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 wherein the self-rotating ultrasound transducer is configured to self- rotate around the longitudinal axis when an acoustic radiation force generates a net momentum from reactive forces from a surrounding environment that has a net non-zero torque around a rotation axis of the self-rotating ultrasound transducer.

Description

ROTATING CYLINDERBACKGROUNDFIELD

[0001] This application relates generally to ultrasonic transducers and in particular, self-rotating ultrasonic transducers.BACKGROUND INFORMATION

[0002] High blood pressure, also known as hypertension, commonly affects adults. Left untreated, hypertension can result in renal disease, arrhythmias, and heart failure. Treatment of hypertension has focused on interventional approaches to inactivate the renal nerves surrounding a renal artery. Intraluminal devices, such as catheters, may reach specific structures, such as the renal nerves, that are proximate to the lumens in which the catheters travel. Accordingly, catheter-based systems can deliver energy from within the lumens to inactivate the renal nerves in the vessel walls.

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

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

[0005] 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 wherein the self-rotating ultrasound transducer is configured to self-rotate around the longitudinal axis when an acoustic radiation force generates a net momentum from reactive forces from a surrounding environment that has a net non-zero torque around a rotation axis of the self-rotating ultrasound transducer.

[0006] There is 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 surface acoustic intensity distribution, wherein the self-rotating ultrasound transducer is configured to self-rotate around the longitudinal axis when an acoustic radiation force generated due to acoustic transmission from the self-rotating ultrasound transducer thereby generates a net momentum from reactive forces from a surrounding environment that has a net non-zero torque around a rotation axis of the self-rotating ultrasound transducer.

[0007] There is a catheter comprising a transducer positioned along a longitudinal axis on a distal region of a catheter shaft, a fixture for mounting the transducer, wherein the fixture is mounted off-centered whereby the transducer self-rotates around the fixture when an acoustic radiation force generated due to acoustic transmission from the transducer thereby generates a net momentum from reactive forces from a surrounding environment that has a net non-zero torque around a rotation axis of the transducer.

[0008] There is a catheter comprising a transducer having a shape that self-rotates about a post positioned along a longitudinal axis on a distal region of a catheter shaft, a first and second ring arranged on each side of the transducer, wherein each ring comprises at least one leg and at least one of the rings is coupled to an ID of the transducer, and a third ring coupled to an OD of the transducer, the third ring located at a same end of the transducer where at least one of the rings is coupled to the ID of the transducer, and wherein the post is mounted off-centered causing the transducer to self-rotate around the post when an acoustic radiation force generated due to acoustic transmission from the transducer thereby generates a net momentum from reactive forces from a surrounding environment that has a net non-zero torque around a rotation axis of the ultrasound transducer.

[0009] There is a catheter comprising a catheter shaft and an ultrasound transducer positioned along a longitudinal axis on a distal region of the catheter shaft, wherein a cross-sectional shape of the transducer perpendicular to the longitudinal axis is asymmetrical about a rotation axis of the transducer.

[0010] There is a catheter comprising a catheter shaft and an ultrasound transducer positioned along a longitudinal axis on a distal region of the catheter shaft, wherein in a non-rotating state, a direction in which acoustic radiation forces are transmitted from a surface of the ultrasound transducer is less than 360 degrees with respect to a longitudinal axis of the ultrasound transducer.

[0011] There is a catheter comprising a catheter shaft and an ultrasound transducer rotatably positioned along a longitudinal axis on a distal region of the catheter shaft, wherein the ultrasound transducer has a transducer surface and is configured for a transfer of an acoustic momentum from the transducer surface to a fluid surrounding the transducer to generate an acoustic radiation force that pushes the fluid away from the transducer and causes a net non-zero torque acting on thetransducer around the longitudinal axis. The catheter may be configured as generally presented herein.

[0012] There is a method of operating a catheter comprising a catheter shaft and an ultrasound transducer rotatably positioned along a longitudinal axis on a distal region of the catheter shaft, wherein the ultrasound transducer has a transducer surface, wherein the method comprises energizing the ultrasound transducer to transfer an acoustic momentum from the transducer surface to a fluid surrounding the transducer to generate an acoustic radiation force that pushes the fluid away from the transducer and causes a net non- zero torque that rotates the transducer around the longitudinal axis. The method may comprise one or more further steps as presented herein.

[0013] There is a computer program product comprising program code portions that, when executed on a controller, cause the controller to energize the transducer to perform the method and method aspects presented herein.

[0014] The above summary does not include an exhaustive list of all aspects of the present invention. It is contemplated that the invention includes all systems and methods that can be practiced from all suitable combinations of the various aspects summarized above, as well as those disclosed in the Detailed Description below and particularly pointed out in the claims filed with the application. Such combinations have particular advantages not specifically recited in the above summary.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The various features of the present disclosure and the manner of attaining them will be described in greater detail with reference to the following description, claims, and drawings,wherein reference numerals are reused, where appropriate, to indicate a correspondence between the referenced items, and wherein:

[0016] FIG. 1 illustrates an ultrasound-based tissue treatment system, in accordance with an embodiment.

[0017] FIG. 2 illustrates a perspective view of selected components of the ultrasound-based tissue treatment system introduced in FIG. 1 , inserted into a body lumen, in accordance with an embodiment.

[0018] FIG. 3 illustrates a longitudinal cross-sectional view of a distal portion of a catheter of an ultrasound-based tissue treatment system, in accordance with an embodiment.

[0019] FIG. 4 illustrates acoustic radiation force based self-rotation of a spiral-shaped transducer, in accordance with an embodiment.

[0020] FIG. 5A illustrates a perspective view of a spiral-shaped transducer, in accordance with an embodiment.

[0021] FIG. 5B illustrates a cross-sectional view of a spiral-shaped transducer shown in FIG.5A, in accordance with an embodiment.

[0022] FIG. 6 illustrates a cross-sectional view of a transducer experiencing rotational momentum generated by acoustic radiation force, in accordance with an embodiment.

[0023] FIG. 7 illustrates a perspective view of a spiral-shaped transducer rotating about a post, in accordance with an embodiment.

[0024] FIG. 8 illustrates a detail view of the spiral-shaped transducer in FIG. 7, in accordance with an embodiment.DETAILED DESCRIPTION

[0025] A self-rotating ultrasound transducer around a vessel center axis can uniformly ablate tissue around a vessel. The transducer simultaneously heats the surrounding tissues uniformlybecause of the self-rotating mechanism. It is not necessary for the transducer to have a cylindrical or tube shape to be able to deliver cylindrical ablation to the tissues around the vessel because of the self-rotating mechanism. The ultrasound transducer can be a regular or irregular shape or the ultrasound transducer can be a regular or irregular polygon (e.g., rectangular, triangular, parallelogram, hexagon, square, pentagon, quadrilateral, or ellipse), oval or asymmetrical shape in cross-section perpendicular to the longitudinal axis. The ultrasound transducer can be an enclosed or non-enclosed shape in cross-section perpendicular to the longitudinal axis. In addition to the shape of the transducer, the surface acoustic intensity distribution can also cause a transducer to self-rotate. A larger surface area is typically desired within the application geometry constraints to maximize the energy transfer rate or power output. The rotation speed of the self-rotating ultrasound transducer can be controlled by the transducer geometries 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, in accordance with an embodiment. Referring to FIG. 1 , an ultrasound-based tissue treatment system is shown in accordance with an embodiment. The tissue treatment system 100 is shown as including a catheter 102, a controller 120, and a connection cable 140. In certain embodiments, the 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. However, it is not necessary for the transducer 111 to be surrounded by a balloon 112.

[0027] The controller 120 is shown as being connected to the catheter 102 through the cartridge 130 and the connection 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 can be made from, e.g., nylon, a polyimide film, a thermoplastic elastomer (such as those marked under the trademark PEBAX™), a medical-grade thermoplasticpolyurethane elastomer (such as Pellethane®, Isothane®, or other suitable polymers or any combination thereof), but is not limited thereto.

[0028] Referring to FIG. 2, a perspective view of an ultrasound-based tissue treatment system inserted into a body lumen is shown in accordance with an embodiment. Components of the distal portion of the catheter 102 may be inserted into a body lumen of a subject. In FIG. 2, the body lumen is a blood vessel (e.g., a renal artery) that has a plurality of nerves 401 in an outer layer (e.g., adventitia layer) of the blood vessel. The distal portion may include the ultrasound transducer 111, the balloon 112 filled with a cooling fluid 403, the catheter shaft 214, and / or a guidewire support tip 404 configured to receive a guidewire 406.

[0029] The ultrasound transducer 111 may be disposed partially or completely within the balloon 112, which may be inflated with a cooling fluid 403 so as to contact the interior surface (e.g., intima) of the body lumen. In certain embodiments, the ultrasound transducer 111 may be used to output an acoustic signal when the balloon 112 fully occludes a body lumen of a target vessel 200. The balloon 112 may center the ultrasound transducer 111 within the body lumen. In certain embodiments, e.g., suitable for renal denervation, the balloon 112 is inflated while inserted in the body lumen of the patient during a procedure at a working pressure of about 10 to about 30 psi using the cooling fluid 403. The balloon 112 may be or include a compliant, semi-compliant or non -compliant medical balloon. The balloon 112 is sized for insertion in the body lumen and, in the case of insertion into the renal artery, for example, the balloon 112 may be selected from available sizes including outer diameters of 3.5, 4.2, 5, 6, 7, or 8 mm, but not limited thereto.

[0030] In some embodiments, as shown in FIG. 2, when inflated by being filled with the cooling fluid 403 under the control of the controller 120, the outer wall of the balloon 112 may be generally parallel with the outer surface of the ultrasound transducer 111. Optionally, the balloon 112 may be inflated sufficiently as to be in apposition with the body lumen. For example, wheninflated, the balloon 112 may at least partially contact, and thus be in apposition with, an inner surface of a vessel wall 450 of the body lumen. When the balloon 112 is in apposition with the body lumen, and more specifically the interior circumferential wall of the body lumen, the balloon 112 can substantially stop blood within the body lumen from following past the balloon.

[0031] In other configurations, the balloon 112 is configured not to contact the body lumen when expanded. The balloon 112 may surround the ultrasound transducer 111 in order to cool the ultrasound transducer 111 during sonications, but the balloon may not contact or occlude the body lumen, and the blood within the body lumen may be relied upon to cool the body lumen instead of the cooling fluid. When the balloon 112 surrounds the ultrasound transducer 111, but the balloon does not contact or occlude the body lumen, the balloon 112 may be non-compliant. In certain embodiments, the balloon 112 comprises nylon.

[0032] For a blood vessel that matches the balloon diameter, the non-compliant balloon (e.g., 112) can act as the centering mechanism. The cooling of the vessel wall can be managed by a cooling system of the generator by flowing water or other cooling fluid, such as dextrose or saline, through the balloon if necessary. A non-compliant balloon advantageously offers tighter control of balloon design. The non-compliant balloon (e.g., 112) may be advantageously constructed such that the balloon surface, which is without wrinkles when under inflation, does not interfere with sonication, and holds the desired shape. Additionally, or alternatively, the balloon 112 may be maintained at a specified size by pushing cooling fluid through and / or pulling cooling fluid out of the balloon 112 at a specified flow rate.

[0033] In another embodiment, the ultrasound transducer 111 is mounted on a distal tip of a catheter 102 without a balloon. The blood flow provides cooling for both the transducer 111 and the vessel wall. There is a basket or a coil structure on each of the two ends of the ultrasound transducer111 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 in accordance with an embodiment. The ultrasound transducer 111 may include a cylindrical hollow tube made of a piezoelectric material (e.g., lead zirconate titanate (PZT), etc.), with inner and outer electrodes 502, 504 disposed on the inner and outer surfaces of the cylindrical tube, respectively. Such a cylindrical hollow tube of piezoelectric material is an example of, and thus can be referred to as, a piezoelectric ultrasound transducer body. The piezoelectric ultrasound transducer body can have various other shapes and need not be hollow. The piezoelectric ultrasound transducer body can comprise a groove or a slot. In certain embodiments suitable, e.g., for renal denervation, the piezoelectric material, of which the piezoelectric ultrasound transducer body is made, is lead zirconate titanate 8 (PZT8), which is also known as Navy III Piezo Material. Raw PZT ultrasound transducers may be plated with layers of copper, nickel and / or gold to create electrodes on surfaces (e.g., the inner and outer surfaces) of the piezoelectric ultrasound transducer body. Application of a voltage and alternating current across inner and outer electrodes 502, 504 causes the piezoelectric material to vibrate transverse to the longitudinal direction of the cylindrical tube and radially emit ultrasonic waves.

[0035] In an embodiment, the ultrasound transducer 111 can be positioned within an interior 506 of the balloon 112. The balloon 112 can have the interior 506 in fluid communication with a fluid lumen 508 of the catheter shaft 214. The fluid lumen 508 can convey cooling fluid 403 into the interior 506 to cool the ultrasound transducer 111. More particularly, the balloon 112 can contain the ultrasound transducer 111 within the interior 506 such that the ultrasound transducer 111 is contacted and cooled by cooling fluid 403 that passes into the interior 506 from the fluid lumen 508. In other embodiments, there is no balloon 112 and the ultrasound transducer 111 is positioned in the body lumen.

[0036] As shown in FIG. 3, the ultrasound transducer 111 can be generally supported via a backing member or post 507. In certain embodiments, the backing member 507 comprises stainless steel coated with nickel and gold, wherein nickel is used as a bonding material between the stainless steel and gold plating. The range of the outer diameter of the ultrasound transducer 111 is about 1 - 5 mm. In certain embodiments suitable, e.g., for renal denervation, an outer diameter of the ultrasound transducer 111 is about 1.5 mm, an inner diameter of the ultrasound transducer 111 is about 1 mm, and the ultrasound transducer 111 has a length of about 6 mm. Ultrasound transducers 111 having other inner diameters, outer diameters, and lengths, and more generally dimensions and shapes, are also within the scope of the embodiments described herein. Further, it is noted that the drawings in the figures are not necessarily drawn to scale, and often are not drawn to scale.

[0037] The backing member 507 may extend from the distal portion of the catheter shaft 214 to a 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 moveably coupled to the distal portion of the catheter shaft 214 via the electrical cabling 230. In other embodiments, there is a gap 512 between the distal end of the catheter shaft 214 and the proximal end of the ultrasound transducer 111.

[0038] In order to permit liquid cooling along both the inner and outer electrodes 502, 504, the backing member 507 may include one or more stand-off assemblies 512. The stand-off assemblies 512 may define one or more annular openings through which cooling fluid 403 may enter the space of the ultrasound transducer 111 (which may be selectively insulated) between the backing member 507 and the inner electrode 504. Accordingly, the backing member 507 may serve 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] In accordance with certain embodiments, the stand-off assemblies 512 are electrically conductive, so as to electrically couple the inner electrode 504 of the ultrasound transducer 111 to the backing member 507. In certain embodiments, stand-off assemblies 512 form a circular seal to establish an air-back for the PZT transducer. As such, no cooling is provided for the ID. One or more conductors of the electrical cabling 230 may be electrically coupled to the backing member 507. Thus, as the controller 120 is activated, current may be delivered from the electrical cabling 230 to the inner electrode 504 of the ultrasound transducer 111 via the backing member 507 and the stand-off assemblies 512, which advantageously eliminates the need to couple the cabling 230 directly to the inner electrode 504 of the ultrasound transducer 111. In other embodiments, the backing member 507 and the stand-off assemblies 512 are made of one or more electrical insulator material(s), or if made of an electrically conductive material(s) are coated with one or more electrical insulator material(s). In certain embodiments, one or more electrical conductors of the cabling 230 are directly coupled (e.g., soldered) to the inner electrode 504 of the ultrasound transducer 111.

[0040] The backing member 507 may have an isolation tube 520 disposed along its interior surface to prevent or reduce the likelihood of electrical conduction between the guidewire 406 and the backing member 507, for use in embodiments where such an electrical conduction is not desired. The isolation tube 520 can be formed of a non-electrically conductive material (e.g., a polymer, such as polyimide), which can also be referred to as an electrical insulator. As illustrated in FIG. 3, the isolation tube 520 may extend through the lumen of the backing member 507 within the ultrasound transducer 111 toward the distal tip 510. In this manner, the ultrasound transducer 111 is distally offset from the distal end of the catheter shaft 214.

[0041] FIG. 4 illustrates acoustic radiation force based self-rotation of a spiral-shaped ultrasound transducer 111 , in accordance with an embodiment. The ultrasound-based tissuetreatment system transmits from an ultrasound transducer 111. Acoustic radiation force is generated to push the fluid away from the transducer surface as a result of acoustic momentum transfer from the transducer surface to the fluid surrounding the transducer. Reciprocally, the fluid exerts a reactant force on the transducer surface. This force is normal or perpendicular to the transducer surface. This force amplitude is proportional to the acoustic power transmitted from the transducer and inversely proportional to the speed of sound of the fluid.

[0042] According to FIG. 4, when the acoustic transducer 111 has a normal symmetrical cylindrical shape the acoustic beams (acoustic radiation force) transmitted from the cylindrical ultrasound transducer 111, produce acoustic radiation forces going through the center of the cylindrical ultrasound transducer 111. This leads to the rotational momentum F(0, z) being zero due to the alignment in direction between the radius vectors and surface normal vectors. Thus, a cylindrical transducer does not generate self-rotation. In a different shape, when the summation or the net rotational momentumis zero, there is no rotation either. For example, any enclosed shape around the central axis with uniform surface acoustic intensity output generates no rotational momentum.

[0043] When the shape of the ultrasound transducer 111 is changed, for example, to a spiralshaped ultrasound transducer 111, as illustrated in FIG. 4, the normal forces do not pass through the central axis of the spiral- shaped ultrasound transducer 111. Instead, there is a deviation from the central axis. This deviation, where the normal forces do not pass through the center of the spiralshaped ultrasound transducer 111, creates torque and causes the ultrasound transducer 111 to selfrotate. This deviation is illustrated in FIG. 4 by the arrows showing the rotation component of the reactive force. There is self-rotation of the ultrasound transducer 111 when the cross-sectional shape of the ultrasound transducer 111 is asymmetrical about a rotational longitudinal axis of the transducer.

[0044] As mentioned above, the shape of the ultrasound transducer 111 can be any shape (e.g., rectangular, triangular, oval, spiral), so long as the acoustic radiation force generated due to acoustic transmission from the ultrasound transducer thereby generating a net momentum from reactive forces from a surrounding environment has a net non-zero torque around the rotation axis of the self-rotating ultrasound transducer 111. The surrounding environment can be blood, water, tissue, or air. Rotational momentum or speed can be controlled by variables such as shape / parameters of the ultrasound transducer 111, sonication / emission power, sonication / emission power-time curve, e.g., pulsing. As power is emitted from the ultrasound transducer 111, the ultrasound transducer 111 self-rotates, and self-rotation stops when power is not emitted. The therapy intended for the ultrasound-based system determines the sonication / emission power.

[0045] FIG. 5 A illustrates a perspective view of a spiral-shaped ultrasound transducer 111, in accordance with an 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 can comprise rolling bearings that allow 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 can be any length so long as it serves the therapy purpose. In an embodiment, the length of the ultrasound transducer 111 can be 6 mm. The instantaneous power generated to self-rotate the ultrasound transducer 111 can be in the range of 1 - 100 Watts. In an embodiment, the range can be 25-40 Watts per 7 seconds of ultrasound treatment. In yet another embodiment, the range can be 60-70 Watts per 5 seconds of ultrasound treatment.

[0046] Although FIG. 5 A illustrates a spiral-shaped ultrasound transducer 111. The ultrasound transducer 111 can comprise any shape or the ultrasound transducer 111 can be enclosed or nonenclosed, so long as when an acoustic radiation force generated due to acoustic transmission from the ultrasound transducer generates a net momentum from reactive forces from a surroundingenvironment that has a net non-zero torque around the rotation axis of the ultrasound transducer111. An enclosed shape occurs when there is no break / opening in the shape (e.g., spiral, cylinder). A non-enclosed shape occurs when there is a break / opening in the shape (e.g., spiral, cylinder). A break / opening in the shape can be accomplished when a nick or a dent is created on a portion of the ultrasound transducer 111. For example, a nick or dent can be made on a cylindrical transducer to make its shape non-enclosed. The shape of the ultrasound transducer 111 can be non-enclosed when a portion of the ultrasound transducer 111 does not comprise piezoelectric material, a portion of the ultrasound transducer 111 has a different thickness than another portion, a portion of the ultrasound transducer 111 is not plated, or a portion of the ultrasound transducer has a thicker piezoelectric material than another portion. These are examples and the list is not meant to be exhaustive.

[0047] The non-enclosed shape of the ultrasound transducer 111 affects its efficiency. In other words, the efficiency of the ultrasound transducer 111 can be destroyed when a portion of the shape of the ultrasound transducer I l l is not operating as efficiently as the rest of the transducer 111.The efficiency of an ultrasound transducer 111 is the ratio of the power output in the required form to the total power input. For example, the shape can comprise of two or more ultrasound transducer pieces, wherein one ultrasound transducer piece is powered at a higher or lower voltage than another transducer piece, causing the ultrasound transducer 111 to self-rotate around the longitudinal axis 300. In an embodiment, the ultrasound transducer 111 can be arranged in an array configuration rather than a cylindrical shape. With an array configuration, at least one ultrasound transducer 111 can be powered at a different voltage than the other ultrasound transducers 111, causing the ultrasound transducer 111 to self-rotate.

[0048] FIG. 5B illustrates a cross-sectional view of a spiral-shaped ultrasound transducer 111 shown in FIG. 5A, in accordance with an embodiment. In some embodiments, the backingmaterial 614 can be air or water. In an embodiment as illustrated in FIG. 5B, there is a crosssectional shape of the transducer perpendicular to the longitudinal axis. A post 514 is a mounting piece / fixture and used to hold the ultrasound transducer 111. The post 514 is positioned along the longitudinal axis 300. The longitudinal axis 300 can comprise a rolling bearing. The rolling bearing can be balls, cylindrical rollers, spherical rollers, tapered rollers, or needle rollers. The rolling bearing can comprise rotating electrical contacts to cause electrical current to be passed between two mechanical components, one of which is rotationally movable in relation to the other. These mechanisms can be a carbon brush bearing, slip ring, or inductive coupling. When the rotary component is supported by a rolling bearing, the rotating electrical contacts are generally assemblies separated and insulated electrically from the rolling bearing (See FIG. 8). The post 514 in FIG. 5B, can be mounted in any location for the ultrasound transducer 111 to self-rotate, so long as the post 514 is not mounted in the center (i.e., off-the-center mount).

[0049] As illustrated in FIG. 6, there are radial lines passing the rotation axis. FIG. 6 also illustrates the normal direction of the ultrasound transducer 111 surface. Assuming (r, 0) is the position of any point on the transducer outer surface, y is the angle between the radial line and surface normal vector, P is the total power, I is the temporal average spatial intensity, and c is the speed of sound, thus:The rate of radius increase is:

[0050] During acoustic transmission, the ultrasound transducer 111 generates an acoustic radiation force, which pushes the fluid away from the surface along the surface normal.Conversely, the reactant forces from the fluid pushes the ultrasound transducer surface. At any given point (r,0), the force F (r,0), is:F(r,0) = / (0) / c

[0051] The rotational momentum at (r,0) generated by the acoustic radiation force is:

[0052] Thus, the total rotational momentum is: ■ tcmy)

[0053] FIG. 7 illustrates a perspective view of a spiral-shaped transducer 111 rotating about a post 514, in accordance with an embodiment. The transducer 111 rotates about the post 514 using rings 604a, 604b, and 610. Ring 604a comprises bearings, such as ring bearings, to allow the transducer 111 to rotate about the post 514 and the ring 604a holds the post 514 in place. Ring 604a is soldered to the ID. There exist no electrical connections at ring 604a. The rings 610, 604a, 604b can be made of low-friction, relatively hard materials (e.g., Teflon, Ruland gold, diamond coated) so that it can easily rotate about the post 514. The post 514 can be coated with Teflon. Ring 604b is connected to the ID as shown in FIG. 8 and rotates about the post 514. When the post 514 or central axis is on a rolling bearing, the rotational momentum (M) pushes the ultrasound transducer 111 to rotate. As shown above from the equation, the spiral parameter y and the transducer radius are geometric design parameters that impact the generation of momentum. Power (P) can be used to control rotational acceleration and speed. Ring 610 rotates about the post 514 because it is connected by at least one wire to the transducer 111 OD (as shown in FIG. 8). Wires 602a, 602b can be embedded in the post 514 and connect rings 604b, 610 to the main coax or cable.

[0054] FIG. 8 illustrates a detail view of the spiral-shaped transducer in FIG. 7, in accordance with an embodiment. Ring 604b comprises legs 608, which are connected to the transducer 111 by soldering or conductive epoxy. In an embodiment shown in FIG. 8, there are three legs 608; however, any quantity of legs 608 can work, so long as it provides stability to the transducer 111 asit rotates about the post 514. For example, one leg 608 can be used, so long as the rings 604a, 604b holds the transducer 111 in place for rotation and provides mechanical stability. The legs 608 are different lengths and are not necessarily equal to the width of the PZT transducer 111. The legs 608 gives the rings 604a, 604b its rotational motion because it creates a deviation from the central axis (i.e., off-the -center mount).

[0055] Ring 610 is a slip ring comprising a bearing, such as a ring bearing. For example, ring 604b can make contact to wire 602a and ring 610 can make contact to wire 602b. Ring 610 is also soldered to the outer surface of the 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 comprising a bearing, such as a ring bearing. Generally, rings 604b, 610 comprise a slip-ring configuration, having brushes made of carbon materials and slip-ring bodies, wherein the brushes are electrically conductively connected to slip rings of the slip-ring bodies. The slip rings can be formed of metals such as copper or copper alloys such as, for example, bronze, tin bronzes, nickel bronze, silver or steel. The slip rings are connected by insulating fastenings to the shaft of the post 514 to form slipring bodies. Electrically conductive brushes are disposed stationarily along the circumference of the slip rings and are held in contact with the surface of the slip rings by spring force. The sliding contacts (brushes) generally are formed of carbon materials, possibly in combination with metals, for example metal graphite. Terminal 612 acts as a terminal for the wires. In an embodiment, terminal 612 does not have a rotating feature.

[0056] In the embodiment shown in FIG. 8, when an acoustic radiation force generated due to acoustic transmission from the self-rotating ultrasound transducer 111 thereby generating a net momentum from reactive forces from a surrounding environment that has a net non-zero torque around the rotation axis of the self-rotating ultrasound transducer, the net non-zero torque momentum causes the transducer 111 to rotate about the post 514. When the transducer 111rotates, ring 610 rotates with the transducer 111 because they are connected via the wire 602c.Wire 602c is substantially rigid and ring 610 is made of a low-friction material that when the transducer 111 rotates about the post 514, it pulls with it the ring 610. The rotation of the transducer 111 can be modified to go either clockwise or counter-clockwise about the post 514.

[0057] The ring 610 rotates using carbon brush rings which makes electrical connections using wire 602a or wire 602b. The wires 602a, 602b are embedded in the post 514. The shaft of the post 514 can have two components to facilitate assembly. One component can be non-conductive towards the connection end and the other component can be conduct! ve / me tai to give the post 514 rigidity, which allows the transducer 111 to freely rotate about the post 514. The components are located at the end near ring 610 and ring 604b. Ring 604b rotates with ring 610 using carbon brush rings; however, inductive coupling or a mercury slip ring can 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 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 sense rather than a restrictive sense.

Claims

CLAIMSWhat is claimed is:

1. 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 wherein the self-rotating ultrasound transducer is configured to self-rotate around the longitudinal axis when an acoustic radiation force generates a net momentum from reactive forces from a surrounding environment that has a net non-zero torque around a rotation axis of the selfrotating ultrasound transducer.

2. The catheter of claim 1, wherein the shape is non-enclosed in a cross-section perpendicular to the longitudinal axis.

3. The catheter of claim 1 or 2, wherein the shape comprises an array of transducers.

4. The catheter of any of claims 1 to 3, wherein the shape is triangular in a cross-section perpendicular to the longitudinal axis and each side comprises a transducer plate.

5. The catheter of any of claims 1 to 3, wherein the shape is an irregular polygon in a crosssection perpendicular to the longitudinal axis.

6. The catheter of any of claims 1 to 5, wherein the shape is a cylinder.

7. The catheter of any of claims 1 to 3, wherein the shape is a spiral in a cross-section perpendicular to the longitudinal axis.

8. The catheter of claim 7, wherein a first diameter of the spiral is less than a second diameter of the spiral.

9. The catheter of claim 6, wherein the cylinder comprises a groove.

10. The catheter of claim 6 or 9, wherein the cylinder comprises a slot.The catheter of any of claims 1 to 10, wherein the surrounding environment comprises water. The catheter of any of claims 1 to 10, wherein the surrounding environment comprises air. The catheter of any of claims 1 to 10, wherein the surrounding environment comprises blood. The catheter of any of claims 1 to 13, wherein the longitudinal axis comprises a rolling bearing. The catheter of any of claims 1 to 14, wherein the self-rotating transducer comprises a length of about 6 mm. The catheter of any of claims 1 to 15, wherein the self-rotating transducer comprises an outer diameter of about 1.5 mm. The catheter of any of claims 1 to 16, wherein the self-rotating transducer comprises an inner diameter of about 1 mm. The catheter of any of claims 1 to 17, wherein the self-rotating transducer rotates at a power range of 10-60 Watts. The catheter of claim 18, wherein the power range is 25-40 Watts. The catheter of any of claims 1 to 19, further comprising a balloon. The catheter of claim 20, wherein the balloon surrounds the self-rotating transducer. The catheter of any of claims 1 to 21, wherein the acoustic radiation force is generated due to acoustic transmission from the self-rotating ultrasound transducer. A catheter, comprising: a catheter shaft; anda 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, wherein the self-rotating ultrasound transducer is configured to selfrotate around the longitudinal axis when an acoustic radiation force generated due to acoustic transmission from the self-rotating ultrasound transducer thereby generates a net momentum from reactive forces from a surrounding environment that has a net non-zero torque around a rotation axis of the self-rotating ultrasound transducer.

24. The catheter of claim 23, wherein the ultrasound transducer is non-enclosed in a crosssection perpendicular to the longitudinal axis.

25. The catheter of claim 23 or 24, wherein the ultrasound transducer comprises an array of transducers.

26. The catheter of any of claims 23 to 25, wherein the ultrasound transducer is triangular in a cross-section perpendicular to the longitudinal axis and each side comprises a transducer plate.

27. The catheter of any of claims 23 to 25, wherein the ultrasound transducer is an irregular polygon in a cross-section perpendicular to the longitudinal axis.

28. The catheter of any of claims 23 to 27, wherein the ultrasound transducer is a cylinder.

29. The catheter of any of claims 23 to 25, wherein the ultrasound transducer is a spiral in a cross-section perpendicular to the longitudinal axis.

30. The catheter of claim 29, wherein a first diameter of the spiral is less than a second diameter of the spiral.

31. The catheter of claim 28, wherein the cylinder comprises a groove.

32. The catheter of claim 28 or 31 , wherein the cylinder comprises a slot.

33. The catheter of any of claims 23 to 32, wherein the surrounding environment comprises water.

34. The catheter of any of claims 23 to 32, wherein the surrounding environment comprises air.

35. The catheter of any of claims 23 to 32, wherein the surrounding environment comprises blood.

36. The catheter of any of claims 23 to 35, wherein the longitudinal axis comprises a rolling bearing.

37. The catheter of any of claims 23 to 36, wherein the ultrasound transducer comprises a length of about 6 mm.

38. The catheter of any of claims 23 to 37, wherein the ultrasound transducer comprises an outer diameter of about 1.5 mm.

39. The catheter of any of claims 23 to 38, wherein the ultrasound transducer comprises an inner diameter of about 1 mm.

40. The catheter of any of claims 23 to 39, wherein the ultrasound transducer rotates at a power range of 10-60 Watts.

41. The catheter of claim 40, wherein the power range is 25-40 Watts.

42. The catheter of any of claims 23 to 41, further comprising a balloon.

43. The catheter of claim 42, wherein the balloon surrounds the ultrasound transducer.

44. A catheter, comprising: a transducer positioned along a longitudinal axis on a distal region of a catheter shaft; a fixture for mounting the transducer, wherein the fixture is mounted off-centered whereby the transducer self-rotates around the fixture when an acoustic radiation force generated due to acoustic transmission from the transducer thereby generates a netmomentum from reactive forces from a surrounding environment that has a net non-zero torque around a rotation axis of the transducer.

45. The catheter of claim 44, wherein the transducer is an ultrasound transducer.

46. A catheter, comprising: a transducer having a shape that self-rotates about a post positioned along a longitudinal axis on a distal region of a catheter shaft, a first and second ring arranged on each side of the transducer, wherein each ring comprises at least one leg and at least one of the rings is coupled to an ID of the transducer, and a third ring coupled to an OD of the transducer, the third ring located at a same end of the transducer where at least one of the rings is coupled to the ID of the transducer, and wherein the post is mounted off-centered causing the transducer to self-rotate around the post when an acoustic radiation force generated due to acoustic transmission from the transducer thereby generates a net momentum from reactive forces from a surrounding environment that has a net non-zero torque around a rotation axis of the ultrasound transducer.

47. The catheter of claim 46, wherein the shape is non-enclosed in a cross-section perpendicular to the longitudinal axis.

48. The catheter of claim 46 or 47, wherein the shape comprises an array of transducers.

49. The catheter of any of claims 46 to 48, wherein the shape is triangular in a cross-section perpendicular to the longitudinal axis and each side comprises a transducer plate.

50. The catheter of any of claims 46 to 48, wherein the shape is an irregular polygon in a cross-section perpendicular to the longitudinal axis.

51. The catheter of any of claims 46 to 50, wherein the shape is a cylinder.

52. The catheter of any of claims 46 to 48, wherein the shape is a spiral in a cross-section perpendicular to the longitudinal axis.

53. The catheter of any of claims 46 to 52, wherein the transducer is an ultrasound transducer.

54. The catheter of any of claims 46 to 53, wherein the one ring of the set of rings is a slip ring.

55. The catheter of claim 54, wherein the slip ring comprises bearings.

56. The catheter of any of claims 46 to 53, wherein the third ring is a slip ring.

57. The catheter of claim 56, wherein the slip ring comprises bearings.

58. The catheter of any of claims 46 to 57, wherein the set of rings comprise legs that are of different lengths.

59. A catheter, comprising: a catheter shaft; and an ultrasound transducer positioned along a longitudinal axis on a distal region of the catheter shaft, wherein a cross-sectional shape of the transducer perpendicular to the longitudinal axis is asymmetrical about a rotation axis of the transducer.

60. The catheter of claim 59, wherein the rotation axis is off-centered.

61. A catheter, comprising: a catheter shaft; and an ultrasound transducer positioned along a longitudinal axis on a distal region of the catheter shaft, wherein in a non-rotating state, a direction in which acoustic radiation forces are transmitted from a surface of the ultrasound transducer is less than 360 degrees with respect to a longitudinal axis of the ultrasound transducer.The catheter of claim 61, further comprising a balloon. The catheter of claim 61 or 62, wherein the ultrasound transducer comprises a length of about 6 mm. The catheter of any of claims 61 to 63, wherein the ultrasound transducer comprises an outer diameter of about 1.5 mm. The catheter of any of claims 61 to 64, wherein the ultrasound transducer comprises an inner diameter of about 1 mm. A catheter, comprising: a catheter shaft; and an ultrasound transducer rotatably positioned along a longitudinal axis on a distal region of the catheter shaft, wherein the ultrasound transducer has a transducer surface and is configured for a transfer of an acoustic momentum from the transducer surface to a fluid surrounding the transducer to generate an acoustic radiation force that pushes the fluid away from the transducer and causes a net non-zero torque acting on the transducer around the longitudinal axis. A method of operating a catheter comprising a catheter shaft and an ultrasound transducer rotatably positioned along a longitudinal axis on a distal region of the catheter shaft, wherein the ultrasound transducer has a transducer surface, the method comprising: energizing the ultrasound transducer to transfer an acoustic momentum from the transducer surface to a fluid surrounding the transducer to generate an acoustic radiation force that pushes the fluid away from the transducer and results in a net nonzero torque that rotates the transducer around the longitudinal axis.A computer program product comprising program code portions that, when executed on a controller, cause the controller to energize the transducer to perform the method of claim 67.

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