Ultrasound imaging-guided focused ultrasound system and related methods

Abstract

A transducer is provided that includes an acoustic stack including a composite piezoelectric layer, where the composite piezoelectric includes multiple regions made of piezoelectric material, each region separated from the other by a non-piezoelectric matrix material, and the composite piezoelectric layer has a length and width that define a high aspect ratio, where the length and width of the composite piezoelectric layer form a high aspect ratio acoustic aperture. The acoustic stack also includes a thermally and electrically conductive layer, a thermally and electrically insulating layer, a lens, and at least one matching layer. The acoustic stack is configured to generate a field that defines an acoustic focal region, where the acoustic focal region has wide lateral dimensions, narrow lateral dimensions, and a low focal length to focal width ratio. The transducer also includes a backing structure that contacts the aft end of the acoustic stack.

Description

[Technical Field]

[0001] The technical field relates generally to the field of acoustic energy, and more particularly to ultrasound imaging-guided focused ultrasound systems and related methods. [Background technology]

[0002] Because many FUS treatment methods require specific acoustic frequencies and other parameters to achieve the desired results, there is a need for a single-element focused ultrasound transducer (referred to as "FUS") that can generate a wide acoustic focal zone with a relatively short focal length without the need to change frequency or limit treatment power. As anatomical structures vary in size and location under the skin, it becomes necessary to have different focal zones (FZs) to effectively treat different anatomical structures or portions thereof while minimizing the risk of thermally or otherwise damaging the skin.

[0003] There remains a need for techniques, apparatus, devices and methods that alleviate or mitigate the problems of the prior art. Summary of the Invention

[0004] The present technology generally relates to a relatively high aspect ratio aperture-focused ultrasound (HARFUS) transducer with a thermally efficient, electrically isolated, acoustically matched lens. The technology also relates to a modular high aspect ratio single-element focused ultrasound transducer. In some embodiments, the transducer enables one-shot treatment of a wide, uniform, square aspect ratio focal region, which may enable a single transcutaneous ultrasound treatment or a round superficial nerve with a large diameter compared to the ideal FUS wavelength. In some embodiments, the transducer is configured to generate an acoustic focal region having a pumpkin seed shape, i.e., wide and short in the treatment plane transverse to the nerve (e.g., relative to the nerve) and relatively thin in the orthogonal direction. In some embodiments, the shape and dimensions of the focal region can be tailored to enable neuromodulation across the entire cross-section of the nerve with a single ultrasound treatment. According to one aspect, a high aspect ratio aperture-focused ultrasound (HARFUS) transducer is provided, the HARFUS transducer including a high aspect ratio acoustic stack having a front end and a rear end, and a support structure in contact with the rear end of the acoustic stack. the acoustic stack includes a composite piezoelectric layer including a plurality of regions made of piezoelectric material, each region separated from the other by a non-piezoelectric matrix material, the composite piezoelectric layer having a length and width that define a high aspect ratio, the length and width of the composite piezoelectric layer forming a high aspect ratio acoustic aperture; a thermally conductive and electrically conductive layer in physical contact with the piezoelectric layer, the composite piezoelectric layer being acoustically matched to the thermally conductive and electrically conductive layer; a thermally conductive and electrically insulating layer in contact with the thermally conductive and electrically conductive layer; a lens in contact with the thermally conductive and electrically insulating layer; and at least one matching layer extending at least partially over the lens; the acoustic stack is configured to generate a field that defines an acoustic focal region, the acoustic focal region having a relatively wide lateral dimension, a relatively narrow lateral dimension, and a relatively low focal length to focal width ratio.

[0005] In some embodiments, the acoustic focal region is shaped like a pumpkin seed. Geometrically, the acoustic focal region may have an axial length to lateral width ratio of, for example, less than 3:1. In some embodiments, the acoustic focal region may also have a second orthogonal lateral width that is less than half the first lateral width.

[0006] In some embodiments, the at least one matching layer includes a front matching layer extending over a rear matching layer.

[0007] In some embodiments, the lens has a tapered edge and a tapered width.

[0008] In some embodiments, the lens has a periphery, which is threaded or includes an anechoic feature.

[0009] In some embodiments, the lens curvature is spherical or elliptical.

[0010] In some embodiments, the HARFUS transducer further includes a mismatching layer contacting the back end of the high aspect ratio acoustic stack, the mismatching layer directly contacting one of the composite piezoelectric layer and the support structure.

[0011] In some embodiments, the support structure is a double layer mismatched support structure.

[0012] In some embodiments, the HARFUS transducer further comprises a heat sink.

[0013] According to one aspect, a modular system is provided that includes a plurality of HARFUS transducers as disclosed herein arranged to produce laterally merged focal regions that have a lower axial focal length to lateral focal width ratio than a single HARFUS transducer.

[0014] According to one aspect, a high aspect ratio aperture-focused ultrasound (HARFUS) transducer is provided, the HARFUS transducer including a high aspect ratio acoustic stack having a front end and a rear end, and a support structure in contact with the rear end of the high aspect ratio acoustic stack. the acoustic stack includes a composite piezoelectric layer including a plurality of regions made of piezoelectric material, each region separated from the other by a non-piezoelectric matrix material, the composite piezoelectric layer having a length and width that define a high aspect ratio, the length and width of the composite piezoelectric layer forming a high aspect ratio acoustic aperture; a thermally and electrically conductive layer in physical contact with the piezoelectric layer, the composite piezoelectric layer being acoustically matched to the thermally and electrically conductive layer; a lens in contact with the thermally and electrically insulating layer; and at least one matching layer extending at least partially over the lens; the acoustic stack is configured to generate a field that defines an acoustic focal region, the acoustic focal region having a relatively wide lateral dimension, a relatively narrow lateral dimension, and a relatively low focal length to focal width ratio.

[0015] In some embodiments, the acoustic focal region is shaped like a pumpkin seed.

[0016] In some embodiments, the at least one matching layer includes a front matching layer extending over a rear matching layer.

[0017] In some embodiments, the lens has a tapered edge and a tapered width.

[0018] In some embodiments, the lens has a periphery, which includes anechoic features such as a wedge, threads, or sound absorbing material.

[0019] In some embodiments, the lens curvature is spherical or elliptical.

[0020] In some embodiments, the HARFUS transducer further includes a mismatching layer contacting the back end of the high aspect ratio acoustic stack, the mismatching layer directly contacting one of the composite piezoelectric layer and the support structure.

[0021] In some embodiments, the support structure is a double layer mismatched support structure.

[0022] In some embodiments, the HARFUS transducer further comprises a heat sink.

[0023] A modular system includes multiple HARFUS transducers as disclosed herein arranged to provide laterally merged focal regions having a lower axial focal length to lateral focal width ratio than a single HARFUS transducer.

[0024] According to one aspect, a method is provided for aligning a treatment head including a HARFUS transducer and a diagnostic imaging system with a sample to be characterized, the method including: acoustically coupling the treatment head with an ultrasound sensing phantom; performing a co-registration ultrasound processing sequence using the HARFUS transducer to determine an acoustic focal region using the ultrasound sensing phantom; positioning an imaging plane of the diagnostic imaging system within the treatment head at the center of the acoustic focal region of the HARFUS transducer; locking the position of the HARFUS transducer relative to the treatment head; acoustically coupling and characterizing the treatment head with respect to the sample based on the locked position of the HARFUS transducer; and operating the treatment head to characterize the sample being guided within the treatment head by the diagnostic imaging system.

[0025] According to one aspect, a modular HARFUS transducer is provided that is configured to generate an acoustic focal region resembling the shape of a pumpkin seed, with a relatively wide lateral dimension, a relatively narrow lateral dimension, and a relatively low focal length-to-focal width ratio. The modular HARFUS transducer includes multiple HARFUS transducers arranged together to form a module. In these embodiments, the focal region of each modular transducer can be directed toward a common spot or region, thereby effectively increasing the width of the effective −3 dB focal region but not its depth, thereby resulting in a focal width-to-focal length ratio of 1:1. In some embodiments, the focal region may be wider than its length. A focal length ratio of approximately 1:1 allows for the treatment of the entire cross-section of a nerve with little unintended high-intensity energy present outside the target nerve or other structures. In some embodiments, the transducer can be used for neuromodulation. In these embodiments, the transducer can treat the entire nerve with a single ultrasound treatment. Such treatment can be facilitated by transducers, such as those presented herein, that can produce precisely tailored focal regions in the target anatomy.

[0026] Other features and advantages of the present description will appear more clearly on reading the following non-limiting description of particular embodiments thereof, given by way of example only with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0027] [Figure 1] 1 is an isometric view of an exemplary embodiment of a high aspect ratio focused ultrasound transducer having a 1:3 ratio aperture with a single focal length, resulting in a 1:3 ratio f-number ratio. [Figure 2] 2 is a cross-sectional view of the HARFUS transducer of FIG. 1 illustrating aspects of an exemplary embodiment including a cooling structure, an acoustic stack, an electrically insulating and acoustically matched ceramic composite layer, and a thermally conductive lens. [Figure 3]2 illustrates a high aspect ratio focal region and associated acoustic field produced by the exemplary HARFUS transducer shown in FIG. 1. [Figure 4] FIG. 10 is another view showing the broad lateral dimension of the HARFUS focal region. [Figure 5] A 1:4.5 ratio HARFUS acoustic field is overlaid onto a virtual 3.5 mm cylindrical structure (such as a nerve), bisected by the high aspect ratio focal region of the HARFUS transducer, with the -3 dB focal region having a 4 mm lateral focal region width and a width of approximately 8 mm focal length at 1.5 MHz, originating approximately 50 mm from the face of the HARFUS transducer. [Figure 6] FIG. 1 shows three 1:3 F-number HARFUS transducers co-aligned to form a single merged lateral focal region with a first −3 dB width of approximately 12 mm, a second orthogonal width of 1.4 mm, and a height of approximately 18 mm. [Figure 7] FIG. 7 is an alternative view of the three modular co-aligned HARFUS transducers shown in FIG. 6. [Figure 8] Figure 1 shows an exemplary embodiment of a compact HARFUS transducer operating at 1.5 MHz, suitable for neuromodulation in small animals, in which a focal region having a first -3 dB width of 2.75 mm, a second orthogonal width of 0.8 mm, and a length of 6.4 mm occurs approximately 18 mm from the face of the focal region transducer with an F-number ratio of 1:4.5 at 1.5 MHz. This embodiment demonstrates the ability to partially decouple focal region size and location from frequency by using both aperture size and a high aspect ratio to control the focal region length and width. [Figure 9] 9 is a cross-sectional view of the HARFUS transducer of FIG. 8. Note that in this exemplary embodiment, the lens is not electrically isolated from the ground plane as in the exemplary embodiment of FIG. [Figure 10] FIG. 9 is a close-up view of the acoustic stack of the transducer of FIG. 8. [Figure 11]2 is a series of diagrams illustrating the size and location of the −3 dB focal region of the exemplary 1.5 MHz HARFUS transducer shown in FIG. 1. [Figure 12] 2 is a series of diagrams illustrating the size and location of the −3 dB focal region of the exemplary 1.5 MHz HARFUS transducer shown in FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0028] In the following description, like features in the figures are given like reference numerals, and to avoid unduly cluttering the figures, some elements may not be shown in some figures if they are already identified in one or more previous figures. It should also be understood that elements in the figures are not necessarily drawn to scale herein, with emphasis instead being placed on clearly illustrating the elements and structures of the present embodiments. The terms "a," "an," and "one" are defined herein to mean "at least one," i.e., these terms do not exclude a plurality of elements unless otherwise specified. It should also be noted that terms such as "substantially," "generally," and "about," which modify a value, condition, or characteristic of an exemplary embodiment, should be understood to mean that the value, condition, or characteristic is defined within an acceptable tolerance for proper operation of this exemplary embodiment for its intended use.

[0029] In this description, the terms "connected" and "coupled," as well as their derivatives and variations, refer to any connection or coupling, either direct or indirect, between two or more elements. The connection or coupling between the elements may be acoustic, mechanical, physical, optical, operational, electrical, wireless, or a combination thereof.

[0030] The terms "match," "matching," and "matched," as used herein, are intended to refer to a state in which two elements are the same or within a predetermined tolerance of one another. That is, these terms are meant to encompass not only "exactly" or "identically" matching two elements, but also "substantially," "approximately," or "subjectively" matching two elements, as well as providing a higher or best match among multiple possible matches.

[0031] In this description, the phrase "based on" is intended to mean "based at least in part on," i.e., it can mean "based only on" or "based in part on," and therefore should not be interpreted as limiting. More specifically, the phrase "based on" can be understood to mean "depends on," "represents," "indicates," "associated with," or similar phrases.

[0032] It will be understood that position descriptors indicating the location or orientation of one element relative to another are used herein for ease and clarity of description and, unless otherwise indicated, should be interpreted in the context of the drawings and should not be considered limiting. It will be understood that spatially relative terms (e.g., "external" and "internal," "outer" and "inner," "peripheral" and "center," "above" and "below," and "top" and "bottom") are intended to encompass different positions and orientations in use or operation of the present embodiments in addition to the positions and orientations illustrated in the drawings.

[0033] In the context of this disclosure, the following reference numbers may be used: 1-Anterior matching layer. 2- Posterior matching layer. 3- Lens: A thermally efficient aluminum or other material lens, width and edges tapered to allow for adjacent assembly into a multi-module treatment head. 4- Acoustically matched thermally conductive composite electrical insulation layer. 5- Thermally and electrically conductive layer - also acts as redundant ground. 6 - Aluminum matched single element piezoelectric composite material approximately 17 MR, specific to high aspect ratio rectangular aperture material. Can be elliptical aperture or other high aspect ratio shapes to optimize the acoustic field as needed. 7-Mismatched layer - High acoustic impedance and excellent thermal and electrical conductivity (e.g. tungsten, tungsten carbide, molybdenum, etc.). 8-DLDB 1 / 4 lambda layer, low acoustic impedance, electrically and thermally conductive (e.g. graphite). 9-DLDB 1 / 4 lambda layer, high acoustic impedance layer, electrically and thermally conductive (e.g. tungsten). 10-DLDB 1 / 4 lambda layer, low acoustic impedance, electrically and thermally conductive (e.g. graphite). 11-DLDB layer, a high acoustic impedance layer, electrically and thermally conductive (such as copper or tungsten or other electrically conductive high acoustic impedance material). 12-Aluminum nitride or other thermally conductive but electrically insulating material. 13-A and B Liquid Cooling Block Base and Liquid Cooling Block Body for Liquid Cooling Block Base. Air based cooling solutions etc. can also be used. 14—Aluminum nitride or other thermally conductive, electrically insulating material that forms the heat return path plate for coupling thermal energy from the front (5) plate to the rear of the liquid cooling block. 15—Copper housing lid, electrically and thermally conductive, forms an electrical shield and a possible ground connection path for the RF connector (not shown). 16-Liquid cooling inlet / outlet pipe. 17—An electrically and thermally conductive housing that forms both an electrical ground connection to the transducer and a thermal cooling path for the front surface of the piezoelectric composite. 18—A thermally and electrically conductive lens that forms both a ground connection to the piezoelectric composite and acoustic lens and a thermal cooling path for the front surface of the piezoelectric composite. 19 - Signal wire connected between the RF connector and the rear electrode of the acoustic stack. 20 - RF coaxial connector connected to the signal line and grounded via an electrically and thermally conductive housing 17; 21-Anechoic feature. 22-A diagrammatic representation of the range of the acoustic field produced by the HARFUS transducer. 23 - Diagrammatic representation of the -3 dB range of the acoustic field including the focal region of an exemplary HARFUS transducer having an F-number ratio of 1:3. 24--A diagrammatic representation of the -3 dB range of the acoustic field including the focal region of an exemplary HARFUS transducer having an F-number ratio of 1:4.5. 25—An exemplary cylindrical target representing a typical nerve or other cylindrical FUS target.

[0034] Although the HARFUS transducer embodiments described throughout the description are described as including a piezoelectric material, those skilled in the art will note that the HARFUS transducers of the present disclosure may instead include any ferroelectric material, any single crystal or polycrystalline material, any electromechanical transduction material, where such materials have one or more of the following properties: ferroelectric, pyroelectric, piezoelectric, electrostrictive, and / or other related properties. It should be noted that in the context of this specification, the expression "piezoelectric material" may also refer to ferroelectric materials, pyroelectric materials, relaxor materials, and electrostrictive materials, as will be readily understood by those skilled in the art.

[0035] The present specification generally relates to a relatively high aspect ratio aperture-focused ultrasound (HARFUS) transducer with a thermally efficient, electrically isolated, acoustically matched lens. The HARFUS transducer embodiments described herein include an aperture having a relatively long axis in a first direction and a relatively short axis in a second direction. In some embodiments, the aperture may have a length twice its width. In some embodiments, the aperture may have a length three times its width. In some embodiments, this ratio may be 4.5:1. The focus of the HARFUS transducer is adjusted by a lens. In some embodiments, the lens may be a spherical lens, an elliptical lens, or any other refractive focusing lens that allows for adjusting the ultrasound waves to a point or focal region. In some embodiments, the lens may have a symmetrical design, which may allow for creating a high aspect ratio focal region at (or near) the focal point of the lens.

[0036] According to one aspect, a high aspect ratio aperture-focused ultrasound (HARFUS) transducer is provided, the HARFUS transducer including a high aspect ratio acoustic stack having a front end and a rear end, and a support structure in contact with the rear end of the acoustic stack. the acoustic stack includes a composite piezoelectric layer including a plurality of regions made of piezoelectric material, each region separated from the other by a non-piezoelectric matrix material, the composite piezoelectric layer having a length and width that define a high aspect ratio, the length and width of the composite piezoelectric layer forming a high aspect ratio acoustic aperture; a thermally conductive and electrically conductive layer in physical contact with the piezoelectric layer, the composite piezoelectric layer being acoustically matched to the thermally conductive and electrically conductive layer; a thermally conductive and electrically insulating layer in contact with the thermally conductive and electrically conductive layer; a lens in contact with the thermally conductive and electrically insulating layer; and at least one matching layer extending at least partially over the lens; the acoustic stack is configured to generate a field that defines an acoustic focal region, the acoustic focal region having a relatively wide lateral dimension, a relatively narrow lateral dimension, and a relatively low focal length to focal width ratio.

[0037] In some embodiments, the composite piezoelectric layer includes individual pillars, such as 13 or 22 composite piezoelectric pillars. The apertures are associated with a high aspect ratio, i.e., the entire composite piezoelectric layer is in the form of, for example, a long, narrow strip or a high aspect ratio ellipse. Note that the composite piezoelectric layer is acoustically matched to a thermally and electrically conductive layer. In some embodiments, the thermally and electrically conductive layer may be thermally conductive only and may be sputtered or otherwise coated with an electrically conductive layer.

[0038] In some embodiments, the acoustic focal region is shaped like a pumpkin seed.

[0039] In some embodiments, the at least one matching layer includes a front matching layer extending over a rear matching layer.

[0040] In some embodiments, the lens has a tapered edge and a tapered width.

[0041] In some embodiments, the lens has a periphery that is threaded or otherwise features an anechoic structure or coating.

[0042] In some embodiments, the lens curvature is spherical or elliptical.

[0043] In some embodiments, the HARFUS transducer further includes a mismatching layer contacting the back end of the high aspect ratio acoustic stack, the mismatching layer directly contacting one of the composite piezoelectric layer and the support structure.

[0044] In some embodiments, the support structure is a double layer mismatched support structure.

[0045] In some embodiments, the HARFUS transducer further comprises a heat sink.

[0046] According to one aspect, a modular system is provided that includes a plurality of HARFUS transducers as disclosed herein arranged to produce laterally merged focal regions that have a lower axial focal length to lateral focal width ratio than a single HARFUS transducer.

[0047] According to one aspect, a high aspect ratio aperture-focused ultrasound (HARFUS) transducer is provided, the HARFUS transducer including a high aspect ratio acoustic stack having a front end and a rear end, and a support structure in contact with the rear end of the high aspect ratio acoustic stack. the acoustic stack includes a composite piezoelectric layer including a plurality of regions made of piezoelectric material, each region separated from the other by a non-piezoelectric matrix material, the composite piezoelectric layer having a length and width that define a high aspect ratio, the length and width of the composite piezoelectric layer forming a high aspect ratio acoustic aperture; a thermally and electrically conductive layer in physical contact with the piezoelectric layer, the composite piezoelectric layer being acoustically matched to the thermally and electrically conductive layer; a lens in contact with the thermally and electrically conductive layer; and at least one matching layer extending at least partially over the lens; the acoustic stack is configured to generate a field that defines an acoustic focal region, the acoustic focal region having a relatively wide lateral dimension, a relatively narrow lateral dimension, and a relatively low focal length to focal width ratio.

[0048] In some embodiments, the acoustic focal region is shaped like a pumpkin seed.

[0049] In some embodiments, the at least one matching layer includes a front matching layer extending over a rear matching layer.

[0050] In some embodiments, the lens has a tapered edge and a tapered width.

[0051] In some embodiments, the lens has a periphery, and the periphery is threaded.

[0052] In some embodiments, the lens curvature is spherical or elliptical.

[0053] In some embodiments, the HARFUS transducer further includes a mismatching layer contacting the back end of the high aspect ratio acoustic stack, the mismatching layer directly contacting one of the composite piezoelectric layer and the support structure.

[0054] In some embodiments, the support structure is a double layer mismatched support structure.

[0055] In some embodiments, the HARFUS transducer further comprises a heat sink.

[0056] A modular system comprising a plurality of HARFUS transducers as disclosed herein arranged to provide a laterally merged focal region having a lower axial focal length to lateral focal width ratio than a single HARFUS transducer.

[0057] In some embodiments, the system may include a liquid-cooled FUS transducer contained within an articulating treatment head, and further includes a micro-positioning and clamping mechanism that provides co-registration of the imaging plane of a suitable high-resolution diagnostic ultrasound imaging ultrasound (DIUS) with the focal zone (FZ) of the FUS transducer or other diagnostic imaging scan head, such as a wobbler-based scanner. Additionally, the system may include a water bath and a small animal handling platform with a positioning system for orienting the co-registered FUS and imaging transducers relative to a small animal (e.g., a rat), enabling precise visualization and subsequent insonification of peripheral nerves to achieve precise peripheral nerve blockade. In some embodiments, the liquid-cooled FUS transducer includes acoustic stack technology, enabling highly thermally efficient operation, allowing FUS treatments to be performed at up to 100% duty cycle for long durations with little or only minimal heating of the device or lens surface, and enabling a very wide parameter space to be tested. The system's FUS transducer incorporates high-lateral aspect ratio aperture and lens technology, resulting in a relatively short focal length while providing the focal width necessary to treat an entire peripheral nerve with a single sonication. To that end, one exemplary embodiment of a 1.5 MHz HARFUS transducer with a 1:4.5 f-number ratio and 18 mm focal depth is configured to generate a focal spot suitable for small-animal PNB studies, with a nominal -3 dB azimuthal focal width of approximately 2.5 mm, an elevation focal width of less than approximately 1.0 mm, and a nominal -3 dB focal length of approximately 6.5 mm, with the center of the focal spot occurring approximately 18 mm from the face of the transducer. These FZ parameters are expected to facilitate precise treatment of small-animal peripheral nerves with a single sonication while minimizing the potential for skin burns.Co-registration (CR) of a high-resolution diagnostic imaging array with respect to the FZ of the FUS transducer can be achieved by positioning DIUS while performing real-time imaging of an echogenic object placed in a visible lesion created at the FZ of the FUS transducer in a HIFU phantom consisting of an ultrasound-transparent polymer container placed in a water bath and filled with commercially available optically clear HIFU phantom gel (Onda Corp). The USgFUS device can be positioned so that the FZ of the FUS transducer is inside the HIFU phantom. Then, by operating the FUS transducer at a sufficiently high intensity, the temperature of the HIFU phantom gel near the FZ rises to above 70 °C, inducing the formation of a persistent, visually opaque thermal lesion corresponding to the FZ of the FUS transducer. The resulting lesion can be imaged in real time by DIUS, placed in the FZ of the FUS transducer, either directly or by placing an echogenic marker within the lesion boundary. By operating the multi-axis positioning system of the co-registration alignment system, it is possible to position the DIUS so that the image of the lesion appears at a predetermined location in the ultrasound image, allowing real-time visualization of the FUS FZ. When the desired alignment of the DIUS and FUS FZ is obtained, the CR positioning system can be locked in place, maintaining the co-registration of the DIUS and FUS transducers as the USgFUS treatment head is positioned for subsequent treatment.

[0058] The FUS transducer includes a structure that allows for active cooling of the piezoelectric crystals from both the front and back of the piezoelectric layer (e.g., 13-composite piezoelectric layer), meaning that the FUS transducer includes a thermal management module or structure. This allows the transducer to operate at high intensities (piezoelectrically) for long durations and high duty cycles up to continuous wave ultrasound treatment without thermal damage or performance drift. Furthermore, the FUS transducer includes thermally efficient, electrically isolated lens technology that allows heat to be removed from the treatment site through the transducer during operation. In some embodiments, this structural configuration may be similar to that described in PCT / CA2020 / 051563, the contents of which are incorporated herein by reference. This minimizes bubble formation at the lens surface and reduces the water flow rate required to keep the skin cool. The transducer includes a high-lateral aspect ratio aperture and is focused through a single, thermally efficient lens to provide an FUS beam with a complex f-number that can be optimized to provide the focal width required for single-shot PNB treatment without the typically long focal length that would result from using a circular or square focal region. In some embodiments, the transducer can generate a -3 dB focal region with a horizontal dimension of 4.5 mm, a vertical dimension of 1.4 mm, and a focal length of approximately 18 mm. This focal region is estimated to be sufficient for treating small peripheral nerves less than 5 mm in diameter using a single ultrasound treatment, for example, in clinical applications or animal studies, without the need to scan or treat subsequent locations to cover the entire cross-section of the PN. This approach is potentially much more cost-effective than high-element-count rectangular matrix arrays that could also be used in this manner. Additionally, the focal region can be created to achieve low energies in the near field using a relatively wide parameter space to optimize treatment of the targeted PN while simplifying acoustic coupling and minimizing the possibility of skin burns.

[0059] Using 1.5 MHz ultrasound as an example of a typical focused ultrasound treatment frequency, the upper limit for a circular spherically focused transducer, considering typical anatomical depths relative to the skin line, is an f-number approximately equal to 4. Theory indicates that for a spherically focused transducer, the -3 dB transmit focal length and focal width are equal to the following, respectively:

[0060]

number

[0061] For example, a 4 mm wide -3 dB FZ at 1.5 MHz, when generated by a circular aperture transducer using, for example, a spherical focusing lens, can produce a -3 dB focal length of anywhere between 75 mm and 100 mm deep. This focal region can result in the unintentional sonication of, for example, a long cylindrical section of tissue above and below the target nerve.

[0062] In light of the above, it is necessary to separate the focal region in at least one axis from the focal length of the single element FUS transducer.

[0063] Note that as the upper limit of focal width is approached, one limiting factor is the reduction in focal gain achieved with high f-number lenses. To achieve high focal intensities, the transducer must be driven at high transmit power levels. To this end, one exemplary embodiment described herein includes a high-thermal-conductivity lens, e.g., aluminum, in contact with an acoustically matched, thermally conductive but electrically insulating ceramic composite, e.g., a 1 / 3 composite of aluminum nitride, beryllium oxide, or alumina, inserted between the piezoelectric composite transducer elements, which themselves are bonded to a thermally and electrically conductive ground plane, e.g., an aluminum plate of substantial thickness, e.g., 1 / 4 lambda, 1 / 3 lambda, or several wavelengths thick. The acoustically matched, electrically insulating layer composite 13 allows the lens to be actively cooled by the transducer cooling solution while maintaining patient current leakage levels safe for medical devices, e.g., less than 100 μA for floating-body devices.

[0064] The combination of cooling on both sides of the piezoelectric crystal and the lens of the transducer also allows for very high duty cycle operation of the FUS transducer, further enhancing the treatment parameter space that this device provides access to. For example, one exemplary embodiment of the present technology can be run continuously at pressure and intensity levels sufficient for therapy without experiencing thermal performance degradation, with only a few degrees of temperature rise in the lens.

[0065] In some embodiments, the HARFUS transducers of this technology utilize a horizontal F-number of 6 and a vertical F-number of 1.7 to produce a high-aspect ratio -3 dB focal width of 4.5 mm x 1.4 mm wide with a depth focal length of only 1.66 cm. This allows for treatment of anatomical structures relatively close to the skin in sizes up to 4-4.5 mm with a single ultrasound treatment. In some embodiments, several of these HARFUS transducers can be collocated such that the horizontal aspects of the focal regions merge into one very wide focal region. For example, in some embodiments, three modular HARFUS transducers at 1.5 MHz can produce a -3 dB focal region greater than 10 mm wide with a focal length of 1.6 cm.

[0066] Referring to FIG. 1, an embodiment of a HARFUS transducer is shown. The HARFUS transducer includes a front matching layer 1, a rear matching layer 2, and a thermally efficient lens 3 of aluminum or other material. In some embodiments, the lens 3 has a width and edges that may be tapered to allow for adjacent assembly into a multi-module treatment head. The HARFUS transducer further includes an acoustically matched, thermally conductive, composite, electrically insulating layer 4 and a thermally and electrically conductive layer that also serves as a redundant ground 5. Still referring to FIG. 1, the HARFUS transducer includes a high-aspect-ratio, rectangular-aperture, unique single-element piezoelectric composite 6 matched (at approximately 17 MR) to aluminum. Note that the aperture can be an elliptical aperture or other high-aspect-ratio shape to optimize the acoustic field as needed. The HARFUS transducer also includes a mismatching layer 7, preferably with a high acoustic impedance. The mismatching layer 7 is preferably thermally and electrically conductive and may be made of a material such as tungsten, tungsten carbide, or other molybdenum. The HARFUS transducer also includes a double-layer mismatched support (DLDB) 1 / 4 lambda layer 8 (having a low acoustic impedance, layer 8 being made of an electrically and thermally conductive material such as graphite), as described in PCT / CA2020 / 051563. The HARFUS transducer also includes a DLDB 1 / 4 lambda layer 9 (having a high acoustic impedance layer, layer 9 being made of an electrically and thermally conductive material such as tungsten). The HARFUS transducer also includes a DLDB 1 / 4 lambda layer 10 (having a low acoustic impedance, layer 10 being made of an electrically and thermally conductive material such as graphite). The HARFUS transducer also includes a DLDB layer 11 (a high acoustic impedance layer, layer 11 made from an electrically and thermally conductive material such as copper, tungsten, or other electrically conductive high acoustic impedance material). The HARFUS transducer also includes an aluminum nitride layer 12. Layer 12 can be replaced by a layer made from any other thermally conductive material that is also electrically insulating, such as boron nitride, beryllium oxide, aluminum oxide, or other suitable thermally conductive and electrically insulating material.The HARFUS transducer also includes a heat sink, which may be embodied by a liquid-cooled block base 13A and a liquid-cooled block body 13B for the liquid-cooled block 13A, or a finned air heat sink including multiple fins. In some embodiments, air may be used as the cooling mechanism. In some embodiments, the cooling water block may be made of a single component or multiple components. The HARFUS transducer also includes an aluminum nitride layer 14. Layer 14 may be replaced by a layer made of any other thermally conductive, electrically insulating material that can form a heat return path for coupling thermal energy from the front (5) plate to the rear of the liquid-cooled block. The HARFUS transducer also includes an electrical shield 15, which may be embodied by a copper housing lid. The shield 15 is made of an electrically and thermally conductive material, which can provide an electrical shield and, in some cases, a ground connection path for an RF connector (not shown). The HARFUS transducer also includes liquid-cooled inlet / outlet tubes 16. The HARFUS transducer also includes an electrically and thermally conductive housing 17, which provides both an electrical ground connection to the transducer and a thermal cooling path for the front surface of the piezoelectric composite.

[0067] Other visual representations of the HARFUS transducer are shown in Figures 2-7.

[0068] Referring now to Figures 8-10, a modular FUS transducer will be described. These figures illustrate a three-module therapeutic FUS system with co-aligned focal regions positioned to allow the -3 dB lateral focal regions of each module to merge in one axis. The merged lateral focal region has a -3 dB focal width approximately three times larger than that of a single module. Note that the three focal regions maintain approximately the same focal width in the direction orthogonal to the lateral field and approximately the same -3 dB focal length as a single module. The result is a wide focal region that is many times wider and many times shorter than that which can be produced by a single-element FUS transducer at a given frequency.

[0069] Referring now to Figures 11 and 12, results that can be obtained using this technique are shown (lateral results, -3 dB). Figure 11 shows the lateral focal area of ​​a high-aspect ratio FUS transducer, with a focal area measuring 4.5 mm wide by 1.4 mm wide and only 1.66 cm long, occurring at a depth of approximately 3.5 cm to 4 cm from the skin line. The HARFUS transducer allows for direct translation from studies of single ultrasound neuromodulation (NM) of peripheral nerves (PN) at, for example, 1.5 MHz, on subjects ranging from rats to larger animal models, to clinical studies using the same frequency and ultrasound parameters. At a single frequency, for example, 1.5 MHz, a single set of FUS parameters can be used to translate studies from small animals to clinical studies. This can be achieved using some of the exemplary HARFUS transducers disclosed herein, such as those shown in Figure 8, followed by those shown in Figure 1, and then those shown in Figure 6. This series of multiple HARFUS transducers, each operating at 1.5 MHz, may be optimized for small-animal HARFUS treatment, producing a relatively small focal region, e.g., approximately 2.5 mm x less than 1 mm x approximately 6.7 mm long; a single larger 1.5 MHz HARFUS treatment head may produce a larger focal region, e.g., 4.5 mm x 1.3 mm x approximately 17 mm; and finally, a modular treatment head containing several co-located 1.5 MHz HARFUS transducers may be used to laterally merge focal regions up to 10.6 mm x 1.3 mm wide x 1.66 cm long -3 dB FZs. It should be appreciated that this technology can be applied across a wide range of frequencies for many possible FUS applications in addition to neuromodulation. One important aspect of this technology is the possibility of linearly scaling the lateral width and axial length of the focal region at a given frequency across a wide parameter space, thus enabling small-animal translation studies and freeing the use of optimal acoustic parameters for a wide variety of anatomical structures at various depths below the skin line.

[0070] For example, note that using a single-element FUS transducer with a circular aperture according to the prior art method, a focal length of approximately 80 mm long (-3 dB) is generated approximately 7.5 cm from the skin line to obtain a 3.5 mm wide acoustic focal region at 1.5 MHz. This result can be easily simulated using a circular single-element FUS model with a short focal length, requiring a nominal aperture f-number of approximately 4.5 and a relatively small k-wavenumber aperture product of only 65, resulting in a diffraction-limited focal width less than the f-number. Note that to achieve a wider focal region with this type of transducer from the prior art, a larger transducer aperture is required, with the focal region moving deeper. While it may be possible to use diffraction-corrected lenses beyond those used in the present technology, the exponential growth of focal length versus focal width versus increasing f-number seems impossible to overcome. Such prior art devices could not be safely used to treat small targets such as nerves with a focal length of 8 cm, especially near the skin or above or below sensitive organs or structures.

[0071] Using finite element modeling techniques, it can be shown that conventional circular single-element FUS transducer geometries have an upper -3 dB focal region width limitation of approximately 4 mm at 1.5 MHz, resulting in nearly unusable focal lengths of greater than 80 mm. These figures are consistent with theory, which predicts that the lateral focal region is proportional to the product of the f-number and wavelength, and that the focal length is proportional to a constant (approximately 7 for typical single-element FUS transducers) and the product of the f-number squared and lambda. This is an important reason why the 4-5 mm focal region required to sonicate even a relatively small 4 mm diameter peripheral nerve, for example, is such a challenge. Those skilled in the art will understand that many neuromodulation studies are performed at 1.5 MHz and will further appreciate that at 1.5 MHz in tissue, lambda is approximately 1 mm, which means that an f=4-5 number is required to achieve a focal region width that can sonicate a 4 mm diameter nerve in a single sonication, and that the focal region is approximately 7-4-5 times the size of the lateral focal region, or approximately 14 cm long if the focal region is 4.5 mm long.

[0072] By using the HARFUS transducer of the present invention, it is possible to produce a focal region that is 4.5 mm wide and 1.4 mm thick, while still producing a much shorter focal length of 16.6 mm long.

[0073] One exemplary embodiment of the present technology is a small animal ultrasound-guided focused ultrasound (USgFUS) device that includes a liquid-cooled FUS transducer contained in an articulating treatment head and further includes a micro-positioning and clamping mechanism that provides co-registration of the focal zone (FZ) of the FUS transducer with the imaging plane of a suitable high-resolution US diagnostic imaging ultrasound scanner (DIUS). The device further includes a water bath and a small animal handling platform with a positioning system for orienting the FUS and imaging transducers in co-registration with the rat, enabling precise visualization and subsequent insonification of the PN to achieve accurate PNB.

[0074] In this exemplary embodiment, the liquid-cooled FUS transducer includes an acoustic stack incorporating a material-specific piezoelectric composite stack, with or without a composite dielectric isolation layer between the material-specific composite piezoelectric, aluminum ground reinforcement electrode and cooling layer, and aluminum acoustic lens, which allows for very thermally efficient operation, allowing for long FUS treatments to be performed at up to 100% duty cycle with little heating of the device or lens surface, and allowing for testing of a very wide parameter space. Non-limiting examples of stacks, structures, and materials are provided in PCT / CA2019 / 051046, PCT / CA2020 / 051563, and / or PCT / CA2022 / 050387.

[0075] Furthermore, the FUS transducer includes high-lateral aspect ratio aperture and lens technology with a 4 mm elevation aperture (or short-axis aperture), an 18 mm azimuthal aperture (or long-axis aperture), and a 15 mm focal depth, resulting in a relatively short focal length while providing the focal width necessary to treat an entire peripheral nerve in a small animal model, e.g., a rat, with a single sonication. In one embodiment intended for small animal testing, the transducer provides a focal spot with a nominal -3 dB azimuthal focal width of approximately 2.8 mm, an elevation focal width of <1.0 mm, and a nominal -3 dB focal length of approximately 6.8 mm, with the center of the focal spot located approximately 15 mm from the face of the transducer. These FZ parameters are expected to facilitate precise neuromodulation of peripheral PNs in small animal models, e.g., a rat, with a single sonication while minimizing the potential for skin burns. High-resolution DIUS co-registration (CR) with the FUS transducer FZ was achieved by positioning DIUS while performing real-time imaging of an echogenic object placed at a visible lesion created at the FUS transducer FZ in a HIFU phantom made from an ultrasound-transparent polymer container placed in a water bath and filled with commercially available optically clear HIFU phantom gel (Onda Corp). The USgFUS device can be positioned so that the FUS transducer FZ is inside the HIFU phantom. Then, by operating the FUS transducer at a sufficiently high intensity, the temperature of the HIFU phantom gel near the FUS FZ can be raised to above 70°C, inducing the formation of a persistent, visually opaque thermal lesion corresponding to the FUS transducer FZ. The resulting lesion, located at the FUS transducer FZ, can be imaged in real time by DIUS, either directly or by placing an echogenic marker within the lesion boundary. By operating the multi-axis positioning system of the mutual registration alignment system, it becomes possible to position the DIUS so that the image of the lesion appears at a predetermined position in the ultrasound image, allowing real-time visualization of the FUS FZ.When the desired alignment of the DIUS and FUS FZs is achieved, the mutual registration (CR) positioning system can be locked in place to maintain the mutual registration of the DIUS and FUS transducers when the USgFUS treatment head is positioned for subsequent treatments.

[0076] In another embodiment intended to provide single-site, single-sonication neuromodulation of small peripheral nerves approximately 4 mm in diameter, the USgFUS transducer includes an elevation aperture of approximately 7 mm and an azimuthal aperture of approximately 24 mm, resulting in a focal depth of approximately 3.5 cm. An investigational ultrasound-guided FUS device can be used, for example, to perform percutaneous PNB in ​​peripheral nerves up to 4 mm in diameter using a single sonication from a single location. This device includes a custom 1.5 MHz liquid-cooled, high-lateral aspect ratio aperture FUS transducer that provides a low-aspect ratio FZ for safe, single-shot treatment of PN, placed, for example, 2 cm to 5 cm below the skin. Furthermore, this device includes an articulated, locking articulated arm or robotic arm to facilitate placement of the FUS FZ relative to the anatomical structure to be treated. Guidance to the treatment location can be provided by a co-registered high-resolution diagnostic imaging array (DIA), such as the Sonosite L38 10-5 linear array, and a diagnostic ultrasound (DUS) system. The means for co-registering the DIUS and FUS FZ includes, for example, a device containing provisions for positioning a HIFU-compatible phantom filled with a thermosensitive HIFU phantom gel (Onda Co., Ltd.) to enable visualization of the focal region of the FUS transducer. Once co-registration is complete, the treatment head, which includes both the FUS transducer, the DIUS co-registration mechanism, and the DIUS, as well as the means for acoustically coupling the US transducer to the subject, can be positioned by the articulating arm using the DIUS and US imaging systems to provide real-time guidance to the PN to be treated. Once the optimal position and acoustic treatment window are reached, the articulating arm can be locked in place to enable precise treatment for the duration of the FUS sonication.

[0077] The FUS transducer includes a structure that allows the piezoelectric crystal to be actively cooled from both the front and back of the piezoelectric. This allows the transducer to operate at high intensities (piezoelectrically) for long durations and high duty cycles up to continuous wave ultrasound treatment without thermal damage or performance drift. Furthermore, the transducer includes thermally efficient, electrically isolated lens technology that allows heat to be removed from the treatment site through the transducer while it is operating. This minimizes bubble formation at the lens surface and reduces the water flow rate required to keep the skin cool. This design includes a high horizontal aspect ratio aperture and is focused through a single, thermally efficient lens to provide a FUS beam with a compound f-number that can be optimized to provide the focal width required for single-shot FUS treatments without the typically long focal lengths resulting from using circular or square focal areas. One exemplary embodiment includes a single FUS transducer that produces a -3 dB focal area of ​​4.5 mm horizontally and 1.3 mm vertically, with a -3 dB focal length of approximately 17 mm. This focal region is estimated to be sufficient to treat nerves 4 mm or less below the skin line without the need to scan the FZ or treat subsequent locations to cover the entire cross-section of the PN. This approach is potentially much more cost-effective than high-element-count rectangular matrix arrays that could also be used in this manner. Additionally, the focal region can be created to achieve low energies in the near field using a relatively wide parameter space to optimize treatment of the targeted PN while simplifying acoustic coupling and minimizing the possibility of skin burns.

[0078] Ultrasound imaging guidance of FUS treatment is important to achieve precise transcutaneous sonication of target anatomy, such as peripheral nerves. FUS sonication cannot be directly visualized in vivo during treatment without the use of contrast-enhancing agents; alternatives include elastography, ARFI, or MRI. It is important to note that these options are all costly, and the low levels of ultrasound exposure associated with NM FUS can be prohibitive. In one exemplary embodiment, the FUS transducer is mounted within a system that includes a means for co-registering high-resolution DIUS with the focal region of the FUS transducer via an ultrasound-transparent hollow cylindrical tissue-mimicking phantom with an outer diameter of approximately 5 cm, an inner diameter of approximately 4 cm, and an absorbent back wall. The phantom is filled with a transparent HIFU phantom gel (ONDA Corp.), which transforms into a stable, opaque material when the gel's temperature is increased by thermal FUS ablation within the gel. The FUS transducer treatment head is positioned over a custom HIFU phantom, and both the FUS and DIUS transducers are acoustically coupled to the phantom using the same acoustic coupling method used, for example, to treat peripheral nerves. The FUS transducer is then driven at an appropriate level to rapidly induce thermal lesions within the phantom corresponding to the FUS transducer's FZ. The lesion is then visualized by the DIUS and ultrasound imaging system, with provision for adjusting the relative position of the DIUS within the treatment head to achieve centering of the lesion on the ultrasound imaging system screen. Once the desired relative positioning is achieved—e.g., centering the longitudinal FZ on the DUS image—the relative position of the DIUS is locked, and the operator can freely position the treatment head on the subject using the co-registered DUS image to find the optimal treatment position for FUS treatment. When the optimal position is obtained, the articulating arm can be locked by a remote switch, such as a footswitch or button on the treatment head. Treatment can then proceed.

[0079] According to one aspect, a method is provided for aligning a treatment head including a HARFUS transducer and a diagnostic ultrasound examination system with a sample to be characterized, the method including acoustically coupling the treatment head with an ultrasound sensing phantom, performing a co-registration ultrasound processing sequence using the HARFUS transducer to determine an acoustic focal region using the ultrasound sensing phantom, positioning an imaging plane of the treatment head at the center of the acoustic focal region of the HARFUS transducer, locking the position of the HARFUS transducer relative to the treatment head, and based on the locked position of the HARFUS transducer, acoustically coupling the treatment head to the sample to be characterized and operating the treatment head to characterize the sample.

[0080] The initial design of the FUS transducer was 30 W / cm at the transducer element. 2 The proposed transducer focal region was simulated using OnScale numerical simulation software, using a model validated at intensities above 1000 Hz. The focal region of the proposed transducer can be achieved using a high aspect ratio aperture with dimensions of approximately 6 mm x 20 mm and a focal depth of approximately 3.5 cm for a hybrid F-number of 6 / 1.8. According to the simulation results, the initial design provides a focal region with a vertical -3 dB focal width (relative to the peripheral nerve) of 1.3 mm and a horizontal -3 dB focal width of 4.5 mm. The simulation of the -3 dB focal region is shown in the figure below.

[0081] The depth of focus and FZ size can be adjusted during development by changing the aperture size and aspect ratio, as well as the focal properties of the lens.

[0082] The FUS device allows for submillimeter positional accuracy of the treatment head and submillimeter co-registration with high frequency DIUS and DIS, allowing FUS treatments such as neuromodulation to be performed with a high degree of spatial precision and in short time intervals with minimal training. Furthermore, when paired with an appropriate RF power source of, for example, 150 W, the FUS transducer can deliver 1000 W / cm2 over a 4.5 mm x 16 mm focal region for several minutes continuously. 2 It should be possible to generate peak intensities exceeding .

[0083] It should be noted that the present technology, or at least some of its embodiments, is compatible with the technology described in Canadian Patent Nos. 2019 / 051046, 2020 / 051563, and 2022 / 050387, the contents of which are incorporated herein by reference.

[0084] Turning now to the advantages and benefits of this technology, the need to partially decouple the frequency of focused ultrasound treatment from the size of the focal region in a cost-effective single-element solution is significant. The further ability to combine such devices in a modular fashion to extend the focal region laterally without increasing the risk of skin burns or the need to add expensive 2D arrays and associated electronics and treatment planning software and image guidance is practical and has hindered the adoption of FUS in the clinic.

[0085] Furthermore, the need to translate preclinical studies using the same parameters on small animals to clinical studies with much larger anatomy but similar tissues is a significant barrier to translating preclinical FUS results to the clinic. The ability of the HARFUS device disclosed herein to produce identical acoustic signatures in the focal region that can vary by an order of magnitude is a potentially groundbreaking advance for translating preclinical FUS studies to the clinic.

[0086] All of this is enhanced by the possibility of using diagnostic ultrasound to guide these HARFUS devices to the target anatomy. The safety and practicality of US-guided FUS (USgFUS) is dramatically enhanced by the ability to control the target focal length while matching the focal region width to the target anatomy, meaning that complex treatment planning of small focal regions within larger anatomy, and long treatment times, which often require complex software and MRI guidance, are not required.

[0087] The present technology presents a high aspect ratio aperture that generates a wide lateral focal region with a relatively short focal length, combined with exceptional cooling on both sides of the piezoelectric element, and the lens can enable both FUS research and clinical treatments at lower cost and higher efficacy when a single insonification of an anatomical structure is critical, reducing treatment time and cost relative to complex 2D array-based treatments.

[0088] Several alternative embodiments and examples have been described and illustrated herein. The above-described embodiments are intended to be exemplary only. Those skilled in the art will appreciate the features of each individual embodiment and the possible combinations and variations of the components. Those skilled in the art will further appreciate that any of the embodiments may be provided in any combination with the other embodiments disclosed herein. The present examples and embodiments are therefore to be considered in all respects as illustrative and not restrictive. Thus, while specific embodiments have been illustrated and described, numerous modifications are contemplated without significantly departing from the scope defined in this specification and the appended claims.

Claims

1. 1. A high aspect ratio aperture-focused ultrasound (HARFUS) transducer, comprising:

1. A high aspect ratio acoustical stack having a front end and a rear end, the acoustical stack comprising: a composite piezoelectric layer including a plurality of regions made of piezoelectric material, each region separated from another by a non-piezoelectric matrix material, the composite piezoelectric layer having a length and a width that define a high aspect ratio, the length and the width of the composite piezoelectric layer forming a high aspect ratio acoustic aperture; a thermally and electrically conductive layer in physical contact with the piezoelectric layer, the composite piezoelectric layer being acoustically matched to the thermally and electrically conductive layer; a thermally conductive and electrically insulating layer in contact with the thermally conductive and electrically insulating layer; a lens in contact with the thermally conductive and electrically insulating layer; at least one matching layer extending at least partially over the lens, the acoustic stack configured to generate a field that defines an acoustic focal region, the acoustic focal region having relatively wide lateral dimensions, relatively narrow lateral dimensions, and a relatively low focal length to focal width ratio; and a support structure in contact with the back end of the acoustic stack.

2. The HARFUS transducer of claim 1 , wherein the acoustic focal region is shaped like a pumpkin seed.

3. 3. The HARFUS transducer of claim 1, wherein the at least one matching layer comprises a front matching layer extending over a rear matching layer.

4. 4. A HARFUS transducer according to claim 1, wherein the lens has a tapered edge and a tapered width.

5. 5. A HARFUS transducer according to any one of claims 1 to 4, wherein the lens has a periphery, the periphery being threaded or including anechoic features.

6. 6. The HARFUS transducer according to claim 1, wherein the lens curvature is a spherical curvature or an elliptical curvature.

7. 7. A HARFUS transducer as described in any one of claims 1 to 6, further comprising a mismatching layer contacting the rear end of the high aspect ratio acoustic stack, the mismatching layer directly contacting one of the composite piezoelectric layer and the support structure.

8. 8. A HARFUS transducer according to any one of claims 1 to 7, wherein the support structure is a double layer mismatched support structure.

9. 9. A HARFUS transducer according to any one of claims 1 to 8, further comprising a heat sink.

10. 10. A modular system comprising a plurality of HARFUS transducers according to any one of claims 1 to 9, arranged to produce laterally merged focal regions having a lower axial focal length to lateral focal width ratio than a single HARFUS transducer.

11. 1. A high aspect ratio aperture-focused ultrasound (HARFUS) transducer, comprising:

1. A high aspect ratio acoustical stack having a front end and a rear end, the acoustical stack comprising: a composite piezoelectric layer, the composite piezoelectric layer including a plurality of regions made of piezoelectric material, each region separated from another by a non-piezoelectric matrix material, the composite piezoelectric layer having a length and width that define a high aspect ratio, the length and width of the composite piezoelectric layer forming a high aspect ratio acoustic aperture; a thermally and electrically conductive layer in physical contact with the piezoelectric layer, the composite piezoelectric layer being acoustically matched to the thermally and electrically conductive layer; a lens in contact with the thermally and electrically conductive layer; at least one matching layer extending at least partially over the lens, the acoustic stack configured to generate a field that defines an acoustic focal region, the acoustic focal region having relatively wide lateral dimensions, relatively narrow lateral dimensions, and a relatively low focal length to focal width ratio; and a support structure in contact with the back end of the acoustic stack.

12. 12. The HARFUS transducer of claim 11, wherein the acoustic focal region is shaped like a pumpkin seed.

13. 13. The HARFUS transducer of claim 11 or 12, wherein the at least one matching layer includes a front matching layer extending over a rear matching layer.

14. A HARFUS transducer according to any one of claims 11 to 13, wherein the lens has a tapered edge and a tapered width.

15. 15. A HARFUS transducer according to any one of claims 11 to 14, wherein the lens has a periphery, the periphery being threaded or including an anechoic feature.

16. 16. A HARFUS transducer according to any one of claims 11 to 15, wherein the lens curvature is a spherical curvature or an elliptical curvature.

17. 17. A HARFUS transducer as described in any one of claims 11 to 16, further comprising a mismatching layer contacting the rear end of the high aspect ratio acoustic stack, the mismatching layer directly contacting one of the composite piezoelectric layer and the support structure.

18. 18. A HARFUS transducer according to any one of claims 11 to 17, wherein the support structure is a double layer mismatched support structure.

19. A HARFUS transducer according to any one of claims 11 to 18, further comprising a heat sink.

20. 20. A modular system comprising a plurality of HARFUS transducers according to any one of claims 11 to 19, arranged to produce laterally merged focal regions having a lower axial focal length to lateral focal width ratio than a single HARFUS transducer.

21. 1. A method for aligning a treatment head comprising a HARFUS transducer and a diagnostic imaging system with a specimen to be characterized, the method comprising: acoustically coupling the treatment head to an ultrasound sensing phantom; performing a co-registered ultrasound processing sequence with the HARFUS transducer to determine an acoustic focal region using an ultrasound sensing phantom; positioning the imaging plane of the treatment at the center of the acoustic focal region of the HARFUS transducer; locking the position of the HARFUS transducer relative to the treatment head; acoustically coupling and characterizing the treatment head to the sample based on the locked position of the HARFUS transducer; and and operating the treatment head to characterize the sample.

Images