 4, or by applying a radially inward force from the catheter 26 around the wire 4, as also shown diagrammatically in Figure 4. Squeezing or forcing the wire to be radially constrained using a collar such as a balloon has different effects depending on the frequency at hand and the relative location of the acoustic source and its coupling with the wire.

[0123] The diameters of the various portions 16, 18, 20 of the wire 4 are selected for an optimal balance between pushability and trackability, in addition to allowing subsequent devices of standard dimensions to use the wire 4 as a guidewire. By way of example, the proximal portion 16 may have a diameter of 0.43 mm and the distal portion 18 may have a diameter of 0.18 mm or 0.25 mm. The taper of the intermediate transition portion 20 is slight and is therefore greatly exaggerated in FIG. 2. The transition portion 20 may extend over a multiple of λ in length or a fraction of λ in length, which fraction is preferably a numerator of 1 and an even number in the denominator (e.g., an arrangement of 1 / 2, 1 / 4, 1 / 8...), whereas the distal portion 18 may be λ / 2 in length or a multiple of λ / 2 or a fraction of λ / 2, such as λ / 4. The optimum lengths we have found for the materials under consideration for sections 18 and 20 are λ, λ / 2, and potentially λ / 4 at lower subharmonics and for fine wires.

[0124] The overall geometry of the wire 4, including its nominal diameter and length, as well as the drive frequency of the system, are determined by the characteristic speed of sound in the wire's material. This characteristic is a function of the properties of that material and its geometry. The selected frequency creates harmonics along the length of the wire, and the load at the tip of the wire 4 helps establish a standing wave. The system can create lateral and longitudinal displacements over a range of frequencies away from the frequency range of the drive frequency, often occurring at subharmonics of the frequency at the distal section 18.

[0125] In one example, without excluding other dimensions, a wire 4 having a core cross-sectional diameter of 0.43 mm defining a proximal portion 16 has a tapered transition portion 20 optimally positioned to transition to a distal portion 18 having a diameter of 0.18 mm. The length of each portion 16, 18, 20 of the wire 4 can be selected to have a longitudinal resonant mode at or near the drive frequency, e.g., 40 kHz, with strong subharmonics at or near 20 kHz, 10 kHz, etc. With proper design, there are adjacent transverse modes near 40 kHz and near 20 kHz, etc. There may be an amplification of about 2.4 times across the tapered transition portion 20, or other suitable value.

[0126] As a result, even when the wire 4 is driven with longitudinal vibrations, by proper selection of materials, geometry, and distal design features, the desired transverse modes are excited, as shown in Figure 2. Both longitudinal and transverse vibrations contribute together to drilling the lesion, such that the wire 4 opens an opening or lumen in the lesion whose inner diameter is substantially larger than the diameter of the wire 4.

[0127] Thus, upon actuation, the wire 4 functions as an excavation tool that excavates a tunnel through itself by excavating material distal to the tip 18 of the wire 4 through longitudinal motion of the wire 4 and then providing a lateral offset that widens the diameter of the tunnel through offset translational or lateral motion of the wire 4 within the vasculature. As a result, the wire 4 scrapes the inner surface of the occlusion not only at its distal tip but also along a portion of its length extending proximally from the distal tip, creating a wider opening for passage of a subsequent treatment device on the wire 4. This effect is illustrated in Figures 5-8 of the drawings.

[0128] 5 illustrates how the distal portion 18 of the wire 4 can drill an opening 28 in the lesion 30 that is larger in diameter than the diameter of the wire 4 to create a larger lumen through which therapy can be introduced to the lesion 30. The active wire 4 performs both longitudinal, axial, or directional drilling, and radial, lateral, or orbital drilling by circling the wire 4 at different harmonics outside of the axial plane of the wire 4 in a consistent and monotonous manner.

[0129] The wire 4 can be guided along the blood vessel 32 to the lesion 30 in either an active or passive mode. Upon actuation and contact with the lesion 30, the wire 4 transitions from a "fixed-free" state to a "fixed-fixed" state, which attenuates some of the amplitude exhibited by the wire 4. As the wire 4 passes through the lesion 30, subharmonic displacements are exhibited, and then as the wire 4 returns to the "fixed-free" state, lateral subharmonic components are exhibited, excavating a larger opening 28. In this manner, the lateral vibration of the wire 4 carves out a flow path through the lesion 30 within the lumen of the blood vessel 32.

[0130] Figures 6, 7, and 8 illustrate how the ability to change the relative longitudinal positions of the wire 4 and catheter 26 can be utilized to affect lateral movement of the distal end of the wire 4, thereby affecting secondary or lateral drilling, perforation, or tunneling of the lesion 30 by the wire 4 within the lesion 30. In particular, Figures 6, 7, and 8 illustrate generally how the distal end of the wire 4 may first penetrate the lesion 30 as shown in Figure 6 to form a longitudinal opening 28, and then the lateral vibration of the wire 4 may be optimized to widen the opening 28 to form a lumen of a desired diameter, as shown in Figures 7 and 8.

[0131] When a sufficient free end length of the wire 4 extends distally beyond the lesion 30, lateral vibration at that free end portion begins to laterally excavate a distal segment of the lesion 30, as shown in Figure 7. The actuated wire 4 is then pulled back proximally through the lesion 30, which dilates and widens the opening 28, aided by optimized lateral vibration in the portion of the wire 4 between the catheter 26 and the lesion 30, as shown in Figure 8. If desired, the actuated wire 4 can be pushed back distally through the lesion 30 to further widen the opening 28.

[0132] 2-8, it will be apparent that the behavior of the active wire 4, and particularly its distal tip 18, changes as the wire 4 is subjected to changing environmental influences during use within the anatomy. Thus, the behavior of the wire 4 depends on the location of the distal tip 18 in the anatomy, the medium through which the distal tip 18 moves, and particularly the materials and structures with which the distal tip 18 comes into contact. These behaviors, and the changes between behaviors, are manifested in terms of wavelength, frequency, amplitude, and the expression of subharmonic and complex waveforms.

[0133] The present invention embodies the principle that these features of the behavior of the active wire 4 produce characteristic acoustic emissions that can be detected and analyzed to determine the behavior of the active wire 4 and thereby infer the factors that produce that behavior. The acoustic signature can thus be used to infer information such as the medium through which the distal tip 18 is moving, as well as the materials and structures with which the distal tip 18 is in contact.

[0134] To illustrate this principle, FIG. 9 shows the acoustic signature of the active wire 4 on the left before contact with the lesion 30 and on the right while in contact with the lesion 30. Two acoustic signatures are shown on the right side of FIG. 9, one from an acoustic sensor located distally close to the active tip of the wire 4 and one from an acoustic sensor located proximally, for example in or adjacent to the actuation unit 2. The acoustic signatures are plotted as frequency on the vertical axis against time on the horizontal axis. In this example, the lesion 30 was represented by a sample of calcium carbonate in the form of chalk. The wire 4 was driven at a frequency of 40 kHz.

[0135] As shown on the left side of FIG. 9, it is clear that prior to contacting the lesion 30, the wire 4 exhibits vibrations primarily around 20 kHz subharmonic. Conversely, as shown on the right side of FIG. 9, while in contact with the lesion 30, the wire 4 begins to exhibit vibrations at various subharmonic frequencies below 20 kHz, as indicated by oval A. The acoustic signature thus reflects that the wire 4 is currently in the process of passing through the lesion 30. Furthermore, aspects of the acoustic signature can be analyzed and compared to known signatures to characterize the lesion 30 itself. For example, the onset of cavitation is typically characterized by an increase in broadband noise.

[0136] Figure 10 shows components and elements of a system 34 that detects and acts on acoustic feedback from the active wire 4. Figure 10 also shows the flow of data through the system, including communications. A controller 36, which may be located within the housing of the actuation unit 2, controls an ultrasonic generator 38 to generate signals that are converted into ultrasonic energy by a transducer 40. The ultrasonic energy is delivered via a coupling 42, such as the collet described above, and an optional acoustic horn, to the active wire 4, which is guided through the vasculature and crosses an occlusion, such as a CTO.

[0137] Acoustic feedback from the active wire 4 is received by one or more acoustic sensors 44 or other transducers, such as microphones, amplified by amplifiers 46, filtered by a series of bandpass filters 48, and then undergoes analog-to-digital conversion 50 to generate feedback data that is transmitted to a processor 52. The controller 36 preferably controls a wireless communication system 54, for example using a Wi-Fi network or a Bluetooth connection, to receive the data from the processor 52 and communicate the data to local storage 56 and / or the cloud 58. Figure 10 further illustrates means for providing feedback to the user, such as a display 60 and / or a haptic feedback system as previously discussed.

[0138] System 62 shown in Figure 11 is an improvement over system 34 of Figure 10. Like features are numbered similarly. In system 62 of Figure 11, non-acoustic feedback is obtained from a second additional source, namely electrical feedback receiver 64. The signal from electrical feedback receiver 64 is amplified by amplifier 46 and filtered by band pass filter 48 before undergoing analog-to-digital conversion 50 to generate additional auxiliary feedback data that is sent to processor 52.

[0139] The electrical feedback receiver 64 can, for example, detect changes in the impedance of the transducer 40 driving the wire 4, which are due to changes in losses in the system as the wire 4 becomes damped or more or less constrained. For example, increased damping reduces the Q of the system.

[0140] The Q value can be measured as shown in Figure 12. The upper trace in Figure 12 shows the voltage applied to the transducer 40 by the ultrasonic generator 38. The lower trace shows the current through the transducer as measured by the electrical feedback receiver 64. If the voltage signal is suddenly stopped, the system will continue to resonate for a length of time proportional to Q. By curve fitting an exponential decay function to the current signal, the processor 52 can derive the value of Q, and therefore the decay. This value is affected by the nature of the lesion 30.

[0141] Characterization of impedance changes may include isolating differences based on position or dynamic variations and comparing variations in voltage, current, and phase angle over different times. The overlay of data representing this electrical response with data representing the corresponding acoustic response at a given time point can be used to more accurately analyze and describe the characteristics of the blood vessel 32, its lumen, and lesion 30.

[0142] Similarly, two or more acoustic sensors 44 could be employed at different locations within the system or relative to the lesion 30 to provide additional acoustic data to corroborate and confirm the measured characteristics of the blood vessel 32, its lumen, and any lesion 30. While Figures 12-20 illustrate various possibilities in this regard, it is understood that one, two, or more acoustic sensors 44 may be employed at or near any of the locations described and illustrated.

[0143] In general, the acoustic sensor 44 may be placed in any of a variety of locations within the system. Different sensor locations will result in different acoustic signatures. By placing multiple acoustic sensors around the transducer 40 and associated collets, different relative patterns of characteristic spectra can be produced that can be examined for correlation with various features. The external acoustic sensor may also integrate lighting, such as LEDs, to provide visual feedback on the performance of the system. This may be interpolated from changes in the acoustic signature or by overlaying the acoustic response on top of the electronic or electrical response of the system.

[0144] Reference is now made to Figure 13, which shows an ultrasonic actuation unit 2 having a longitudinally extending wire 4. In this example, the actuation unit 2 is externally powered and optionally supplied with an ultrasonic signal via a cable 12.

[0145] FIG. 13 shows that the actuation unit 2 includes an ultrasonic transducer 40 and a distally tapered acoustic horn 66 attached to a distal face of the transducer 40. A collet 68 couples the wire 4 to the distal end of the horn 66. The transducer 40, horn 66, and collet 68 have a central lumen through which the wire 4 can pass, such that the wire 4 extends the entire length of the actuation unit 2 and exits proximally from the actuation unit 2. The actuation unit 2 can be moved along the wire 4 and then coupled at any of a variety of positions along the wire 4 to transfer ultrasonic energy to the wire 4. In an alternative arrangement, the wire 4 can instead exit laterally from the actuation unit 2 at a position proximal to the collet 68.

[0146] 13, a catheter 26 that surrounds and supports the wire 4 may be bonded to a distal region of the wire 4. In this example, the bond is made by a distal annular balloon 70 in the catheter 26 that expands into the distal lumen of the catheter 26 around the wire 4. The balloon 36 may be inflated through an inflation port 38 on the catheter 26. The catheter 26 may also include additional ports and lumens, for example, for aspiration of emboli or aspiration of debris or particles generated during drilling.

[0147] Optionally, the balloon 70 or other coupling may be configured to grip the wire 4 and apply an inward clamping force to a distal portion of the wire 4. In this manner, ultrasonic energy may be coupled through the waveguide element of the catheter 26 and electromechanical energy may be transferred from the catheter 26 through the balloon 70 coupling to the distal tip region of the wire 4.

[0148] The proximal end of catheter 26 is coupled to transducer 40 by adapter element 72. The proximal end of adapter element 72 abuts the distal end of horn 66 about collet 68 and is thereby coupled to transducer 40 to receive ultrasonic energy. In principle, adapter element 72 can facilitate the transfer of energy from transducer 40 in any of three modes of operation: independently actuating wire 4, independently actuating catheter 26, or simultaneously actuating catheter 26 and wire 4.

[0149] The acoustic sensor 44 may be located on the outside of the actuation unit 2, within the body of the actuation unit 2, or in different parts of the catheter 26. Different locations of the acoustic sensors may provide unique interference and signature patterns in the acoustic spectrum.

[0150] In the example shown in FIG. 13, the acoustic sensor 44 is disposed adjacent to and proximal to the collet 68 on an adapter element 72 , which here is attached to the housing of the actuation unit 2 .

[0151] In addition to locating the acoustic sensors 44 within the housing or casing of the actuation unit 2, it is also possible to locate the acoustic sensors 44 outside the housing, for example along the catheter 26. In this regard, FIG. 14 shows an external view of the actuation unit 2 with the catheter 26 extending distally from the unit 2, where the various acoustic sensors 44 are located distal to the collet 68. One acoustic sensor 44 is located at the distal end of the unit 2, specifically on or in the toggle 8 acting on the internal collet 68. Two further acoustic sensors 44 are shown on the catheter 26, one near the proximal end and one near the distal end of the catheter 26.

[0152] 15 shows the catheter 26 and the wire 4 therein, separated from the working unit 2. An acoustic sensor 44 is shown near the distal end of the catheter 26. The catheter 26 thus provides a means for introducing the acoustic sensor into the blood vessel.

[0153] Incorporating an acoustic sensor 44 into the catheter 26 and introducing the catheter 26 onto the wire 4 to the location of the occlusion or to the distal end of the wire 4 provides a method for measuring the manner in which the wire 4 interacts with the blood and any acoustic effects resulting from the interaction of the wire 4 with the blood vessel 32 or any occlusion 30 therein. As previously mentioned, it is possible to adjust and control the distance that the wire 4 extends beyond the microcatheter sleeve and therefore the length of the wire 4 that is exposed within the lumen of the blood vessel 32. This adds additional control over how the wire 4 is excited and how acoustic emissions can be generated from within the blood vessel 32.

[0154] Containing the acoustic sensor 44 in or on the catheter 26 makes the overall system more efficient. The proximity of the wire 4 to the acoustic sensor 44 and its ability to capture emissions from the catheter 26 makes the acoustic sensing more reliable, reducing variations that may result from tissue variability, while being more sensitive to variations that may result in the pattern of acoustic emissions resulting from the interaction of the wire 4 with the catheter 26.

[0155] FIG. 16 shows that a sensor may also be affixed to the wire 4 itself, for example in the form of an electrical or optical strain gauge 74. In this example, the strain gauge is attached to the proximal portion 16 of the wire 4, near the tapered transition 20 that leads to the thinner distal portion 18 of the wire 4. Such a sensor may function as an acoustic sensor, or the behavior of the wire 4 may be determined more directly from the strain induced in the wire 4 when actuated. For example, the incorporation of an acoustic emitter or microarray on the surface of the wire 4 may provide a means to optimize radiation in a particular range of interest. The signal from the strain gauge 74 may further corroborate the data received from the acoustic sensor 44 in addition to, or instead of, non-acoustic feedback from an electrical feedback receiver 64 as shown in FIG. 11.

[0156] 17-21 illustrate various methods of placing an acoustic sensor on or within a patient's body, exemplified here by the patient's leg 76. In each case, an active wire 4 is advanced through the patient's vasculature and into a blood vessel 32 that is occluded by a lesion 30, shown here in the leg 76. The distal tip of the wire 4 has engaged the lesion 30 and is about to be activated with ultrasonic energy to begin excavating a flow channel through the lesion 30.

[0157] 16 to 19 show an external placement of the acoustic sensor 44. By placing the acoustic sensor 44 outside the body, acoustic emissions from the wire 4 and blood vessel 32 can be examined through the surrounding tissue.

[0158] In Fig. 16, the acoustic sensor 44 is incorporated into a surgical patch or embodied in a surgical band or the like to bring the acoustic sensor 44 in close proximity to tissue. The acoustic sensor 44 is placed near the area of ​​interest along the length of the blood vessel 32 or in the area of ​​the patient's body affected by disease in the blood vessel 32. Alternatively, an ultrasound probe can function as the acoustic sensor 44 to detect acoustic emissions, as shown in Fig. 17 as a fixed unit and in Fig. 18 as a handheld unit that can be swept over the patient's skin proximate to the lesion 30. Data from the probe can then be used directly to interpolate the location and proximity of the lesion 30 and the manner in which the wire movement is impeded to characterize any occlusions present.

[0159] 20 and 21 show an internal placement of the acoustic sensor 44 on a probe 78 that is placed inside the body, allowing the acoustic sensor 44 to be introduced through tissue into the compartment surrounding the blood vessel 32 to access an area of ​​the blood vessel 32 where a lesion 30 is to be treated or an area of ​​the blood vessel 32 that is to be evaluated for diseased medial tissue.

[0160] Surgical insertion into tissue of a probe 78 carrying an acoustic sensor 44 at its distal tip provides access to the region of the lesion 30 or blood vessel 32. This allows detection of acoustic radiation generated by the interaction of the wire 4 with its surroundings and transmitted through the blood vessel 32 without the loss and aberration of the acoustic spectrum that can occur from passing through significant thicknesses of muscle and skin.

[0161] Figures 22 to 27 show how the acoustic signal emitted by the active wire, especially the specific frequencies, evolves as it passes through various materials. The materials chosen are chalk (Figures 22 and 23), BegoStone (Figures 24 and 25) and water (Figures 26 and 27). BegoStone® is a commercially available ultra-hard gypsum originally developed for dental applications. In each case, the wire and sample were placed in a water bath and the signal was acquired using a hydrophone placed near the distal tip of the wire. The signal was captured on an oscilloscope and no post-processing was performed.

[0162] For each material, the acoustic signal is shown over a wide frequency range up to 125 kHz (Figures 22, 24, 26) and a narrower low (audible) resonance range up to 10 kHz (Figures 23, 25, 27). The lower range is taken from a larger data set which is itself a sample in time.

[0163] Nominally, the system is designed to be driven at 40 kHz, but with the wire 4 and collet 68 in place, the system actually resonates (and thus the electronics drive the system) at a slightly different frequency of about 38 kHz. It is therefore expected that, when all other acoustic effects are subtracted, a line will only be visible at a frequency of about 38 kHz. Such a line is obvious and can also be measured electronically by the electrical feedback receiver 64, as well as the 40 kHz line at which the wire 4 is designed to resonate. However, several more emitted resonant frequencies are observed as features that appear at different frequencies, particularly harmonics of the system's drive frequency, but also at other frequencies. Thus, in addition to the 38 kHz line, large amplitude acoustic emissions can be seen at harmonics of 8 kHz, 19 kHz, and 76 kHz, as well as at even higher frequencies such as 114 kHz. Other characteristic features appear around and between these harmonics of the drive frequency. Characteristic emissions at different frequencies also appear in the lower ranges shown in Figures 23, 25, and 27.

[0164] In summary, a preferred embodiment of the present invention comprises an ultrasonic generator, a transducer, an active elongate element such as a wire and / or catheter, a signal processing system, and a controller that monitors the sensor data output of the signal processing system, including both the electrical feedback signal from the microphone and the acoustic signal.

[0165] The sensor data, whether in raw or processed form, can provide real-time information to the controller for autonomous and adaptive control of the system. The sensor data can further provide the user with real-time or follow-up information regarding the condition of a vessel or cavity within the body, such as the nature of an occlusion being crossed by the active element. The sensor data can further be communicated to a secondary system via a wired or wireless interface for further processing.

[0166] In the embodiment shown in Figure 28, a vibration or acoustic sensor, such as a surface microphone 80, is placed outside the patient's body. For example, a piezoelectric contact microphone 80 may be adhered to the patient's skin in a location best suited to detect emissions from the active element. The active element is illustrated here as a wire 82 that projects distally from within a surrounding catheter 84 and is driven by a handheld actuation unit 86 external to the body 88 to drill an opening 90 in an occlusion 92 blocking a blood vessel 94.

[0167] The controller 96 shown in Fig. 28 comprises a processor 98, a user interface 100 and an integrated data acquisition system 102. The controller 96 is shown here as a separate unit from the actuation unit 86, but may alternatively be incorporated into the actuation unit 86. The microphone 80 may be connected to the actuation unit 86 or the controller 96 via a wired or wireless signal transmission connection for communicating acoustic emission data 104 to the controller 96. The data acquisition system 102 may capture both electrical performance data from the actuation unit 86 and acoustic signals from the microphone 80 at an appropriate resolution and data sampling rate.

[0168] In other embodiments, the microphone 80, hydrophone, or other vibration or acoustic sensor may be located elsewhere, for example by being mounted on, integrated with, or otherwise positioned on or near the distal tip of the support catheter 84. In this case, the microphone 80 is most conveniently connected to the actuation unit 86 or controller 96 via a wired signal transmission connection running along the catheter 84, although a wireless connection is in principle possible. The catheter 84 supporting the microphone 80 may house the active wire 82, or may be separate from the active wire / catheter system.

[0169] The microphone 80 or other vibration or acoustic sensor may be designed to operate in the audible acoustic range, thus from 20 Hz to 20 kHz and / or 250 kHz, or any other suitable frequency range.

[0170] In one embodiment of the processing algorithm of the present invention illustrated in Figure 29, the acoustic emission data signal 104 acquired from the microphone 80 is converted from the time domain to the frequency domain by the data acquisition system 102. The conversion from the time domain to the frequency domain may be accomplished by a Fast Fourier Transform (FFT), a power spectrum, or other known methods. The data acquisition system 102 further acquires electrical performance data 106, such as transducer voltages and currents acquired from the transducers of the operational unit 86.

[0171] The frequency domain data at 108 and the power spectrum data at 110 are evaluated to determine characteristic features such as peaks in the frequency or power spectrum at 112 and power in frequency band ranges at 114. Once determined, the features are compared to threshold parameters evaluated through extensive testing to determine interactions between the active elements and the patient's tissue, which may include occlusions in blood vessels or cavities within the patient's body.

[0172] The detected peaks at 112, the power within the frequency bands at 114, and the electrical performance data 106 are combined to form a feature dataset at 116. The features in the dataset 116 can then be interpreted by a pre-trained machine learning decision algorithm at 118 for classification. In particular, such algorithms 118 are pre-trained on supervised datasets derived from data with extensive test runs and classification labels. The feature dataset can be expanded over time as new information-bearing features are discovered and added.

[0173] Characteristic features of the processed data are not limited to frequency peaks 112 and bands 114. For example, the entire frequency spectrum can itself serve as a characteristic feature. In this regard, the complete frequency spectrum may contain information that is not human observable and requires machine learning algorithms to extract. For example, sequence images of spectrograms sampled at regular intervals can be subjected to deep learning neural nets or similar image processing techniques to identify and classify the images and thus, for example, to identify and characterize stages in the wire crossing process.

[0174] The described system employs a sensor fusion approach by combining electrical and acoustic sensor data while driving the transducer of the actuation unit 86 in a "normal" mode in which the wire 82 excavates an opening 90 in the occlusion 92. Combining data from two different sources in this way provides a richer data set 116 with multiple features that can be extracted simultaneously. This allows for more sophisticated analysis and improves the reliability of the measurements.

[0175] In "normal" mode excitation, the system integrates electrical feedback data with acoustic emission data for the purpose of analyzing and determining device performance and inferring interactions between the wire 82 or other active elements and tissue. This is done by examining extracted features such as peaks and maxima / minima in the measured quantities. Such interactions may include, but are not limited to, wire-tissue contact, characterization of tissue composition, wire emergence distal to the occlusion 92, and the resulting profile of the opening 90 after passing through the occlusion 92.

[0176] Figure 30 shows an FFT plot of the acoustic emission signal 104 of the actuated wire 82 captured via the external microphone 80. The detected peaks relate to the drive frequency, but other harmonics are indicative of the wire configuration, and the position and amplitude of the peaks, indicated by the arrows, change in response to changes in the wire configuration. For example, as the length of the wire 82 emerging from the distal end of the catheter 84 increases, the peak position changes in response, as indicated by the arrows in Figure 30.

[0177] FIG. 31 shows how a wire-tissue contact event, again indicated by an arrow, can be detected by monitoring the power or the power within a frequency band.

[0178] Figure 32 shows another example where the acoustic emission data 104 from the microphone 80 is transformed into the frequency domain. Here, the power in a particular band (in this case 600Hz to 800Hz) is extracted and the total power is plotted over time as the system traverses a 3mm lesion.

[0179] The example shown in FIG. 32 reflects experimental work demonstrating how it is possible to assess the diameter of any opening or openings 90 created within the occlusion 92, and the composition or "tone" of the surrounding vessel 94. This is done by advancing the wire 82 a distance distally past the occlusion 92 to establish the lateral displacement of the wire 82 as shown in FIGS. 6-8 for a given wire profile. The diameter of the opening 90 can then be estimated by examining the characteristic power band response or power variations in the frequency spectrum. Real-time monitoring and processing of the variations or deformations of the primary electrical and acoustic signals by digital signal processing or image processing using various mathematical processes can also be used to determine the diameter and mechanical tone of the vessel 94.

[0180] More specifically, advancing the distal tip of wire 82 a distance beyond occlusion 92 allows for the manifestation of a lateral mode of displacement of wire 82 at a characteristic subharmonic frequency. This lateral hypotrochoidal displacement set up within wire 82, as determined by its geometry, opens up any openings or apertures 90, creating a tunnel of a particular diameter extending longitudinally through occlusion 92.

[0181] The power and gradients of the electrical and acoustic responses in the system are characteristic of the way in which the wire 82 interacts with the materials or structures it contacts, and are therefore characteristic of the properties of those materials and structures. By mathematically processing the data, the geometry and composition of the occlusion 92 and the blood vessel 94 through which the wire 82 is threaded can be characterized.

[0182] Line 120 in Figure 32 illustrates wire 82 in a simple active mode, where ultrasonic energy produces a primarily axial vibration of the distal tip, but has not yet contacted and therefore has not ablated any material in occlusion 92. Conversely, line 122 in Figure 32 illustrates ablation of occlusion 92 by radial vibration of the distal tip after contacting occlusion 92.

[0183] Line 124 in Figure 32 shows the gradient of power attenuation as material from occlusion 92 is ablated by wire 82, widening opening 90 in occlusion 92. Line 126 in Figure 32 corresponds to line 124, but shows the situation when wire 82 is advanced distally a greater distance than line 124 ("y" mm is greater than "x" mm), excavating a larger diameter tunnel-like opening 90 through occlusion 92.

[0184] Various other distinctive features that can be observed in this example are annotated in Figure 32, namely: a general increase in broadband noise when the ultrasonic generator begins to apply power to the transducer of the actuation unit 86; a significant increase in band power when the wire 82 contacts the occlusion 92 or other tissue; a significant decrease in band power as the wire 82 passes through the occlusion 92; and A gradual attenuation of band power as lateral movement of wire 82 continues to widen the opening 90 or lumen through occlusion 92 .

[0185] The noise floor in Figure 32 is due to background noise from the environment, which can be measured while the ultrasound generator is off and then subtracted from all subsequent measurements.

[0186] The example shown in Figure 32 uses only one extracted characteristic feature. In other examples, features extracted from other frequency ranges may be used independently or in combination with the range of features identified, such as the location of the frequency peaks, the amplitude of the peaks or power within the bands, or how any of these features change over time or relative to some baseline value.

[0187] Another aspect of the system is the ability to multiplex or switch between "normal" and "probe" modes. In this regard, the goal of characterizing tissue composition is achieved by a system identification approach in which statistical methods build a mathematical model of the dynamic system from the measured data. More specifically, since it is possible to control the stimuli to the system of the present invention, an input-output system identification approach may be employed. In other words, extraction of characteristic features may be facilitated by selecting a particular type of stimuli designed to generate a particular type of response.

[0188] During operation, a vibrating active element, such as intravascular wire 82, interacts with fluid and tissue in and around the nearby vasculature. The vibrating wire 82 is itself a source of acoustic energy, as its movement within the body 88 results in the generation of acoustic emissions and reflections. During operation, the dynamics of the transducer-wire system also determine the exact nature of the electrical feedback signal.

[0189] In the "probe" mode, deliberate manipulation of the input stimuli allows for the creation of more explicit features that can be extracted and exported for use in characterizing or classifying the structure or material with which the wire 82 is interacting. One example of this approach, namely the measurement of the Q value, which may be affected by the nature of the occlusion 92 with which the wire 82 is in contact, has already been described above with reference to FIG. 12. It will be recalled that when the input voltage signal is stopped, the system continues to resonate for a length of time proportional to Q. By curve fitting an exponential decay function, the controller 96 can derive a value of Q in order to determine the decay effect of the occlusion 92 and thus characterize the nature of the occlusion 92 itself.

[0190] The controller 96 can periodically alternate between "normal" and "probe" modes without significantly affecting the primary function of the device, particularly for traversing occlusions 92. This ability to multiplex different modes and search for different characteristic features allows for a richer data set to characterize materials or structures in contact with or surrounding the active wire 82.

[0191] It is possible to purposefully vary the nature of the stimulus signal applied to the transducer of the actuation unit 86. In the general case (and as shown in Figures 21-26), the applied stimulus is a continuous sine wave of one frequency. However, by using other waveforms such as pulsed waveforms, multi-tone waveforms, chirp waveforms, noise waveforms, etc., different features can be extracted from the corresponding response signal. This takes advantage of the ability of the controller 96 to correlate input stimuli with output responses.

[0192] Figure 33 shows, by way of example, a spectrogram of the current signal as the amplitude of the drive current is varied. This is taken from the paper "Self-Sensing Ultrasound Transducer for Cavitation Detection" by Bornmann et al., published in the 2014 IEEE International Ultrasonics Symposium Proceedings. Broadband changes and / or changes at distinct frequencies can indicate different features of the system, such as the onset of cavitation.

[0193] 34 shows another example where the complex impedance of the transducer of the actuation unit 86 is plotted against frequency. The response can be measured using a variety of different stimuli, including a single tone frequency sweep, a chirp signal, or broadband noise. In this example, a parasitic resonance just below 43 kHz is indicative of an extra vibrational mode in the system, in this case caused by the short length of unsupported wire 82 extending distally beyond the support catheter 84.

[0194] Combining these examples with the example shown in Figure 32, it will be apparent that the combination of electrical and acoustic data allows for a more accurate characterization of the opening 90 in the occlusion 92. This information can be used in a variety of ways, such as to inform the user of the diameter of the opening 90 or to recommend retracting or advancing the support catheter 84 to modify the activity of the distally protruding wire 82 to create the required opening 90.

[0195] As the feature dataset 116 grows, the correlation between tissue characteristics and data features becomes more complex. This classification problem lends itself to the application of machine learning techniques, including feature learning techniques. Thus, another aspect of the system may allow the data to be processed in any type of machine learning model, including artificial neural networks.

[0196] The machine learning model can be pre-trained using a standard set of training data and the model's algorithms can be programmed accordingly. However, the system also allows the training data to be updated over time. For example, if a particular device is successfully used to cross an occlusion 92, the user has the ability to upload the associated data to the server. The user also has the option to manually enter and upload metadata about the procedure, for example to confirm tissue classification, etc.

[0197] Following independent validation, this uploaded data and metadata may then be incorporated into the training data, allowing for unsupervised learning using unlabeled data, supervised learning using labeled data, or semi-supervised learning using a mixture of labeled and unlabeled data. The updated training data allows for the identification of previously unrecognized features and the creation of new algorithms for their extraction. The new algorithms can then be downloaded to any device of the present invention at any time.

[0198] The machine learning models of the present invention can be executed on any available hardware as performance requirements dictate. For example, the controller 96 can execute the machine learning models locally on the device operating on a standalone basis. Alternatively, the device can communicate data to a networked local server that offers more processing power but is located on the same computer network. In this example, real-time feedback is still possible, with the possibility of aggregating data across multiple laboratories and users in a hospital, or indeed any medical facility or organization connected by a private network. Another option is for the device to communicate data to a cloud-based service, offering elastic, scalable performance and the possibility of aggregating data across multiple hospitals, laboratories, and locations. Again, real-time feedback remains possible in a cloud-based solution.

[0199] Finally, referring to Figures 35-37, these figures illustrate the possibility of incorporating inertial sensing into the handheld actuation unit 2 of the present invention. The availability of inertial data representing the orientation and acceleration of the actuation unit 2 adds another source of non-acoustic motion feedback that can usefully enrich the motion data set.

[0200] 35 shows the X, Y and Z axes about which the actuation unit 2 can rotate and along which it can undergo acceleration when manipulated by a physician during use. Specifically, when the Y axis coincides with the longitudinal axis of the actuation unit 2 held horizontally, the actuation unit 2 can pitch about the horizontal X axis, roll about the horizontal Y axis and yaw about the vertical Z axis.

[0201] Figure 36 generally corresponds to Figure 13 and includes like numbers for like features, but also shows an inertial measurement unit comprising an inertial sensor 128 within the housing of the actuation unit 2. By sensing the orientation and acceleration of the actuation unit 2, the inertial sensor 128 can generate information in real time regarding the precise hand movements of the physician holding the actuation unit 2. To this end, the inertial measurement unit is suitable for employing MEMS (Micro Electro Mechanical Systems) technology and can comprise the inertial sensor 128 being a 3-axis accelerometer for measuring linear acceleration and a 3-axis gyroscope for measuring angular velocity.

[0202] FIG. 37 generally corresponds to FIGS. 10 and 11 and includes like numerals for like features, but also includes the inertial sensor 128 of the inertial measurement unit shown in FIG. 36. Thus, briefly summarized, the system 130 shown in FIG. 37 includes a controller 36, which may be in the housing of the actuation unit 2. The controller 36 controls an ultrasonic generator 38 to generate a signal that is converted into ultrasonic energy by a transducer 40. The ultrasonic energy is provided via a coupling 42 to an active wire 4 that is guided through the vasculature to cross an occlusion such as a CTO. FIG. 37 further illustrates a catheter 26 that may surround the wire 4. The catheter 26 may be passive or may be actuated by the actuation unit 2 using ultrasonic energy.

[0203] Acoustic feedback from the active wire 4 is received by one or more acoustic sensors 44. In this example, acoustic sensors 44 are shown positioned in or on the actuation unit 2, on or adjacent to the catheter 26 and / or wire 4, and elsewhere, such as inside, outside, or against the patient's body at a location distal to the actuation unit 2 and near the active distal portion of the wire 4. In practice, acoustic sensors 44 may be positioned at any, some, or all of these locations.

[0204] Acoustic feedback from each acoustic sensor 44 is amplified at 46, filtered at 48, and converted to digital feedback data at 50 and sent to a processor 52. The controller 36 controls a communications system 54 to receive data from the processor 52 and communicate the data to local storage 56 and / or the cloud 58. Figure 37 also illustrates means for providing feedback to the user, such as the display 60 and / or haptic feedback system previously described.

[0205] 37, non-acoustic feedback is obtained from one or more additional sources, namely an electrical feedback receiver 64 and / or an inertial sensor 128, which may be located in or on the actuation unit 2. Signals from the electrical feedback receiver 64 and / or the inertial sensor 128 are amplified at 46, filtered at 48 and then analog-to-digital converted at 50. This generates additional auxiliary feedback data that is typically streamed to a processor 52 via a serial peripheral interface.

[0206] In this manner, the processor 52 can correlate changes in other sensor signals, such as electrical impedance or acoustic emission, with the movement of the actuation unit 2 and thus the movement of the active wire 4. In one embodiment, this will facilitate the algorithmic identification of contact and breakthrough events when the active wire 4 encounters and crosses a lesion. These events cause significant changes in the electrical or acoustic response signals that can be correlated with the forward movement of the active wire 4 represented by a simultaneous change in the output of the inertial sensor 128.

[0207] In another embodiment, a significant change in the electrical or acoustic response signal when the active wire 4 is moved slightly posteriorly or proximally would indicate that the distal tip of the active wire 4 has contacted a hard material such as a calcified lesion. Conversely, if the electrical or acoustic response signal does not change significantly when the active wire 4 is moved slightly posteriorly or proximally, this indicates that the distal tip of the active wire 4 is within the homogenous fluid-filled portion of a blood vessel.

[0208] Orientation and acceleration information derived from the inertial sensor 128 may also be used to monitor the rate of lesion traversal. This information may be used to provide feedback to the physician on how well the system is working, and potentially to recommend to the physician that the active wire 4 should be advanced faster or slower as necessary.

[0209] In another potential application, the inertial sensor 128 can be used to record all movements of the actuation unit 2, and therefore the active wire 4, during the procedure. This allows for subsequent playback in conjunction with a time-correlated sequence of events involving the active wire 4. This can be used for various purposes, such as to provide feedback to the physician to improve his technique, to fine-tune machine learning models, and / or to facilitate clinical reviews, e.g. to investigate professional negligence claims.

[0210] The accelerometers in the inertial sensor 128 can be used to control the actuation unit 2 by detecting tactile control inputs, such as single or double taps, on the housing or control elements of the actuation unit 2. In principle, changes in the orientation of the actuation unit 2 can also be used as control input to the system 130.

[0211] Many other variations are possible within the concept of the invention. For example, one or more acoustic sensors 44 can be disposed on a distal tube, similar to that disclosed in our previous patent application published as WO 2021 / 224357. Such a tube extends distally from the actuation unit 2 to protect and guide, strain relieve, and / or apply damping forces to the wire 4 therein. Such a tube can also function as a connector to a structure disposed distally of the actuation unit 2, such as a luer fitting or other inlet port.

[0212] To maximize the sensitivity of the system when analyzing the response signals from the electrical feedback receiver 64, the inertial sensor 128, and / or the acoustic sensor 44, it is possible to create a "baseline" response signal that can later be subtracted from the varying response signals. The baseline is most usefully obtained when the distal tip of the wire 4 is close to, but not touching, the lesion 30. In this way, the baseline response signal encapsulates all of the fundamental features of the system, including the tortuosity of the vasculature through which the wire 4 extends to the lesion 30. Alternatively, the baseline may be acquired continuously and automatically, and the system itself can determine when to apply the subtraction algorithm.

[0213] As shown in FIGS. 36 and 37, in an example workflow for acquiring a baseline response signal using tactile control input detected by the inertial sensor 128, the user first positions the distal tip of the wire 4 in the vicinity of the lesion. The user then selects an activation mode on the controller of the actuation unit 2 to activate the wire 4 with ultrasonic energy. That operation may require the user to momentarily look away and slightly move the actuation unit 2. The user then double-tap the housing of the actuation unit 2 with one finger while holding the actuation unit 2 steady after fine-tuning the exact positioning of the distal tip of the active wire 4. This triggers the processor 52 to acquire one or more baseline response signals.

Claims

1. 1. An intravascular device for determining the condition of a vessel, cavity, or structure within a body, said device comprising: an elongated waveguide element; an actuation unit including a source of ultrasonic energy and a coupling for coupling the source to the waveguide element to activate the waveguide element, thereby transmitting ultrasonic energy from the source along the waveguide element to an active distal portion of the waveguide element; a signal acquisition system configured to acquire a feedback signal from the device to interpret a condition of the vessel, cavity, or structure; The signal acquisition system includes: at least one acoustic sensor for acquiring an acoustic feedback signal generated by the device when the wave-guiding element is activated; and / or An apparatus comprising at least one inertial sensor for obtaining information representative of an orientation and / or an acceleration of the actuation unit.

2. The apparatus of claim 1 , wherein the at least one acoustic sensor is mounted in or on the actuation unit.

3. The device of claim 2 , wherein the at least one acoustic sensor is mounted in longitudinal alignment with or proximal to the coupling of the actuation unit.

4. The device according to any one of claims 1 to 3, wherein the at least one acoustic sensor is mounted distally relative to the actuation unit.

5. The device according to any one of claims 1 to 4, wherein the at least one acoustic sensor is mounted on or parallel to the waveguide element.

6. The apparatus of claim 5 , wherein the at least one acoustic sensor is mounted proximally or distally relative to the length of the waveguide element.

7. 7. Apparatus according to claim 5 or claim 6, wherein the wave-guiding element is, comprises or is surrounded by a catheter, and at least one acoustic sensor is attached to the catheter.

8. 7. Apparatus according to claim 5 or claim 6, wherein the wave-guiding element is or comprises a wire, and at least one acoustic sensor is attached to the wire.

9. An apparatus according to any one of the preceding claims, wherein a strain gauge is fixed to the waveguide element for obtaining a motion feedback signal from the wire.

10. 10. Apparatus according to claim 9 when dependent on claim 8, wherein the wave-guiding element is or comprises a wire and the strain gauge functions as the at least one acoustic sensor.

11. The device according to any one of claims 1 to 10, wherein the at least one acoustic sensor is an extracorporeal sensor arranged to contact a part of the body.

12. The device according to any one of claims 1 to 11, wherein the at least one acoustic sensor is an internal sensor arranged for insertion into the body.

13. Apparatus according to any one of the preceding claims, wherein the signal acquisition system comprises at least two acoustic sensors longitudinally spaced apart from each other.

14. Apparatus according to any one of claims 1 to 13, configured to be controlled by sensing the orientation and / or acceleration of the actuation unit using the at least one inertial sensor of the signal acquisition system.

15. The apparatus according to any one of claims 1 to 14, further comprising a recorder for recording the orientation and / or acceleration of the actuation unit sensed by the at least one inertial sensor of the signal acquisition system during a surgical procedure.

16. 16. The apparatus of any one of claims 1 to 15, wherein the signal acquisition system further comprises at least one electronic sensor configured to acquire operational feedback signals representative of operational parameters of the source of ultrasonic energy.

17. 17. The apparatus of claim 16, wherein the operating parameter is the frequency and / or amplitude and / or phase of the current drawn by the source of ultrasonic energy or the voltage dropped across the source of ultrasonic energy.

18. 18. Apparatus according to claim 16 or claim 17, wherein the signal acquisition system is configured to monitor variations in frequency or amplitude of vibration of the waveguide element via the coupling.

19. Apparatus according to any one of claims 1 to 18, further comprising a signal processing system for processing a feedback signal acquired by the signal acquisition system.

20. 20. The apparatus of claim 19, wherein the signal processing system is configured to employ a numerical algorithm selected for the particular type of the waveguide element.

21. 21. Apparatus according to claim 19 or claim 20, wherein the signal processing system is configured to determine a characteristic of an occlusion from the obtained feedback signal.

22. The device of any one of claims 19 to 21, wherein the signal processing system is configured to compare the relative contributions of losses from anatomical tortuosity in guiding the active distal portion to an occlusion and losses incurred when the active distal portion passes through the occlusion.

23. 23. The apparatus of any one of claims 19 to 22, wherein the signal processing system is configured to compare the obtained feedback signal with stored data characterizing known occlusions and to characterize the occlusion with reference to the comparison.

24. Apparatus according to any one of claims 19 to 23, wherein the signal processing system further comprises an output to a user interface and / or an output to an external data acquisition system.

25. Apparatus according to any one of claims 19 to 24, wherein the signal processing system further comprises an input from a user interface and / or an input from an external data network.

26. Apparatus according to any one of claims 19 to 25, wherein the signal processing system is configured to transform the acoustic feedback signal from the time domain to the frequency domain.

27. Apparatus according to any one of claims 19 to 26, wherein the signal processing system is configured to evaluate frequency domain data and / or power spectral data.

28. 28. Apparatus according to claim 27, wherein the signal processing system is configured to determine characteristic features from peaks in the frequency domain data and / or power spectrum data.

29. Apparatus as described in claim 27 or claim 2289, wherein the signal processing system is configured to determine characteristic features from power within a frequency band range.

30. Apparatus according to any one of claims 19 to 29, wherein the signal processing system is configured to determine characteristic features of the entire frequency spectrum of the acoustic feedback signal.

31. 31. The apparatus of claim 30, wherein the signal processing system is configured to sample and process a sequence of spectrogram images.

32. Apparatus according to any one of claims 28 to 31, wherein the signal processing system is configured to compare the characteristic features with threshold parameters assessed through prior testing.

33. An apparatus according to any one of claims 28 to 32, wherein the signal processing system is configured to form a characteristic data set by combining the characteristic features with electrical performance data relating to the source of ultrasonic energy.

34. 34. The apparatus of claim 33, wherein the signal processing system is configured to subject the feature dataset to classification by a machine learning algorithm.

35. Apparatus according to any one of claims 28 to 34, wherein the signal processing system is configured to evaluate and compare two or more of the characteristic features.

36. Apparatus according to any one of claims 19 to 35, wherein the signal processing system is configured to detect and monitor harmonics in the acoustic feedback signal indicative of a configuration of the wave-directing element.

37. Apparatus according to any one of claims 19 to 36, wherein the signal processing system is configured to detect and monitor power in two or more frequency bands of the acoustic feedback signal.

38. Apparatus according to any one of claims 19 to 37, wherein the signal processing system is configured to subtract background noise from the acoustic feedback signal.

39. An apparatus according to any one of claims 19 to 38, further comprising a controller responsive to the signal processing system.

40. 40. The apparatus of claim 39, wherein the controller is configured to modulate an excitation voltage applied to the source of ultrasonic energy or an excitation current supplied to the source of ultrasonic energy.

41. 41. The apparatus of claim 40, wherein the controller is configured to control the source of ultrasonic energy by varying a frequency and / or an amplitude of an excitation voltage applied to the source of ultrasonic energy.

42. 42. The apparatus of claim 40 or claim 41, wherein the controller is configured to drive the frequency of the excitation voltage by using a phase difference between the excitation voltage and the excitation current in combination with an amplitude of the excitation voltage.

43. Apparatus according to any one of claims 39 to 42, wherein the controller comprises an amplitude feedback controller and is configured to use a resonant frequency as an operating point for control.

44. 44. Apparatus according to any one of claims 39 to 43, wherein the controller is configured to pulse or vary a drive signal to the source of ultrasonic energy.

45. The controller: monitoring modulation of a transmitted signal and automatically controlling the source of ultrasonic energy to compensate for background energy losses occurring in the waveguiding element as the active distal section approaches an occlusion; 45. The device of any one of claims 39 to 44, configured to distinguish between the background energy loss and additional energy loss as the active distal portion passes through the occlusion, and to compensate for the background energy loss to maintain displacement in the active distal portion.

46. 46. ​​The device of any one of claims 39 to 45, wherein the controller is configured to modify or change a control algorithm in response to variations in operating parameters of the source of ultrasonic energy resulting from interaction of the active distal portion with an occlusion during use.

47. 47. The apparatus of any one of claims 39 to 46, wherein the controller is configured to multiplex or switch between operational modes, and in at least one of the operational modes the source of ultrasound energy is driven to optimize diagnosis of a lesion or condition.

48. 48. The apparatus of claim 47, wherein the controller is configured to alternate between the operational modes, and in at least one of the operational modes the source of ultrasound energy is driven to optimize treatment of a lesion or condition.

49. A communication system comprising an apparatus according to any one of claims 1 to 48, in data communication with a computer system configured to receive data from said apparatus, optimise and update a control algorithm accordingly, and output said optimised and updated control algorithm to said apparatus.

50. 50. The communication system of claim 49, wherein two or more of the devices are in data communication with the computer system, the computer system configured to optimize a control algorithm according to data received from multiple procedures performed using the devices, and output the optimized and updated control algorithm to the devices.

51. 1. A method for determining a condition of a vessel, cavity, or structure in a body, the method comprising: directing a distal portion of an elongated waveguide element to a site within the vessel, cavity, or structure; actuating the waveguide element by transmitting ultrasonic energy to the distal portion; obtaining a feedback signal, which is an acoustic signal generated when the wave-directing element is actuated, and / or an inertial signal representative of an orientation and / or an acceleration of an actuation unit that actuates the wave-directing element; and interpreting the feedback signal to characterize the condition of the vessel, the cavity, or the structure.

52. 52. The method of claim 51 , comprising engaging the distal portion of the actuated waveguiding element with a lesion within the vessel, cavity, or structure, and interpreting a resulting change in the acoustic feedback signal to characterize the lesion.

53. 53. The method of claim 52, comprising destroying the lesion with the distal portion of the activated waveguide element.

54. 54. The method of claim 52 or claim 53, further comprising comparing sensed data representative of the response of the activated waveguide element to the lesion with stored data representative of the response of a corresponding activated waveguide element to interaction with a known lesion.

55. 55. The method of any one of claims 51 to 54, comprising obtaining the acoustic feedback signal in an extracorporeal actuation unit located proximal to the wave-guiding element.

56. A method according to any one of claims 51 to 55, comprising obtaining the acoustic feedback signal at one or more positions along the waveguide element.

57. 57. The method of claim 56, comprising obtaining the acoustic feedback signal at a distal internal location along the waveguide element.

58. 58. A method according to any one of claims 51 to 57, comprising obtaining the acoustic feedback signal at one or more locations outside the blood vessel or cavity.

59. A method according to any one of claims 51 to 58, comprising obtaining the acoustic feedback signal at two or more locations longitudinally spaced from one another.

60. 60. The method of any one of claims 51 to 59, comprising obtaining the acoustic feedback signal at one or more locations distal to an actuation unit that actuates the wave-directing element.

61. 61. A method according to any one of claims 51 to 60, comprising obtaining the acoustic feedback signal at one or more positions on or beside the waveguide element, or on a tube or catheter surrounding the waveguide element.

62. A method according to any one of claims 51 to 61, comprising obtaining the acoustic feedback signal at one or more positions along the body.

63. 63. The method of claim 62, wherein the or each of the locations within the body is outside the blood vessel, the cavity or the structure.

64. A method according to any one of claims 51 to 63, comprising obtaining the acoustic feedback signal at one or more locations external to the body.

65. A method according to any one of claims 51 to 64, comprising controlling the actuation unit by responding to the inertial feedback signal representative of an orientation and / or an acceleration of the actuation unit.

66. 66. The method according to any one of claims 51 to 65, comprising recording the orientation and / or acceleration of the actuation unit during a procedure involving the method.

67. 67. A method according to claim 65 or claim 66, comprising correlating the inertial feedback signal with the acoustic feedback signal.

68. 68. The method of any one of claims 51 to 67, further comprising obtaining an electrical feedback signal representative of an operating parameter of a source of ultrasonic energy coupled to the waveguide element.

69. 69. The method of claim 68, comprising determining from the operating parameters how the source responds to the waveguiding element encountering the vessel, cavity, or structure, and any lesions within the vessel, cavity, or structure.

70. 70. The method of claim 68 or claim 69, wherein the non-acoustic feedback signal represents variations in frequency and / or amplitude and / or phase of the current drawn by the source of ultrasonic energy or the voltage dropped across the source of ultrasonic energy.

71. 71. The method of claim 70, comprising determining the attenuation of the waveguide element by monitoring the attenuation of a current signal over time.

72. A method according to any one of claims 68 to 71, comprising monitoring variations in frequency or amplitude of vibration of the wave-guiding element.

73. 73. A method according to any one of claims 68 to 72, comprising generating datasets from the acoustic feedback signal and the non-acoustic feedback signal, and using a combination of, or a comparison between, the respective datasets to characterise the condition of the vessel, cavity or structure.

74. 74. The method of any one of claims 68 to 73, further comprising adjusting an amplitude or frequency of the ultrasonic energy transmitted along the waveguide element to the distal portion in response to the non-acoustic feedback signal.

75. A method according to any one of claims 68 to 74, further comprising controlling the source in response to the non-acoustic feedback signal to maintain a resonant frequency in the wave-directing element.

76. A method according to any one of claims 68 to 75, comprising correlating the electrical feedback signal with the inertial feedback signal and / or the acoustic feedback signal.

77. 77. A method according to any one of claims 68 to 76, comprising generating datasets from the inertial feedback signal, the acoustic feedback signal and / or the electrical feedback signal, and using a combination of, or a comparison between, the respective datasets to characterise the condition of the vessel, cavity or structure.

78. 78. A method according to any one of claims 51 to 77, comprising outputting data to an external data network, receiving data from said network in response, and modifying or altering a control algorithm in response to receiving data from said network.

79. 79. A method according to any one of claims 51 to 78, comprising outputting data to an external computer system, optimizing and updating a control algorithm in the external computer system according to the data, outputting the optimized and updated control algorithm from the external computer system, and controlling operation of the wave-guiding element using the optimized and updated control algorithm.

80. 80. The method of claim 79, wherein the computer system optimizes the control algorithm according to data received from multiple procedures.

81. 81. A method according to any one of claims 51 to 80, comprising evaluating an attenuation in amplitude or a shift in frequency of the displacement of the wave-guiding element caused by losses arising from contact with a wall of the blood vessel or with material within the blood vessel.

82. 82. The method of any one of claims 51 to 81, comprising sequentially applying two or more different waveforms to the source of ultrasonic energy, the waveforms being selected from a sinusoidal waveform, a pulse waveform, a multi-tone waveform, a chirp waveform, or a noise waveform.

83. advancing the distal portion of the activated waveguide element proximate a lesion within the blood vessel; Obtaining a baseline feedback signal; advancing the distal portion of the activated waveguide element to engage the lesion; Obtaining a motion feedback signal; subtracting the baseline feedback signal from the operational feedback signal; The method of any one of claims 51 to 82, comprising:

84. A method according to any one of claims 51 to 83, comprising transforming the acoustic feedback signal from the time domain to the frequency domain.

85. A method according to any one of claims 51 to 84, comprising evaluating frequency domain data and / or power spectral data.

86. 86. A method according to claim 85, comprising determining characteristic features from peaks in the frequency domain data and / or power spectrum data.

87. 87. A method according to claim 85 or claim 86, comprising determining characteristic features from power within frequency band ranges.

88. A method according to any one of claims 51 to 87, comprising determining characteristic features of the entire frequency spectrum of the acoustic feedback signal.

89. 90. The method of claim 88, comprising sampling and processing a sequence of spectrogram images.

90. A method according to any one of claims 86 to 89, comprising comparing said characteristic features with threshold parameters assessed through prior testing.

91. A method according to any one of claims 86 to 90, comprising forming a characteristic dataset by combining the characteristic features with electrical performance data relating to the source of ultrasonic energy.

92. 92. The method of claim 91, comprising subjecting the feature dataset to classification by a machine learning algorithm.

93. 93. A method according to any one of claims 86 to 92, comprising evaluating and comparing two or more of said characteristic features.

94. A method according to any one of claims 51 to 93, comprising detecting and monitoring harmonics in the acoustic feedback signal indicative of a configuration of the wave-directing element.

95. A method according to any one of claims 51 to 94, comprising detecting and monitoring power in two or more frequency bands of the acoustic feedback signal.

96. A method according to any one of claims 51 to 95, comprising subtracting background noise from the acoustic feedback signal.

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