Rotating Cylinder

Abstract

A catheter comprising: a catheter shaft; and a self-rotating ultrasound transducer positioned along a longitudinal axis on a distal region of the catheter shaft, the self-rotating ultrasound transducer having a shape configured to self-rotate about the longitudinal axis when an acoustic radiation force generates a net momentum from a reaction force from the surrounding environment that has a non-zero net torque about the rotation axis of the self-rotating ultrasound transducer.

Description

[Technical Field]

[0001] This application relates generally to ultrasound transducers, and more particularly to self-rotating ultrasound transducers. [Background technology]

[0002] High blood pressure, also known as hypertension, commonly occurs in adults. If left untreated, high blood pressure can lead to kidney disease, arrhythmias, and heart failure. Treatment of high blood pressure focuses on interventional approaches to deactivate the renal nerves surrounding the renal arteries. Intraluminal devices, such as catheters, can reach specific structures, such as renal nerves, that are close to the body cavity through which the catheter passes. Thus, catheter-based systems can deliver energy from within the body cavity to deactivate renal nerves within the blood vessel wall.

[0003] A uniform lesion around a body cavity (e.g., a blood vessel wall) is desired to achieve optimal nerve inactivation at different locations around the blood vessel wall. An ultrasound transducer with a large surface area can be used to transmit a sufficient amount of power in a short time to ensure uniform energy distribution. However, this solution involves stringent manufacturing requirements. Rotating the ultrasound transducer around the body cavity using a preloaded spring / coil, a guidewire, a micromotor, or using the ultrasound transducer as an actuator are methods to achieve cylindrical ablation. However, these methods require the use of an additional motor along with the ultrasound transducer. Therefore, there is a need for a self-rotating ultrasound transducer that can emit energy to form a uniform lesion around a body cavity without using a motor. Summary of the Invention

[0004] The invention is defined in the independent claims. Further embodiments of the invention are defined in the dependent claims.

[0005] The catheter comprises a catheter shaft and a self-rotating ultrasound transducer positioned along a longitudinal axis on a distal region of the catheter shaft, the self-rotating ultrasound transducer having a shape configured to self-rotate about the longitudinal axis when an acoustic radiation force generates a net momentum from a reaction force from the surrounding environment that has a non-zero net torque about the rotation axis of the self-rotating ultrasound transducer.

[0006] A catheter is provided that includes a catheter shaft and a self-rotating ultrasound transducer positioned along a longitudinal axis on a distal region of the catheter shaft, the self-rotating ultrasound transducer having a surface acoustic intensity distribution and configured to self-rotate about the longitudinal axis when acoustic radiation forces generated due to acoustic transmission from the self-rotating ultrasound transducer generate a net momentum from reaction forces from the surrounding environment that have a non-zero net torque about the rotation axis of the self-rotating ultrasound transducer.

[0007] A catheter is provided having a transducer positioned along a longitudinal axis on a distal region of a catheter shaft, and a fixture for mounting the transducer, the fixture being mounted off-center so that the transducer self-rotates about the fixture when acoustic radiation forces generated due to acoustic transmission from the transducer create a net momentum from reaction forces from the surrounding environment that have a non-zero net torque about the transducer's axis of rotation.

[0008] A catheter is provided comprising: a transducer shaped to self-rotate about a post positioned along a longitudinal axis on a distal region of a catheter shaft; first and second rings disposed on either side of the transducer; and a third ring coupled to an outer diameter of the transducer, wherein each of the first and second rings has at least one leg; at least one of the first and second rings is coupled to an inner diameter of the transducer; the third ring is located at the same end of the transducer as at least one of the first and second rings is coupled to the inner diameter of the transducer; and the post is mounted off-center, such that the transducer self-rotates about the post when acoustic radiation forces generated due to acoustic transmission from the transducer generate a net momentum having a non-zero net torque about the axis of rotation of the ultrasound transducer from reaction forces from the surrounding environment.

[0009] A catheter is provided that includes a catheter shaft and an ultrasound transducer positioned along a longitudinal axis on a distal region of the catheter shaft, the cross-sectional shape of the transducer perpendicular to the longitudinal axis being asymmetric about an axis of rotation of the transducer.

[0010] A catheter is provided that includes a catheter shaft and an ultrasound transducer positioned along a longitudinal axis on a distal region of the catheter shaft, wherein, in a non-rotated state, a direction in which acoustic radiation force is emitted from a surface of the ultrasound transducer subtends less than 360 degrees relative to the longitudinal axis of the ultrasound transducer.

[0011] A catheter is provided that includes a catheter shaft and an ultrasound transducer rotatably positioned along a longitudinal axis on a distal region of the catheter shaft, the ultrasound transducer having a transducer surface configured such that transfer of acoustic momentum from the transducer surface to a fluid surrounding the transducer generates an acoustic radiation force that pushes the fluid away from the transducer, resulting in a non-zero net torque acting on the transducer about the longitudinal axis. The catheter may be configured as generally presented herein.

[0012] A method of operating a catheter including a catheter shaft and an ultrasound transducer rotatably positioned along a longitudinal axis on a distal region of the catheter shaft, the ultrasound transducer having a transducer surface, is provided, comprising the steps of energizing the ultrasound transducer to generate an acoustic radiation force that transfers acoustic momentum from the transducer surface to a fluid surrounding the transducer, pushing the fluid away from the transducer and resulting in a non-zero net torque that rotates the transducer about the longitudinal axis. The method may include one or more of the further steps provided herein.

[0013] A computer program product is provided having program code portions that, when executed on a controller, cause the controller to energize the transducer and perform a method or aspect of a method presented herein.

[0014] The above summary does not contain an exhaustive list of all features of the present invention. The present invention includes all systems and methods that may be practiced from all suitable combinations of the various features of the above summary, the various features disclosed in the detailed description below, and the various features particularly pointed out in the claims as filed. Such combinations have certain advantages not specifically recited in the above summary.

[0015] 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]

[0016] [Figure 1] FIG. 1 illustrates an ultrasound-based tissue treatment system, according to one embodiment.

[0017] [Figure 2] FIG. 2 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 3] FIG. 3 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 4] FIG. 4 illustrates acoustic radiation force-based self-rotation of a helical transducer, according to one embodiment.

[0020] [Figure 5A] FIG. 5A shows a perspective view of a helical transducer, according to one embodiment.

[0021] [Figure 5B] FIG. 5B shows a cross-sectional view of the helical transducer shown in FIG. 5A, according to one embodiment.

[0022] [Figure 6] FIG. 6 shows a cross-sectional view of a transducer experiencing rotational momentum generated by acoustic radiation force, according to one embodiment.

[0023] [Figure 7]FIG. 7 shows a perspective view of a helical transducer rotating around a post, according to one embodiment.

[0024] [Figure 8] FIG. 8 shows a detailed view of the helical transducer shown in FIG. 7, according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0025] An ultrasound transducer that self-rotates around the central axis of a blood vessel can uniformly ablate tissue around the blood vessel. Due to the self-rotation mechanism, the transducer simultaneously heats the surrounding tissue uniformly. Due to the self-rotation mechanism, the transducer does not need to have a cylindrical or tubular shape to deliver cylindrical ablation to the tissue around the blood vessel. The ultrasound transducer can be of a regular or irregular shape, or it can be a regular or irregular polygon (e.g., a rectangle, a triangle, a parallelogram, a hexagon, a square, a pentagon, a rectangle, or an ellipse), an oval, or an asymmetric shape in a cross section perpendicular to the longitudinal axis. The ultrasound transducer can be of an enclosed (closed) or non-enclosed (unclosed) shape in a cross section perpendicular to the longitudinal axis. In addition to the transducer shape, the surface acoustic intensity distribution can also cause the transducer to self-rotate. Typically, a larger surface area is desired to maximize energy transfer rate or power output, within the constraints of the application geometry. The rotational speed of a self-rotating ultrasound transducer can be controlled by the transducer geometry and ablation power. These controls can be applied to enhance lesion uniformity.

[0026] FIG. 1 illustrates features of an ultrasound-based tissue treatment system 100, according to one embodiment. Referring to FIG. 1, an ultrasound-based tissue treatment system is shown, according to one embodiment. 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 transmission cartridge 130, and a control mechanism, such as a handheld remote control. However, transducer 111 need not be surrounded by balloon 112.

[0027] 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).

[0028] Referring to Figure 2, 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 of a catheter 102 may be inserted into a body cavity of a subject. In Figure 2, the body cavity is a blood vessel (e.g., a renal artery) having multiple nerves 401 in its outer layer (e.g., adventitial layer). The distal portion 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.

[0029] The ultrasound 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 ultrasound 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 ultrasound 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.

[0030] 2, 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 ultrasound 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 the inner surface of a blood vessel wall 450 of the body cavity, and be in apposition with the inner surface. When balloon 112 is in apposition with the body cavity, or more specifically, the inner circumferential wall of the body cavity, balloon 112 can substantially prevent blood in the body cavity from passing through the balloon.

[0031] In other embodiments, the balloon 112 is configured so that it does not contact the body cavity when inflated. The balloon 112 may surround the ultrasound transducer 111 to cool the ultrasound transducer 111 during sonication, but may not contact or occlude the body cavity, relying instead on blood within the body cavity to cool the cavity. When the balloon 112 surrounds the ultrasound 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.

[0032] 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.

[0033] In another embodiment, the ultrasound transducer 111 is attached to the distal tip of the balloon-less catheter 102. Blood flow provides cooling to both the transducer 111 and the vessel wall. At each end of the ultrasound transducer 111 are basket or coil structures that are used to provide support and centering.

[0034] Referring to FIG. 3 , 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 ultrasound transducer body and may therefore be referred to as a piezoelectric transducer body. The piezoelectric ultrasound transducer body may have a variety of other shapes and need not be hollow. The piezoelectric ultrasound transducer body may have grooves or slots. In a specific embodiment, suitable for renal denervation, for example, the piezoelectric material comprising the piezoelectric ultrasound transducer body is lead zirconate titanate 8 (PZT8), also known as Navy III piezoelectric material. The bare PZT ultrasound 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 ultrasound 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.

[0035] In one embodiment, the ultrasound transducer 111 may be positioned within the interior 506 of the balloon 112. The balloon 112 may have the interior 506 in fluid communication with the 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 ultrasound transducer 111. More specifically, the balloon 112 may house the ultrasound transducer 111 within the interior 506, and the ultrasound transducer 111 may be contacted and cooled by the cooling fluid 403 flowing from the fluid lumen 508 into the interior 506. In other embodiments, the balloon 112 is not present, and the ultrasound transducer 111 is positioned within a body cavity.

[0036] As shown in FIG. 3 , 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. The outer diameter of the ultrasound transducer 111 ranges from approximately 1 to 5 mm. For example, in certain embodiments suitable for renal denervation, the outer diameter of the ultrasound transducer 111 is approximately 1.5 mm, the inner diameter of the ultrasound transducer 111 is approximately 1 mm, and the ultrasound transducer 111 has a length of approximately 6 mm. Ultrasound transducers 111 having other inner diameters, outer diameters, and lengths, or more generally, sizes and shapes, are within the scope of the embodiments described herein. Furthermore, it is noted that the drawings in the figures are not necessarily, and often are not, drawn to scale.

[0037] 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 512 exists between the distal end of the catheter shaft 214 and the proximal end of the ultrasound transducer 111.

[0038] 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 of the ultrasonic transducer 111 (which may be selectively insulated) between the backing member 507 and the inner electrode 504. Thus, the backing member 507 may 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.

[0039] 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. In certain embodiments, the standoff assembly 512 forms a circular seal to establish an airbag for the PZT transducer. In this case, no cooling function is provided at the inner diameter (ID). 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, 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, advantageously eliminating the need to directly couple the cable 230 to the inner electrode 504 of the ultrasonic transducer 111. In other embodiments, the backing member 507 and the standoff assembly 512 are made of one or more electrically insulating materials, or, even if they are made of conductive materials, are coated with one or more electrically insulating materials. In certain embodiments, one or more electrical conductors of the cable 230 are directly coupled (eg, soldered) to the inner electrode 504 of the ultrasonic transducer 111 .

[0040] The backing member 507 may have an insulating tube 520 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 520 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. 3 , the insulating tube 520 may extend through the lumen of the backing member 507 within the ultrasound transducer 111 toward the distal tip 510. In this embodiment, the ultrasound transducer 111 is offset distally from the distal end of the catheter shaft 214.

[0041] 4 illustrates acoustic radiation force-based self-rotation of a helical ultrasonic transducer 111, according to one embodiment. An ultrasound-based tissue treatment system transmits from the ultrasonic transducer 111. As a result of the transfer of acoustic momentum from the transducer surface to the fluid surrounding the transducer, an acoustic radiation force is generated, pushing the fluid away from the transducer surface. Conversely, the fluid exerts a reaction force on the transducer surface. This force is perpendicular (normal) to the transducer surface. The amplitude of this force is proportional to the acoustic power transmitted from the transducer and inversely proportional to the speed of sound in the fluid.

[0042] 4, when the acoustic transducer 111 has a regular symmetric cylindrical shape, an acoustic beam (acoustic radiation force) emitted (transmitted) from the cylindrical ultrasonic transducer 111 generates an acoustic radiation force passing through the center of the cylindrical ultrasonic transducer 111. This is because there is alignment between the radius vector and the surface normal vector, resulting in zero rotational momentum. TIFF2026500466000002.tif6150. Therefore, a cylindrical transducer does not generate self-rotation. Even with different shapes, the total or net rotational momentum When TIFF2026500466000003.tif6150 is zero, there is also no rotation. For example, an enclosed (closed) shape around any central axis with uniform surface acoustic intensity output will not generate rotational momentum.

[0043] When the shape of the ultrasonic transducer 111 is changed to a helical ultrasonic transducer 111, for example, as shown in FIG. 4, the normal force does not pass through the central axis of the helical ultrasonic transducer 111. Instead, there is a deviation (deviation) from the central axis. This deviation (the deviation that the normal force does not pass through the center of the helical ultrasonic transducer 111) generates a torque, causing the ultrasonic transducer 111 to self-rotate. This deviation is illustrated in FIG. 4 by the arrows indicating the rotational component of the reaction force. When the cross-sectional shape of the ultrasonic transducer 111 is asymmetric about the rotational longitudinal axis of the transducer, there is self-rotation of the ultrasonic transducer 111.

[0044] As previously mentioned, the shape of the ultrasonic transducer 111 can be any shape (e.g., rectangular, triangular, oval, spiral) as long as the acoustic radiation force generated due to acoustic transmission from the ultrasonic transducer creates a net momentum from the reaction force from the surrounding environment, resulting in a non-zero net torque about the axis of rotation of the self-rotating ultrasonic transducer 111. The surrounding environment can be blood, water, tissue, or air. The rotational momentum or speed can be controlled by variables such as the shape / parameters of the ultrasonic transducer 111, the sonication / emission power, and the sonication / emission power-time curve (e.g., pulse). When power is emitted from the ultrasonic transducer 111, the ultrasonic transducer 111 self-rotates, and when power is not emitted, the self-rotation stops. The intended therapy for the ultrasound-based system determines the sonication / emission power.

[0045] FIG. 5A shows a perspective view of a helical ultrasound transducer 111 according to one embodiment. The self-rotating ultrasound transducer 111 rotates around a longitudinal axis 300 (center of rotation) of the catheter shaft 214. The longitudinal axis 300 may include a rolling bearing that allows the ultrasound transducer 111 to self-rotate around a fixture such as a post 514 (see FIG. 7). The length of the ultrasound transducer 111 may be any length that serves the therapeutic purpose. In one embodiment, the length of the ultrasound transducer 111 may be 6 mm. The instantaneous power generated to self-rotate the ultrasound transducer 111 may range from 1 to 100 watts. In one embodiment, the range may be 25 to 40 watts per 7 seconds of ultrasound treatment. In yet another embodiment, the range may be 60 to 70 watts per 5 seconds of ultrasound treatment.

[0046] FIG. 5A shows a helical ultrasonic transducer 111. The ultrasonic transducer 111 can have any shape and can be enclosed (closed) or non-enclosed, as long as the acoustic radiation force generated due to acoustic transmission from the ultrasonic transducer generates a net momentum with a net non-zero torque about the ultrasonic transducer's axis of rotation from the reaction forces from the surrounding environment. An enclosed (closed) shape occurs when there are no breaks or openings in the shape (e.g., a helical or cylindrical shape). An unenclosed (unclosed) shape occurs when there are breaks or openings in the shape (e.g., a helical or cylindrical shape). A break or opening in a shape can be achieved when a cut or depression is created in a portion of the ultrasonic transducer 111. For example, a cylindrical transducer can have a cut or depression to make the shape unenclosed. The shape of the ultrasonic transducer 111 can be unenclosed if some portions of the ultrasonic transducer 111 do not contain piezoelectric material, if some portions of the ultrasonic transducer 111 have a different thickness than other portions, if some portions of the ultrasonic transducer 111 are not plated, or if some portions of the ultrasonic transducer 111 have thicker piezoelectric material than other portions. These are examples, and the above list is not exhaustive.

[0047] The unenclosed shape of the ultrasonic transducer 111 affects its efficiency. In other words, when a portion of the shape of the ultrasonic transducer 111 does not operate as efficiently as the rest of the transducer 111, the efficiency of the ultrasonic transducer 111 may be impaired. The efficiency of the ultrasonic transducer 111 is the ratio of the power output to the total power input in the required form. For example, the shape may be composed of two or more ultrasonic transducer pieces, and one ultrasonic transducer piece may be powered at a higher or lower voltage than the other transducer pieces, causing the ultrasonic transducer 111 to self-rotate about the longitudinal axis 300. In one embodiment, the ultrasonic transducers 111 may be arranged in an array configuration rather than a cylindrical configuration. In an array configuration, at least one ultrasonic transducer 111 may be powered at a different voltage than the other ultrasonic transducers 111, causing the ultrasonic transducer 111 to self-rotate.

[0048] FIG. 5B shows a cross-sectional view of the helical ultrasonic transducer shown in FIG. 5A, according to one embodiment. In some embodiments, the backing material 614 can be air or water. In the embodiment shown in FIG. 5B, there is a cross-sectional shape of the transducer perpendicular to the longitudinal axis. A post 514 is a mounting / fixture used to hold the ultrasonic transducer 111. The post 514 is positioned along the longitudinal axis 300. The longitudinal axis 300 can include a rolling bearing. The rolling bearing can be a ball bearing, a cylindrical roller bearing, a spherical roller bearing, a tapered roller bearing, or a needle roller bearing. The rolling bearing can have a rotating electrical contact that passes current between two mechanical components, one of which can rotate relative to the other. These mechanisms can be carbon brush bearings, slip rings, or inductive couplings. When the rotating components are supported by rolling bearings, the rotary electrical contacts are typically an assembly that is separate and electrically isolated from the rolling bearings (see FIG. 8). The post 514 in FIG. 5B can be mounted in any position that allows the ultrasonic transducer 111 to self-rotate, as long as the post 514 is not centrally mounted (i.e., mounted off-center).

[0049] As shown in Figure 6, there is a radial line passing through the axis of rotation. Figure 6 also shows the normal direction to the surface of the ultrasonic transducer 111. If (r, θ) is the position of any point on the outer surface of the transducer, γ is the angle between the radial line and the surface normal vector, P is the total power, I is the time-averaged spatial intensity, and c is the speed of sound, then the rate of increase of radius is The file is TIFF2026500466000004.tif9150.

[0050] During acoustic transmission, the ultrasonic transducer 111 generates an acoustic radiation force that pushes the fluid along the surface normal and away from the surface. Conversely, a reaction force from the fluid pushes against the surface of the ultrasonic transducer. At a given point (r, θ), the force F(r, θ) is given by: The file is TIFF2026500466000005.tif6150.

[0051] The rotational momentum at point (r,θ) generated by the acoustic radiation force is The file is TIFF2026500466000006.tif9150.

[0052] Therefore, the total rotational momentum is The file is TIFF2026500466000007.tif10150.

[0053] FIG. 7 shows a perspective view of a helical transducer 111 rotating around a post 514, according to one embodiment. The transducer 111 rotates around the post 514 using rings 604a, 604b, and 610. Ring 604a has bearings, such as a ring bearing, to allow the transducer 111 to rotate around the post 514, and ring 604a holds the post 514 in place. Ring 604a is soldered to the inner diameter (ID). There are no electrical connections to ring 604a. Rings 610, 604a, and 604b can be made of a low-friction, relatively hard material (e.g., Teflon, Ruland Gold, diamond coating) to allow them to easily rotate around the post 514. The post 514 can be coated with Teflon. The ring 604b is connected to the inner diameter (ID) and rotates around the post 514, as shown in FIG. 8. When the post 514 or central shaft is on a rolling bearing, rotational momentum (M) pushes the ultrasonic transducer 111 to rotate. As can be seen from the above equation, the helix parameter γ and the transducer radius are geometric design parameters that affect momentum generation. Power (P) can be used to control the acceleration and speed of rotation. The ring 610 is connected to the outer diameter (OD) of the transducer 111 by at least one wire, so that it rotates around the post 514 (see FIG. 8). Wires 602a, 602b can be embedded within the post 514 and connect the rings 604b, 610 to a main coaxial cable or cable.

[0054] FIG. 8 shows a detailed view of the helical transducer of FIG. 7, according to one embodiment. The ring 604b has legs 608 connected to the transducer 111 by soldering or conductive epoxy. In the embodiment shown in FIG. 8, there are three legs 608, but any number of legs 608 would work as long as they provide stability to the transducer 111 as it rotates around the post 514. For example, a single leg 608 could be used as long as the rings 604a, 604b hold the transducer 111 in place for rotation and provide mechanical stability. The legs 608 may have different lengths, not necessarily equal to the width of the PZT transducer 111. The legs 608 create a deviation from the central axis (i.e., are mounted off-center), thereby imparting their rotational motion to the rings 604a, 604b.

[0055] Ring 610 is a slip ring having a bearing, such as a ring bearing. For example, ring 604b may contact wire 602a, and ring 610 may contact wire 602b. Ring 610 is also soldered to the outer surface of transducer 111. Ring 610 has an OD electrical connection via wire 602c. Ring 606 is a washer and acts as an insulator. Ring 604b is a slip ring having a bearing, such as a ring bearing. Typically, rings 604b and 610 have a slip ring configuration with brushes made of a carbon material and a slip ring body, where the brushes are conductively connected to the slip ring of the slip ring body. The slip ring may be formed of a metal such as copper or a copper alloy (e.g., bronze, tin bronze, nickel bronze, silver, steel, etc.). The slip ring is connected to the shaft of post 514 by an insulating fastener to form the slip ring body. Conductive brushes are fixedly positioned around the circumference of the slip ring and are held in contact with the surface of the slip ring by spring force. The sliding contacts (brushes) are typically formed of a carbon material, but may also be used in combination with a metal, for example, metallic graphite. Terminals 612 serve as terminations for the wires. In one embodiment, terminals 612 do not have a rotational function.

[0056] 8, when an acoustic radiation force is generated due to acoustic transmission from the self-rotating ultrasonic transducer 111, which generates a net momentum having a net non-zero torque about the axis of rotation of the self-rotating ultrasonic transducer from a reaction force from the surrounding environment, the momentum of the net non-zero torque causes the transducer 111 to rotate about the post 514. When the transducer 111 rotates, the ring 610 rotates with the transducer 111 because they are connected via the wire 602c. The wire 602c is substantially rigid, and the ring 610 is made of a low-friction material, so that when the transducer 111 rotates about the post 514, it pulls the ring 610 along with it. The rotation of the transducer 111 can be changed to either a clockwise or counterclockwise direction about the post 514.

[0057] Ring 610 rotates using a carbon brush ring that makes the electrical connection using wire 602a or wire 602b. Wires 602a, 602b are embedded within post 514. The shaft of post 514 may have two components for ease of assembly. One component may be non-conductive at the connection end, and the other component may be conductive / metallic to provide rigidity to post 514. This allows transducer 111 to rotate freely around post 514. The two components are located at the ends closest to ring 610 and ring 604b. Ring 604b rotates with ring 610 using a carbon brush ring, although inductive coupling or mercury slip rings could also be used as a mechanism.

[0058] In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will be apparent 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, therefore, to be regarded in an illustrative rather than a restrictive sense.

Claims

1. A catheter shaft; a self-rotating ultrasound transducer positioned along a longitudinal axis on a distal region of the catheter shaft; Equipped with The self-rotating ultrasonic transducer has a shape and is configured to self-rotate about the longitudinal axis when an acoustic radiation force generates a net momentum from a reaction force from the surrounding environment that has a non-zero net torque about the rotation axis of the self-rotating ultrasonic transducer. A catheter characterized by:

2. The shape is unenclosed in a cross section perpendicular to the longitudinal axis. The catheter according to claim 1 .

3. The shape includes an array of transducers.

3. The catheter according to claim 1 or 2.

4. the shape is triangular in cross section perpendicular to the longitudinal axis; Each side has a transducer plate 4. The catheter according to claim 1.

5. The shape is an irregular polygon in cross section perpendicular to the longitudinal axis.

4. The catheter according to claim 1.

6. The shape is cylindrical 6. The catheter according to claim 1.

7. The shape is helical in a cross section perpendicular to the longitudinal axis.

4. The catheter according to claim 1.

8. The first diameter of the spiral is smaller than the second diameter of the spiral. The catheter according to claim 7.

9. The cylinder has grooves The catheter according to claim 6.

10. The cylinder has a slot 10. The catheter according to claim 6 or 9.

11. The surrounding environment comprises water.

11. The catheter according to claim 1.

12. The ambient environment comprises air.

11. The catheter according to claim 1.

13. The surrounding environment comprises blood.

11. The catheter according to claim 1.

14. The longitudinal axis has a rolling bearing 14. A catheter according to any one of claims 1 to 13.

15. The self-rotating transducer has a length of about 6 mm.

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

16. The self-rotating transducer has an outer diameter of about 1.5 mm.

16. A catheter according to any one of claims 1 to 15.

17. The self-rotating transducer has an inner diameter of about 1 mm.

17. A catheter according to any one of claims 1 to 16.

18. The self-rotating transducer rotates in a power range of 10 to 60 watts.

18. A catheter according to any one of claims 1 to 17.

19. The power range is 25 to 40 watts 19. The catheter of claim 18.

20. balloon 20. The catheter of claim 1, further comprising:

21. The balloon surrounds the self-rotating transducer.

21. The catheter of claim 20.

22. The acoustic radiation force is generated due to acoustic emission from the self-rotating ultrasonic transducer.

22. A catheter according to any one of claims 1 to 21.

23. A catheter shaft; a self-rotating ultrasound transducer positioned along a longitudinal axis on a distal region of the catheter shaft; Equipped with The self-rotating ultrasonic transducer has a surface acoustic intensity distribution and is configured to self-rotate about the longitudinal axis when an acoustic radiation force generated due to acoustic transmission from the self-rotating ultrasonic transducer generates a net momentum from a reaction force from the surrounding environment having a non-zero net torque about a rotation axis of the self-rotating ultrasonic transducer. A catheter characterized by:

24. The ultrasonic transducer is unenclosed in a cross section perpendicular to the longitudinal axis.

24. The catheter of claim 23.

25. The ultrasonic transducer includes an array of transducers.

25. The catheter according to claim 23 or 24.

26. the ultrasonic transducer is triangular in cross section perpendicular to the longitudinal axis; Each side has a transducer plate 26. A catheter according to any one of claims 23 to 25.

27. The ultrasonic transducer is an irregular polygon in cross section perpendicular to the longitudinal axis.

26. A catheter according to any one of claims 23 to 25.

28. The ultrasonic transducer is cylindrical.

28. A catheter according to any one of claims 23 to 27.

29. The ultrasonic transducer is helical in cross section perpendicular to the longitudinal axis.

26. A catheter according to any one of claims 23 to 25.

30. The first diameter of the spiral is smaller than the second diameter of the spiral.

30. The catheter of claim 29.

31. The cylinder has grooves 29. The catheter of claim 28.

32. The cylinder has a slot 32. The catheter of claim 28 or 31.

33. The surrounding environment comprises water.

33. A catheter according to any one of claims 23 to 32.

34. The ambient environment comprises air.

33. A catheter according to any one of claims 23 to 32.

35. The surrounding environment comprises blood.

33. A catheter according to any one of claims 23 to 32.

36. The longitudinal axis has a rolling bearing 36. A catheter according to any one of claims 23 to 35.

37. The ultrasonic transducer has a length of about 6 mm.

37. A catheter according to any one of claims 23 to 36.

38. The ultrasonic transducer has an outer diameter of about 1.5 mm.

38. A catheter according to any one of claims 23 to 37.

39. The ultrasonic transducer has an inner diameter of about 1 mm.

39. A catheter according to any one of claims 23 to 38.

40. The ultrasonic transducer rotates in a power range of 10 to 60 watts.

40. A catheter according to any one of claims 23 to 39.

41. The power range is 25 to 40 watts 41. The catheter of claim 40.

42. balloon 42. The catheter of claim 23, further comprising:

43. The balloon surrounds the self-rotating transducer.

43. The catheter of claim 42.

44. a transducer positioned along the longitudinal axis on the distal region of the catheter shaft; a fixture for mounting the transducer; Equipped with The fixture is mounted off-center so that the transducer self-rotates about the fixture when acoustic radiation forces generated due to acoustic transmission from the transducer create a net momentum from reaction forces from the surrounding environment that have a non-zero net torque about the transducer's axis of rotation. A catheter characterized by:

45. The transducer is an ultrasonic transducer.

45. The catheter of claim 44.

46. a transducer configured to self-rotate about a post positioned along a longitudinal axis on a distal region of the catheter shaft; first and second rings disposed on either side of the transducer; a third ring coupled to an outer diameter of the transducer; Equipped with each of the first and second rings having at least one leg; At least one of the first and second rings is coupled to an inner diameter of the transducer; the third ring is located at the same end of the transducer as at least one of the first and second rings is coupled to the inner diameter of the transducer; The post is mounted off-center so that the transducer self-rotates about the post when acoustic radiation forces generated due to acoustic transmission from the transducer create a net momentum with a non-zero net torque about the axis of rotation of the ultrasonic transducer from reaction forces from the surrounding environment. A catheter characterized by:

47. The shape is unenclosed in a cross section perpendicular to the longitudinal axis.

47. The catheter of claim 46.

48. The shape includes an array of transducers.

48. A catheter according to claim 46 or 47.

49. the shape is triangular in cross section perpendicular to the longitudinal axis; Each side has a transducer plate 49. A catheter according to any one of claims 46 to 48.

50. The shape is an irregular polygon in cross section perpendicular to the longitudinal axis.

49. A catheter according to any one of claims 46 to 48.

51. The shape is cylindrical 51. A catheter according to any one of claims 46 to 50.

52. The shape is helical in a cross section perpendicular to the longitudinal axis.

49. A catheter according to any one of claims 46 to 48.

53. The transducer is an ultrasonic transducer.

53. A catheter according to any one of claims 46 to 52.

54. One ring of the set of rings is a slip ring 54. A catheter according to any one of claims 46 to 53.

55. The slip ring has a bearing.

55. The catheter of claim 54.

56. The third ring is a slip ring.

54. A catheter according to any one of claims 46 to 53.

57. The slip ring has a bearing.

57. The catheter of claim 56.

58. The set of rings has legs of different lengths 58. A catheter according to any one of claims 46 to 57.

59. A catheter shaft; an ultrasound transducer positioned along a longitudinal axis on a distal region of the catheter shaft; Equipped with The cross-sectional shape of the transducer perpendicular to the longitudinal axis is asymmetric about the axis of rotation of the transducer. A catheter characterized by:

60. The axis of rotation is off-center 60. The catheter of claim 59.

61. A catheter shaft; an ultrasound transducer positioned along a longitudinal axis on a distal region of the catheter shaft; Equipped with In a non-rotating state, the direction in which acoustic radiation force is emitted from the surface of the ultrasonic transducer is less than 360 degrees with respect to the longitudinal axis of the ultrasonic transducer. A catheter characterized by:

62. balloon 62. The catheter of claim 61 further comprising:

63. The ultrasonic transducer has a length of about 6 mm.

63. A catheter according to claim 61 or 62.

64. The ultrasonic transducer has an outer diameter of about 1.5 mm.

64. A catheter according to any one of claims 61 to 63.

65. The ultrasonic transducer has an inner diameter of about 1 mm.

65. A catheter according to any one of claims 61 to 64.

66. A catheter shaft; an ultrasound transducer rotatably positioned along a longitudinal axis on a distal region of the catheter shaft; Equipped with The ultrasonic transducer has a transducer surface and is configured such that transfer of acoustic momentum from the transducer surface to a fluid surrounding the transducer produces an acoustic radiation force that pushes the fluid away from the transducer and results in a non-zero net torque acting on the transducer about the longitudinal axis. A catheter characterized by:

67. a catheter shaft; and an ultrasound transducer rotatably positioned along a longitudinal axis on a distal region of the catheter shaft, the ultrasound transducer having a transducer surface. A method of operating the energizing the ultrasonic transducer to generate an acoustic radiation force that transfers acoustic momentum from the transducer surface to a fluid surrounding the transducer, pushing the fluid away from the transducer and resulting in a non-zero net torque that rotates the transducer about the longitudinal axis. A method comprising:

68. Program code part A computer program product comprising: The program code portion, when executed on a controller, causes the controller to energize the transducer to perform the method of claim 67.

1. A computer program product comprising:

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