Radial Artery Access Catheter

Abstract

The catheter includes a catheter shaft deliverable via a radial artery access approach. The catheter shaft has a fluid lumen. A balloon is attached to the catheter shaft and has an interior in fluid communication with the fluid lumen. An ultrasound transducer is in the interior. A flow control device has an inlet port for receiving fluid from the fluid lumen through the interior. The flow control device is configured to expel fluid to the surrounding environment when the fluid has a predetermined pressure. Other embodiments are also described and claimed.

Description

[Technical Field]

[0001] [Priority] This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 375,357, entitled "Radial Artery Access Catheter," filed September 12, 2022, which is incorporated by reference in its entirety to provide continuity of disclosure.

[0002] [Technical field] This application relates generally to minimally invasive devices, systems, and methods for providing energy delivery to targeted anatomical locations in a subject, and more particularly to catheter-based intraluminal devices 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. Left untreated, hypertension can lead to kidney disease, arrhythmias, and heart failure. In recent years, treatment for hypertension has focused on minimally invasive interventional approaches to inactivate the renal nerves surrounding the renal artery. Autonomic nerves tend to follow blood vessels toward the organs they innervate. Catheters can reach specific structures within the body cavity they navigate. For example, one system uses a radiofrequency (RF) generator connected to a catheter with multiple electrodes placed against the intima of the renal artery to generate an electric field in the blood 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 around the inside of the renal artery several times. However, the relatively limited electric field generated by the RF electrodes can 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 lead to 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 uses vibrational energy to cause frictional heating and destruction of tissue, raising tissue temperature sufficiently to induce ablation and remodeling.

[0005] U.S. Patent 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, disclose systems that use unfocused ultrasound to ablate nerves. An 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). An electrical cable received within a cable lumen of the catheter can be used to power the ultrasound transducer. 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. The system may also include a balloon attached to the distal end of the catheter, which may be used to circulate a coolant through the balloon before, during, and after transducer activation to cool the transducer and help prevent thermal damage to the inner surface of the blood vessel wall during deep nerve heating and damage. The circulation of coolant occurs through two fluid lumens: an input fluid lumen that carries fluid distally toward the balloon, and an output fluid lumen that returns fluid proximally from the balloon.

[0006] 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, thereby treating hypertension in patients while reducing damage to the blood vessel and surrounding organs.

[0007] An ultrasound transducer may include first and second electrodes disposed on opposite sides 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 generates vibrational energy that radiates radially outward from the transducer. The transducer is designed to provide a substantially uniform and predictable radiation profile.

[0008] Systems that use unfocused ultrasound to ablate nerves can be delivered to the target anatomy via a variety of access routes. For example, a catheter carrying a transducer can be inserted via a femoral access route through the femoral artery. Summary of the Invention

[0009] The invention is defined in the independent claims. Further embodiments of the invention are defined in the dependent claims.

[0010] Provided herein is a catheter comprising a catheter shaft having a fluid lumen, a balloon attached to the catheter shaft and having an interior in fluid communication with the fluid lumen, an ultrasound transducer located within the interior, and a flow control device having an inlet port for receiving fluid from the fluid lumen through the interior, the flow control device configured to expel the fluid to the surrounding environment when the fluid has a predetermined pressure.

[0011] Provided herein is a catheter. The catheter includes a balloon having an interior. The catheter includes an ultrasound transducer located within the interior. The catheter includes a catheter shaft having an outer member with a central lumen, an inner member with a fluid lumen extending through the central lumen for delivering fluid to the interior, and one or more steering wires extending through the central lumen between the inner wall of the outer member and the outer wall of the inner member. The one or more steering wires connect to the outer member or the inner member at an anchor point proximal to the balloon.

[0012] The foregoing summary does not contain an exhaustive list of all aspects of the present invention. The present invention includes all systems and methods that may be practiced from all appropriate combinations of the various aspects described above, as well as those disclosed in the following detailed description and particularly pointed out in the claims. Such combinations have particular advantages not specifically described in the foregoing summary.

[0013] Various features of the present disclosure and the manner in which they are achieved will be described in more detail with reference to the following detailed description, claims and drawings, in which reference characters are re-used where appropriate to indicate correspondence between referenced items. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 illustrates an ultrasound-based tissue treatment system, according to one embodiment.

[0015] [Figure 2] FIG. 2 illustrates a side view of selected components of the ultrasound-based tissue treatment system shown in FIG. 1, according to one embodiment.

[0016] [Figure 3] FIG. 3 illustrates a side view of selected components of the ultrasound-based tissue treatment system shown in FIG. 1, according to one embodiment.

[0017] [Figure 4] FIG. 4 illustrates a perspective view of selected components of the ultrasound-based tissue treatment system shown in FIG. 1 inserted into a body cavity, according to one embodiment.

[0018] [Figure 5] FIG. 5 shows a longitudinal cross-sectional view of a distal portion of a catheter of an ultrasound-based tissue treatment system, according to one embodiment.

[0019] [Figure 6] FIG. 6 shows a cross-sectional view of the distal portion of a catheter of an ultrasound-based tissue treatment system along line AA of FIG. 5, according to one embodiment.

[0020] [Figure 7] FIG. 7 shows a cross-sectional view of the distal portion of a catheter of an ultrasound-based tissue treatment system along line AA of FIG. 5, according to one embodiment.

[0021] [Figure 8] FIG. 8 is a side view of a distal portion of a catheter of an ultrasound-based tissue treatment system including a flow control device, according to one embodiment.

[0022] [Figure 9] FIG. 9 is a cross-sectional view of a flow control device in a catheter of an ultrasound-based tissue treatment system, according to one embodiment.

[0023] [Figure 10] FIG. 10 is a cross-sectional view of a flow control device in a catheter of an ultrasound-based tissue treatment system, according to one embodiment.

[0024] [Figure 11] FIG. 11 is a cross-sectional view of a flow control device in a catheter of an ultrasound-based tissue treatment system, according to one embodiment.

[0025] [Figure 12]FIG. 12 is a side view of a flow control device for a catheter of an ultrasound-based tissue treatment system, according to one embodiment.

[0026] [Figure 13] FIG. 13 is a cross-sectional view of a flow control device in a catheter of an ultrasound-based tissue treatment system, according to one embodiment.

[0027] [Figure 14] FIG. 14 is a cross-sectional view of a flow control device in a catheter of an ultrasound-based tissue treatment system, according to one embodiment.

[0028] [Figure 15] FIG. 15 is a cross-sectional view of a flow control device in a catheter of an ultrasound-based tissue treatment system, according to one embodiment.

[0029] [Figure 16] FIG. 16 is a cross-sectional view of a flow control device in a catheter of an ultrasound-based tissue treatment system, according to one embodiment.

[0030] [Figure 17] FIG. 17 is a cross-sectional view of a flow control device in a catheter of an ultrasound-based tissue treatment system, according to one embodiment.

[0031] [Figure 18] FIG. 18 is a cross-sectional view of a catheter shaft of a catheter of an ultrasound-based tissue treatment system, according to one embodiment.

[0032] [Figure 19] FIG. 19 is a side view of a catheter of an ultrasound-based tissue treatment system, according to one embodiment.

[0033] [Figure 20] FIG. 20 is a side view of a catheter of an ultrasound-based tissue treatment system, according to one embodiment.

[0034] [Figure 21] FIG. 21 is a side view of a catheter of an ultrasound-based tissue treatment system, according to one embodiment.

[0035] [Figure 22] FIG. 22 is a side view of a catheter of an ultrasound-based tissue treatment system, according to one embodiment.

[0036] [Figure 23] FIG. 23 is a schematic diagram of an ultrasound-based tissue treatment system, according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0037] Systems and methods of use for treating tissue using unfocused ultrasound energy are provided herein. In certain embodiments, acoustic-based tissue treatment transducers, devices, systems, and portions thereof are provided. The systems may be catheter-based. The systems may be delivered intraluminally (e.g., intravascularly) to position the transducer within a target anatomical region of a subject, e.g., within an appropriate body cavity such as a blood vessel. Once properly positioned within the target anatomical region, the transducer may be activated to deliver unfocused ultrasound energy radially outward to appropriately heat and treat tissue within the target anatomical region. The transducer or piezoelectric material may be activated at a frequency, duration, and energy level appropriate for treating the target tissue. In one non-limiting example, unfocused ultrasound energy generated by a transducer or piezoelectric material or radio frequency (RF) energy transmitted by an electrode can target (select) neural tissue of a subject and heat such tissue in a manner that neuromodulates (e.g., completely or partially ablates, necrotizes, or stimulates) the neural tissue.

[0038] Neuromodulation of renal nerves, as described in the aforementioned Warnking, Schaer, and Taylor patents, can be used to treat a variety of conditions, such as hypertension, chronic kidney disease, atrial fibrillation, the autonomic nervous system for use in treating various medical conditions, arrhythmias, heart failure, end-stage renal disease, myocardial infarction, anxiety, contrast nephropathy, diabetes, metabolic disorders, insulin resistance, etc. However, it should be understood that balloon catheters can also be suitably used to treat other nerves and conditions, such as the sympathetic nerves of the hepatic plexus in the hepatic artery, which are involved in blood glucose levels important in treating diabetes, or any suitable tissue, such as cardiac tissue causing abnormal heart rhythms, and are not limited to use in treating (e.g., neuromodulation of) renal nerve tissue. In another example, tissue treatment catheters are used to ablate sympathetic nerves in the renal and hepatic arteries to treat diabetes and other metabolic disorders. In certain embodiments, the tissue treatment catheter is used to treat autoimmune and / or inflammatory diseases, such as rheumatoid arthritis, sepsis, Crohn's disease, ulcerative colitis, and / or gastrointestinal motility disorders, by neuromodulating sympathetic nerves in one or more of the splenic, celiac, superior mesenteric, or inferior mesenteric arteries. In certain embodiments, the tissue treatment catheter is used to ablate nerve fibers in the celiac ganglion and / or renal artery to treat hypertension. In certain embodiments, the transducer is used to treat (reduce) pain, such as pain associated with pancreatic cancer, by neuromodulating nerves innervating the pancreas. Ultrasound or RF energy may also be used to ablate nerves in both the pulmonary veins and renal arteries to treat atrial fibrillation. In yet another example, ultrasound or RF energy may additionally or alternatively be used to ablate nerves innervating the carotid body to treat hypertension and / or chronic kidney disease.

[0039] In an intraluminal system, an ultrasound transducer may be placed within a balloon that is filled with a cooling fluid before and during treatment. More specifically, the balloon may surround the transducer. The balloon may contact the interior surface (e.g., the intima) of the body cavity. In certain embodiments, the transducer may be used to output an acoustic signal when the balloon completely occludes the body cavity, and the cooling fluid within the balloon may be used to cool both the body cavity and the transducer. In certain embodiments, a balloon may surround the transducer to cool the transducer during sonication, but the balloon may not contact or occlude the body cavity, and the blood within the body cavity may be relied upon to cool the body cavity instead of the cooling fluid.

[0040] In certain embodiments, the transducer may be connected to a controller using one or more conductive wires. The controller may be configured to power or transmit electrical signals to the transducer. In one embodiment, the controller generates a radio frequency (RF) signal to the transducer. The balloon ablation therapy device may include one or more lumens, such as a guidewire lumen, one or more fluid lumens, and / or a cable lumen.

[0041] Existing tissue treatment systems are sized to be delivered to target anatomical structures via a femoral access route. However, the femoral access route can be painful for the patient, require long procedure times, and may result in health complications. Delivery via a radial access route via the radial artery may reduce pain, procedure times, and complications. More specifically, radial access is a more comfortable delivery route than groin access and is associated with fewer complications, such as bleeding.

[0042] To provide a catheter suitable for tissue treatment via the radial artery access route, it is advantageous to provide a catheter that is longer than that required for access via the femoral artery. More specifically, radial access may require a longer catheter than that required for femoral access. On the other hand, an increase in length may require an increase in the cross-sectional area of ​​the fluid lumen used to circulate cooling fluid to the transducer within the balloon. Increasing the cross-sectional area of ​​the fluid lumen may maintain appropriate pressure and fluid flow rates for safe and effective energy delivery. Furthermore, increasing the cross-sectional area of ​​the fluid lumen may facilitate effective priming of the system, as a larger diameter fluid lumen may prime more reliably. On the other hand, because the radial artery is typically smaller than the femoral artery, the overall diameter of the catheter must be reduced to 5 French or less to ensure patient comfort and safety. In other words, the conflicting requirements of increasing the diameter of the fluid lumen and reducing the overall catheter diameter limit the ability of existing catheter designs to be adapted to the radial artery access platform.

[0043] In one aspect, a catheter is provided having a cross-sectional area and length suitable for radial artery access. The catheter may include a single fluid lumen with a cross-sectional area suitable for providing safe and effective nerve ablation and system priming. In one aspect, the catheter, unlike existing tissue treatment systems, does not require a second fluid lumen, and therefore the catheter can be delivered to a target anatomical structure through a radial artery access pathway. Eliminating the second fluid lumen may allow the size of the single fluid lumen to be large enough to provide sufficient cooling fluid flow to the transducer, yet small enough to provide a catheter shaft that can be delivered through a radial artery access pathway. The catheter may include a flow control device for passing fluid delivered from a fluid reservoir to the catheter and into the surrounding environment. Thus, fluid may flow distally through the catheter to cool the catheter's transducer before being expelled into the surrounding environment. By draining the fluid rather than returning it to a fluid reservoir, the need for a second fluid lumen can be eliminated, allowing the catheter to be delivered to the target anatomy through a radial artery access route.

[0044] 1, 2, and 3 illustrate features of an ultrasound-based tissue treatment system according to various aspects provided herein. Referring to FIG. 1, an ultrasound-based tissue treatment system according to one embodiment is shown. Tissue treatment system 100 is shown as including a catheter 102, a controller 120, and a connecting cable 140. In certain embodiments, system 100 further includes an ultrasound transducer within a balloon 112, a reservoir 110, a fluid transfer cartridge 130, and a control mechanism, such as a handheld remote control.

[0045] 1, the controller 120 is shown connected to the catheter 102 via a cartridge 130 and a 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 fabricated from, for example, but not limited to, nylon, polyimide film, a thermoplastic elastomer (such as those sold under the trademark PEBAX®), a medical-grade thermoplastic polyurethane elastomer (such as Pellethane®, Isothane®, other suitable polymers, or any combination thereof).

[0046] Referring to FIG. 2, a side view of an ultrasound-based tissue treatment system according to one embodiment is shown. The tissue treatment catheter 102 may include a distal region 210 and a proximal region 220. The catheter 102 may have a length depending on the treatment application. For example, in a particular embodiment suitable for renal nerve denervation via a radial access delivery method, the catheter 102 may have a working length of 150-160 cm (e.g., 155 cm). Furthermore, the overall length of the catheter 102 for such applications may be longer, including the length of the electrical cable 230 extending to the electrical coupling 232. More specifically, the cable 230 may have a length of approximately 305 cm from the proximal hub 240 to the electrical coupling 232.

[0047] The catheter 102 may have a profile suitable for accessing the renal arteries through a radial artery access site. For example, the catheter 102 may include a catheter shaft 214 having a shaft diameter of 4 to 6 French, e.g., 5 French or less. This profile is facilitated in part by the catheter shaft 214 having an outer diameter in the range of 0.050 to 0.060 inches (e.g., 0.057 inches).

[0048] The distal region 210 of the tissue treatment catheter 102 may be a portion of a device that is advanced into a target anatomical structure, such as a target blood vessel having a vascular wall, to treat the target blood vessel. The distal region 210 may include a balloon 112 attached to a catheter shaft 214. The catheter shaft 214 may be an elongated tubular structure extending longitudinally from a proximal end to a distal end. The balloon 112 may be attached to and supported by the catheter shaft 214 at its distal end. Additionally, an ultrasound transducer 111 may be attached to the catheter shaft 214 and housed within the balloon 112. Thus, the catheter shaft 214 may facilitate delivery of cooling fluid to the balloon 112 and electrical energy to the transducer 111.

[0049] The catheter shaft 214 may include one or more lumens that may be used as fluid conduits, electrical cable passageways, guidewire lumens, etc. In one embodiment, for example, the catheter shaft 214 may include a guidewire lumen 213 shaped, sized, and otherwise configured to receive a guidewire. In one embodiment, the guidewire lumen 213 is a wire-over-guidewire lumen that extends from the distal tip of the catheter 102 through the entire length of the catheter shaft 214 to the exit port 225 of the proximal hub 240 of the catheter 102. As described below, the lumen of the catheter shaft 214 may conduct inflation / cooling fluid from the proximal region 220 to the balloon 112 during balloon inflation.

[0050] In one embodiment, the transducer 111 is attached to the catheter shaft 214 at the distal region 210, inside the balloon 112. The transducer 111 may be an ultrasound transducer used to emit energy toward the vessel wall. For example, the transducer 111 may emit ultrasound energy circumferentially, e.g., 360 degrees, around the vessel wall. In one embodiment, an electrical cable 230 extends from the proximal region 220 to the distal region 210 and is connected to the transducer 111 to generate energy for emission to the target tissue.

[0051] The ultrasound transducer 111 may include first and second electrodes disposed on opposite sides of a cylindrical piezoelectric material, such as lead zirconate titanate (PZT). To energize the transducer 111, a voltage is applied between the first and second electrodes at a frequency selected to resonate the piezoelectric material. This generates vibrational energy that radiates radially outward from the transducer 111. The transducer 111 is designed to provide a substantially uniform and predictable radiation profile to minimize damage to surrounding non-target tissue. Additionally, before, during, and after activation of the transducer 111, a cooling fluid is circulated through the balloon 112 to reduce heating of the inner lining of the body cavity and cool the transducer 111. In this manner, the peak temperature achieved by tissue within the cooling zone remains lower than that of tissue located outside the cooling zone.

[0052] The proximal region 220 may include one or more connectors or couplings that may be electrically connected to the transducer 111 via an electrical cable 230. For example, the proximal region 220 may include one or more electrical couplings 232 that connect to the proximal end of the electrical cable 230. The distal end of the electrical cable 230 may be connected to the transducer 111.

[0053] Catheter 102 may be coupled to controller 120 by connecting electrical coupling 232 to 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. Thus, controller 120 may be used with multiple catheters 102 during a procedure by disconnecting the coupling of a first catheter, replacing it with a second catheter, and connecting the coupling of the second catheter to controller 120. In certain embodiments, for example, if only one catheter needs to be used during a procedure, connecting cable 140 may be permanently connected to controller 120.

[0054] In certain embodiments, the proximal region 220 of the catheter 102 may further include one or more fluid ports. For example, the proximal hub 240 may include a fluid port 234, through which the expandable member (e.g., the balloon 112) may be fluidly connected to the reservoir 110 (see FIG. 1 ). The reservoir 110 may therefore supply cooling fluid to the balloon 112 via the fluid port 234. The reservoir 110 may optionally be provided with the controller 120, for example, attached to the outer housing of the controller 120, as shown in FIG. 1 . Alternatively, the reservoir 110 may be provided separately.

[0055] Referring to FIG. 3, a side view of an ultrasound-based tissue treatment system according to one embodiment is shown. In one embodiment, the catheter 102 may have a rapid-exchange guidewire lumen 213. More specifically, the guidewire lumen 213 may extend from the distal tip of the catheter 102 through a portion of the length of the catheter shaft 214 to the exit port 225 of the distal portion 210 of the catheter 102. For example, the distance from the distal tip to the rapid-exchange port may be within a range of 20-30 cm, e.g., 23 cm. The proximal hub 240 shown in FIG. 3 may differ from the proximal hub 240 shown in FIG. 2 given that the exit port may be moved from the proximal portion 220 to the distal portion 210. Other components of the rapid-exchange version of the catheter 102 may be similar to those of the wire-over-wire version of the catheter 102, and therefore the description of the components shown in FIG. 2 may also apply to the similarly numbered components shown in FIG. 3.

[0056] Referring to Figure 4, a perspective view of an ultrasound-based tissue treatment system inserted into a body cavity is shown, according to one embodiment. Components of a distal portion 210 of a catheter 102 may be inserted into a body cavity of a subject. In Figure 4, the body cavity is a blood vessel (e.g., a renal artery) having multiple nerves 401 in its outer layer (e.g., adventitial layer). As previously described, the distal portion 210 may include an ultrasound transducer 111, a balloon 112 filled with a cooling fluid 403, a catheter shaft 214, and / or a guidewire support tip 404 configured to receive a guidewire 406.

[0057] The transducer 111 may be partially or completely disposed within the balloon 112. The balloon 112 may be inflated with a cooling fluid 403 so that it contacts the inner surface (e.g., the intima) of the body cavity. In certain embodiments, the transducer 111 may be used to output an acoustic signal when the balloon 112 completely occludes the body cavity, i.e., the target blood vessel 200. The balloon 112 may center the transducer 111 within the body cavity. In certain embodiments, suitable for renal denervation, for example, the balloon 112 is inflated while inserted into the body cavity of the patient under treatment using the cooling fluid 403 at an operating pressure of about 10 to about 30 psi. The balloon 112 may be or include a compliant, semi-compliant, or non-compliant medical balloon. The balloon 112 is sized for insertion into a body cavity; for example, when inserted 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.

[0058] 4, when filled with cooling fluid 403 and inflated under the control of controller 120, the outer wall of balloon 112 can be approximately parallel to the outer surface of transducer 111. Optionally, balloon 112 can be sufficiently inflated to be in apposition with the body cavity. For example, when inflated, balloon 112 can at least partially contact and be in apposition with the inner surface of a blood vessel wall 450 of the body cavity. When balloon 112 is in apposition with the body cavity, or more specifically, with the inner circumferential wall of the body cavity, balloon 112 can substantially prevent blood in the body cavity from passing through the balloon.

[0059] In other forms, the balloon 112 is configured so that it does not contact the body cavity when inflated. The balloon 112 may surround the transducer to cool the transducer during sonication, but may not contact or occlude the body cavity, relying instead on blood within the body cavity to cool the cavity instead of a cooling fluid. When the balloon 112 surrounds the transducer 111 but does not contact or occlude the body cavity, the balloon 112 may be non-compliant. In certain embodiments, the balloon 112 comprises nylon.

[0060] For vessels that conform to the balloon's diameter, a non-compliant balloon (e.g., 112) can act as a centering mechanism. Cooling of the vessel wall can be managed by the generator's cooling system by flowing water or other cooling fluid (e.g., dextrose or saline) through the balloon as needed. A non-compliant balloon advantageously provides tighter control over the balloon design. A non-compliant balloon (e.g., 112) can be advantageously configured such that upon inflation, a wrinkle-free balloon surface maintains a desired shape without interfering with sonication. Additionally or alternatively, the balloon 112 can be maintained at a specified size by forcing and / or withdrawing cooling fluid through and / or from the balloon 112 at a specified flow rate.

[0061] Referring to FIG. 5, a longitudinal cross-sectional view of a distal portion of a catheter of an ultrasound-based tissue treatment system is shown, according to one embodiment. The ultrasound transducer 111 may include a cylindrical hollow tube made of a piezoelectric material (e.g., lead zirconate titanate (PZT)) with an inner electrode 504 and an outer electrode 502 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 a piezoelectric transducer body. The piezoelectric transducer body may have a variety of other shapes and need not be hollow. For example, in a specific embodiment suitable for renal denervation, the piezoelectric material comprising the piezoelectric transducer body is lead zirconate titanate 8 (PZT8), also known as Navy III piezoelectric material. The bare 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. Application of a voltage and alternating current between the inner electrode 504 and the outer electrode 502 causes the piezoelectric material to vibrate transversely to the longitudinal direction of the cylindrical tube and to radiate ultrasonic waves radially.

[0062] In one embodiment, the ultrasound transducer 111 may be positioned in an interior 506 of the balloon 112. The balloon 112 may have the interior 506 in fluid communication with a fluid lumen 508 of the catheter shaft 214. The fluid lumen 508 may deliver a cooling fluid 403 to the interior 506 to cool the transducer 111. More specifically, the balloon 112 may house the transducer 111 in the interior 506, and the transducer 111 may be contacted and cooled by the cooling fluid 403 flowing from the fluid lumen 508 into the interior 506.

[0063] As shown in FIG. 5 , the ultrasound transducer 111 may generally be supported via a backing member or post 507. In certain embodiments, the backing member 507 comprises stainless steel coated with nickel and gold, with nickel used as a bonding material between the stainless steel and the gold plating. For example, in certain embodiments suitable for renal denervation, the outer diameter of the transducer 111 is approximately 1.5 mm, the inner diameter of the transducer 111 is approximately 1 mm, and the transducer 111 has a length of approximately 6 mm. Transducers having other inner diameters, outer diameters, and lengths, or more generally, sizes and shapes, are within the scope of the embodiments described herein. Additionally, it is noted that the drawings in the figures are not necessarily, and often are not, drawn to scale.

[0064] The backing member 507 may extend from the distal portion of the catheter shaft 214 to the distal tip 510 of the catheter 102. For example, the distal end of the backing member 507 may be positioned within an adjacent opening in the distal tip 510, and the proximal end of the backing member 507 may be movably coupled to the distal portion of the catheter shaft 214 via the electrical cable 230. In other embodiments, a gap exists between the distal end of the catheter shaft 214 and the proximal end of the ultrasound transducer 111.

[0065] To allow liquid cooling along both the inner electrode 504 and the outer electrode 502, the backing member 507 may include one or more standoff assemblies 512. The standoff assemblies 512 may define one or more annular openings through which the cooling fluid 403 can enter the space in the transducer 111 (which may be selectively insulated) between the backing member 507 and the inner electrode 504. The backing member 507 may thus function as a fluid barrier between the cooling fluid 403 circulated within the balloon 112 and the lumen of the backing member 507 that receives the guidewire 406.

[0066] According to certain embodiments, the standoff assembly 512 is electrically conductive to electrically couple the inner electrode 504 of the ultrasonic transducer 111 to the backing member 507. One or more conductors of the electrical cable 230 may be electrically coupled to the backing member 507. Thus, when the controller 120 is activated, electrical current may be delivered from the electrical cable 230 to the inner electrode 504 of the ultrasonic transducer 111 through the backing member 507 and the standoff assembly 512, which advantageously eliminates the need to directly couple the cable 230 to the inner electrode 504 of the transducer 111. In other embodiments, the backing member 507 and the standoff assembly 512 are made of one or more electrical insulator materials, or even if they are made of a conductive material, are coated with one or more electrical insulator materials. In certain embodiments, one or more electrical conductors of the cable 230 are directly coupled (e.g., soldered) to the inner electrode 504 of the transducer 111.

[0067] The backing member 507 may have an insulating tube disposed along its inner surface to prevent or reduce the possibility of electrical conduction between the guidewire 406 and the backing member 507. This is used in embodiments where such electrical conduction is undesirable. The insulating tube 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. 5, the insulating tube may extend through the lumen of the backing member 507 within the transducer 111 toward the distal tip 510. In this embodiment, the transducer 111 is offset distally from the distal end of the catheter shaft 214.

[0068] Referring to Figure 6, a cross-sectional view of the distal portion of a catheter of an ultrasound-based tissue treatment system is shown along line AA in Figure 5, according to one embodiment. The catheter shaft 214 includes one or more lumens. For example, the catheter shaft 214 may include a fluid lumen 508 for transferring an inflation / cooling fluid (e.g., water, sterile water, saline, 5% dextrose (D5W), other liquids, or gases) to or from a fluid source, such as the reservoir 110, located at the proximal region 220 of the catheter 102 outside the patient. In one embodiment, the catheter shaft 214 includes a single fluid flow path (channel) for moving fluid toward the balloon 112. For example, the fluid flow path may deliver inflation fluid from the fluid port 234 to the balloon 112 under the control of the controller 120. Thus, the flow path inlet is in fluid communication with the balloon 112 and passes fluid through the balloon 112 at a selected flow rate to inflate the balloon 112. The flow rate controls heat transfer between the balloon 112 and the vessel wall to reduce the likelihood of overheating of the tissue during treatment. For example, the flow rate may provide active cooling of approximately the first millimeter of tissue to maintain the integrity of, for example, the renal artery wall.

[0069] In one embodiment, the catheter shaft 214 includes a guidewire lumen 213. The guidewire lumen 213 may extend through the catheter shaft 214 and, optionally, through the transducer 111. Further, the guidewire lumen 213 may extend through the distal tip 510. Thus, the distal tip 510 may travel over the guidewire 406 and through the patient's anatomy. As previously mentioned, the catheter 102 may include an electrical cable 230. The electrical cable 230 may be a single electrical cable that extends longitudinally through the catheter shaft 214.

[0070] 7, a cross-sectional view of the distal portion of a catheter of an ultrasound-based tissue treatment system, taken along line AA in FIG. 5, is shown according to one embodiment. The catheter shaft 214 can include a fluid lumen 508 and a guidewire lumen 213, as previously described. In one embodiment, the electrical cable 230 includes multiple electrical cables. For example, a first electrical cable 702 and a second electrical cable 704 can run parallel to each other within a common sheath.

[0071] In one embodiment, the catheter 102 includes a unidirectional fluid flow of cooling fluid 403 from the controller 120 through the balloon 112 to the surrounding environment. As the cooling fluid 403 passes through the balloon 112, it cools the transducer 111 and transfers heat downstream down the blood vessel. The catheter 102 may include a flow controller for regulating the flow rate of the cooling fluid 403 to the surrounding environment. It will be appreciated that the difference in flow rate between the cooling fluid 403 entering the balloon 112 and the cooling fluid 403 exiting the balloon 112 may affect the inflation of the balloon. For example, when the inflow flow rate is higher than the outflow flow rate, the balloon 112 will inflate, and vice versa. Thus, a flow controller may be used to control the inflation of the balloon 112.

[0072] 8 , a side view of a distal portion of a catheter of an ultrasound-based tissue treatment system including a flow control device is shown according to one embodiment. In one embodiment, the catheter 102 includes a flow control device 802. The flow control device 802 may be located at the distal tip 510 of the catheter 102. For example, the flow control device 802 may be attached to an inner member 804 of the catheter shaft 214. The inner member 804 may include one or more holes 806 in fluid communication with a fluid lumen 508. More specifically, the fluid lumen 508 may be coupled to the lumen of the inner member 804 to pass (pump) the cooling fluid 403 through the holes 806 of the inner member 804 and into the interior 506 of the balloon 112.

[0073] The flow control device 802 may also be coupled to the balloon 112. More specifically, the balloon 112 may be sealed to the outer surface of the flow control device 802. Thus, the cooling fluid 403 may flow from the interior 506 of the balloon 112 to the flow control device 802 and distally to the ambient environment. By flowing the cooling fluid 403 through the balloon interior 506 to the ambient environment rather than directly through the fluid lumen 508, the exchange of cooling fluid within the balloon may be promoted, enhancing cooling of the transducer and / or tissue. For example, cooling fluid 403 warmed by sonication within the balloon 112 may be evacuated and replenished with fresh cooling fluid. Such replenishment may be performed without the need for a return lumen, allowing the overall size of the device to be reduced.

[0074] As described below, the flow control device 802 can provide unidirectional fluid flow to provide variable pressure to the balloon 112, e.g., a compliant balloon. The flow control device 802 can have an inlet port 808 for receiving fluid from the fluid lumen 508 through the interior 506. The flow control device 802 can also have an outlet port, e.g., on a distal or side face of the device, for expelling the fluid outward to the surrounding environment. Fluid flow through the flow control device 802 can occur when the fluid reaches a predetermined pressure. More specifically, flow through the flow control device 802 can be regulated to be on when the fluid pressure exceeds a threshold value and to be off when the fluid pressure falls below the threshold value. In this manner, the flow control device 802 is configured to pass fluid to the surrounding environment when the fluid has a predetermined pressure.

[0075] Referring to FIG. 9 , a cross-sectional view of a flow control device for a catheter of an ultrasound-based tissue treatment system is shown, according to one embodiment. The flow control device 802 exhausts the cooling fluid 403 rather than circulating it, allowing the second fluid lumen to be omitted, and a one-way valve may be used to control outlet flow. In one embodiment, the flow control device 802 includes a check valve 902. The check valve 902 may be located at the distal tip 510 of the catheter 102, such that a pressure on the input side of the valve, e.g., a cracking pressure, greater than the pressure on the output side of the valve, e.g., the outlet port 904, may cause the check valve 902 to open. When the valve is open, the cooling fluid 403 may flow through the valve and the distal tip 510 of the catheter 102 to the surrounding environment. In contrast, when the pressure on the input side is lower than the cracking pressure, the valve may close, and fluid may not flow through the valve and the distal tip 510 to the surrounding environment.

[0076] The check valve 902 may include an inlet port 808 for receiving fluid from the interior 506 of the balloon 112. The inlet port 808 may convey fluid toward an elastomeric valve 906 of the check valve 902. The elastomeric valve 906 may be, for example, a duckbill valve, a slit membrane, or the like. The elastomeric valve 906 may be backed by a sealing plunger 908. By backing the elastomeric valve 906, the sealing plunger 908 may maintain the shape of the elastomeric valve 906 and may prevent deformation of the elastomeric valve 906, which may cause, for example, unwanted fluid ejection.

[0077] In one embodiment, the elastomeric valve 906 can be formed from a soft polyurethane, such as Shore A polyurethane, and can recover consistently when opened and closed under pressure. The elastomeric valve 906 can have a crack pressure equal to a predetermined pressure at which the check valve 902 is to open. For example, the predetermined pressure can be a desired inflation pressure of the balloon 112. The desired inflation pressure can be the pressure required to inflate the balloon 112 to a predetermined corresponding diameter. Thus, when the fluid pressure in the balloon interior 506 is at a predetermined pressure, the balloon 112 can have a predetermined diameter and the elastomeric valve 906 can open, allowing the cooling fluid 403 to pass to the surrounding environment, cooling the transducer 111 and maintaining the balloon at the predetermined diameter.

[0078] 10 , a cross-sectional view of a flow control device of a catheter of an ultrasound-based tissue treatment system is shown, according to one embodiment. The flow control device 802 may include one or more vent holes 1002 for venting or dumping the cooling fluid 403 to the surrounding environment. The vent holes 1002 may extend through an outer wall 1004 of the flow control device 802. More specifically, the flow control device 802 may have an outer wall 1004 surrounding an interior channel 1006, and the vent holes 1002 may extend from the interior channel 1006 through the outer wall 1004 to the surrounding environment. Thus, the vent holes 1002 provide an exit path for the cooling fluid 403.

[0079] The internal channel 1006 may be in fluid communication with the interior 506 of the balloon 112 via the inlet port 808. Thus, the cooling fluid 403 may flow from the interior 506 through the inlet port 808 toward the vent hole 1002. However, in one embodiment, the fluid flow is regulated by a plunger 1008. The plunger 1008 is movable within the internal channel 1006 relative to the vent hole 1002. For example, the plunger 1008 may include an annulus that rides on the guidewire lumen 213. The movement of the plunger 1008 may be influenced by other components of the flow controller 802. For example, the flow controller 802 may include a spring 1010 to bias the plunger 1008 against the vent hole 1002.

[0080] The spring 1010 may bias the plunger 1008, for example, proximally, within the internal channel 1006. In the biased position, the plunger 1008 may be adjacent to the vent hole 1002 and may seal against the outer wall 1004, preventing fluid from flowing through the vent hole 1002. Meanwhile, as fluid pressure increases, the fluid pressure may push against the plunger 1008 against the biasing force of the spring 1010. When the fluid pressure reaches a predetermined pressure, it may overcome the biasing force of the spring 1010 and compress the spring 1010, causing the plunger 1008 to slide distally. In this actuated position, the plunger 1008 may be distal to the vent hole 1002. Thus, cooling fluid 403 may flow into the internal channel 1006 and through the vent hole 1002 proximal to the plunger 1008 to the ambient environment. The flow rate and / or pressure of the fluid may be automatically adjusted by the spring 1010 .

[0081] Referring to FIG. 11 , a cross-sectional view of a flow control device of a catheter of an ultrasound-based tissue treatment system is shown, according to one embodiment. The position of a plunger 1008 relative to a vent hole 1002 can be adjusted using one or more pull wires 1102. The pull wires 1102 can be connected to the plunger 1008, for example, by thermal or adhesive bonding, and can extend proximally through the catheter 102 to the proximal end. The proximal end can be coupled to an actuation member, such as a lever, knob, or the like, that allows a user to pull and / or push the pull wires 1102. Pulling or pushing the pull wires 1102 can control the position of the plunger 1008 relative to the vent hole 1002. More specifically, the pull wires 1102 can move the plunger 1008 relative to the vent hole 1002. The flow rate and / or pressure of the fluid can be manually adjusted by the pull wires 1102.

[0082] The flow control device 802 may have several vent holes 1002, and the position of the plunger 1008 may determine the amount of fluid flow through the vent holes 1002. For example, several vent holes 1002 may be axially staggered, e.g., a first vent hole 1002A may be distally offset from a second vent hole 1002B. The plunger 1008 may slide past the first vent hole 1002A, exposing the first vent hole 1002A to the cooling fluid 403, while the second vent hole 1002B remains blocked. Thus, when the plunger 1008 is in the first position, the cooling fluid 403 may flow through the first vent hole 1002A but not through the second vent hole 1002B. The plunger 1008 may then slide past the second vent hole 1002B, exposing both vent holes 1002 to the cooling fluid 403. Thus, the cooling fluid 403 may flow through both vent holes 1002A, 1002B. In this manner, the position of the plunger may control the open vent area for venting the cooling fluid 403 to the ambient environment and, therefore, the amount of fluid passing through the vent holes 1002. Varying the outlet flow of the cooling fluid 403 may affect the pressure of the cooling fluid 403 in the interior 506 of the balloon 112.

[0083] 12 , a side view of a flow control device of a catheter of an ultrasound-based tissue treatment system is shown, according to one embodiment. The flow control device 802 can include multiple orifices that crack (open) at a predetermined fluid pressure. For example, in one embodiment, the flow control device 802 includes several vent holes 1002 for leaking cooling fluid 403 having a predetermined pressure. The vent holes 1002 can extend through an outer wall 1004 of the flow control device 802. Each hole can be in fluid communication with the interior 506 of the balloon 112 and can have a crack pressure to allow the flow of cooling fluid 403 when the fluid pressure in the interior 506 reaches the predetermined pressure.

[0084] The crack pressure of each hole may be the same. Each hole may have the same shape and size so that each hole has similar resistance to flow. Thus, the vent holes 1002 may discharge fluid at a constant flow rate. More specifically, the vent holes 1002 may each discharge the cooling fluid 403 to the ambient environment at the same rate.

[0085] The crack pressure of each hole, or of each group of holes, may be different. For example, some of the vent holes 1002 may have a smaller diameter than other vent holes 1002. The smaller vent holes 1002 may have a higher flow impedance and therefore a higher crack pressure than the larger vent holes 1002. Flow may selectively pass through the larger holes 1002 at a first inflation pressure, and then pass through both the larger and smaller holes 1002 when the fluid pressure exceeds the crack pressure of the smaller holes 1002. Thus, the vent holes 1002 may vent more fluid as the inflation pressure increases, maintaining the balloon inflation pressure within a desired range above the predetermined pressure.

[0086] In one embodiment, the flow control device 802 includes a plug 1202. The plug 1202 can have several holes 1204 axially and / or radially extending through the plug body. For example, the plug 1202 can be formed from a semi-permeable material, such as an electrospun fiber material. The holes and / or channels formed in the plug 1202 can receive the cooling fluid 403 from the interior 506 of the balloon 112 and pass the cooling fluid 403 distally and outwardly toward the vent holes 1002 of the flow control device 802. Thus, the plug 1202 can provide some resistance to the distal flow of the cooling fluid 403 while transmitting the cooling fluid 403 toward the vent holes 1002 for discharge to the surrounding environment.

[0087] 13, a cross-sectional view of a flow control device is shown according to one embodiment. The cross-section reveals a network of channels formed by a plurality of holes. The network of channels can carry cooling fluid 403 from the interior 506 of the balloon 112 to the vent holes 1002 in the outer wall 1004 of the flow control device. Thus, when the balloon 112 is inflated to a pressure that exceeds the crack pressure, e.g., the combined impedance, of the channel network and the vent holes 1002, fluid can be expelled from the interior 506.

[0088] 14 , a cross-sectional view of a flow control device of a catheter of an ultrasound-based tissue treatment system is shown, according to one embodiment. The flow control device 802 may allow relative movement between the distal end of the balloon 112 and the catheter shaft 214. Such movement may groom the balloon 112. More specifically, by allowing the distal end of the balloon 112 to move relative to the catheter shaft 214, the balloon 112 may be stretched, thereby reducing its profile. When the balloon 112 is stretched and its profile is reduced, it may more easily track through the target anatomical structure. The reduced profile may allow the balloon 112 to track through narrow vessels, such as the radial artery, during delivery and / or retrieval.

[0089] In one embodiment, the self-grooming balloon 112 includes a flow control device 802 having a proximal tip 1402 and a distal tip 1404. The balloon 112 may self-groom because it may be biased to wrap or adjust (e.g., stretch) to a lower profile when fluid pressure within the balloon 112 is removed. For example, the balloon 112 may be manufactured in a wrapped and / or stretched configuration and may preferentially return to that configuration upon deflation based on the biasing force provided by the flow control device 802. When the balloon 112 is in a lower profile, it can track through narrow passages or vessels. For example, the balloon 112 may be delivered through the radial artery or retracted into a guide sheath without catching on or damaging adjacent structures.

[0090] The proximal tip 1402 may be independently movable relative to the distal tip 1404. For example, the proximal tip 1402 may be attached to the catheter shaft 214, and the distal tip 1404 may be movably attached to the proximal tip 1402. The proximal tip 1402 may be fixed relative to the catheter shaft 214, and the distal tip 1404 may be coupled to the balloon 112. Thus, when the distal tip 1404 moves relative to the proximal tip 1402, the distal end of the balloon 112 may move relative to the catheter shaft 214.

[0091] In one embodiment, the distal tip 1404 is slidable over the proximal tip 1402. The distal tip 1404 can have a recess 1403 that extends to the proximal end of the portion. The recess 1403 can be sized to receive a distal protrusion on the proximal tip 1402. More specifically, the protrusion on the proximal tip 1402 can extend into the recess 1403 on the distal tip 1404. Thus, the distal tip 1404 can move axially and be constrained radially by the proximal tip 1402. The distal tip 1404 is movable relative to the proximal tip 1402 essentially as a collar and is constrained by the shaft.

[0092] The flow control device 802 may include a spring 1406 that applies a counter force to the distal tip 1404, thereby biasing the distal tip 1404 toward the proximal tip 1402. The counter force may oppose a proximal load applied to the distal tip 1404 by the balloon 112. When the balloon 112 is inflated, the walls of the balloon expand radially outward, decreasing the length of the balloon. As the balloon 112 grows, the distal end of the balloon 112 pulls the distal tip 1404 proximally. This proximal load may act in a different direction than the biasing force of the spring 1406. More specifically, the spring 1406 may be a compression spring that biases the distal tip 1404 away from the proximal tip 1402. When the fluid pressure in the interior 506 of the balloon 112 is at a lower level, the spring force of the spring can overcome the contraction force applied to the distal tip 1404 by the distal end of the balloon 112. Thus, the spring 1406 can expand the balloon and maintain the balloon at a small profile.

[0093] 15 , a cross-sectional view of a flow control device for a catheter of an ultrasound-based tissue treatment system is shown, according to one embodiment. When fluid pressure in the interior 506 of the balloon 112 is at a higher level, the spring force of the spring 1406 may be insufficient to overcome the contraction force applied to the distal tip 1404 by the distal end of the balloon 112. As the balloon 112 grows, the distal tip 1404 may be pulled proximally and move relative to the proximal tip 1402. This contraction and retraction action may compress the spring 1406 between the distal tip 1404 and the proximal tip 1402. For example, the distal tip 1404 may slide over the proximal tip 1402, reducing the gap between the proximal end of the distal section and the adjacent wall at the base of the proximal tip 1402.

[0094] When the fluid pressure within the balloon 112 drops from that higher level, for example due to the venting of cooling fluid 403 through vent holes 1002 in the distal tip 510, the spring 1406 may again overcome the proximally directed force applied by the balloon 112 and return the distal tip 1404 away from the proximal tip 1402. Thus, the flow control device 802 may be a self-grooming device that both vents the cooling fluid 403 to the surrounding environment and stretches the balloon 112 after balloon deflation to a profile suitable for tracking the balloon through narrow blood vessels.

[0095] 16 , a cross-sectional view of a flow control device of a catheter of an ultrasound-based tissue treatment system is shown, according to one embodiment. In one embodiment, the distal tip 1404 of the flow control device 802 can be rotatable on the proximal tip 1402. For example, the portions can have mating threads, such as helical external threads on the proximal tip 1402 that engage with internal threads on the distal tip 1404, to allow the portions to be threaded onto one another. More specifically, the distal tip 1404 can be threadedly coupled to the proximal tip 1402. The threads can cause the distal tip 1404 to slide and rotate on the proximal tip 1402 when a proximal load on the distal tip 1404 of the balloon 112 pulls the portion proximally. The balloon 112 may be twisted in a low-profile state prior to inflation of the balloon, so that when the balloon is inflated, rotation of the distal tip 1404 may unwind the balloon 112 to an untwisted state. Similarly, when the cooling fluid 403 within the balloon 112 is released into the surrounding environment and the balloon deflates, the distal tip 1404 may be urged forward by the spring 1406 and rotated in the opposite direction, twisting the balloon 112. The twisted balloon may be rolled into a low profile suitable for tracking through narrow blood vessels.

[0096] Referring to FIG. 17 , a cross-sectional view of a flow control device of a catheter of an ultrasound-based tissue treatment system is shown, according to one embodiment. The flow control device 802 may include a self-grooming device incorporating one or more actuatable vent holes 1002. The distal portion may have vent holes 1002 extending along the central axis of the flow control device 802 to vent fluid from the balloon 112, similar to the embodiment described with respect to FIGS. 14-16 . The axial vent holes 1002 may be always open or may vent fluid each time the cooling fluid 403 is circulated through the balloon 112. Additionally, the distal portion may include side vent holes 1701 extending radially outward relative to the central axis. The distal tip 1404, and therefore the side vent holes 1701, may move relative to the proximal tip 1402.

[0097] In one embodiment, the proximal tip 1402 includes a fluid port 1702. The fluid port 1702 can extend through the proximal tip 1402 from an inlet in fluid communication with the interior 506 of the balloon 112 to an outlet on a side of the proximal tip 1402. For example, the fluid port 1702 can face laterally outward from a protrusion of the proximal tip 1402 that slides within the distal tip 1404. Thus, when the fluid port 1702 and the vent hole 1002 are axially aligned, the outlet of the fluid port 1702 can face the side vent hole 1701. More specifically, the distal tip 1404 can be movable relative to the proximal tip 1402 to align the side vent hole 1701 with the fluid port 1702. 17, the fluid port 1702 and the side vent hole 1701 are aligned, allowing cooling fluid 403 to flow to the surrounding environment through the fluid port 1702 and the side vent hole 1701. In particular, in this actuated state, when the balloon 112 is inflated and the distal tip 1404 is pulled proximally, compressing the spring 1406, fluid flow can be established.

[0098] As fluid exits the vent holes 1002 through the sidewall of the distal tip 1404, pressure may be released within the balloon 112, causing the spring 1406 to bias the distal tip 1404 away from the proximal tip 1402. The flow control device 802 may be biased to an activated state in which the fluid port 1702 and the side vent holes 1701 are misaligned. The distal tip 1404 and the proximal tip 1402 may be engaged with a snug fit with insufficient clearance between the components to allow for fluid flow when the fluid port 1702 and the side vent holes 1701 are misaligned. Thus, in the activated state, the cooling fluid 403 may be exhausted only through the vent holes 1002. Thus, when the balloon pressure rises above a threshold limit, the side vent holes 1701 may be activated, rapidly exhausting the cooling fluid 403 and rapidly reducing the balloon pressure to a predetermined pressure. At that given pressure, the balloon 112 may have a given inflated diameter.

[0099] In the above-described embodiment, actuation of the flow control device to move the distal tip 1404 relative to the proximal tip 1402 is controlled automatically. More specifically, pressure within the balloon 112 applies a counter load to the distal tip 1404 that acts against the biasing force of the spring. Thus, the spring 1406 and the balloon 112 may work in conjunction to determine whether the flow control device 802 is actuated. However, in one embodiment, actuation of the flow control device 802 is performed manually. For example, the catheter 102 may include a pull wire that extends from a handle at the proximal end of the device to the distal tip 1404. The pull wire may retract the distal tip 1404 relative to the proximal tip 1402, or may be pushed to advance the distal tip 1404 over the proximal tip 1402. Relative movement of distal tip 1404 and proximal tip 1402 may control the flow of cooling fluid 403 and / or groom balloon 112, as previously described.

[0100] 18 , a cross-sectional view of a catheter shaft of a catheter of an ultrasound-based tissue treatment system is shown, according to one embodiment. As previously mentioned, the catheter shaft 214 may have a shaft diameter of 5 French or less to facilitate radial artery access. To achieve such a diameter, the catheter shaft 214 may not include a guidewire lumen 213. More specifically, omitting the guidewire lumen 213 may reduce the components of the catheter shaft 214 and, therefore, the overall dimensions of the catheter shaft 214. However, without a guidewire lumen 213 for tracking the catheter 102 over a guidewire 406, another method of steering the device through the vasculature may be required. Thus, the catheter 102 may be configured as a steerable catheter.

[0101] In one embodiment, the catheter shaft 214 includes an outer member 1802 having a central lumen 1804. The outer member 1802 may comprise a tubular structure having an inner wall 1806 that houses the central lumen 1804. In one embodiment, the inner member 804 of the catheter 102 may extend through the central lumen 1804. For example, the inner member 804 may comprise a tubular structure that extends from the proximal end of the catheter 102 to the distal end of the catheter 102, e.g., through the balloon 112. The inner member 804 may have a fluid lumen 508 for delivering fluid to the interior 506 of the balloon 112. For example, the inner member 804 may include holes 806 for diffusing the cooling fluid 403 into the interior 506 of the balloon 112 ( FIG. 8 ). The wall 1808 of the inner member 804 provides a tubular structure having an outer wall 1808 that faces radially outward toward the inner wall 1806 of the outer member 1802. Thus, outer member 1802 and inner member 804 may be coaxial tubular structures that define a gap between outer wall 1808 and inner wall 1806 .

[0102] The gap between the inner member 804 and the outer member 1802 can be part of a central lumen 1804 through which one or more steering wires 1810 extend. More specifically, the steering wire(s) 1810 can extend through the central lumen 1804 between the inner wall 1806 of the outer member 1802 and the outer wall 1808 of the inner member 1804. The steering wires 1810 can be pulled or pushed, for example, via actuation of handle elements, to steer the catheter 102.

[0103] In one embodiment, the catheter 102 includes a first steering wire 1820 extending through the central lumen 1804. The catheter 102 may also include a second steering wire 1822 extending through the central lumen 1804. The first steering wire 1820 may be located diametrically opposite the second steering wire 1822 within the central lumen 1804. More specifically, the first steering wire 1820 may be located on a first side of the inner member 804, and the second steering wire 1822 may be located on a second side of the inner member 804 opposite the first steering wire 1820.

[0104] The steering wires 1810 may be formed from elongated elements of metal or polymer, such as polyimide wire. In one embodiment, at least one of the one or more steering wires 1810 may be an electrical cable 1824. The electrical cable 1824 may extend to the distal end of the catheter 102 and deliver energy to the ultrasound transducer 111.

[0105] 19, a side view of a catheter of an ultrasound-based tissue treatment system is shown according to one embodiment. One or more steering wires 1810 may connect to the outer member 1802 or the inner member 804 of the catheter shaft 214. More specifically, each steering wire 1810 may be attached to the catheter shaft 214 at a respective anchor point 1902. The anchor points 1902 may be located proximal to the balloon 112, for example.

[0106] 20 , a side view of a catheter of an ultrasound-based tissue treatment system is shown, according to one embodiment. Pulling the steering wire 1810 can transmit force to the anchor point 1902, which can transmit force to the catheter shaft 214. For example, pulling the first steering wire 1820 compresses the outer member 1802 along the side adjacent the first steering wire 1820, causing the catheter to flex, e.g., bend, toward that side. Similarly, pulling the second steering wire 1822 can steer the catheter 102 in the opposite direction, i.e., toward the side adjacent the second steering wire 1822. The steering wire 1810 can be bidirectional and can also be pushed to steer the catheter 102. More specifically, the catheter 102 can be steered by applying a load to the catheter 102 via the steering wire 1810 by pushing or pulling the wire. Thus, the catheter 102 can be tracked through the vasculature and maneuvered to the target anatomy without the aid of a guidewire.

[0107] Referring to FIG. 21 , a side view of a catheter of an ultrasound-based tissue treatment system is shown, according to one embodiment. Eliminating the guide sheath can facilitate reducing the overall size of the catheter system introduced into a patient's anatomy. A guide sheath is typically used to introduce the catheter 102 into a particular anatomy and can have a complex curvature that facilitates delivery to that anatomy. However, the guide sheath has a thick wall and can increase the overall size of the catheter system. Therefore, eliminating the guide sheath can reduce the overall size and allow the catheter system to more easily access a particular anatomy.

[0108] In one embodiment, the catheter 102 is configured to bend from a straight configuration to a curved configuration. In the curved configuration, the catheter 102 may have a complex curvature. More specifically, various sections (portions) of the catheter 102 may be curved differently such that the overall profile of the curved catheter shaft 214 exhibits various curvatures from the proximal end of the catheter 102 to the distal end of the catheter 102. The catheter shaft 214 may include several shaft sections 2102. Each shaft section 2102 may have a respective stiffness. For example, the shaft section 2102 may include a distal section 2104, an intermediate section 2106, and a proximal section 2108. As an example, the distal section 2104 may include the distal-most 1-3 cm, e.g., 2 cm, of the catheter shaft 214 extending proximally from the balloon 112, the middle section 2106 may include the 3-5 cm, e.g., 4 cm, of the catheter shaft 214 extending proximally from the distal section 2104, and the proximal section 2108 may include the remaining length of the catheter shaft extending proximally from the middle section 2106. The stiffness of each of these sections may be different and may increase distally. Thus, the stiffness of each of the distal sections 2104 may be lower than the stiffness of each of the middle sections 2106, which may be lower than the stiffness of each of the proximal sections 2108.

[0109] In one embodiment, the catheter 102 includes a steering wire 1810 attached to the catheter shaft 214 at an anchor point 1902. The anchor point 1902 may be located at the distal end of the catheter shaft 214, for example, in the distal section 2104 of the catheter 102. The steering wire 1810 may have a structure similar to that described above with respect to Figures 18-20.

[0110] The stiffness of the catheter 102 can also be affected by the central support 2103. The central support 2103 can be a reinforcing member that extends through the central lumen 1804 of the catheter shaft 214. The central support 2103 can be, for example, a hypotube. The hypotube can have a semi-rigid structure and can have sufficient stiffness to contribute to pushability onto the catheter shaft 214.

[0111] Referring to FIG. 22 , a side view of a catheter of an ultrasound-based tissue treatment system is shown, according to one embodiment. The variable stiffness of the catheter shaft 214 can cause the catheter 102 to assume a complex curvature when the steering wire 1810 is pulled. Pulling the steering wire 1810 can exert a bending load on the anchor point 1902, bending the catheter 102 throughout the shaft section 2102. The shaft can have discrete angular changes at the transitions between sections. More specifically, when the catheter 102 is flexed (deflected), the radius of curvature of the proximal section 2108 can be greater than the radius of curvature of the middle section 2106, which can be greater than the radius of curvature of the distal section 2104. The change in bending curvature from section to section can be based on the stiffness of the outer member 1802 or inner member 804 throughout the sections.

[0112] Variations in catheter stiffness that contribute to complex curvatures can also be influenced by the central support 2103. In one embodiment, the central support 2103 includes the inner member 804. For example, the inner member 804 can be a hypotube for carrying the cooling fluid 403 to the balloon 112. The inner member 804 can have a wall 1808 ( FIG. 18 ), which in one embodiment is thinner in the distal section 2104 than in the middle section 2106. For example, the hypotube can be centerless ground to vary the wall thickness over its length. The thinner wall 1808 over the distal section 2104 can make the distal section 2104 more flexible than the middle section 2106 or the proximal section 2108. Thus, similar to the variations in stiffness of the outer member 1802 described above, variations in stiffness of the inner member 804 can cause the sections to deflect in different directions as the catheter is steered, resulting in complex curvatures. The complex curvature may have a shape that would otherwise be provided by a guide sheath, so that catheter 102 may be used in a radial artery access approach without the need for such a guide sheath.

[0113] 23 , a schematic diagram of an ultrasound-based tissue treatment system is shown in accordance with one embodiment. In one embodiment, the system incorporates a hybrid flow configuration, where cooling fluid 403 is exhausted through the distal end of catheter 102 to the ambient environment and is also returned to controller 120. Thus, catheter 102 may include an inlet line 2301 that delivers cooling fluid 403 from an inlet pump 2302 of controller 120 to balloon 112, and an outlet line 2303 that delivers cooling fluid 403 from balloon 112 to controller 120 (e.g., reservoir 110). Catheter 102 may also include a flow control device 802 for exhausting fluid to the ambient environment. Thus, the hybrid flow system may deliver more fluid to balloon 112 than needs to be returned to reservoir 110 via outlet line 2303.

[0114] The flow of fluid circulated to / from the controller 120 may be regulated by a valve control 2310. For example, the valve control 2310 may be integrated within the controller 120 and electrically coupled to a flow valve 2312. The flow valve 2312 may be integrated within a catheter hub 2314 of the catheter 102. Alternatively, the flow valve 2312 may be integrated within the controller 120. The flow valve 2312 may be actuated by the valve control 2310 to allow or restrict flow from the balloon 112 to the reservoir 10.

[0115] When the flow valve 2312 is integrated into the catheter hub 2314, the flow valve 2312 can be manually activated. For example, the catheter hub 2314 can have a switch, button, or knob to allow a user to manually adjust the valve state (open or close the valve). When the flow valve 2312 is closed, the balloon 112 can inflate. When the flow valve 2312 is open, the balloon 112 can deflate. Thus, the user can manually control the inflation diameter of the balloon by activating the flow valve 2312.

[0116] When some fluid is being exhausted to the ambient environment and some cooling fluid 403 is being recirculated to the controller 120, the rate of infusion from the inlet pump 2302 and return to the reservoir 110 can be adjusted to control the inflation of the balloon. For example, when the flow rate to the balloon 112 is equal to the sum of the exhaust and return flow rates, the inflated diameter of the balloon can remain constant. Increasing the inlet (inlet) flow rate greater than the sum of the exhaust and return flow rates can increase the balloon diameter. In contrast, decreasing the inlet (inlet) flow rate (or increasing the exhaust and return flow rates) can decrease the balloon diameter by allowing more fluid to exit the balloon than enter it. Thus, the inlet pump 2302, flow control device 802, and / or flow valve 2312 can be controlled to regulate the inflation and deflation of the balloon.

[0117] In one embodiment, the outlet line 2303 may include a lumen for delivering the cooling fluid 403 to the controller 120. The return fluid flow rate may be less than the fluid flow rate to the balloon 112, as described above, and therefore the outlet line 2303 may have a smaller lumen than the lumen delivering fluid to the balloon 112. More specifically, because the amount of returned fluid is less, the return lumen may be smaller. Reducing the lumen size may lead to a reduction in the overall dimensions of the catheter 102. Thus, a smaller return line may contribute to making the catheter shaft 214 suitable for radial artery access.

[0118] On the other hand, the fluid lumen 508 of the catheter 102 may be sized to avoid clogging of the catheter shaft 214 during priming. Because smaller lumens may become clogged by air bubbles generated during priming, it may be advantageous to increase the size of certain lumens that are prone to such clogging. In one embodiment, the return line has a larger lumen than the lumen of the inlet line. This may make the return line less susceptible to clogging, for example, reducing the likelihood of clogging by air bubbles during priming.

[0119] In one embodiment, a catheter includes a catheter shaft, a balloon, an ultrasound transducer, and a flow control device. The catheter shaft has a fluid lumen. The balloon is attached to the catheter shaft and has an interior in fluid communication with the fluid lumen. The ultrasound transducer is in the interior. The flow control device has an inlet port for receiving fluid from the fluid lumen passing through the interior. The flow control device is configured to expel the fluid to the surrounding environment when the fluid has a predetermined pressure.

[0120] In one embodiment, the flow control device comprises a check valve.

[0121] In one embodiment, the check valve includes a sealing plunger backing an elastomeric valve, the elastomeric valve having a crack pressure equal to the predetermined pressure.

[0122] In one embodiment, the flow control device includes a vent hole extending from an interior channel through the exterior wall, and a plunger movable within the interior channel relative to the vent hole.

[0123] In one embodiment, the catheter includes a spring for biasing the plunger against the vent hole.

[0124] In one embodiment, the catheter includes a pull wire for moving the plunger relative to the vent hole.

[0125] In one embodiment, the flow control device includes a plug having a number of holes for leaking the fluid having the predetermined pressure.

[0126] In one embodiment, the flow control device has a proximal tip, a distal tip movable relative to the proximal tip, and a spring between the proximal and distal tips.

[0127] In one embodiment, the proximal tip is attached to the catheter shaft and the balloon is coupled to the distal tip.

[0128] In one embodiment, the distal tip is slidable over the proximal tip.

[0129] In one embodiment, the distal tip is rotatable on the proximal tip.

[0130] In one embodiment, the distal tip is threadedly coupled to the proximal tip.

[0131] In one embodiment, the distal tip includes a vent hole, the proximal tip includes a fluid port, and the distal tip is movable relative to the proximal tip to align the vent hole with the fluid port.

[0132] In one embodiment, the catheter shaft has a shaft diameter of 5 French or less.

[0133] In one embodiment, a catheter includes a catheter shaft, a balloon, an ultrasound transducer, and a check valve. The catheter shaft has a fluid lumen. The balloon is attached to the catheter shaft and has an interior in fluid communication with the fluid lumen. The ultrasound transducer is in the interior. The check valve has an inlet port for receiving fluid from the fluid lumen passing through the interior. The check valve is configured to expel the fluid to the surrounding environment when the fluid has a predetermined pressure.

[0134] In one embodiment, the check valve includes a sealing plunger backing an elastomeric valve, the elastomeric valve having a crack pressure equal to the predetermined pressure.

[0135] In one embodiment, a catheter includes a catheter shaft, a balloon, an ultrasound transducer, and a flow control device. The catheter shaft has a fluid lumen. The balloon is attached to the catheter shaft and has an interior in fluid communication with the fluid lumen. The ultrasound transducer is in the interior. The flow control device has an inlet port for receiving fluid from the fluid lumen through the interior. In one embodiment, the flow control device includes a vent hole and a plunger. The vent hole extends from an interior channel through an outer wall. The plunger is movable within the interior channel relative to the vent hole. The flow control device is configured to expel the fluid to the surrounding environment.

[0136] In one embodiment, the catheter includes a spring for biasing the plunger against the vent hole.

[0137] In one embodiment, the catheter includes a pull wire for moving the plunger relative to the vent hole.

[0138] In one embodiment, a catheter includes a catheter shaft, a balloon, an ultrasound transducer, and a flow control device. The catheter shaft has a fluid lumen. The balloon is attached to the catheter shaft and has an interior in fluid communication with the fluid lumen. The ultrasound transducer is in the interior. The flow control device has an inlet port for receiving fluid from the fluid lumen through the interior. The flow control device includes a plug with several holes for leaking the fluid to the surrounding environment when the fluid has a predetermined pressure.

[0139] In one embodiment, a catheter includes a catheter shaft, a balloon, an ultrasound transducer, and a flow control device. The catheter shaft has a fluid lumen. The balloon is attached to the catheter shaft and has an interior in fluid communication with the fluid lumen. The ultrasound transducer is in the interior. The flow control device has an inlet port for receiving fluid from the fluid lumen passing through the interior. The flow control device has a proximal tip attached to the catheter shaft, a distal tip coupled to the balloon and movable relative to the proximal tip, and a spring between the proximal tip and the distal tip. The flow control device is configured to expel the fluid to the surrounding environment when the fluid has a predetermined pressure.

[0140] In one embodiment, a catheter includes a catheter shaft, a balloon, an ultrasound transducer, and a flow control device. The catheter shaft has a fluid lumen. The balloon is attached to the catheter shaft and has an interior in fluid communication with the fluid lumen. The ultrasound transducer is in the interior. The flow control device has an inlet port for receiving fluid from the fluid lumen through the interior. The flow control device has a proximal tip, a distal tip movable relative to the proximal tip, and a spring between the proximal tip and the distal tip. The flow control device is configured to expel the fluid to the surrounding environment when the fluid has a predetermined pressure.

[0141] In one embodiment, the distal tip is slidable over the proximal tip.

[0142] In one embodiment, the distal tip is rotatable on the proximal tip.

[0143] In one embodiment, the distal tip is threadedly coupled to the proximal tip.

[0144] In one embodiment, the distal tip includes a vent hole, the proximal tip includes a fluid port, and the distal tip is movable relative to the proximal tip to align the vent hole with the fluid port.

[0145] In one embodiment, a catheter includes a catheter shaft, a balloon, an ultrasound transducer, and a flow control device. The catheter shaft has a fluid lumen. The catheter shaft has a shaft diameter of 5 French or less. The balloon is attached to the catheter shaft and has an interior in fluid communication with the fluid lumen. The ultrasound transducer is in the interior. The flow control device has an inlet port for receiving fluid from the fluid lumen passing through the interior. The flow control device is configured to expel the fluid to the surrounding environment when the fluid has a predetermined pressure.

[0146] In one embodiment, a catheter includes a catheter shaft, a balloon, an ultrasound transducer, and a flow control device. The balloon has an interior. The ultrasound transducer is located in the interior. The catheter shaft includes an outer member having a central lumen, an inner member having a fluid lumen extending through the central lumen for delivering fluid to the interior, and one or more steering wires extending through the central lumen between the inner wall of the outer member and the outer wall of the inner member. The one or more steering wires connect to the outer member or the inner member at an anchor point proximal to the balloon.

[0147] In one embodiment, the one or more steering wires include a first steering wire diametrically opposite a second steering wire.

[0148] In one embodiment, one or more of the first steering wire and the second steering wire include an electrical cable for delivering energy to the ultrasound transducer.

[0149] In one embodiment, the catheter shaft comprises several shaft sections, each having a respective stiffness.

[0150] In one embodiment, the number of shaft sections includes a distal section, a middle section, and a proximal section, wherein each of the distal sections has a stiffness lower than each of the middle sections, and each of the middle sections has a stiffness lower than each of the proximal sections.

[0151] In one embodiment, the inner member has a wall that is thinner in the distal section than in the middle section.

[0152] In one embodiment, an ultrasound-based tissue treatment system comprises the catheter of any of the previous embodiments, a controller, and a connecting cable interconnecting the catheter and the controller.

[0153] In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the invention as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

Claims

1. a catheter shaft having a fluid lumen; a balloon attached to the catheter shaft and having an interior in fluid communication with the fluid lumen; an ultrasonic transducer disposed therein; a flow control device having an inlet port for receiving fluid from the fluid lumen through the interior; Equipped with The flow control device is configured to discharge the fluid to the ambient environment when the fluid has a predetermined pressure. A catheter characterized by:

2. The flow control device includes a check valve. The catheter according to claim 1 .

3. the check valve includes a sealing plunger backed by an elastomeric valve; The elastomeric valve has a crack pressure equal to the predetermined pressure. The catheter according to claim 2 .

4. The flow control device includes a vent hole extending from an interior channel through an exterior wall, and a plunger movable within the interior channel relative to the vent hole. The catheter according to claim 1 .

5. a spring for biasing the plunger against the vent hole; The catheter of claim 4, further comprising:

6. a pull wire for moving the plunger relative to the vent hole; The catheter according to claim 4 or 5, further comprising:

7. The flow control device includes a plug having a plurality of holes for leaking the fluid having the predetermined pressure. The catheter according to claim 1 .

8. The flow control device has a proximal tip, a distal tip movable relative to the proximal tip, and a spring between the proximal tip and the distal tip. The catheter according to claim 1 .

9. the proximal tip is attached to the catheter shaft; The balloon is coupled to the distal tip. The catheter according to claim 8.

10. The distal tip is slidable over the proximal tip.

10. The catheter according to claim 8 or 9.

11. The distal tip is rotatable on the proximal tip.

11. The catheter according to claim 8.

12. The distal tip is threadedly coupled to the proximal tip. The catheter of claim 11.

13. the distal tip includes a vent hole; the proximal tip includes a fluid port; The distal tip is movable relative to the proximal tip to align the vent hole with the fluid port.

13. The catheter according to any one of claims 8 to 12.

14. The catheter shaft has a shaft diameter of 5 French or less.

14. A catheter according to any one of claims 1 to 13.

15. a catheter shaft having a fluid lumen; a balloon attached to the catheter shaft and having an interior in fluid communication with the fluid lumen; an ultrasonic transducer disposed therein; a check valve having an inlet port for receiving fluid from the fluid lumen through the interior; Equipped with The check valve is configured to discharge the fluid to the ambient environment when the fluid has a predetermined pressure. A catheter characterized by:

16. the check valve includes a sealing plunger backed by an elastomeric valve; The elastomeric valve has a crack pressure equal to the predetermined pressure.

16. The catheter of claim 15.

17. a catheter shaft having a fluid lumen; a balloon attached to the catheter shaft and having an interior in fluid communication with the fluid lumen; an ultrasonic transducer disposed therein; a flow control device having an inlet port for receiving fluid from the fluid lumen through the interior; Equipped with the flow control device includes a vent hole extending from an interior channel through an exterior wall, and a plunger movable within the interior channel relative to the vent hole; The flow control device is configured to discharge the fluid into the ambient environment. A catheter characterized by:

18. a spring for biasing the plunger against the vent hole; 18. The catheter of claim 17, further comprising:

19. a pull wire for moving the plunger relative to the vent hole; 19. The catheter according to claim 17 or 18, further comprising:

20. a catheter shaft having a fluid lumen; a balloon attached to the catheter shaft and having an interior in fluid communication with the fluid lumen; an ultrasonic transducer disposed therein; a flow control device having an inlet port for receiving fluid from the fluid lumen through the interior; Equipped with The flow control device includes a plug having a plurality of holes for leaking the fluid into the surrounding environment when the fluid has a predetermined pressure. A catheter characterized by:

21. a catheter shaft having a fluid lumen; a balloon attached to the catheter shaft and having an interior in fluid communication with the fluid lumen; an ultrasonic transducer disposed therein; a flow control device having an inlet port for receiving fluid from the fluid lumen through the interior; Equipped with the flow control device has a proximal tip attached to the catheter shaft, a distal tip coupled to the balloon and movable relative to the proximal tip, and a spring between the proximal tip and the distal tip; The flow control device is configured to discharge the fluid to the ambient environment when the fluid has a predetermined pressure. A catheter characterized by:

22. a catheter shaft having a fluid lumen; a balloon attached to the catheter shaft and having an interior in fluid communication with the fluid lumen; an ultrasonic transducer disposed therein; a flow control device having an inlet port for receiving fluid from the fluid lumen through the interior; Equipped with the flow control device has a proximal tip, a distal tip movable relative to the proximal tip, and a spring between the proximal tip and the distal tip; The flow control device is configured to discharge the fluid to the ambient environment when the fluid has a predetermined pressure. A catheter characterized by:

23. The distal tip is slidable over the proximal tip.

23. The catheter of claim 22.

24. The distal tip is rotatable on the proximal tip.

24. The catheter according to claim 22 or 23.

25. The distal tip is threadedly coupled to the proximal tip.

25. The catheter of claim 24.

26. the distal tip includes a vent hole; the proximal tip includes a fluid port; The distal tip is movable relative to the proximal tip to align the vent hole with the fluid port.

26. A catheter according to any one of claims 22 to 25.

27. a catheter shaft having a fluid lumen; a balloon attached to the catheter shaft and having an interior in fluid communication with the fluid lumen; an ultrasonic transducer disposed therein; a flow control device having an inlet port for receiving fluid from the fluid lumen through the interior; Equipped with the catheter shaft has a shaft diameter of 5 French or less; The flow control device is configured to discharge the fluid to the ambient environment when the fluid has a predetermined pressure. A catheter characterized by:

28. a balloon having an interior; an ultrasonic transducer disposed therein; a catheter shaft having an outer member having a central lumen, an inner member having a fluid lumen extending through the central lumen for delivering fluid thereto, and one or more steering wires extending through the central lumen between an inner wall of the outer member and an outer wall of the inner member; Equipped with The one or more steering wires connect to the outer member or the inner member at anchor points proximal to the balloon. A catheter characterized by:

29. The one or more steering wires include a first steering wire diametrically opposite a second steering wire.

29. The catheter of claim 28.

30. One or more of the first steering wire and the second steering wire includes an electrical cable for delivering energy to the ultrasonic transducer.

30. The catheter of claim 29.

31. the catheter shaft having a plurality of shaft sections; Each shaft section has its own stiffness 31. A catheter according to any one of claims 28 to 30.

32. the plurality of shaft sections include a distal section, a middle section, and a proximal section; a stiffness of each of the distal sections is less than a stiffness of each of the intermediate sections; The stiffness of each of the intermediate sections is less than the stiffness of each of the proximal sections.

32. The catheter of claim 31.

33. the inner member has a wall; The wall is thinner in the distal section than in the middle section.

33. The catheter of claim 32.

34. A catheter according to any one of claims 1 to 33; A controller; a connecting cable interconnecting the catheter and the controller; 1. An ultrasound-based tissue treatment system comprising:

35. a catheter shaft having a fluid lumen; a balloon attached to the catheter shaft and having an interior in fluid communication with the fluid lumen; an ultrasonic transducer disposed therein; a flow control device having an inlet port positioned to receive fluid passing through said interior; Equipped with The flow control device is configured to discharge the fluid to the ambient environment when the fluid has a predetermined pressure. A catheter characterized by:

36. The flow control device comprises: non-return valve, a vent hole extending from the interior channel through the exterior wall, and a plunger movable within the interior channel relative to the vent hole; a plug having a plurality of holes for leaking the fluid having the predetermined pressure; and a proximal tip, a distal tip movable relative to the proximal tip, and a spring between the proximal tip and the distal tip; Contains at least one of 36. The catheter of claim 35.

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