Selectively isolated ultrasonic transducer

Abstract

Disclosed herein is an ultrasonic transducer that is selectively insulated, thereby allowing the transducer to be exposed to a conductive fluid without causing a short circuit between electrodes of the transducer. Such a transducer comprises a piezoelectric transducer body having a first surface and a second surface that are spaced apart from each other and do not intersect each other. The ultrasonic transducer also comprises a first electrode disposed on the first surface, a second electrode disposed on the second surface, and an electrical insulator configured to cover only one of the first and second electrodes and inhibit electrical conduction between the first and second electrodes when the ultrasonic transducer is disposed in a conductive fluid. Apparatus and systems including such a transducer are also disclosed herein. Related methods are also disclosed herein.

Description

[Technical field]

[0001] [Priority] This application claims priority to U.S. patent application Ser. No. 17 / 457,997, filed December 7, 2021, by Thirumalai et al., and entitled "Selectively Isolated Ultrasonic Transducer," and U.S. Provisional Patent Application Ser. No. 63 / 151,514, filed February 19, 2021, by Thirumalai et al., and entitled "Selectively Isolated Ultrasonic Transducer."

[0002] [Technical field] The present application relates generally to minimally invasive devices, systems, and methods for providing energy delivery to targeted anatomical locations in a subject, and more specifically to catheter-based intraluminal devices, systems, and methods that include or utilize ultrasound transducers configured to emit ultrasound energy for the treatment of tissue, such as neural tissue. [Background technology]

[0003] According to the Centers for Disease Control and Prevention (CDC), approximately one in three adults suffers from high blood pressure, known as hypertension. If left untreated, hypertension can lead to kidney disease, arrhythmias, and heart failure. In recent years, the treatment of high blood pressure has focused on interventional approaches to inactivate the renal nerves around the renal artery. Autonomic nerves tend to follow blood vessels toward the organs they control. A catheter can reach certain structures that may be in close proximity within the body cavity through which the catheter travels. For example, one system uses a radio frequency (RF) generator connected to a catheter with multiple electrodes placed against the intima of the renal artery to generate an electric field in the vessel wall and surrounding tissue, causing resistive (ohmic) heating of the tissue to a temperature sufficient to ablate the tissue and the renal nerves that pass through it. To treat all of the renal nerves surrounding the renal artery, the RF electrodes are repositioned several times around the inside of the renal artery. However, the relatively limited electric field generated by the RF electrodes may miss some of the renal nerves, resulting in incomplete treatment. Additionally, heating the renal nerves requires that the RF electrodes come into contact with the intima, which may risk damaging or necrosing the intima, which may result in thrombus formation, fibrosis of the vessel wall, mechanical weakening of the vessel, and possible vascular injury.

[0004] Another approach to renal nerve deactivation is the use of high intensity focused ultrasound (HIFU), which utilizes vibrational energy to cause frictional heating and destruction of tissue, raising the tissue temperature sufficiently to cause ablation and remodeling. However, the use of HIFU in blood vessels can at best result in the formation of a thin focal ring on the blood vessel and surrounding tissue. When applied to renal denervation, it is difficult to align this thin ring with the renal nerve, because the renal nerve is located at different radial distances along the length of the renal artery. Another problem is that the focal ring is thin, resulting in a small longitudinal treatment zone relative to the axial direction of the blood vessel.

[0005] U.S. Patents Nos. 9,943,666, 9,981,108, and 10,039,901 to Warnking, 9,700,372, 9,707,034, and 10,368,944 to Schaer, and 10,350,440 and 10,456,605 to Taylor, each of which is incorporated by reference in its entirety, overcome many of the shortcomings of RF and HIFU systems as described above. An exemplary embodiment of the system includes an ultrasound transducer positioned along the distal end of a catheter designed to be inserted into a blood vessel (e.g., a renal artery). The ultrasound transducer emits one or more therapeutic doses of unfocused ultrasound energy, which heats tissue adjacent to the body cavity in which the transducer is located. Such unfocused ultrasound energy may ablate target nerves around the body cavity without damaging non-target tissues, such as the lining of the body cavity or unintended organs outside the body cavity. The system may include a balloon attached to the distal end of the catheter, the balloon designed to cool the blood vessel when a cooling fluid is delivered to the balloon. Such a design allows for the creation of one or more ablation zones sufficient to achieve long-term nerve inactivation at different locations around the blood vessel.

[0006] The ultrasound transducer may include first and second electrodes disposed on either side of a cylindrical piezoelectric material, such as lead zirconate titanate (PZT). To energize the transducer, a voltage is applied between the first and second electrodes at a frequency selected to resonate the piezoelectric material. This produces vibrational energy that radiates radially outward from the transducer. The transducer is designed to provide a substantially uniform and predictable radiation profile to limit damage to surrounding non-target tissue. Additionally, a cooling fluid is circulated through the balloon both before, during, and after activation of the transducer to reduce heating of the inner wall of the body cavity. In this manner, the peak temperature achieved by tissue within the cooling zone remains lower than tissue located outside the cooling zone.

[0007] It is desirable to suppress electrical shorts that may occur between the electrodes of the ultrasound transducer through the fluid. One way to suppress such electrical shorts is to use a non-conductive cooling fluid, such as deionized water, in the balloon, which has a sufficiently low electrical conductivity. However, it is desirable to have more flexibility in the selection of the type of cooling fluid used in the balloon. Additionally, it may be desirable to use an ultrasound transducer without a balloon, in which case the ultrasound transducer may be inserted directly into a body cavity through which conductive blood flows. In such procedures, it is desirable to suppress electrical shorts between the electrodes of the ultrasound transducer through the conductive blood. Summary of the Invention

[0008] Various ultrasound transducers are disclosed herein. Only one of the electrodes of such transducers is covered by an electrical insulator to prevent electrical shorting between the electrodes of the ultrasound transducer via a conductive fluid (e.g., cooling fluid in a balloon, or blood when the transducer is directly inserted into a body cavity through which conductive blood flows). Such ultrasound transducers may be referred to herein as selectively insulated or partially insulated transducers. Or, more simply, as transducers. Ultrasound-based tissue treatment devices and systems having selectively insulated transducers are also disclosed herein. The systems are catheter-based and may be delivered intraluminally (e.g., intravascularly) to position the selectively insulated transducer in a suitable body cavity, such as a blood vessel (e.g., renal artery). The selectively insulated transducer may be activated to deliver unfocused ultrasound energy radially outward to neuromodulate tissue in a target anatomical region, thereby treating a condition, such as hypertension. Additionally, the selectively insulated transducer may be placed within a balloon that is filled with a cooling fluid prior to and during treatment, which may act to transfer heat away from the ultrasound transducer and surrounding tissue during use. In such embodiments, the cooling fluid may be electrically conductive.

[0009] In accordance with certain embodiments of the present technology, an ultrasonic transducer includes a piezoelectric transducer body having a first surface and a second surface that are spaced apart from each other and do not intersect with each other. The ultrasonic transducer also includes a first electrode disposed on the first surface, a second electrode disposed on the second surface, and an electrical insulator that directly or indirectly covers the first electrode. The second electrode is not covered by the electrical insulator and is thereby configured to contact a conductive fluid when the ultrasonic transducer is disposed in the conductive fluid.

[0010] According to a particular embodiment of the present technology, the electrical insulator covers the first electrode and is configured to prevent the first electrode from contacting the conductive fluid when the ultrasonic transducer is placed in the conductive fluid, thereby preventing electrical conduction between the first electrode and the second electrode when the ultrasonic transducer is placed in the conductive fluid. In such an embodiment, the second electrode is not covered by the electrical insulator. Because the second electrode is not covered by the electrical insulator, the second electrode comes into contact with the conductive fluid when the ultrasonic transducer is placed in the conductive fluid.

[0011] According to certain embodiments of the present technology, the piezoelectric transducer body is configured to generate ultrasonic waves in response to a voltage being applied between the first electrode and the second electrode, which may also be referred to as applying a voltage between the first electrode and the second electrode. In such embodiments, the electrical insulator covering the first electrode is configured to inhibit, and preferably prevent, a short circuit from occurring between the first electrode and the second electrode when the ultrasonic transducer is placed in the conductive fluid and the voltage is applied between the first electrode and the second electrode.

[0012] According to certain embodiments of the present technology, the piezoelectric transducer body comprises a hollow tube of piezoelectric material having an inner surface and an outer surface, the inner surface being one of the first and second surfaces of the piezoelectric transducer body, and the outer surface being the other of the first and second surfaces of the piezoelectric transducer body. In certain such embodiments, the first electrode is disposed on one of the inner surface and the outer surface of the hollow tube of piezoelectric material, and the second electrode is disposed on the other of the inner surface and the outer surface of the hollow tube of piezoelectric material. According to certain embodiments of the present technology, the hollow tube of piezoelectric material is cylindrical in shape and has a circular radial cross-section. In other specific embodiments, the hollow tube of piezoelectric material may have other shapes besides a cylinder with a circular cross-section. Other cross-sectional shapes of the hollow tube of piezoelectric material, and more generally of the piezoelectric transducer body, include, but are not limited to, oval or elliptical cross-sections, square or rectangular cross-sections, pentagonal cross-sections, hexagonal cross-sections, heptagonal cross-sections, octagonal cross-sections, etc. In yet other embodiments, the piezoelectric transducer body is not hollow, for example, the piezoelectric transducer body may have a generally solid rectangular shape or some other solid shape. For example, the piezoelectric transducer body may be a solid piezoelectric transducer body.

[0013] According to certain embodiments of the present technology, the piezoelectric transducer body is configured to deliver acoustic energy in the frequency range of 8.5 to 9.5 MHz. According to certain embodiments of the present technology, the piezoelectric transducer body is configured to generate an acoustic output power in the range of 5 to 45 Watts in response to an input power in the range of 10 to 80 Watts.

[0014] According to certain embodiments of the present technology, the electrical insulator covering the first electrode inhibits (and preferably prevents) the first electrode from contacting the conductive fluid when the ultrasonic transducer is positioned in the conductive fluid. In such embodiments, if the electrical insulator does not cover the second electrode, the second electrode will come into contact with the conductive fluid when the ultrasonic transducer is positioned in the conductive fluid. In other words, only one of the first electrode and the second electrode is covered by the electrical insulator.

[0015] In one embodiment, the conductive fluid comprises one of blood, saline, non-pure water, or a sodium lactate solution. Thus, in this embodiment, the conductive fluid is selected from the group consisting of blood, saline, non-pure water, a sodium lactate solution, and combinations thereof.

[0016] In one embodiment, the first electrode includes a major perimeter and longitudinal ends. In such an embodiment, a portion of the electrical insulator covers the major perimeter of the first electrode and is made from a first type of electrically insulating material. In such an embodiment, another portion or remainder of the electrical insulator covers the longitudinal ends of the first electrode and is made from the first type of electrically insulating material or is made from a second, different type of electrically insulating material.

[0017] According to certain embodiments of the present technology, the ultrasonic transducer is configured to be disposed within a balloon that is at least partially filled with the conductive fluid, the balloon being used to cool a portion of a body cavity within which the ultrasonic transducer may be positioned. The cooling fluid may also be used to cool the transducer positioned within the balloon. In certain such embodiments, the conductive fluid that at least partially fills the balloon includes at least one of saline, non-pure water, or a sodium lactate solution. Thus, in such embodiments, the conductive fluid is selected from the group consisting of saline, non-pure water, a sodium lactate solution, and combinations thereof. Use of other conductive fluids is possible and within the scope of the embodiments described herein.

[0018] According to certain embodiments of the present technology, which may be referred to as balloon-less embodiments, the ultrasound transducer is configured to be directly exposed to blood flowing through a body cavity within which the ultrasound transducer may be positioned, in such embodiments, the conductive fluid includes or is blood.

[0019] According to certain embodiments of the present technology, the electrical insulator comprises parylene. Alternative or additional materials may be used to provide the electrical insulator, including, but not limited to, cyanoacetate, epoxy, nylon, polytetrafluoroethylene (PTFE), polyimide, polyethylene, polyethylene terephthalate, polyvinyl chloride (PVC), synthetic diamond coating, or combinations thereof. For example, in one embodiment, the electrical insulator comprises parylene disposed on and covering the outer periphery of the first electrode, and epoxy disposed on and covering the longitudinal ends of the first electrode. In another embodiment, the electrical insulator is made of parylene.

[0020] In one embodiment, the ultrasonic transducer further comprises a cable configured to contact the first electrode and provide power to the first electrode. In this embodiment, the electrical insulator covers both the periphery of the first electrode and the contact portion between the cable and the first electrode.

[0021] In one particular embodiment, the electrical insulator includes a first insulator disposed on the first electrode and a second insulator disposed on the contact portion, the second insulator being the same as or different from the first insulator.

[0022] The above-described embodiments of the ultrasonic transducer may be combined.

[0023] Certain embodiments of the present technology are directed to an apparatus that includes a balloon configured to receive a cooling fluid and an ultrasound transducer disposed within the balloon. In certain such embodiments, the ultrasound transducer comprises a hollow tube of piezoelectric material having an inner surface and an outer surface. A first electrode is disposed on one of the inner surface and the outer surface of the hollow tube of piezoelectric material. A second electrode is disposed on the other of the inner surface and the outer surface of the hollow tube of piezoelectric material. An electrical insulator covers the first electrode and is configured to inhibit contact of the first electrode with the cooling fluid received by the balloon. Thus, in such embodiments, the electrical insulator is configured to inhibit electrical conduction between the first electrode and the second electrode.

[0024] In one embodiment, the hollow tube of piezoelectric material is a cylindrically shaped hollow tube of piezoelectric material.

[0025] In one embodiment, the conductive cooling fluid may include, but is not limited to, at least one of saline, non-pure water, or a sodium lactate solution. Thus, in one embodiment, the conductive cooling fluid is selected from the group consisting of saline, non-pure water, a sodium lactate solution, and combinations thereof.

[0026] In certain embodiments, the first electrode (covered by the electrical insulator) is disposed on the exterior surface of the hollow tube of piezoelectric material. In other embodiments, the first electrode (covered by the electrical insulator) is disposed on the interior surface of the hollow tube of piezoelectric material. In certain such embodiments, the second electrode is not covered by an electrical insulator and will be in contact with the cooling fluid received by the balloon.

[0027] In accordance with certain embodiments of the present technology, the device further comprises a controller configured to apply a voltage between the first electrode and the second electrode, thereby causing the ultrasound transducer to generate ultrasound waves. In such embodiments, the electrical insulator inhibits (and preferably prevents) a short circuit from occurring between the first electrode and the second electrode when the cooling fluid contained within the balloon is a conductive cooling fluid and the voltage is applied between the first electrode and the second electrode by the controller. In some such embodiments, the first electrode is an outer electrode. In other embodiments, the first electrode is an inner electrode.

[0028] In one embodiment, the electrical insulator comprises one or more of the following: parylene, cyanoacetate, epoxy resin, nylon, polytetrafluoroethylene (PTFE), polyimide, polyethylene, polyethylene terephthalate, polyvinyl chloride (PVC), and a synthetic diamond coating.

[0029] According to a specific embodiment of the present technology, a method includes providing an ultrasonic transducer having a first surface and a second surface that are spaced apart from each other and do not intersect with each other, a first electrode disposed on the first surface and a second electrode disposed on the second surface. The method also includes covering only one of the first electrode and the second electrode with an electrical insulator, and exposing the ultrasonic transducer to a conductive fluid that contacts the second electrode but is prevented from contacting the first electrode by the electrical insulator covering the first electrode. Additionally, while the ultrasonic transducer is exposed to the conductive fluid, the method includes applying a voltage between the first electrode and the second electrode to cause the ultrasonic transducer to generate ultrasonic waves. The method further includes utilizing the electrical insulator to prevent a short circuit between the first electrode and the second electrode while the ultrasonic transducer is exposed to the conductive fluid and the voltage is applied between the first electrode and the second electrode. The conductive fluid may include, but is not limited to, at least one of saline, non-pure water, or a sodium lactate solution. Alternatively, the conductive fluid may be blood flowing through the body cavity.

[0030] According to certain embodiments, the method further comprises disposing the ultrasound transducer within a balloon. In such embodiments, exposing the ultrasound transducer to the conductive fluid comprises at least partially filling the balloon with the conductive fluid. Such methods may also comprise inserting the balloon with the ultrasound transducer therein into a body cavity. In such embodiments, applying a voltage between the first electrode and the second electrode to cause the ultrasound transducer to generate ultrasound waves occurs while the balloon is within the body cavity.

[0031] According to an alternative embodiment, which may be referred to as a balloon-less embodiment, the method further comprises inserting the ultrasound transducer into a body cavity through which blood flows such that the ultrasound transducer is in contact with the blood, in such an embodiment, the conductive fluid comprises the blood, and exposing the ultrasound transducer to the conductive fluid comprises exposing the ultrasound transducer to the blood.

[0032] According to certain principles of the present technology, a conductive cooling fluid, such as saline or sodium lactate solution, may be used with the selectively isolated transducer. Saline and sodium lactate solutions are readily available in hospitals and other treatment centers, which may increase the ease of integrating the system of the present technology into a surgical environment. Thus, the selectively isolated transducer may include an electrical insulator covering one of the inner or outer electrodes of the isolated transducer, which inhibits shorting between the electrodes of the transducer via the conductive fluid in the balloon. Specifically, in the absence of an electrical insulator, when the balloon is filled with a conductive fluid, application of a voltage between the inner and outer electrodes may cause an electrical short, which inhibits the ultrasonic material of the transducer from generating ultrasonic waves of the desired output power.

[0033] This summary is not intended to be a complete description of embodiments of the present technology. Other features and advantages of embodiments of the present technology will become apparent from the following description, taken in conjunction with the accompanying drawings and claims, in which preferred embodiments are set forth in detail.

[0034] Various features of the present disclosure and the manner in which they are accomplished will be described in more detail with reference to the following detailed description, claims and drawings, in which reference characters have been re-used where appropriate to indicate correspondence between referenced items. [Brief description of the drawings]

[0035] [Figure 1]FIG. 1 illustrates selected components of an ultrasound-based tissue treatment system in accordance with a particular embodiment of the present technique.

[0036] [Figure 2A] FIG. 2A illustrates a side view of selected components of the ultrasound-based tissue treatment system shown in FIG.

[0037] [Figure 2B] FIG. 2B illustrates a perspective view of additional selected components of an ultrasound-based tissue treatment system inserted into a body cavity in accordance with various aspects provided herein.

[0038] [Figure 2C] FIG. 2C shows a longitudinal cross-sectional view of a distal portion of a catheter of an ultrasound-based tissue treatment system in accordance with one embodiment of the present technology.

[0039] [Figure 3A1] FIG. 3A1 shows a cross-sectional view of a catheter shaft along line AA of FIG. 2C, according to one embodiment.

[0040] [Figure 3A2] FIG. 3A2 shows a cross-sectional view of a catheter shaft along line AA of FIG. 2C according to another embodiment.

[0041] [Figure 3B] FIG. 3B shows a cross-sectional view across a portion of the ultrasound transducer of the catheter taken along line BB in FIG. 2C.

[0042] [Figure 4A] FIG. 4A is a side view of a distal portion of a catheter of an ultrasound-based tissue treatment system including a selectively isolated transducer, in accordance with a specific embodiment of the present technique.

[0043] [Figure 4B]4B is a perspective view of a selectively insulated transducer in accordance with a specific embodiment of the present technique, in which the outer electrode of the piezoelectric transducer is covered by an electrical insulator.

[0044] [Figure 4C] FIG. 4C shows a cross-sectional view of the selectively isolated transducer shown in FIGS. 4A and 4B.

[0045] [Figure 4D] FIG. 4D shows a radial cross-section of the selectively isolated transducer shown in FIGS. 4A and 4B.

[0046] [Figure 5A] 5A shows a cross-sectional view of a selectively insulated transducer in accordance with another embodiment of the present technique. The inner electrode of a piezoelectric transducer is covered by an electrical insulator.

[0047] [Figure 5B] Figure 5B is a radial cross-section of the selectively insulated transducer shown in Figure 5A. The inner electrode of the piezoelectric transducer is covered by an electrical insulator.

[0048] [Figure 6A] 6A shows a longitudinal cross-sectional view of the transducer. Both the inner and outer electrodes of the piezoelectric transducer are covered by an electrical insulator.

[0049] [Figure 6B] Figure 6B shows a radial cross-section of the transducer shown in Figure 6 A. Both the inner and outer electrodes of the piezoelectric transducer are covered by an electrical insulator.

[0050] [Figure 7]FIG. 7 is a graph of input power versus acoustic output power for a piezoelectric transducer, illustrating how isolating various different electrodes or combinations thereof affects the performance of the transducer.

[0051] [Figure 8A] FIG. 8A shows a perspective view of an alternative form of piezoelectric transducer in which the transducer body is rectangular and the transducer electrodes are planar.

[0052] [Figure 8B] FIG. 8B shows a cross-sectional view of the piezoelectric transducer shown in FIG. 8A.

[0053] [Figure 9] FIG. 9 illustrates a cross-sectional view of a selectively isolated transducer in accordance with another embodiment of the present technique.

[0054] [Figure 10] FIG. 10 illustrates a cross-sectional view of a selectively isolated transducer in accordance with yet another embodiment of the present technique.

[0055] [Figure 11] FIG. 11 is a high level flow chart used to summarize methodologies in accordance with various embodiments of the present technique. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0056] Acoustic-based tissue treatment transducers, devices, and systems are provided herein. Preferably, the systems are catheter-based and can be delivered intraluminally (e.g., intravascularly) to place the transducer in a target anatomical region of a subject, e.g., in a suitable body cavity such as a blood vessel. Once properly positioned in the target anatomical region, the transducer can be activated to deliver unfocused ultrasound energy radially outward to appropriately heat and treat tissue in the target anatomical region. The transducer can be activated at a frequency, time, and energy level appropriate for treating the target tissue. In one non-limiting example, the unfocused ultrasound energy generated by the transducer can target (select) neural tissue of the subject and heat such tissue in a manner that neuromodulates (e.g., completely or partially ablates, necrotizes, or stimulates) the neural tissue. Neuromodulation of renal nerves, in the manner described in the aforementioned Warnking, Schaer, and Taylor patents, may be used to treat a variety of conditions, such as hypertension, chronic kidney disease, atrial fibrillation, arrhythmias, heart failure, chronic kidney disease, end stage renal failure, myocardial infarction, anxiety, contrast nephropathy, diabetes, metabolic disorders, insulin resistance, etc. However, it should be understood that the transducer may be suitably used to treat other nerves and conditions, such as the sympathetic nerves of the hepatic plexus in the hepatic artery responsible for blood glucose levels important in treating diabetes, or any suitable tissue, such as cardiac tissue causing abnormal heart rhythms, and is not limited to use in treating (e.g., neuromodulation) renal nerve tissue.

[0057] In an endoluminal system, the ultrasound transducer may be placed within a balloon that is filled with a cooling fluid before and during treatment. Alternatively, the ultrasound transducer may be exposed directly to the bloodstream, without a surrounding balloon, in what may be referred to as a balloon-less embodiment.

[0058] [System components and functions overview] 1, 2A, and 2B illustrate features of an ultrasound-based tissue treatment system 100 according to various aspects provided herein. Referring initially to FIG. 1, the system 100 is shown as including a catheter 102, a controller 120, and a connecting cable 140. In certain embodiments, the system 100 further includes an ultrasound transducer 111 in a balloon 112, a reservoir 110, a cartridge 130, and a control mechanism, such as a handheld remote control. In certain embodiments, which may be referred to as "balloon-less" embodiments, the system 100 does not include a balloon 112. In certain such balloon-less embodiments, the system 100 also does not include a reservoir 110 and a cartridge 130. In other certain balloon-less embodiments, the system 100 includes a reservoir 110 and / or a cartridge 130.

[0059] 1, the controller 120 is shown as connected to the catheter 102 via the cartridge 130 and connecting cable 140. In certain embodiments, the controller 120 interfaces with the cartridge 130 to provide a cooling fluid to the catheter 102 for selectively inflating and deflating the balloon 112. The balloon 112 may be manufactured from, for example, but not limited to, nylon, polyimide film, thermoplastic elastomers (such as those sold under the trademark PEBAX®), medical grade thermoplastic polyurethane elastomers (such as those sold under the trademark PELLETHANE®), pellethane, isothane, other suitable polymers, or any combination thereof.

[0060] 2A, the catheter 102 includes a distal portion 210 and a proximal portion 220. The catheter 102 includes a catheter shaft 214, which may include one or more lumens extending therethrough. By way of example, the catheter shaft 214 includes a guidewire lumen 225 shaped, sized, and otherwise configured to receive a guidewire. In a particular embodiment, for example suitable for renal denervation, the catheter 102 may be approximately 6 French in diameter and approximately 85 cm in length. The proximal portion 220 of the catheter 102 may include one or more connectors or couplings. For example, the proximal portion 220 may include one or more electrical couplings 232. The catheter 102 may be coupled to the controller 120 by connecting the electrical couplings 232 to a connecting cable 140. Connecting cable 140 may be removably connected to controller 120 and / or catheter 102 via ports on controller 120 and / or catheter 102 to allow for the use of multiple catheters during a procedure. In certain embodiments, for example, if only one catheter 102 needs to be used during a procedure, connecting cable 140 may be permanently connected to controller 120.

[0061] In certain embodiments, the proximal portion 220 of the catheter 102 may further include one or more fluid ports, such as a fluid inlet port 234a and a fluid outlet port 234b. Through these ports, an expandable member (e.g., the balloon 112) may be fluidly connected to a reservoir 110 (shown in FIG. 1 ), which provides a cooling fluid. The reservoir 110 may optionally be included within the controller 120, attached to the outer housing of the controller 120 as shown in FIG. 1 , or provided separately. In other embodiments, the fluid inlet port 234a and the fluid outlet port 234b, the balloon 112, and the reservoir 110 may all (or none) be present in the system 100. Other variations are possible and are within the scope of the embodiments described herein.

[0062] 2B shows a perspective view of selected components of the catheter 102, such as components of a distal portion 210 that may be inserted into a body lumen BL of a subject. In FIG. 2B, the body lumen BL is a blood vessel (e.g., a renal artery) having multiple nerves N in an outer layer (e.g., an adventitial layer) of the blood vessel. As shown in FIG. 2B, the distal portion 210 may include an ultrasound transducer 111, a balloon 112 filled with a cooling fluid 213, a catheter shaft 214, and / or a guidewire support tip 215 configured to receive a guidewire 216.

[0063] The transducer 111 may be partially or completely disposed within the balloon 112. The balloon 112 may be inflated with cooling fluid 213 so as to contact the inner surface (e.g., the intima) of the body cavity BL. In certain embodiments, the transducer 111 may be used to output an acoustic signal when the balloon 112 completely occludes the body cavity BL. The balloon 112 may center the transducer 111 within the body cavity BL. In certain embodiments, suitable for example for renal denervation, the balloon 112 is inflated while inserted into the body cavity BL of the patient under treatment at an operating pressure of about 1.4 to 2 atmospheres (atm) using the cooling fluid 213. The balloon 112 may be or include a compliant, semi-compliant, or non-compliant medical balloon. The balloon 112 is sized to be insertable into the body cavity BL, for example, for insertion into a renal artery, the balloon 112 may be selected from available sizes including, but not limited to, outer diameters of 3.5 mm, 4.2 mm, 5 mm, 6 mm, 7 mm, 8 mm, etc. In some embodiments, as shown in FIG. 2B, when filled with cooling fluid 213 and inflated under the control of the controller 120, the outer wall of the balloon 112 may be approximately parallel to the outer surface of the transducer 111. Optionally, the balloon 112 may be sufficiently inflated to be in apposition with the body cavity BL. For example, the balloon 112 may at least partially contact the inner wall of the body cavity BL when inflated, and may be in apposition with the inner wall of the body cavity BL. In other forms, the balloon 112 is configured not to contact the body cavity BL when inflated. Additionally or alternatively, the balloon 112 may be maintained at a specified size by pushing or withdrawing cooling fluid into or from the balloon 112 at a specified flow rate. In the balloon-less embodiment, the transducer 111 is not disposed within a balloon.

[0064] FIG. 2C shows a longitudinal cross-sectional view of the distal portion 210 of the catheter 102. FIG. 3A1 shows a cross-sectional view of the catheter shaft 214 along line AA of FIG. 2C, according to one embodiment. FIG. 3A2 shows a cross-sectional view of the catheter shaft 214 along line AA of FIG. 2C, according to another embodiment. FIG. 3B shows a cross-sectional view of the ultrasound transducer 111 along line BB of FIG. 2C, according to one embodiment. In a particular embodiment, the catheter shaft 214 may be about 1.8 mm in diameter. The catheter shaft 214 includes one or more lumens, which may be used as fluid conduits, electrical cable passages, guidewire lumens, etc., as described in more detail below with reference to FIGS. 3A1 and 3A2. In a particular embodiment suitable for renal denervation, for example, the guidewire 216 has a diameter of about 0.36 mm and a length of about 180 cm to about 300 cm, delivered using a 7 French guide catheter having a minimum inner diameter of 2.06 mm and a length of less than about 80 cm. In certain embodiments, a 6 French guide catheter is used to deliver the guidewire 216. In certain embodiments, the guide catheter has a length of about 55 cm. In certain embodiments, the guide catheter has a length of about 85 cm, and a hemostasis valve is attached to the hub of the guide catheter to allow continuous irrigation of the guide catheter to reduce the risk of thromboembolism.

[0065] Referring again to FIG. 2C, the ultrasound transducer 111 may include a cylindrical hollow tube 201 made of a piezoelectric material (e.g., lead zirconate titanate (PZT) or the like) with an inner electrode 202 and an outer electrode 203 disposed on the inner and outer surfaces, respectively. Such a cylindrical hollow tube of piezoelectric material is an example of a piezoelectric transducer body 201 and may therefore be referred to as the piezoelectric transducer body 201. As described in more detail below, the piezoelectric transducer body may have a variety of other shapes and need not be hollow. In a particular embodiment suitable for, for example, renal denervation, the piezoelectric material that makes up the piezoelectric transducer body 201 is lead zirconate titanate 8 (PZT8), also known as Navy III piezoelectric material. The raw PZT transducer may be plated with layers of copper, nickel and / or gold to create electrodes on the surfaces (e.g., inner and outer surfaces) of the piezoelectric transducer body (e.g., 201). Application of a voltage and alternating current between the inner electrode 202 and the outer electrode 203 causes the piezoelectric material to vibrate transversely to the longitudinal direction of the cylindrical tube 201 and emit ultrasonic waves radially. It is noted that although the ultrasonic transducer 111 in Figure 2C is not shown as surrounded by a balloon, the ultrasonic transducer 111 may be positioned within a balloon (e.g., 112), as shown, for example, in Figure 2B.

[0066] As shown in FIG. 2C, the ultrasound transducer 111 is generally supported via a backing member or post 218. In a particular embodiment, the backing member 218 comprises stainless steel coated with nickel and gold, with nickel being used as a bonding material between the stainless steel and the gold plating. In a particular embodiment suitable for renal denervation, for example, the outer diameter of the transducer 111 is about 1.5 mm, the inner diameter of the transducer 111 is about 1 mm, and the transducer 111 has a length of about 6 mm. Transducers having other inner diameters, outer diameters and lengths, or more generally sizes and shapes, are also within the scope of the embodiments described herein. Additionally, it is noted that the drawings in each figure are not necessarily, and often are not, drawn to scale.

[0067] 2C, the backing member 218 may extend from the distal portion 210 of the catheter shaft 214 to the distal tip 215. For example, the distal end of the backing member 218 may be positioned within an adjacent opening in the tip 215 and the proximal end of the backing member 218 may be movably coupled to the distal portion 210 of the catheter shaft 214 via an electrical cable 282. In other embodiments, a gap (e.g., as indicated by letter D in FIG. 2C) exists between the distal end of the catheter shaft 214 and the proximal end of the ultrasound transducer 111.

[0068] To permit liquid cooling along both the inner electrode 202 and the outer electrode 203, the backing member 218 may include one or more standoff assemblies 230a and 230b. The standoff assemblies 230a, 230b may define one or more annular openings through which the cooling fluid 213 may enter a space in the transducer 111 (which may be selectively insulated according to certain embodiments described below) between the backing member 218 and the inner electrode 202. Thus, the backing member 218 may function as a fluid barrier between the cooling fluid 213 circulated within the balloon 112 and the lumen of the backing member 218 that receives the guidewire 216. For example, as shown generally in FIG. 2C, a standoff assembly 230a, 230b of the backing member 218 may be positioned along or adjacent each longitudinal end of the ultrasonic transducer 111 (separated by a main post body 289) to couple the cylindrical tube 201 of the ultrasonic transducer 111 to the backing member 218. With reference to FIG. 3B, the standoff assembly 230 (230a or 230b) may have a number of lugs, ribs, or attachment points 334 that engage with the inner electrode 202 of the transducer 111. In certain embodiments, the attachment points 334 are soldered to the inner electrode 202 of the transducer 111. The number, size, and arrangement of the ribs 334 may be varied as desired or needed. For example, as shown in FIG. 3B, a total of three ribs 334 may be positioned approximately equally spaced at an angle of 120° from each other to define an opening 336. Through the openings 336, cooling fluid or blood can enter the interior space of the cylindrical tube 201 between the inner electrode 2 disposed along the inner surface of the cylindrical tube 201 and the backing member 218. In a particular embodiment, the maximum outer diameter of the standoff assemblies 230a and 230b is about 1 mm, the outer diameter of the main post body 289 is about 0.76 mm, and the inner diameter of the backing member 218 is about 0.56 mm.

[0069] According to certain embodiments, the standoff assemblies 230a, 230b are electrically conductive to electrically couple the inner electrode 202 of the ultrasonic transducer 111 to the backing member 218. One or more conductors of the electrical cable 282 may be electrically coupled to the backing member 218. Thus, when the controller 120 is activated, electrical current may be delivered from the electrical cable 282 through the backing member 218 and the standoff assemblies 230a, 230b to the inner electrode 202 of the ultrasonic transducer 111, which advantageously eliminates the need to directly couple the cable 282 to the inner electrode 202 of the transducer 111. In other embodiments, the backing member 218 and the standoff assemblies 230a, 230b are made of one or more electrically insulating materials or, even if they are made of a conductive material, are coated with one or more electrically insulating materials.

[0070] Additionally, as shown in FIG. 2C, the backing member 218 may have an insulating tube 219 disposed along its inner surface to prevent or reduce the possibility of electrical conduction between the guidewire 216 (shown in FIG. 2B) and the backing member 218. This is used in embodiments where such electrical conduction is not desired. The insulating tube 219 may be formed of a non-conductive material (e.g., a polymer such as polyimide), which may also be referred to as an electrical insulator. As shown in FIG. 2C, the insulating tube 219 may extend from the catheter shaft 214 through the lumen of the backing member 218 within the transducer 111 to the tip 215. In this aspect, the transducer 111 is offset distally from the distal end of the catheter shaft 214.

[0071] 2C, the catheter 102 may include a bore 277 extending proximally within the catheter 102 from a distal end of the catheter 102. The bore 277 is sized and shaped to receive at least a portion of the backing member 218, thereby electrically isolating the insulating tube 219 and / or the ultrasonic transducer 111. Thus, during delivery of the catheter 102 to the anatomical region to be treated, the backing member 218, the insulating tube 219 and / or the ultrasonic transducer 111 may be at least partially retracted within the bore 227 of the catheter 102, for example by retracting the electrical cable 282, thereby providing sufficient stiffness to the catheter 102 such that it may be delivered in a safe manner.

[0072] As shown in Figures 3A1 and 3A2, the catheter shaft 214 includes one or more lumens that may be used as fluid conduits, electrical cable passages, guidewire lumens, etc. For example, as shown in Figures 3A1 and 3A2, the catheter shaft 214 may include a guidewire lumen 325 shaped, sized, and otherwise configured to receive a guidewire 216. In certain embodiments, as shown in Figure 3A1, the guidewire lumen 325 is located in the center of the catheter shaft 214 to center the transducer 111 within the catheter shaft 214. Alternatively, as shown in Figure 3A2, for example, the guidewire lumen 325 may be offset from the center of the catheter shaft 214. The catheter shaft 214 may also include a cable lumen 326 for receiving an electrical cable. Additionally, the catheter shaft 214 may include one or more fluid lumens 327, 328 for transporting a cooling fluid 213 (e.g., water, sterile water, saline, 5% dextrose (D5W)) or other liquid or gas from a fluid source (external to the patient), such as a reservoir 110, in the proximal portion 220 of the catheter 102 to the balloon 112 under the control of the controller 120. Active cooling of approximately the first millimeter of tissue is designed to maintain the integrity of the vessel wall, such as the renal artery wall.

[0073] The catheter 102 may include only a single fluid lumen or may include two or more fluid lumens (e.g., three, four, five or more, etc.) as desired or required. As shown in FIG. 3A1, in one embodiment, the fluid lumens 327 and 328 and the cable lumen 326 all have kidney-shaped or D-shaped cross-sections configured to maximize the efficiency of fluid flow delivery and distribute the fluid evenly throughout the ultrasonic transducer 111 by maximizing the area while minimizing the perimeter of each lumen 326, 327, and 328. In certain embodiments, each of the fluid lumens 327 and 328 and the cable lumen 326 are substantially symmetrical, substantially identical in size, substantially identical in geometric shape, and / or substantially interchangeable, as shown, for example, in FIG. 3A1. Fluid flow rate variations within the catheter may result in delayed or incomplete therapy. In certain embodiments, the catheter shaft 214 is configured to allow a fluid flow rate of about 40 mL / min. In certain embodiments, the catheter shaft 214 is configured to allow a fluid flow rate of about 35-45 mL / min. In certain embodiments, the catheter shaft 214 is configured to allow a fluid flow rate of about 20-45 mL / min. For example, in certain embodiments suitable for radial delivery during a renal denervation procedure, the catheter shaft 214 is configured to allow a fluid flow rate of about 10-20 mL / min. Each of the one or more lumens (e.g., 328) may be in fluid communication with the same or separate individual fluid sources outside the patient's body at the proximal portion 220 of the catheter 102.

[0074] As another example, the catheter shaft 214 may include any suitable number of fluid lumens for transporting cooling fluid from the reservoir 110 to the balloon 112 (or to the transducer 111 in balloon-less embodiments) in response to commands executed by the controller 120. In certain balloon-less embodiments, the catheter shaft 214 may omit the fluid lumens 327, 328 and the system 100 may omit the reservoir 110. In certain balloon-less embodiments, the catheter shaft 214 includes the fluid lumens 327, 328 and the system 100 includes the reservoir 110.

[0075] In certain embodiments, as shown in FIG. 3A2, the guidewire lumen 325 is located proximal to and / or shares a wall with the catheter shaft 214 to allow for rapid exchange of the catheter during a procedure. In such embodiments, the cable lumen 326 is located opposite the guidewire lumen 325 and shares a wall with the catheter shaft 214. The cable lumen 326 may be, for example, triangular or rectangular in shape and may be configured to maximize the area available to the fluid lumens 327 and 328 and minimize the circumference of the fluid lumens 327 and 328, thereby allowing for a higher flow rate at the same pressure. The fluid lumens 327 and 328 may be shaped to optimize flow rate and reduce drag on the catheter 102. In such embodiments, the area of ​​the fluid lumens 327 and 328 may not be maximized, but instead the walls of the fluid lumens 327 and 328 may be rounded to avoid pockets that may cause drag, thereby optimizing the flow rate of the cooling fluid 213 within the fluid lumens 327 and 328.

[0076] The catheter shaft 214 may include, at least within the cable lumen 326, an electrical cable 282 (e.g., a coaxial cable, a parallel coaxial cable, a shielded parallel pair cable, one or more wires, or one or more other electrical conductors) that couples the inner electrode 202 and the outer electrode 203 of the ultrasound transducer 111 to the controller 120. This allows the controller 120 to apply an appropriate voltage between such electrodes to cause the piezoelectric material of the transducer 111 to emit ultrasonic energy toward the subject. In certain embodiments, the cable lumen 326 is shaped, sized, and otherwise configured to receive the electrical cable 282 (e.g., a coaxial cable, a wire, other electrical conductor, etc.). The electrical cable 282 may allow the electrodes 202, 203 of the ultrasound transducer 111 to be selectively activated to emit acoustic energy toward the subject. More specifically, the electrical cable 282 may allow communication of transducer information, such as operating frequency and power, from the catheter 102 to the controller 120 and / or vice versa, as well as the transmission of electrical energy to the ultrasound transducer 111 during treatment.

[0077] The distal portion 210 of the catheter 102 may be delivered percutaneously to a target anatomical location (e.g., a specific location within the body cavity BL) via any suitable intraluminal access route, such as a gastrointestinal route or an intravascular route, such as a femoral or radial route. In certain embodiments, the controller 120 is configured to fill the balloon 112 with cooling fluid 213 only after the distal portion 210 of the catheter 102 is properly positioned at the target anatomical location. The catheter 102 may be delivered through the body cavity BL with or without the aid of a commercially available guidewire. For example, the catheter 102 and balloon 112 may be delivered through a renal guide catheter along a guidewire 216 (shown in FIG. 2B). For further examples of guidewire-based ultrasound transducer delivery, see U.S. Pat. No. 10,456,605, previously incorporated by reference herein. However, any suitable steerable catheter or sheath, or any other suitable guidance device or method, may be used to deliver the distal portion 210 of the catheter 102 to the target anatomical location of the subject. Once delivered to the appropriate location within the body cavity BL, the balloon 112 may be inflated with cooling fluid 213 (e.g., under the control of the controller 120) and the transducer 111 may be activated (e.g., by applying a voltage between the inner electrode 202 and the outer electrode 203 under the control of the controller 120) to deliver unfocused ultrasound energy to the target anatomical location. The transducer 111 is sized for insertion into the body cavity BL; for example, for insertion into a renal artery, the transducer 111 may have an outer diameter of less than 2 mm, e.g., an outer diameter of about 1.5 mm, and an inner diameter of less than 1.8 mm, e.g., an inner diameter of about 1 mm. As described in more detail below, the length L of the transducer 111 may optionally be selected such that the ultrasound waves it generates have a near-field depth suitable for creating a lesion only within a desired region relative to the wall of the target body cavity BL.

[0078] 1, 2A, 2C, 3A1 and 3A2, according to certain embodiments, a proximal end of a connecting cable 140 connects to the controller 120 and a distal end of the connecting cable 140 connects to an electrical coupling 232 at a proximal portion of the catheter 102. An electrical cable 282 extends through a cable lumen (e.g., 326 in FIG. 3A1 or 3A2) of the catheter shaft 214 to the electrical coupling 232, thereby electrically coupling the transducer 111 to the electrical coupling 232. By electrically coupling the connecting cable 140 between the controller 120 and the electrical coupling 232 and electrically coupling the electrical cable 282 between the electrical coupling 232 and the transducer 111, the controller 120 is electrically coupled to the transducer 111, thereby providing power to and otherwise controlling the transducer 111.

[0079] It will be appreciated that the frequency, power, and time (duration) at which the transducer 111 is suitably activated may be selected based on the treatment to be performed. For example, the frequency is optionally in the range of 1-20 MHz, e.g., 1-5 MHz, 5-10 MHz, 8.5-9.5 MHz, 10-15 MHz, 15-20 MHz, or 8-10 MHz, e.g., about 9 MHz. Alternatively, for example, the frequency is optionally in the range of less than 1 MHz, e.g., 0.1-0.2 MHz, 0.2-0.3 MHz, 0.3-0.4 MHz, 0.4-0.5 MHz, 0.5-0.6 MHz, 0.6-0.7 MHz, 0.7-0.8 MHz, 0.8-0.9 MHz, or 0.9-1.0 MHz. Alternatively, for example, the frequency is optionally in a range greater than 20 MHz, e.g., 20-25 MHz, 25-30 MHz, or greater than 30 MHz. Optionally, the power can be in a range of 5-80 W (e.g., 5-50 W, 5-10 W, 12.1-16.6 W, 10-20 W, 20-30 W, 30-40 W, 40-50 W, 50-60 W, 60-70 W, 70-80 W, or greater than 80 W). For example, the power can be 20-40 W, 20-30 W for balloons with smaller diameters (e.g., 3.5-5 mm), and 30-40 W for balloons with larger diameters (e.g., 5-8 mm). The time period for which the transducer 111 is activated may be sufficient to complete the particular treatment to be performed and may depend on factors such as the power of the transducer, the frequency of the emitted ultrasonic energy, the size of the tissue area to be treated, the age, weight and sex of the patient receiving the treatment, etc. By way of example, in some embodiments, the time for which the transducer 111 may be activated may range from about 3 seconds to 5 minutes, such as 3-10 seconds, 3-30 seconds, 30 seconds to 1 minute, 30 seconds to 5 minutes, 1-3 minutes, about 2 minutes, 10 seconds to 1 minute, 1-2 minutes, 2-3 minutes, 3-4 minutes, or 4-5 minutes. Alternatively, for example, the transducer 111 may be activated for less than 10 seconds, such as 0.1-10 seconds, 1-2 seconds, 2-3 seconds, 3-4 seconds, 4-5 seconds, 5-6 seconds, 6-7 seconds, 7-8 seconds, 8-9 seconds, or 9-10 seconds.Or, for example, the transducer 111 may be activated for more than 5 minutes, such as 5-6 minutes, 6-7 minutes, 7-8 minutes, 8-9 minutes, 9-10 minutes, 10-15 minutes, 15-20 minutes, or for more than 20 minutes.

[0080] In various forms, the delivery of ultrasonic energy during treatment may be continuous or substantially continuous, e.g., without any interruption or variation in frequency, power, duty cycle, and / or any other parameters. Alternatively, one or more of the frequency, power, duty cycle, or any other parameters may be modified during treatment. For example, in some forms, the delivery of ultrasonic energy is modulated, e.g., between on and off, or between a relatively high level and a relatively low level, to prevent or reduce the possibility of overheating of adjacent (e.g., targeted or non-targeted) tissue. For examples of such modulation, see U.S. Patent No. 10,499,937 to Warnking, the entire contents of which are incorporated herein by reference.

[0081] In an exemplary embodiment where nerve tissue is the subject of treatment, e.g., nerve N shown in FIG. 2B is the subject of treatment, transducer 111 (or 411, 511, 811, 911, 1011, 111, etc.) may be positioned and configured to deliver ultrasound energy through a wall of body cavity BL adjacent to the nerve tissue (e.g., through a wall of body cavity BL). In one non-limiting example, a renal nerve to be treated using transducer 111 may be located about 0.5 mm to 8 mm (e.g., about 1 mm to 6 mm) from an inner wall of a renal artery. In other examples, the nerve tissue to be treated may be located about 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, 7.5 mm, 8 mm, less than 0.5 mm, or more than 8 mm from an inner wall of the body cavity in which the transducer is placed. Under the control of the controller 120, the transducer 111 (or 411, 511, 811, 911, 1011, 111, etc.) generates unfocused ultrasound energy that heats any suitable neural tissue and at least partially neuromodulates such neural tissue, for example resulting in complete or partial ablation, necrosis, or stimulation of such neural tissue. The ultrasound energy generated by the transducer 111 (or 411, 511, 811, 911, 1011, 111, etc.) may radiate radially outward to target such neural tissue regardless of the radial orientation of such neural tissue relative to the body cavity. In some forms, the unfocused ultrasound energy is delivered along the entire continuous circumference of the transducer 111 (or 411, 511, 811, 911, 1011, 111, etc.). In other configurations, the ultrasound energy is emitted non-continuously or intermittently around the transducer 111 (or 411, 511, 811, 911, 1011, 111, etc.). It should be understood that nerve tissue, and more specifically renal nerves, is only one example of tissue that may be treated using an ultrasound transducer. Other examples of target anatomical regions that may be treated using the ultrasound transducer 11 are described elsewhere herein.

[0082] Regardless of the particular shape or range of acoustic energy that the transducer delivers to the target anatomical region, the cooling fluid 213 in the balloon 112 surrounding the transducer may protect certain tissues of the subject. For example, the cooling fluid 213 may prevent or reduce the possibility of stenosis or other damage to the walls of the body cavity BL to which energy is delivered during treatment. In some forms, the cooling fluid 213 may flow across one or both of the exterior and interior surfaces of the transducer 111 (or 411, 511, 811, 911, 1011, 111, etc.), for example, directly contacting one or both of the exterior and interior surfaces of the transducer. In certain embodiments described in more detail below, the electrical insulators of the transducer inhibit electrical shorting between the electrodes of the transducer through the conductive cooling fluid 213 or through blood. As used herein, the terms "short circuit," "electrical short circuit," and the like are used interchangeably and refer to any conductive path having an impedance of less than 10,000 ohms. Thus, when there is a "short" between a pair of electrodes, this means that there is a conductive path between the pair of electrodes with an impedance of less than 10,000 ohms. Such a conductive path may be provided by, but is not limited to, a conductive fluid.

[0083] [Selectively isolated transducer] Returning to FIG. 2B, according to certain embodiments, the ultrasonic transducer 111 is disposed partially or completely within the balloon 112. As previously mentioned, in the initial discussion of FIG. 2B, the balloon 112 may be inflated with a cooling fluid 213 so as to contact the inner surface (e.g., the intima) of the body cavity BL. More specifically, the cooling fluid 213 is circulated around the ultrasonic transducer 111 to actively cool the area of ​​treatment. The use of a non-conductive cooling fluid 213 maintains electrical insulation between the inner electrode 202 and the outer electrode 203 of the ultrasonic transducer 111. However, medical personnel should remember to stock up on and use the non-conductive cooling fluid 213. For the convenience of medical personnel, ultrasonic transducers according to certain embodiments described herein are designed to operate properly when surrounded by or otherwise exposed to a conductive fluid, such as, but not limited to, saline. As will be appreciated from the following description, such embodiments are implemented by isolating at least a portion of the ultrasonic transducer 111. If an ultrasonic transducer is partially insulated so that it can operate properly when used with a conductive cooling fluid such as blood or when otherwise exposed to a conductive fluid such as blood, the transducer may generally be referred to as a selectively insulated or partially insulated transducer, or more simply as a transducer.

[0084] Advantageously, the selectively insulated transducers disclosed herein allow for the use of a conductive cooling fluid (e.g., 213) and / or the patient's own blood flow to cool the transducer. More specifically, the selectively insulated transducers disclosed herein may be configured to include at least one electrical insulator that inhibits (and preferably prevents) shorting between the transducer's electrodes (e.g., 202 and 203) via a conductive fluid that is in the balloon or blood. By way of example, an insulated transducer of the present invention may comprise a hollow cylindrical tube (e.g., 201) made of a piezoelectric material that may be disposed within the balloon and includes an inner surface and an outer surface. In certain embodiments, such as those described above, the transducer is cylindrical. An inner electrode (e.g., 202) may be disposed on the inner surface of the hollow cylindrical tube (e.g., 201) and an outer electrode (e.g., 203) may be disposed on the outer surface of the hollow cylindrical tube (e.g., 201). The outer or inner electrodes may have an electrical insulator covering them to prevent electrical shorting between the outer electrode (e.g., 203) and the inner electrode (e.g., 202) through the conductive fluid.

[0085] The piezoelectric material constituting the hollow cylindrical tube (e.g., 201) may be activated, for example, by applying a voltage between the inner electrode (e.g., 202) and the outer electrode (e.g., 203) in a manner known in the art. For example, it may be activated by a suitably programmed controller (e.g., 120) in electrical communication with the inner and outer electrodes. In the absence of an electrical insulator according to the invention, in the absence of a balloon or if the balloon is filled with a conductive fluid, applying a voltage between the inner and outer electrodes (e.g., 202 and 203) may cause an electrical short circuit, which may inhibit the piezoelectric material from generating ultrasound. In the absence of an electrical insulator according to the invention, such a short circuit may also be inhibited by using a non-conductive fluid instead in the balloon, for example, appropriately deionized water or dextrose, which may itself provide insulation between the inner and outer electrodes. However, it may not be very convenient to use such a non-conductive fluid in a surgical environment. For example, hospitals and other treatment centers typically do not maintain a source of deionized water within the surgical ward. The selectively isolated transducer described herein allows conductive fluids readily available in hospitals and other treatment centers to be used within the balloon, thereby enhancing the ease of integrating the system into a surgical environment. Examples of conductive fluids readily available in hospitals and other treatment centers include saline, non-pure water, and sodium lactate solution. Sodium lactate solution, also known as lactated Ringer's solution or Hartmann's solution, is a type of isotonic crystalloid solution, further classified as a balanced or buffered solution used for fluid replacement. Such sodium lactate solution includes sodium, chloride, potassium, calcium, and lactate salt in the form of sodium lactate, mixed into a solution having an osmolality of 273 mOsm / L and a pH of about 6.5.

[0086] In certain embodiments, a balloon-less catheter may be used, in which case the electrically conductive blood flowing within the body cavity may be used to cool the transducer. The requirement to use a balloon adds time and complexity to the procedure, as the physician may need to use multiple balloons and catheters during a single procedure. Furthermore, failure to use the correct balloon size may result in renal artery dissection, perforation, aneurysm, significant vasospasm requiring intervention, ablation of unintended tissue or structure, or failure to ablate the target tissue. Furthermore, some arteries, such as accessory arteries, may not be treatable due to balloon size constraints. Untreated accessory arteries may predict a decreased response to renal denervation. To maximize tissue ablation, the inflated balloon needs to be against the renal artery wall, but multiple inflations of the balloon to appose the renal artery wall may result in increased vascular trauma. Advantageously, the selectively insulated transducers disclosed herein allow for the use of balloon-less catheters, allowing the patient's own blood flow to be used as the cooling fluid.

[0087] FIG. 4A is a side view of a distal portion of a catheter (e.g., 102) of an ultrasound-based tissue treatment system (e.g., 100) including a selectively isolated transducer 411 according to certain embodiments of the present technology. The selectively isolated transducer 411 may also be referred to as a selectively isolated transducer 411, or more simply as a transducer 411. FIG. 4B is a perspective view of a selectively isolated transducer 411 according to certain embodiments of the present technology, in which an outer electrode (e.g., 203) of a piezoelectric transducer body (e.g., 202) is covered by an electrical insulator 404. FIGs. 4C and 4D show longitudinal and radial cross-sectional views, respectively, of the selectively isolated transducer 411 shown in FIGs. 4A and 4B.

[0088] In the embodiment of Figures 4A-4D, the piezoelectric transducer body 201 comprises a hollow tube of piezoelectric material having an inner surface and an outer surface, with an inner electrode 202 disposed on the inner surface of the hollow tube of piezoelectric material and an outer electrode 203 disposed on the outer surface of the hollow tube of piezoelectric material. In such an embodiment, the hollow tube of piezoelectric material is an example of a piezoelectric transducer body 201. In Figures 4A-4D, the hollow tube of piezoelectric material, or more generally the piezoelectric transducer body 201, is cylindrical in shape and has a circular radial cross-section, as can be seen from Figure 4D. Although, in alternative embodiments, the hollow tube of piezoelectric material may have other shapes other than a cylinder with a circular radial cross-section. Other cross-sectional shapes of the hollow tube of piezoelectric material, or more generally the piezoelectric transducer body 201, include, but are not limited to, an oval or elliptical cross-section, a square or rectangular cross-section, a pentagonal cross-section, a hexagonal cross-section, a heptagonal cross-section, an octagonal cross-section, etc.

[0089] The hollow tube of piezoelectric material, or more generally the piezoelectric transducer body 201, may be fabricated from a variety of different types of piezoelectric materials, such as, but not limited to, lead zirconate titanate (PZT), polyvinylidene fluoride (PVDF), or other currently available or later developed piezoelectric ceramic materials. As shown in Figures 4A-4C, the transducer 411 may include a stepped portion 417, as described in U.S. Patent No. 10,456,605, the entire contents of which are incorporated herein by reference. In certain embodiments, the stepped portion 417 at the proximal end of the transducer 411 allows for attachment of an electrical cable 282 that delivers energy to the transducer 411, for example, via parallel wires (not shown). In certain embodiments, the electrical cable 282 comprises a parallel coaxial cable with a combined impedance of about 50 ohms. Such a stepped portion 417 may be incorporated into any of the transducers described herein. It is also possible for both the proximal and distal ends of the transducer to include a stepped portion (the same as or similar to 417), which may be referred to as a double stepped embodiment.

[0090] Referring to FIG. 4C, according to a particular embodiment suitable for renal denervation treatment, the outer diameter (OD) of the piezoelectric transducer body 201 is in the range of about 1.3 mm to 1.7 mm, and the inner diameter (ID) of the piezoelectric transducer body 201 is in the range of about 0.8 mm to 1.2 mm. In a specific embodiment, the OD is about 1.5 mm, and the ID is about 1 mm. According to a particular embodiment, the wall thickness (W-TH) of the piezoelectric material of the piezoelectric transducer body 201, between its inner diameter (ID) and its outer diameter (OD), is in the range of 0.2 mm to 1.0 mm. More specifically, the wall thickness (W-TH) may be in the range of 0.2 mm to 0.5 mm. Even more specifically, the wall thickness (W-TH) may be in the range of 0.24 mm to 0.26 mm (and even more specifically, 0.25 mm + / - 0.01 mm). This may provide an ultrasound transducer that generates acoustic energy having a frequency of about 9 MHz. In certain embodiments, the ultrasound transducers described herein (e.g., 211, 411, 511, 811, 911, 1011, 1211, etc.) are configured to deliver acoustic energy in the frequency range of 8.5-9.5 MHz. In certain embodiments, such transducers are configured to deliver acoustic energy in the frequency range of 8.7-9.3 MHz or 8.695-9.304 MHz. Transducers delivering acoustic energy in the frequency range of 8.7-9.3 MHz have been shown to produce ablation to an average depth of up to 6 mm. The piezoelectric transducer body 201 and the outer and inner electrodes 203 and 202 may be formed using any suitable method, such as, for example, the method described in U.S. Patent No. 10,140,041 to Taylor, the entire contents of which are incorporated herein by reference. The thickness (I-TH) of the electrical insulator 404 (and other electrical insulators described herein) can be, but is not limited to, in the range of about 10 μm to 20 μm. The foregoing dimensions and thicknesses are described with reference to the embodiment shown in Figures 4A-4D, but are also applicable to other embodiments described herein, including those described below.

[0091] In the embodiment of Figures 4A-4D, no electrical insulator is disposed on the inner electrode 202. In other words, in the embodiment of Figures 4A-4D, with respect to the inner electrode 202 and the outer electrode 203, only the outer electrode 203 is covered by the electrical insulator 404. In such an embodiment, the electrical insulator 404 disposed on and covering the outer electrode 203 inhibits (preferably prevents) the outer electrode 203 from contacting a conductive fluid (e.g., 213) when the ultrasonic transducer 411 is positioned in the conductive fluid. In other words, in such an embodiment, the electrical insulator 404 provides both electrical and physical insulation from the conductive fluid in which the transducer is disposed. However, since no electrical insulator is disposed on the inner electrode 202, the inner electrode 202 may contact the conductive fluid (e.g., 213) when the ultrasonic transducer 411 is positioned in the conductive fluid. In such an embodiment, an electrical insulator 404 disposed on the outer electrode 203 inhibits (preferably prevents) electrical conduction between the inner electrode 202 and the outer electrode 203 when the ultrasonic transducer 411 is disposed in a conductive fluid. The piezoelectric transducer body 201 is configured to generate ultrasonic waves in response to a voltage being applied between the inner electrode 202 and the outer electrode 203. The electrical insulator 404 inhibits (preferably prevents) a short circuit from occurring between the inner electrode 202 and the outer electrode 203 when the ultrasonic transducer 411 is disposed in a conductive fluid and a voltage is applied between the inner electrode 202 and the outer electrode 203. More specifically, the controller 120 may be electrically coupled to the inner electrode 202 and the outer electrode 203 via the electrical cable 282 and may activate the selectively isolated transducer 411 (or any of the other selectively isolated transducers described herein) by applying a voltage between the inner and outer electrodes, causing the piezoelectric material of the piezoelectric transducer body 201 to generate unfocused ultrasound waves that radiate radially outward.

[0092] In certain embodiments, the ultrasonic transducer 411 is disposed within a balloon (e.g., 112) that is at least partially filled with a cooling fluid (e.g., 213) that is an electrically conductive fluid. The cooling fluid is used to cool a portion of the body cavity BL within which the ultrasonic transducer 411 may be positioned. The electrically conductive fluid with which the balloon is at least partially filled may be, for example, but is not limited to, saline, non-pure water, sodium lactate solution, or combinations thereof. In an alternative embodiment, which may be referred to as a balloon-less embodiment, the ultrasonic transducer 411 is directly exposed to blood flowing through the body cavity BL within which the ultrasonic transducer may be positioned. In this case, the electrically conductive fluid includes blood. In certain embodiments, the electrical insulator 404 is parylene, and more specifically, a parylene conformal coating.

[0093] Materials from which electrical insulator 404 can be fabricated include, but are not limited to, parylene, cyanoacetate, epoxy resin, nylon, polytetrafluoroethylene (PTFE), polyimide, polyethylene, polyethylene terephthalate, polyvinyl chloride (PVC), or combinations thereof. In a particular embodiment, parylene C is used to coat the gold-containing electrodes using a chemical vapor deposition process, such as described in U.S. Patent No. 5,908,506. As another example, electrical insulator 404 can be a synthetic diamond coating, which can be deposited using, for example, chemical vapor deposition (CVD). In one embodiment, the surface of the electrode is treated with an adhesion promoter such as, for example, silane, titanium (Ti), silicon oxide (SiOx), diamond-like carbon (DLC), tetramethylsilane (TMS), aluminum oxide (AlOx), a solution of 1 gram of 2-methylthioethyl methacrylate or 1 gram of 4-chlorothiophenol in 1 L of propanol (available from Th. Geyer GmbH & Co. KG, Renningen, Germany, AdPro Plus® or AdPro Poly® available from Specialty Coating Systems, Inc., Indianapolis, Indiana, USA, and many other suppliers) before being coated with the electrical insulator 404 (e.g., parylene). In certain embodiments, a plasma surface treatment method may be used to prevent delamination of parylene. Polytetrafluoroethylene (PTFE) is often sold under the trademark TEFLON®, a registered trademark of The Chemours Company, headquartered in Wilmington, Delaware, USA, and polyimide is often sold under the trademark KAPTON®, a registered trademark of DuPont, headquartered in Wilmington, Delaware, USA. In one specific embodiment, the periphery of the outer electrode 203 is covered with a parylene coating, and the opposing longitudinal ends of the outer electrode 203 are covered with an epoxy resin. Other combinations of the aforementioned electrical insulator materials are possible and are within the scope of the embodiments described herein.

[0094] A variety of different types of parylene coatings can be used. Such parylene coatings can be conformal coatings, which are extremely thin, pinhole-free polymer coatings with excellent moisture, chemical and dielectric barrier properties, thermal and ultraviolet (UV) stability, and dry film lubricity. Exemplary types of parylene include, but are not limited to, Parylene N, Parylene C, and Parylene D.

[0095] As previously mentioned, the thickness of the electrical insulator (e.g., 404, and other electrical insulators described herein) may be in the range of about 10 μm to 20 μm, but is not limited thereto. According to certain embodiments, an adhesion promoter may be included between the electrode (e.g., outer electrode 203) and the electrical insulator (e.g., 404) to improve adhesion of the electrical insulator to the electrode. To reduce the possibility of small pinholes in the electrical insulator (e.g., 404) that may result in undesirable electrical leakage, multiple layers or coatings of electrical insulator material may be applied in multiple coating cycles. For example, if the electrical insulator is a 15 μm thick parylene coating, the coating may be deposited on the electrode in three separate coating cycles, each of which provides a coating thickness of 5 μm, collectively providing a 15 μm thick parylene coating.

[0096] The inner electrode 202 and the outer electrode 203 may be made of the same conductive material as each other, or may be made of different conductive materials as each other. Examples of conductive materials suitable for use as the inner electrode 202 and the outer electrode 203 include copper, silver, gold, and / or combinations thereof. In certain embodiments, nickel may be used as a barrier layer to prevent lead from degrading the gold plated electrodes. An exemplary thickness of the inner electrode 202 and the outer electrode 203 includes about 120 microinches. In certain embodiments, the electrodes 202, 203 include a base coat of electroless copper of about 15 microinches, a second coat of high phosphorous electroless nickel of about 102-120 microinches, and a third coat of electrolytically plated gold of about 5 microinches. The metal layer provides a way to solder an electrical cable 282, e.g., a parallel coaxial cable, to the surface of the tube without damaging the piezoelectric material, and also allows for an even application of an electrical load to the transducer. In certain embodiments, the metal layer of the electrode coating is configured to produce an electrode that provides a uniform electrical load during ultrasonic processing without peeling or flaking due to mechanical or thermal loading. The inner electrode 202 and the outer electrode 203 may have the same thickness as one another, or may have different thicknesses from one another. The inner electrode 202 and the outer electrode 203 may be formed using any suitable method, such as, but not limited to, electroless plating or vapor deposition.

[0097] To apply a voltage between the inner electrode 202 and the outer electrode 203 (or any other electrode) of a transducer disclosed herein, or more generally to provide input power to the transducer, a cable (e.g., 282) is connected between the controller 120 (or some other voltage source) and the electrodes of the transducer to provide an electrical connection between the controller 120 (or some other voltage source) and the electrodes. For example, one or more coaxial cables or other types of conductive wiring may be soldered to the electrodes of the transducer. One of the electrodes of the transducer may be coated with and covered by an electrical insulator before or after such a cable is attached to the electrode. If an electrical insulator is applied to the electrode before the cable (e.g., 282) is attached (e.g., soldered) to the electrode, a portion of the electrical insulator may be removed (e.g., using an etch) or may be left uninsulated (e.g., using a mask) and the cable (e.g., 282) may be soldered or otherwise attached to the electrode. After soldering or other type of attachment, the solder balls and the like should be covered with an electrical insulator such as, but not limited to, epoxy resin. In other words, the contact points between the cabling (including one or more cables) and the electrodes (to be insulated) should also be insulated. Otherwise, exposing the solder balls (or other electrical contacts between the cable and the electrodes) to a conductive fluid may be equivalent to exposing the entire electrode to a conductive fluid. More generally, if a cabling is connected to one of the electrodes covered with an electrical insulator, care should be taken to ensure that the conductive portions of the cabling or attachment mechanism (e.g., solder balls) are not exposed to a conductive fluid when the transducer is in use. This is applicable to transducer 411, as well as other selectively insulated transducers described herein (e.g., 511, 911, 1011, etc.).

[0098] 5A and 5B respectively show longitudinal and radial cross-sectional views of a selectively insulated transducer 511 according to another embodiment of the present technology, in which the inner electrode 202 of the piezoelectric transducer body 201 is covered by an electrical insulator 504. In such an embodiment, the electrical insulator 504 disposed on and covering the inner electrode 202 inhibits (and preferably prevents) the inner electrode 202 from contacting a conductive fluid (e.g., 213) when the ultrasonic transducer 511 is positioned in the conductive fluid. In other words, in such an embodiment, the electrical insulator 504 provides both electrical and physical insulation from the conductive fluid within which the transducer is disposed. However, since no electrical insulator is disposed on the outer electrode 203, the outer electrode 203 may contact the conductive fluid (e.g., 213) when the ultrasonic transducer 511 is positioned in the conductive fluid. In such an embodiment, the electrical insulator 504 disposed on the inner electrode 202 inhibits (preferably prevents) electrical conduction between the inner electrode 202 and the outer electrode 203 when the ultrasonic transducer 511 is disposed in a conductive fluid. The electrical insulator 504 inhibits (preferably prevents) a short circuit from occurring between the inner electrode 202 and the outer electrode 203 when the ultrasonic transducer 511 is disposed in a conductive fluid and a voltage is applied between the inner electrode 202 and the outer electrode 203.

[0099] In a particular embodiment, the ultrasonic transducer 511 is disposed within a balloon (e.g., 112) that is at least partially filled with a cooling fluid (e.g., 213) that is an electrically conductive fluid. The cooling fluid is used to cool a portion of the body cavity BL within which the ultrasonic transducer 411 may be positioned. Exemplary types of electrically conductive cooling fluids that may be used have been described above with respect to the embodiment of Figures 4A-4D and need not be repeated. The electrical insulator 504 may be made of parylene, any of the other types of electrical insulator materials, or combinations thereof, as described above with respect to the electrical insulator 404. In a specific embodiment, the periphery of the inner electrode 202 is coated with a parylene coating, and the opposing longitudinal ends of the inner electrode 202 are coated with an epoxy resin. Other combinations of the aforementioned electrical insulator materials are possible and are within the scope of the embodiments described herein.

[0100] 6A and 6B respectively show longitudinal and radial cross-sections of a transducer 611 in which both the inner electrode 202 and the outer electrode 203 of the piezoelectric transducer body 211 are covered by electrical insulators. More specifically, the inner electrode 202 is covered by electrical insulator 504 and the outer electrode 203 is covered by electrical insulator 404. As will be explained in more detail below with reference to FIG. 7, insulating both the inner electrode 202 and the outer electrode 203 (or more generally both electrodes) of an ultrasonic transducer may provide inferior performance, particularly where the input power is in the range of about 5-80 watts and the acoustic output power is in the range of about 5-45 watts.

[0101] The selectively isolated transducers described above with reference to Figures 4A-4D, 5A and 5B each include a piezoelectric transducer body 201 having a hollow tube of piezoelectric material, and may also include a backing member (e.g., 218), an insulating tube (e.g., 219), a standoff assembly (e.g., 230), and / or mounting points (334), examples of which are shown and described above with reference to Figures 2C and 3B, although to simplify the drawings, these additional details are not shown in Figures 4A-4D, 5A and 5B.

[0102] FIG. 7 is a graph of input power versus acoustic output power of a piezoelectric ultrasonic transducer, showing how insulating various different electrodes or combinations thereof affects the performance of an ultrasonic transducer immersed in a cooling fluid. Here, the piezoelectric transducer body 201 comprises a hollow tube of piezoelectric material having an inner surface and an outer surface, and an inner electrode 202 and an outer electrode 203 are disposed on the inner surface and the outer surface, respectively. A radiation force balance (RFB) or some other device and technique can be used to measure the acoustic output power of the ultrasonic transducer in response to different electrical input powers. Referring to FIG. 7, curve 701 corresponds to an ultrasonic transducer (e.g., 111 in FIG. 2B) in which both the inner electrode 202 and the outer electrode 203 are not covered by an electrical insulator. As can be seen from curve 701, the acoustic output power increases in response to an increase in the electrical input power until the input power reaches approximately 80 watts (W), after which point the ultrasonic transducer begins to fail and the acoustic output power drops rapidly. Curve 702 corresponds to an ultrasonic transducer (e.g., 411) in which the outer electrode 203 is covered by an electrical insulator (e.g., 404) but the inner electrode 202 is not covered by an electrical insulator. As can be seen from Figure 7, curves 701 and 702 are nearly identical. Thus, in curve 702, the acoustic output power increases in response to an increase in electrical input power until the input power reaches approximately 80 W, after which point the ultrasonic transducer begins to fail and the acoustic output power drops off rapidly.

[0103] Curve 703 corresponds to an ultrasonic transducer (e.g., 511) in which the inner electrode 202 is covered by an electrical insulator (e.g., 504) but the outer electrode 203 is not covered by an electrical insulator. As can be seen from Fig. 7, the efficiency of the ultrasonic transducer (e.g., 511) is slightly lower than if neither electrode 202, 203 is covered by an electrical insulator, or if only the outer electrode 203 is covered by an electrical insulator, but the acoustic output power increases in response to an increase in electrical input power until the input power reaches about 80 W, after which point the ultrasonic transducer begins to fail and the acoustic output power drops off rapidly. Curve 704 corresponds to an ultrasonic transducer (e.g., 611) in which the inner electrode 202 is covered by an electrical insulator (e.g., 504) and the outer electrode 203 is covered by an electrical insulator (e.g., 404). As can be seen from curve 704, the acoustic output power increases in response to an increase in electrical input power until the input power reaches approximately 58 W, after which point the ultrasonic transducer begins to fail and the acoustic output power drops off rapidly. The electrical insulators (e.g., 404 and 504) tested to generate curves 702, 703 and 704 were Parylene C coatings.

[0104] In carrying out the experiments that produced the graph shown in Figure 7, the cooling fluid (in which the tested transducer was immersed) was deionized water, which is a non-conductive fluid. The reason for using a non-conductive fluid in such experiments was that if a conductive cooling fluid was used, an electrical short would have occurred between the non-insulated electrodes of the ultrasound transducer (e.g., 111) whose performance is represented by curve 701. For selectively insulated ultrasound transducers (e.g., 411 and 511) whose performance is represented by curves 702 and 703, and for a transducer in which both electrodes are covered by an electrical insulator (e.g., 611) whose performance is represented by curve 704, it is believed that curves 702, 703, and 704 of Figure 7 respectively show how such transducers would behave when immersed in a conductive cooling fluid such as saline, sodium lactate solution, or blood.

[0105] As can be seen from Fig. 7, the selectively insulated transducer that provided the best performance was the selectively insulated transducer (e.g., 411) in which only the outer electrode 203 was covered by a parylene coating type electrical insulator for input powers below about 90 W (as shown by curve 702). The next best performance was provided by the selectively insulated transducer (e.g., 511) in which only the inner electrode 202 was covered by a parylene coating type electrical insulator (as shown by curve 703). Also, as can be seen from Fig. 7, the transducer (e.g., 611) in which both the inner electrode 202 and the outer electrode 203 were coated by a parylene coating type electrical insulator showed poor performance, failing at a significantly lower input power (as shown by curve 704).

[0106] More specifically, it can be seen from Fig. 7 that covering both the inner electrode 202 and the outer electrode 203 with their respective electrical insulators degrades the transducer's output performance (curve 704) at higher input powers, e.g., above about 30 W, where the ultrasonic output power of the transducer is lower than without the electrical insulator (curve 701) and lower than when only one of the electrodes is covered with the electrical insulator (curves 702 and 703). Without wishing to be bound by any theory, it is believed that such degradation occurs due to thermally induced mechanical stresses within the transducer during operation at higher power levels, for example because the electrical insulators on both electrodes of the piezoelectric transducer body 201 can trap heat in the piezoelectric material, generating mechanical stresses. From FIG. 7, it can be seen that covering only the inner electrode 202 with an electrical insulator can also degrade (degrade) the acoustic output power performance (curve 703) of the transducer at higher input powers, for example, input powers above about 30 W, where the acoustic output power of the transducer is lower than without the electrical insulator. In comparison, the power performance (curve 702) of a selectively insulated transducer in which only the outer electrode 203 is covered with an electrical insulator, such as described with reference to FIGS. 4A-4D, can be similar at all powers to the output performance (curve 701) of a non-insulated ultrasonic transducer. Nevertheless, it is expressly contemplated that in some configurations and implementations, it may be appropriate to cover only the inner electrode 202 with an electrical insulator. It is understood that the operation of the method described with reference to FIG. 11 can be appropriately modified based on the specific arrangement of the electrical insulator of the selectively insulated transducer.

[0107] For example, in certain embodiments suitable for renal denervation, a preferred range of electrical input power may be from about 30 W to about 50 W, which corresponds to an acoustic output power of about 25 W to about 35 W. As can be seen in FIG. 7, coating both the inner electrode 202 and the outer electrode 203 (curve 704) reduces the efficiency of the transducer in these power input ranges compared to a transducer that is not insulated (curve 701) or a transducer in which only the outer electrode 203 is coated (curve 702). Without preconceptions or limitations, it can be theorized that coating both the inner electrode 202 and the outer electrode 203 (or more generally both electrodes) of the transducer 111 may adversely affect the life of the transducer itself by generating more thermal and mechanical stresses on the catheter (e.g., 102) than a transducer with uninsulated electrodes or a transducer in which only the outer electrode 203 is insulated (or only the inner electrode 202 is insulated).

[0108] As can be seen in FIG. 7, covering only the inner electrode 202 with an electrical insulator (curve 703) reduces the efficiency of the transducer in the power input range of about 30 W to about 50 W compared to a transducer without insulation (curve 701) or a transducer with only the outer electrode 203 covered with an electrical insulator (curve 702). Furthermore, it can be theorized that covering only the inner electrode 202 with an electrical insulator (e.g., 504) can adversely affect the life of the transducer by generating more heat and mechanical stress than a transducer with an uninsulated electrode or a transducer with only the outer electrode 203 covered with an electrical insulator (e.g., 404). This can be because the cooling fluid (e.g., 213) inserted within the balloon (or blood in balloon-less embodiments) can only come into contact with the electrical insulator (e.g., 504) covering the inner electrode 202 through the opening (e.g., 336) of the standoff assembly (e.g., 230). This may make it difficult for the cooling fluid to effectively carry heat away from the inner electrode 202. In contrast, if the cooling fluid (e.g., 213) is delivered within the balloon (or blood in balloon-less embodiments), it may be in more complete contact with the electrical insulator (e.g., 404) covering the outer electrode 203 and therefore may more easily carry away heat that may have been trapped by the electrical insulator, e.g., a parylene coating, covering the outer electrode 203.

[0109] In the above embodiment, the piezoelectric transducer body has been illustrated and described as being made of a hollow tube of piezoelectric material and having an inner and outer surface on which the inner and outer electrodes are disposed, respectively. In alternative embodiments, the piezoelectric transducer body need not be hollow. As an example, as shown in FIG. 8A and FIG. 8B, an ultrasonic transducer 811 may include a generally rectangular (approximately cuboid) piezoelectric transducer body 801 with first and second planar opposing surfaces (i.e., top and bottom surfaces in this example) that are parallel to each other. Planar and parallel electrodes 802, 803 are disposed on the first and second planar opposing surfaces. For the purposes of this discussion, the electrodes 802 and 803 are referred to as the lower electrode and the upper electrode, respectively. Referring to FIG. 9, according to a particular embodiment, a selectively insulated ultrasonic transducer 911 includes a generally rectangular piezoelectric transducer body 801 with only the upper electrode 803 covered by an electrical insulator 904. In such an embodiment, the electrical insulator 904 provides both electrical and physical insulation of the upper electrode 803 from the conductive fluid within which the transducer is disposed. Referring to Figure 10, according to a particular embodiment, an ultrasound transducer 1011 comprises a generally rectangular shaped piezoelectric transducer body 801 with only the lower electrode 802 covered by an electrical insulator 1004. In such an embodiment, the electrical insulator 1004 provides both electrical and physical insulation of the lower electrode 802 from the conductive fluid within which the transducer is disposed.

[0110] In certain embodiments, each of the selectively isolated ultrasonic transducers 911, 101 may be disposed within a balloon (e.g., 112) that is at least partially filled with a cooling fluid (e.g., 213), which is an electrically conductive fluid. The electrically conductive cooling fluid is used to cool a portion of the body cavity BL in which the ultrasonic transducer may be positioned. As previously mentioned, the electrically conductive fluid may also cool the ultrasonic transducer itself. Exemplary types of electrically conductive cooling fluids that may be used have been previously described with respect to the embodiment of Figures 4A-4D and need not be repeated. In an alternative embodiment, which may be referred to as a balloon-less embodiment, the selectively isolated ultrasonic transducers 911, 1011 may be directly exposed to blood flowing through the body cavity in which the ultrasonic transducer may be positioned. In this case, the electrically conductive fluid includes blood.

[0111] The electrical insulators 904, 1004 may be made of parylene, any of the other types of materials, or combinations thereof, as previously described with respect to the electrical insulator 404. In one specific embodiment, the periphery of one of the outer electrodes (803 or 802) is coated with a parylene coating, and the opposing longitudinal ends of that one electrode (803 or 802) are coated with an epoxy resin. Other combinations of the aforementioned electrical insulator materials are possible and are within the scope of the embodiments described herein.

[0112] The embodiments of the present technology are not limited to ultrasonic transducers having the particular shapes illustrated in the drawings and described above. As an example, a cylindrical (or other shaped) hollow piezoelectric transducer body need not have a constant outer diameter, but may have stepped distal and / or proximal longitudinal ends, more particularly, they may have a smaller diameter than the remainder (i.e., the unstepped portion) of the transducer body. Other variations are possible and are within the scope of the embodiments described herein. The unstepped portion of the transducer body may constitute a majority of the length of the transducer, e.g., 50-95% or 60-90% (e.g., 50-60%, 60-70%, 70-80%, 80-90%, 90-95%, 90-99%, percentages between the aforementioned ranges, etc.) of the total length of the transducer. However, in other embodiments, as desired or required, the unstepped portion may extend less than 60% (e.g., 40-50%, 50-55%, 55-60%, less than 40%, etc.) or more than 95% (e.g., 95-96%, 96-97%, 97-98%, 98-99%, more than 99%, etc.) of the total length of the transducer.

[0113] Furthermore, if the piezoelectric transducer body is not hollow, as in the embodiment described with reference to Figures 8A-10, the shape of the piezoelectric transducer body may have other shapes than a generally rectangular shape (roughly a rectangular parallelepiped) with parallel upper and lower surfaces. For example, returning to Figures 8A-10, one or more of the upper and lower surfaces of the piezoelectric transducer body 801 shown therein may be concave or convex, or may have some other non-flat shape, which may result in one or more of the lower electrode 802 and the upper electrode 803 having such alternative shapes. If one of such electrodes is coated with an electrical insulator, the electrical insulator may also have such alternative shapes.

[0114] Additional options regarding the design and use of ultrasound transducers and catheter-based ultrasound delivery systems are provided in the following patents and published applications, the entire contents of each of which are incorporated herein by reference: U.S. Patent No. 6,635,054; U.S. Patent No. 6,763,722; U.S. Patent No. 7,540,846; U.S. Patent No. 7,837,676; U.S. Patent No. 9,707,034; U.S. Patent No. 9,981,108; U.S. Patent No. 10,350,440; U.S. Patent No. 10,456,605; U.S. Patent No. 10,499,937; and PCT International Publication No. WO 2012 / 112165.

[0115] The transducers, devices, and systems described herein may be used to treat any suitable tissue, which may be referred to as a target anatomical structure. For example, the use of the inventive system to treat (e.g., neuromodulate) renal nerves has been described above. It is understood that the body cavities in which the inventive system may be positioned to treat tissue are not necessarily limited to naturally occurring cavities. For example, treatment may include creating a cavity in tissue (e.g., using drilling, cannula, laser ablation, etc.) and then positioning an appropriate component within such cavity. Other suitable applications of the inventive system include ablation of veins or pulmonary nerves and tissue involved in arrhythmias, nerves within an intervertebral disc, nerves inside or outside the intervertebral disc, basal spinal nerves within a vertebra, nerves within brain tissue, tissue involved in arrhythmias in cardiac tissue, nerves along the bronchial tree, one or more esophageal branches of the vagus nerve, and one or more nerves surrounding the bladder.

[0116] FIG. 11 is a high level flow chart used to summarize a method according to various embodiments of the present technology. With reference to FIG. 11, step 1102 includes providing a piezoelectric transducer having first and second surfaces spaced apart from one another and not intersecting with one another, with a first electrode disposed on the first surface and a second electrode disposed on the second surface. Step 1104 includes covering only one of the first and second electrodes with an electrical insulator. Step 1106 includes inserting the piezoelectric transducer into a body cavity (e.g., a renal artery), and step 1108 includes exposing the piezoelectric transducer to a conductive fluid that contacts the second electrode but is inhibited from contacting the first electrode (by the electrical insulator covering the first electrode). Step 1110 includes applying a voltage between the first and second electrodes while the piezoelectric transducer is exposed to the conductive fluid (and inserted into the body cavity BL), thereby causing the piezoelectric transducer to generate ultrasound waves. Step 1112 includes using an electrical insulator to reduce (and preferably prevent) a short circuit from occurring between the first and second electrodes while the piezoelectric transducer is exposed to a conductive fluid and a voltage is applied between the first and second electrodes.

[0117] In certain embodiments, the method also includes disposing a piezoelectric transducer within the balloon. In such embodiments, exposing the piezoelectric transducer to a conductive fluid in step 1108 includes at least partially filling the balloon with a conductive fluid. As previously described, the conductive fluid may include, but is not limited to, at least one of saline, non-pure water, or a sodium lactate solution. In such embodiments, the method also includes inserting the balloon with the piezoelectric transducer therein into the body cavity. In such embodiments, applying a voltage between the first electrode and the second electrode to cause the piezoelectric transducer to generate ultrasound waves occurs while the balloon is within the body cavity.

[0118] In other embodiments, referred to herein as balloon-less embodiments, step 1108 is performed by inserting the piezoelectric transducer into a body cavity through which blood flows, such that the piezoelectric transducer is in contact with the blood. In such embodiments, the conductive fluid includes blood, and exposing the piezoelectric transducer to the conductive fluid in step 1108 includes exposing the piezoelectric transducer to the blood.

[0119] Although several embodiments and examples are disclosed herein, the present application extends beyond the specifically disclosed embodiments to other alternative embodiments and / or uses of the present invention, as well as modifications and equivalents thereof. It is also contemplated that various combinations or subcombinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the present invention. Thus, various features and aspects of the disclosed embodiments may be combined with or substituted for one another to form various modes of the disclosed invention. Therefore, it is intended that the scope of the present invention disclosed herein should not be limited by the specific embodiments described above, but should be determined solely by a proper reading of the claims.

[0120] While the invention is susceptible to various modifications and alternative forms, specific examples thereof are shown in the drawings and are described in detail herein. It is understood, however, that the invention is not limited to the particular forms or methods disclosed, but on the contrary, the invention is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the various disclosed embodiments and the appended claims. Any methods disclosed herein do not have to be performed in the order described.

Claims

1. a balloon (122) configured to receive a cooling fluid (213); an ultrasonic transducer (111) disposed within the balloon (112); Equipped with The ultrasonic transducer (111) a hollow tube (201) of piezoelectric material having an inner surface and an outer surface; a first electrode (202, 203) disposed on one of the inner and outer surfaces of the hollow tube (201) of piezoelectric material; a second electrode (203, 202) disposed on the other of the inner and outer surfaces of the hollow tube (201) of piezoelectric material; an electrical insulator (404, 504) configured to be coated on and cover the first electrodes (202, 203) and inhibit the first electrodes (202, 203) from contacting the cooling fluid (213) received by the balloon (112), thereby inhibiting electrical conduction between the first electrodes (202, 203) and the second electrodes (203, 202) when the cooling fluid (213) received by the balloon (112) is an electrically conductive cooling fluid (213); It has The second electrodes (203, 202) are not covered by an electrical insulator and are in contact with the cooling fluid (213) received by the balloon (112).

13. An apparatus (102).

2. the ultrasonic transducer (111) is configured to generate ultrasonic waves in response to application of a voltage between the first electrode (202, 203) and the second electrode (203, 202); The electrical insulator (404, 504) covering the first electrodes (202, 203) prevents a short circuit from occurring between the first electrodes (202, 203) and the second electrodes (203, 202) when the cooling fluid (213) received in the balloon (112) is a conductive cooling fluid (213) and the voltage is applied between the first electrodes (202, 203) and the second electrodes (203, 202).

2. The apparatus (102) of claim 1 .

3. The electrical insulator (404, 504) may include one or more of the following:

3. The device (102) according to claim 1 or 2, characterized in that Parylene; Cyanoacetate; Epoxy resin; nylon; Polytetrafluoroethylene (PTFE); Polyimide; polyethylene; Polyethylene terephthalate; Polyvinyl chloride (PVC); Synthetic diamond coating.

4. The electrical insulator (404, 504) comprises parylene.

4. The apparatus (102) of claim 3.

5. The electrical insulator (404, 504) comprises a parylene coating having a thickness of 15 μm.

5. The apparatus (102) of claim 4.

6. The electrical insulator (404, 504) includes three coatings of parylene, each having a coating thickness of 5 μm, collectively providing the parylene coating with a thickness of 15 μm.

6. The apparatus (102) of claim 5.

7. The electrical insulator (404, 504) includes a synthetic diamond coating.

4. The apparatus (102) of claim 3.

8. The electrical insulator (404, 504) includes multiple layers of electrical insulator material.

2. The apparatus (102) of claim 1 .

9. The first electrode (202, 203) is covered by the electrical insulator (404, 504) and is disposed on the outer surface of the hollow tube (201) of piezoelectric material.

2. The apparatus (102) of claim 1 .

10. The hollow tube (201) of piezoelectric material is cylindrical in shape.

2. The apparatus (102) of claim 1 .

11. The electrical insulator (404, 504) has a thickness selected within the range of 10 μm to 20 μm.

2. The apparatus (102) of claim 1 .

12. The hollow tube (201) of piezoelectric material is configured to deliver acoustic energy in the frequency range of 8.5 to 9.5 MHz.

2. The apparatus (102) of claim 1 .

13. the hollow tube (201) of piezoelectric material is configured to generate an acoustic output power in a range of 5 to 45 watts in response to an input power in a range of 10 to 80 watts; The ultrasonic transducer (111) has a length of about 6 mm; The outer diameter of the ultrasonic transducer (111) is about 1.5 mm; The inner diameter of the ultrasonic transducer (111) is about 1 mm.

2. The apparatus (102) of claim 1 .

14. the first electrode (202, 203) includes a major circumferential surface and longitudinal ends; a portion of the electrical insulator (404, 504) covering the major peripheral surface of the first electrode (202, 203) and made of a first type of electrical insulating material; Another portion of the electrical insulator (404, 504) covers the longitudinal ends of the first electrodes (202, 203) and is made of the same or a different material as the electrical insulating material covering the major circumferential surfaces of the first electrodes (202, 203).

2. The apparatus (102) of claim 1 .

15. The electrical insulator (404, 504) is Parylene is disposed on the outer periphery of the first electrode (202, 203) to cover the outer periphery; an epoxy resin disposed on and covering the longitudinal ends of the first electrodes (202, 203); Includes 15. The apparatus (102) of claim 14.

16. A backing member (218) that supports the ultrasonic transducer (111). Further comprising: the backing member (218) having one or more standoff assemblies (230a, 230b) that couple the hollow tube (201) to the backing member (218); The one or more standoff assemblies (230a, 230b) define one or more annular openings configured to receive the cooling fluid (213) into an interior space of the hollow tube (201) between the backing member (218) and the inner electrode (202).

2. The apparatus (102) of claim 1 .

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