Abstract:
An ultrasonic tissue ablation device comprising a transversely vibrating elongated probe, and a coupling assembly for probe attachment detachment that enables the probe assembly and separation from the device body that includes the ultrasound energy source and a sound conductor, and a method of use for removal of vascular occlusions in blood vessels. The coupling assembly enables incorporation of elongated probes with small cross sectional lumens such as a catheter guidewires. The probe detachability allows insertion manipulation and withdrawal independently of the device body. The probe can be used with acoustic and/or aspirations sheaths to enhance destruction and removal of an occlusion. The horn assembly of the device that contains a sound conducting horn functions as an energy regulator and reservoir for the probe, and precludes loss of probe cavitation energy by its bending or damping within the blood vessel.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Vascular occlusions (clots or thrombi and occlusional deposits, such as calcium, fatty deposits, or plaque) result in the restriction or blockage of blood flow in the vessels in which they occur. Occlusions result in oxygen deprivation (“ischemia”) of tissues supplied by these blood vessels. Prolonged ischemia results in permanent damage of tissue that can lead to myocardial infarction, stroke, or death. Targets for occlusion include coronary arteries, peripheral arteries and other blood vessels. The disruption of an occlusion or thrombolysis can be effected by pharmacological agents and/or or mechanical means.  
           [0002]    Ultrasonic probes are devices which use ultrasonic energy to fragment body tissue (see, e.g., U.S. Pat. Nos. 5,112,300; 5,180,363; 4,989,583; 4,931,047; 4,922,902; and 3,805,787) and have been used in many surgical procedures. The use of ultrasonic energy has been proposed both to mechanically disrupt clots, and to enhance the intravascular delivery of drugs to clot formations (see, e.g., U.S. Pat. Nos. 5,725,494; 5,728,062; and 5,735,811). Ultrasonic devices used for vascular treatments typically comprise an extra-corporeal transducer coupled to a solid metal wire that is attached to a plurality of wires at the distal end, that is then threaded through the blood vessel and placed in contact with the occlusion (see, e.g., U.S. Pat. No. 5,269,297). In some cases, the transducer is delivered to the site of the clot, the transducer comprising a bendable plate (see, U.S. Pat. No. 5,931,805).  
           [0003]    The ultrasonic energy produced by an ultrasonic probe is in the form of very intense, high frequency sound vibrations that result in powerful chemical and physical reactions in the water molecules within a body tissue or surrounding fluids in proximity to the probe. These reactions ultimately result in a process called “cavitation,” which can be thought of as a form of cold (i.e., non-thermal) boiling of the water in the body tissue, such that microscopic bubbles are rapidly created and destroyed in the water creating cavities in their wake. As surrounding water molecules rush in to fill the cavity created by collapsed bubbles, they collide with each other with great force. This process is called cavitation and results in shock waves running outward from the collapsed bubbles which can fragment or ablate material such as surrounding tissue in the vicinity of the probe. Some ultrasonic probes include a mechanism for irrigating an area where the ultrasonic treatment is being performed (e.g., a body cavity or lumen) to wash tissue debris from the area. Mechanisms used for irrigation or aspiration described in the art are generally structured such that they increase the overall cross-sectional profile of the probe, by including inner and outer concentric lumens within the probe to provide irrigation and aspiration channels for removal of particulate matter. In addition to making the probe more invasive, prior art probes also maintain a strict orientation of the aspiration and the irrigation mechanism, such that the inner and outer lumens for irrigation and aspiration remain in a fixed position relative to one another, which is generally closely adjacent the area of treatment. Thus, the irrigation lumen does not extend beyond the suction lumen (i.e., there is no movement of the lumens relative to one another) and any aspiration is limited to picking up fluid and/or tissue remnants within the defined distance between the two lumens.  
           [0004]    Another drawback of existing ultrasonic medical probes is that they typically remove tissue relatively slowly in comparison to instruments that excise tissue by mechanical cutting. Part of the reason for this is that existing ultrasonic devices rely on a longitudinal vibration of the tip of the probe for their tissue-disrupting effects. Because the tip of the probe is vibrated in a direction in line with the longitudinal axis of the probe, a tissue-destroying effect is only generated at the tip of the probe. One solution that has been proposed is to vibrate the tip of the probe in a direction other than perpendicular to the longitudinal axis of the probe, in addition to vibrating the tip in the longitudinal direction. It is proposed that such motions will supplement the main point of tissue destruction, which is at the probe tip, since efficiency is determined by surface area of the probe tip. For example, U.S. Pat. No. 4,961,424 to Kubota, et al. discloses an ultrasonic treatment device that produces both a primary longitudinal motion, and a supplementary lateral motion of the probe tip to increase the tissue disrupting efficiency. The Kubota, et al. device, however, still relies primarily on the tip of the probe to act as a working surface. The ancillary lateral motion of the probe is intended to provide an incremental efficiency for the device operation. Thus, while destruction of tissue in proximity to the tip of the probe is more efficient, tissue destruction is still predominantly limited to the area in the immediate vicinity at the tip of the probe. The said invention is therefore limited in its ability to ablate tissue within inner surfaces of cylindrical blood vessels, for example, in vascular occlusions. U.S. Pat. No. 4,504,264 to Kelman discloses an ultrasonic treatment device containing a probe that is capable of longitudinal vibrations and lateral oscillation. The said invention is intended to improve the efficiency of ultrasonic tissue removal by providing a dual function of a fragmentation and a cutting device. Tissue fragmentation is caused primarily by oscillating the tip of the probe in addition to relying on longitudinal vibrations of the probe, while the lateral oscillations. Tissue fragmentation is caused primarily at the tip of the device, while the oscillatory motion can be employed by the surgeon to cut tissue, thereby increasing efficiency of surgical procedures. The foregoing inventions also require complex instrument design that require incorporation of a plurality of electrodes, ultrasound frequency generating elements, switches or voltage controllers.  
           [0005]    The longitudinal probe vibration required for tissue ablation in prior art devices necessitates the probe lengths to be relatively short, since use of long probes result in a substantial loss of ultrasonic energy at the probe tip due to thermal dissipation and undesirable horizontal vibration that interferes with the required longitudinal vibration.  
           [0006]    Although narrow probe diameters are advantages especially for negotiation through narrow blood vessels and occluded arteries, the utilization of such probes have been precluded by inability to effectively control the vibrational amplitude of thin probes, that result in potential damage to the probe and greater risk of tissue damage resulting from their use. The use of narrow-diameter probes have been disclosed in the art for providing greater maneuverability ease of insertion in narrow blood vessels. U.S. Pat. No. 4,920,954 to Allinger discloses a narrow diameter ultrasonic device wherein a rigid sleeve is used to prevent transverse vibrations U.S. Pat. No. 5,380,274 discloses a narrow diameter probe for improved longitudinal vibration having a sheath to inhibit transverse vibration U.S. Pat. No. 5,469,853 to Law discloses a thin, longitudinally vibrating ultrasonic device with a bendable sheath that facilitates directing the probe within narrow blood vessels. While the prior art has focused on the need for using sheaths on thin ultrasonic devices, their use has been entirely to prevent transverse vibrations of the device and to protect such devices from damage resulting from such vibrations.  
           [0007]    Based on the aforementioned limitations of ultrasonic probes in the art, there is a need for ultrasonic probe functioning in a transverse mode that further obviates the shortcomings of that further overcomes limitations imposed by of narrow diameter requirements for efficient operation of such probes for rapid tissue ablation. Transversely vibrating ultrasonic probes for tissue ablation are described in the Applicant&#39;s co-pending provisional applications U.S. Ser. Nos. 60/178,901 and 60/225,060, and 20563/1010 (Attorney Docket No.) which further describe the design parameters for such a probe its use in ultrasonic devices for tissue ablation. The entirety of these applications are herein incorporated by reference.  
           [0008]    This limitation has precluded the use of ultrasonic tissue ablation devices in surgical procedures wherein access to vascular occlusion requires traversing an anatomically lengthy or sharply curved path along tubular vessels. The self-suggesting idea of effecting ultrasonic transmission through a plurality of flexible thin wires has been found impracticable because (1) relatively high power (˜25 watts) is required to deliver sufficient energy to the probe tip, and (2) such thin wires tend to perform buckling vibrations, resulting in almost the entire ultrasonic power introduced in the probe is dissipated during its passage to the probe tip.  
           [0009]    The relatively high-energy requirement for such devices causes probe heating that can cause fibrin to re-clot blood within the occluded vessel (thermally induced re-occlusion). Additionally, the elevation in probe temperature is not just limited to probe tip, but also occurs at points wherein the narrow diameter wire probes have to bend to conform to the shape of the blood vessel, thereby limiting causing probe damage and limiting its reuse.  
           [0010]    A single thick wire probe on the other hand, cannot negotiate the anatomical curves of tubular arterial and venous vessels due to its inflexibility, and could cause damage to the interior wall of such vessels. Currently, such exchange procedures are not possible because ultrasonic probes used in endovascular procedures are permanently attached to the transducer energy source or a probe handle coupled to such source, such as for example, by welding, thereby precluding probe detachment. Moreover, since probe vibration in such devices in a longitudinal mode, i.e. along the probe longitudinal axis, a proximal contact with the transducer or the probe handle segment connect is essential to prevent a “hammering” effect that can result in probe damage.  
         SUMMARY OF THE INVENTION  
         [0011]    The present invention relates to an ultrasonic device comprising an elongated catheter probe vibrating substantially in a direction transverse to the probe longitudinal axis and capable of emulsifying endovascular materials, particularly tissue. The diameter of the catheter probe is sufficiently small to confer flexibility on said probe so as to enable its negotiation through narrow and anatomically curved tubular vessels to the site of an occlusion that is remotely located from the point of probe insertion into the body. The catheter probe of the invention is designed to work in conjunction with standard vascular introducers and guide catheters. Another aspect of the invention is to provide a rapidly attachable and detachable or “quick attachment-detachment” means (referred to hereinafter as “QAD”) for the catheter probe to and from the ultrasonic energy source, thereby enabling manipulation and positioning of the probe within the body vessel without being limited by the relatively bulky energy generating source. The catheter probe of the invention additionally comprises a concentric tubular sheath to facilitate fluid irrigation, aspiration of ablated tissue fragments and introducing a therapeutic drug to the site of occlusion.  
           [0012]    An ultrasonic probe vibrating in a transverse mode for removal of occlusions in blood vessels has been disclosed in applicants&#39; co-pending application Ser. No. 09/776,015, the entireity of which is incorporated herein as reference. The said reference discloses an ultrasonic device in which a transducer is connected to a probe with a flexible tip capable of vibrating in a direction transverse to the probe longitudinal axis. With such a probe a situation may arise where it will be desirable to utilize an elongated probe resembling a catheter guide-wire probe to make possible exchange procedures often used in angioplasty.  
           [0013]    In general, it is an object of the invention to provide an ultrasonic medical device for removing vascular occlusions comprising a detachable elongated catheter guide wire probe capable of vibrating in a transverse mode.  
           [0014]    Another object of the invention is to provide an elongated guide wire probe of the above character of the above character that is and comparable in size to existing guide wires.  
           [0015]    Another object of the invention is to provide an elongated guide wire probe of the above character which includes a quick attachment-detachment means to an ultrasound energy source.  
           [0016]    Another object of the invention is to provide an elongated guide wire probe of the above characteristics which is compatible with the existing guide wire exchange systems.  
           [0017]    Another object of the invention is to provide a probe attachment-detachment means comprising a coupling assembly.  
           [0018]    Yet another object of the invention is to provide a guide wire of the above character which can be inserted, retracted or torqued in a detached mode to prevent interference with the probe handle and the ultrasound transducer.  
           [0019]    A further object of the invention is to provide a guide wire assembly and system and apparatus utilizing the same of the above character, which permits intravascular ultrasonic tissue ablation.  
           [0020]    Additional objects and features of the invention will appear from the following description in which the preferred embodiments are set forth in detail in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    In order that the invention may be more readily understood, reference is made to the accompanying figures, which illustrate diagramatically and by way of example, several embodiments thereof and in which:  
         [0022]    [0022]FIG. 1 is a general view of the elongated flexible wire probe catheter of the invention.  
         [0023]    [0023]FIGS. 2A and 2B show a varied diameter probe, QAD collet-horn assembly and locking nut in disassembled ( 2 A) and assembled ( 2 B) configurations.  
         [0024]    [0024]FIG. 2C shows an assembled configuration of a uniformly small diameter wire probe.  
         [0025]    [0025]FIG. 3 shows a cross sectional view of the probe assembled to QAD collet (Version 1) assembly.  
         [0026]    [0026]FIGS. 4A and 4B show the locking nut viewed from the opposite cylindrical ends.  
         [0027]    [0027]FIG. 5 shows a cross sectional view of the locking nut coupling the probe to the QAD collet-horn assembly.  
         [0028]    [0028]FIG. 6 shows the threaded horn component of the QAD collet-horn assembly.  
         [0029]    [0029]FIG. 7 shows scaled and cross-sectional views of a second preferred version of the QAD collet assembly.  
         [0030]    [0030]FIGS. 8A and 8B show the QAD collet rod and housing assemblies of the second preferred version.  
         [0031]    [0031]FIG. 9 shows scaled and cross-sectional views of a third preferred version of the QAD collet assembly.  
         [0032]    [0032]FIGS. 10A and 10B show the QAD collet rod and housing assemblies of the third preferred version.  
         [0033]    [0033]FIG. 11 shows scaled and cross-sectional views of a fourth preferred version of the QAD collet assembly.  
         [0034]    [0034]FIGS. 12A, 12B and  12 C show the collet, QAD base component and compression housing of the fourth preferred version. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]    The following terms and definitions are used herein:  
         [0036]    “Anti-node” as used herein refers to a region of minimum energy emitted by an ultrasonic probe on or proximal to a position along the probe.  
         [0037]    “Cavitation” as used herein refers to shock waves produced by ultrasonic vibration, wherein the vibration creates a plurality of microscopic bubbles which rapidly collapse, resulting in molecular collision by water molecules which collide with force thereby producing the shock waves.  
         [0038]    “Fenestration” as used herein refers to an aperture, window, opening, hole, or space.  
         [0039]    “Node” as used herein refers to a region of maximum energy emitted by an ultrasonic probe at or proximal to a specific location along the longitudinal axis probe.  
         [0040]    “Anti-node” as used herein refers to a region of minimum energy emitted by an ultrasonic probe at or proximal to a specific location along the longitudinal axis probe.  
         [0041]    “Probe” as used herein refers to a device capable of being adapted to an ultrasonic generator means, which is capable of propagating the energy emitted by the ultrasonic generator means along its length, resolving this energy into effective cavitational energy at a specific resonance (defined by a plurality of nodes and anti-nodes at a predetermined locations (defined as “active area” of the probe) and is capable of acoustic impedance transformation of ultrasound energy to mechanical energy.  
         [0042]    “Sheath” as used herein refers to a device for covering, encasing, or shielding in whole or in part, a probe or portion thereof connected to an ultrasonic generation means.  
         [0043]    “Transverse” as used herein refers to vibration of a probe at right angles to the axis of a probe. A “transverse wave” as used herein is a wave propagated along an ultrasonic probe in which the direction of the disturbance at each point of the medium is perpendicular to the wave vector.  
         [0044]    “Tuning” as used herein refers to a process of adjusting the frequency of the ultrasonic generator means to select a frequency that establishes a standing wave along the length of the probe.  
         [0045]    The present invention provides an ultrasonic medical device operating in a transverse mode for removing a vascular occlusion by causing fragmentation of occlusion materials such as tissue. Because the device is minimally invasive, flexible and articulable, it can be inserted into narrow, tortuous blood vessels without risking damage to those vessels. Transverse vibration of the probe in such a device generates multiple nodes of cavitation energy along the longitudinal axis of the probe, which are resolved into caviational nodes emanating radially from these nodes at a specific points along the active portion of the probe. The occlusion tissue is fragmented to debris approximately of sub-micron sizes, and the transverse vibration generates a retrograde flow of debris that carries the debris away from the probe tip.  
         [0046]    The transverse mode of vibration of the ultrasonic probe according to the invention differs from the axial (or longitudinal) mode of vibration that is conventional in the prior art. Rather than vibrating in the axial direction, the probe vibrates exclusively in a direction transverse (perpendicular) to the axial direction. As a consequence of the transverse vibration of the probe, the tissue-destroying effects of the device are not limited to those regions of a tissue coming into contact with the tip of the probe. Rather, as the active portion of the probe is positioned in proximity to an occlusion or other blockage of a blood vessel, the tissue is removed in all areas adjacent to the multiplicity of energy nodes that are produced along the entire length of the probe, typically in a region having a radius of up to about  6  mm around the probe.  
         [0047]    By eliminating the axial motion of the probe and allowing transverse vibrations only, fragmentation of large areas of tissue spanning the entire length of the active portion of the probe due to generation of multiple cavitational nodes along the probe length perpendicular to the probe axis. Since substantially larger affected areas within an occluded blood vessel can be denuded of the occluded tissue in a short time, actual treatment time using the transverse mode ultrasonic medical device according to the invention is greatly reduced as compared to methods using prior art probes that primarily utilize longitudinal vibration (along probe axis) for tissue ablation. An distinguishing feature of the present invention is the ability to utilize probes of extremely small diameter (about 0.025″ and smaller) compared to prior art probes without loss of efficiency, since the tissue fragmentation process in not dependent on area of the probe tip (distal end). Highly flexible probes can therefore, be designed to mimic device shapes that enable facile insertion into highly occluded or extremely narrow interstices within blood vessels. Another advantage provided by the present invention is its ability to rapidly remove occlusion tissue from large areas within cylindrical or tubular surfaces such as arteries and arterial valves or selected areas within the tubular walls, which is not possible by previously disclosed devices that rely on the longitudinal vibrating probe tip for effecting tissue fragmentation.  
         [0048]    The number of nodes occurring along the axial length of the probe is modulated by changing the frequency of energy supplied by the ultrasonic generator. The exact frequency, however, is not critical and a ultrasonic generator run at, for example, 20 kHz is generally sufficient to create an effective number of tissue destroying nodes along the axial length of the probe. In addition, as will be appreciated by those skilled in the art, it is possible to adjust the dimensions of the probe, including diameter, length, and distance to the ultrasonic energy generator, in order to affect the number and spacing of nodes along the probe. The present invention allows the use of ultrasonic energy to be applied to tissue selectively, because the probe conducts energy across a frequency range of from about 20 kHz through about 80 kHz. The amount of ultrasonic energy to be applied to a particular treatment site is a function of the amplitude and frequency of vibration of the probe. In general, the amplitude or throw rate of the energy is in the range of 150 microns to 250 microns, and the frequency in the range of 20,000 to 80,000 Hertz (20-80 kHz). In the currently preferred embodiment, the frequency of ultrasonic energy is from 20,000 Hertz to 35,000 Hertz (20-35 kHz). Frequencies in this range are specifically destructive of hydrated (water-laden) tissues and vascular occlusive material, while substantially ineffective toward high-collagen connective tissue, or other fibrous tissues such as, for example, vascular tissues, skin or muscle tissues.  
         [0049]    In a preferred embodiment, the ultrasonic medical device of the present invention, comprises an ultrasonic generator that is mechanically coupled to a probe having a proximal and distal end that is capable of oscillating in a direction transverse to its longitudinal axis. Alternatively, a magneto-strictive generator may be used for generation of ultrasound energy. The preferred generator is a piezoelectric transducer that is mechanically coupled to the probe to enable transfer of ultrasonic excitation energy and cause the probe to oscillate in a transverse direction relative to its longitudinal axis. The device is designed to have a small cross-sectional profile, which also allows the probe to flex along its length, thereby allowing it to be used in a minimally invasive manner. Transverse oscillation of the probe generates a plurality of cavitation nodes along the longitudinal axis of the member, thereby efficiently destroying the occlusion. A significant feature of the invention is the retrograde movement of debris, e.g., away from the tip of the probe i.e. backwards up along the shaft of the probe that results from the transversely generated energy. The amount of cavitation energy to be applied to a particular site requiring treatment is a function of the amplitude and frequency of vibration of the probe, as well as the longitudinal length of the probe tip, the proximity of the tip to a tissue, and the degree to which the probe tip is exposed to the tissues.  
         [0050]    A distinguishing feature of the present invention is the ability to utilize probes of extremely small diameter (narrow diameter probes) compared previously disclosed devices (large diameter probes) without loss of efficiency or efficacy, since the tissue fragmentation process in not dependent on area of the probe tip (distal end). Highly flexible probes can therefore be obtained to mimic device shapes that enable facile insertion into highly occluded or extremely narrow interstices without resulting in breakage of the probe or puncture or damage of the tissue or body cavity while ensuring optimal results.  
         [0051]    A second distinguishing feature of the small diameter probes of the invention is that the probe diameter is approximately the same over their entire length, that is,—the active tip segment (distal end) and the rear segment (proximal end) of the probes are approximately similar in diameter. In a preferred embodiment the probe diameters at the proximal and distal ends respectively are about 0.025 inch. An advantage of the shape configuration of the probes of the invention is that they are adaptable to currently used standard vascular introducers. Since the rear segment (proximal end) of the probes have no non-cylindrical shape or “bulk”, catheters and guides can be introduced over the ends of the elongated wire probes of the invention, thereby—allowing their use in standard-configuration endovascular procedures.  
         [0052]    The ultrasonic device of the invention comprises a longitudinal resonator such as for example, a Mason (Langevin) horn that is in intimate contact with an elongated catheter wire probe through a coupling assembly. The horn assembly is in turn, connected to an ultrasound energy source. Upon device activation, ultrasonic energy from the source is transmitted to the horn assembly wherein it is amplified by the horn and in turn, transmitted to the probe thorough the coupling assembly. Transverse vibrational modes along the longitudinal axis of the probe that lie within the horn resonance are excited.  
         [0053]    The coupling between the elongated probe and the horn is adjusted so as to present a relatively large impedance mismatch, and be located at an anti-node of the horn. Longitudinal waves impinging on the coupling interface are either reflected back into the horn or transmitted out to the probe in proportion to the degree of impedance mismatch at the said coupling interface. In a preferred embodiment, the coupling interface is configured in a manner so as to reflect most of the energy back into the horn. The horn therefore, essentially acts as an energy storage device or “reservoir”, thereby allowing a substantial increase in drive amplitude.  
         [0054]    Since the energy coupled into the elongated probe is a small portion of the energy reflected back to the horn, changes in the transverse oscillation on the probe due to bending or damping have minimal effect on the longitudinal resonance of the horn. By decoupling the transverse probe oscillation from the longitudinal horn resonance, the electrical source of the vibrations (piezoelectric or magnetostrictive) to compensate only for shifts in the resonant frequency of the horn (due to temperature, manufacturing variations, etc.). The drive mechanism is therefore, completely independent of vibrational motions on the probe.  
         [0055]    The transverse vibrating elongated probe of the invention does not require its terminal end be permanently affixed in intimate contact to the horn assembly, since a “hammering” action associated with longitudinal vibration is absent. The elongated probe of the invention can therefore be coupled, and not welded, to the horn via a coupling assembly that grips the probe along the cylindrical surface near its terminal end in a non-permanent way. The coupling assembly of the invention therefore, allows for quick attachment and detachment of the probe from the horn assembly and source components, thereby enabling manipulation of the elongated flexible probe into anatomically curved blood vessels without hindrance by the bulky horn and energy source components. The probe of the invention can therefore be inserted into a venal cavity, positioned near the occlusion site prior to coupling it to the horn source assembly. The device is then activated to effect tissue ablation and removal, after which the probe is decoupled from the horn and source component for its easy removal from the cavity.  
         [0056]    In a preferred embodiment a longitudinal horn is coupled to an elongated wire catheter through a coupling assembly that is rapidly attachable and detachable. In a most preferred embodiment, the coupling assembly comprises a quick attachment-detachment (QAD) collet. The attachment of the coupling assembly to the elongated probe is located at an antinode and the dimensions are scaled (i.e. it collet head has a relatively larger diameter at the attachment point than the diameter of the probe) to produce an optimal impedance mismatch. In another embodiment of the invention, the elongated probe is permanently attached to the coupling assembly by a welded joint.  
         [0057]    The QAD collet of the invention is housed within an externally mounted compressive clamp that is capable of exerting a compressive force on the collet after insertion of the ultrasonic probe into said collet, thereby causing a non-removable attachment of the probe to the coupling assembly. The collet therefore, applies a restraining inwardly compressive force on the probe in a manner so as to not torque or twist the probe material. As a result, the probe can be subject to a multiple attachment and detachment procedures, without causing probe destruction, thereby enabling its extended reuse in surgical procedures.  
         [0058]    The collet of the invention comprises is at least one slit in its terminal compressible segment; alternatively it comprises of a plurality of slits. In a preferred embodiment, the collet, compressive clamp and housing assembly are all attached to the device handle by a mechanical assembly means, such as for example, a screw thread comprising a locking nut, bayonet mount, keyless chuck and cam fittings. Alternatively, the rear segment of the mechanical assembly means is a hollow cylindrical segment comprising a screw thread that allows insertion and attachment of the ultrasonic device handle containing a drive assembly containing a complementary thread arrangement to be inserted into and non-removably attached to said cylindrical segment by applying a torque. In another preferred embodiment, ultrasonic probe is mounted to the attachment means such that the collet holds the probe at a point greater than about 1 mm and less than about 30 from the probe terminal end, or is adjustable to any point in between, to optimize probe vibration based on the frequency of the ultrasound transducer in the device handle. In another preferred embodiment, the probe attachment means comprising the external compressive clamp, collet and collet housing are all attached to the operating handle of the ultrasonic device.  
         [0059]    In another preferred embodiment the collet is retained within the confines of an outer shell that is attached to the collet housing segment of the probe attachment means that to precludes its disassembly, thereby preventing either loss or disengagement of the collet. The outer shell compresses the collet to engage contact with the probe upon its tightening to the collet housing assembly by application of torque, causing the probe to be attached to the collet in a non-removable manner. An inner bias is maintained within the rear portion of the attachment means such that a portion of the probe protruding from the proximal end of the collet maintains contact with the surface of the collet housing within the coupling assembly.  
         [0060]    The terminal ends of the collet are tapered so as to allow the collet to maintain a true axial orientation within the coupling assembly, thereby enabling multiple insertions and retractions of the probe into and from the collet prior to and after device use, without causing the probe to kink. Additionally, the shape of the proximal end of the segment (rear segment with respect to the entering probe), so as to maximize contact area between the collet and the distal end of the transducer-sound conductor assembly (the “drive assembly”). The collet proximal end is shaped in any suitable form providing maximal contact area, including conical, frusto-conical, triangular, square, oblong, and ovoid, upon probe attachment to the collet within the housing assembly, which in turn maintains intimate contact with the drive assembly. The four component assembly that include probe, outer ring, collet and rear drive assembly, form a single assembled component in the device operational state, in terms of their combined ability to transmit sound energy from the transducer in the drive assembly to the probe without energy loss thermally or mechanically. The collets of the invention can be designed to accommodate a series of probe diameters, or for a specific probe diameter by varying the inner diameter of the cylindrical slot. The outer diameters of the collets, however remain unchanged, thereby allowing attachment of probes of differing diameters into a universal coupling and drive assembly.  
         [0061]    The elongated probe of the invention is either a single diameter wire with a uniform cross section offering flexural stiffness along its entire length, or is tapered or stepped along its length to control the amplitude of the transverse wave along its entire longitudinal axis. Alternatively, the probe can be cross-sectionally non-cylindrical that is capable of providing both flexural stiffness and support energy conversion along its entire length. The length or the elongated probe of the invention is chosen so as to be resonant in either in an exclusively transverse mode, or be resonant in combination of transverse and longitudinal modes to provide a wider operating range. In a preferred embodiment, the elongated probe of the invention is chosen to be from about 30 cm to about 300 cm in length. In a most preferred embodiment, the elongated probe of the invention has a length of about 70 cm to about 210 cm in length. Suitable probe materials include metallic materials and metallic alloys suited for ultrasound energy transmission. In a preferred embodiment the metallic material comprising the elongated probe is titanium.  
         [0062]    In another preferred embodiment, the elongated probe of the invention is circumferentially enclosed in a sheath that provides a conduit for irrigation fluids, aspiration of fragmented tissue, or for delivery of therapeutic drugs to the occlusion site. The said sheath can extend either partially or over the entirety of the probe, and can additionally comprise of fenestrations for directing ultrasonic energy from the probe at specific locations within venal cavities for selective ablation of tissue. An ultrasonic tissue ablation device comprising a sheath for removal of occlusions in blood vessels has been disclosed in applicants&#39; co-pending application Ser. No. 09/776,015, the entireity of which is incorporated herein as reference.  
         [0063]    In one embodiment, the elongated catheter probe is comprised of a proximal end and a distal end with respect to the horn assembly, and is in the form of a long small diameter wire incorporating a series of telescoping segments along its longitudinal axis, such that the largest diameter segment is proximal to the horn assembly, and either continually or segmental, sequentially decreasing diameters from the proximal to the distal end. With reference to the probe, coupling and horn assemblies as shown in the figures describing the present invention, the proximal end for each component refers to the end farthest from the probe tip, while distal end refers to the end closest to the probe tip. In another embodiment, the elongated probe is comprised of a non-segmented, uniformly narrow diameter wire, such as for example a guide wire, such as those used in insertion of catheters.  
         [0064]    Referring now to FIG. 1, a preferred embodiment of the elongated ultrasonic probe  10  of the invention comprising a proximal end  12  and a distal end  22 , is shown. Probe  10  is coupled to a transducer and sound conductor assembly (not shown) constructed in accordance with the present invention that function as generation and transmission sources respectively, of ultrasound energy for activation of said probe. The generation source may or may not be a physical part of the device itself. The probe  10  transmits ultrasonic energy received from the sound conductor along its length, and is capable of engaging the sound conductor component at its proximal end  12  via a coupling assembly with sufficient restraint to form an acoustical mass that can propagate the ultrasonic energy provided by the source. The probe diameter decreases at defined segment intervals  14 ,  18 , and  20 . Segment  22  because of its small diameter, is capable of flexing more than segments  14  and  18 , thereby enabling probe  10  to generate more cavitation energy along segment  20  distal end  22 . Energy from the generator is transmitted along the length of the probe, causing the probe to vibrate in a direction that is transverse to its longitudinal axis. Probe interval  14  has a head segment  24  for engaging the coupling assembly for attachment to the sound conductor-transducer assembly. In a preferred embodiment, the sound conductor component of the invention for providing, amplifying and transferring ultrasonic energy to elongated probe  10  is a Mason (Langevin) horn that is detachably connected to said probe through a coupling assembly.  
         [0065]    Referring now to FIGS.  2 A-B, the unassembled and assembled views of individual components comprising the varied diameter probe and sound conductor elements, and the coupling assembly are illustrated. FIG. 2A shows the individual components comprising elongated probe  10 , horn assembly  34  comprising a proximal end  38  and a comprising a cylindrical slot  36  at the distal end, which includes the horn and coupling assembly components, elongated probe  10  and locking nut  30 . The coupling assembly components comprising threading arrangements  40  and  42 , cylindrical slot  36 , and locking nut  30 . Attachment of proximal end  12  of probe  10  is accomplished by insertion of probe head  24  into the cylindrical slot at distal end  36  of the horn assembly, followed by “threading” the probe through locking nut  30  to enable threads on the inner surface of locking nut  30  (not shown) to engage complementary threads  40 , thereby providing intimate contact between probe distal end  12  and the proximal end  36  of the horn assembly. The probe attachment is rendered to be mechanically rigid by tightening locking nut  30 . FIG. 2B shows the enlongated varied diameter probe attached to the horn assembly and held rigidly by the coupling assembly and maintaining intimate contact between the “coupled” components. FIG. 2C shows a similar assembly comprising a uniform narrow diameter wire probe of the invention.  
         [0066]    [0066]FIG. 3 shows a cross-sectional view of the probe-horn assembly shown in a “coupled” mode. The attachment means comprising the coupling assembly of the invention utilized to “couple” the elongated probe to the horn assembly is chosen from conventional means of connecting physically separated components in a manner so as to provide a rigid joining of said components while maintaining intimate material surface contact between the components in the “coupled” state. Suitable attachment means of the present invention include a locking nut comprising a screw thread, and a bayonet or ring clamp mechanism to effect coupling between the elongated probe and the horn assembly. FIGS. 4A and 4B show opposite-end views of a preferred embodiment of the locking means, comprising a locking nut  30  consisting a screw thread arrangement  44  that is capable of engaging a complementary thread arrangement located along the outer diameter of the distal end of the horn assembly. When engaged with the horn assembly  34  with the elongated probe  10  positioned proximally to provide “coupling”, locking nut  30  provides a rigid interface between the probe and horn components and ensures intimate contact between the terminal end surfaces of the said components, which is important for efficient transmission of ultrasound energy to the probe. FIG. 5 shows a cross-sectional view of the horn assembly  34  and elongated probe  10  “coupled” by the locking nut  30  of the invention by engaging screw thread  44  with complementary threads  40  in the horn assembly.  
         [0067]    Now referring to FIG. 6, the horn assembly  34  comprises of a distal end  38  that is capable of being coupled to the enlongated probe of the invention, and a proximal end  38  that is coupled to a transducer (not shown) functioning as an ultrasound energy source by screw threads  40  and  42  located terminally at either end. As mentioned previously, horn assembly  34  comprising the sound conductor or “horn” functions as an energy reservoir that allows only a small fraction of the energy transmitted by the source to the probe, thereby minimizing energy loss due to probe bending or damping that can occur when it is inserted into blood vessels.  
         [0068]    [0068]FIG. 7 shows disassembled and assembled views of another preferred embodiment of the probe attachment means of the invention, including cross-sectional views in the assembled state, that includes a coupling assembly comprising a “quick attachment/detachment” (QAD) collet rod  48  and housing assembly  54  that enables efficient coupling of the elongated catheter probe to the horn assembly (not shown). As seen in the figure, collet rod  48  is configured to slideably receive and retain the proximal end of the ultrasonic probe of the invention within the interior volume of collet housing  64 , and restrained in a rigid, non-removable manner by socket screw  58 , which comprises a cylindrical head  60  with a uniformly flat end to facilitate its intimate contact with other device components, including the terminal end of the horn assembly. FIG. 7 also shows regular and expanded cross-sectional views of QAD collet rod  48  inserted into collet housing  64  that is non-removably retained within said housing by socket screw  58 . As seen in segment “C” of the cross-sectional view, the inner surface of collet housing tapers circumferentially outwardly at the distal end so as to enable partial insertion of the cylindrically slotted head of the QAD collet rod. The inner diameter of the of the circumferentially tapered section of the housing is chosen to be slightly larger then the insertable segment QAD collet rod head so as to create a “clearance” that facilitates easy  20  insertion and retraction of the said collet rod (shown in the detail cross-sectional view in FIG. 7).  
         [0069]    As shown in FIG. 8A, QAD collet rod  48  is comprised of a hollow cylindrical segment  49  with a proximal end  50  and a head segment  51  at distal end  52  (the end farthest from the collet housing and horn assembly) with a diameter larger than that of cylindrical segment. The head segment at distal end  52  comprises a compressible slit  54  that is capable of accommodating the proximal end of the elongated probe. The proximal end  50  of the QAD collet rod comprises a hollow cylindrical opening containing a screw thread inscribed along the inner surface of said opening that is capable of receiving a retaining a socket screw  58  (shown in FIG. 7) inserted from the proximal end of the QAD collet housing, so as to render collet rod  48  with attached probe to be rigidly and non-removably restrained within said collet housing. As shown in FIG. 8B, collet housing  64  comprises a hollow cylinder with a distal end  68  capable receiving the entire cylindrical segment  49  of the probe QAD collet rod (FIG. 8A) and part of the cylindrically slotted head segment  51  when the collet rod is inserted at its proximal end  50  into collet housing  64 , and a distal end  72  comprising a screw-thread  74  along the outer surface. The proximal end  72  of collet housing further comprises a screw thread  74  on its outer surface capable of engaging the terminal end of a horn assembly in a manner so as to provide intimate contact between the horn and the flat head of socket screw  58  restraining QAD collet rod  48  attached to the elongated probe, thereby enabling transmission of ultrasound energy from the horn to the elongated probe.  
         [0070]    The socket screw  58  of the invention is capable of being “tightened” by applying a torque by conventional methods causing it to simultaneously engage the thread assemblies if of collet rod housing  64  and the QAD collet rod  48  respectively, after insertion of the collet rod into said housing. Such a tightening action which is performed after attachment of the elongated probe to collet rod  48  by insertion of the probe into slotted head  54  at the distal end  52  of the collet rod causes retraction of the said slotted head into the collet housing. This in turn, results in elimination of the “clearance” between the collet rod and the collet housing, causing a contraction in the diameter of the slot in the head of collet rod and in turn, resulting in 1) its intimate contact with the surface of the proximal end of the inserted elongated probe, and 2) restraining the probe in a non-detachable manner to the collet rod—housing coupling assembly. The rigid and non-removable mode of probe attachment to the said coupling assembly enables transmission of ultrasound energy from a horn assembly attached to the collet rod housing coupling assembly to the elongated probe so as to cause it to vibrate in a transverse mode, and hence provide cavitation energy for tissue destruction. Conversely, the probe is detached (or “de-coupled”) from the collet rod-housing coupling assembly by loosening the socket screw  58  by application of a torque in a direction opposite to that used for the probe attachment process.  
         [0071]    [0071]FIG. 9 shows disassembled and assembled views of another preferred embodiment of the probe attachment means of the invention, including cross-sectional views in the assembled state, consisting a QAD collet rod -housing assembly that comprises a outwardly cylindrically tapered collet housing component  80  with a proximal end  86  and a distal end  90 , further comprising a centrally located cylindrical bore with open ends extending through its longitudinal axis that is capable of slideably receiving and retaining a collet rod. As seen in segment “C” of the cross-sectional view in FIG. 9, the inner surface of collet housing tapers circumferentially outwardly at the distal end so as to enable partial insertion of the cylindrically slotted head of the QAD collet rod. The inner diameter of the of the circumferentially tapered section of the housing is chosen to be slightly larger then the insertable segment QAD collet rod head so as to create a “clearance” that facilitates easy insertion and retraction of the said collet rod (shown in the detail cross-sectional view). The cross-sectional view of the FIG. 9 shows the QAD collet rod restrained within the collet rod housing by a locking nut  88 . FIGS. 10A and 10B show the collet rod and collet housing respectively, of the embodiment. As seen in FIG. 10A, QAD collet rod comprises a solid cylindrical body  94  with a head segment  98  attached at proximal end  92 . A longitudinal slit  99  extends from head segment  98  partially into the cylindrical body  94 . The distal end  96  of cylindrical body  94  comprises a thread assembly  100 . As seen in FIG. 10B, collet housing  80  comprises a cylindrical rod with a continuously decreasing external diameter from proximal end  86  to distal end  90 , further comprising a centrally located cylindrical inner bore extending along its entire length providing openings at both ends. The diameter of the bore increases proximally to the distal end so as to circumferentially taper outwardly in a manner permitting partial insertion of head segment  98  of the collet rod The cylindrical bore of the collet housing  80  is capable of slideably receiving a collet rod  94  such that thread assembly  100  of the said collet rod extends beyond proximal end  86  of the end proximal end  92  to permit a rigid and non-removable attachment of the collet rod by engaging thread assembly  100  with locking nut  88  (shown in FIG. 9). The locking nut performs a similar function and in a manner that is substantially similar to that of the restraining screw described in a previous embodiment (FIG. 7) in enabling the elongated probe to be non-removably attached to and detached from the QCD collet rod for operation of the device as described previously. Upon rigid non-removable attachment of the elongated probe to the coupling assembly, the threading  88  of the collet housing is engaged to complementary threading of the horn assembly (not shown) of the assembly so as to render intimate contact of the sound conductor (horn) in said horn assembly with the proximal end  92  of the collet rod to enable transmission of ultrasound energy from the horn to the elongated probe attached at proximal end  96  of the collet rod.  
         [0072]    [0072]FIG. 11 shows another preferred embodiment of probe coupling assembly of the invention, including a cross-sectional view, comprising a QAD collet  105  that is insertable into a “compression” collet housing component  115  comprising a circular bore  114  that is detachably connected to a QAD base component  120 . As seen in FIG. 12A, QAD collet  105  comprises a cylindrical segment  106  with a cylindrical slot  108  extending through its longitudinal axis that is capable of slideably receiving the proximal end of the elongated probe, and symmetrically tapered at proximal and distal ends  110 . As seen in FIG. 12B, QAD base component  120  comprises a conical slot  130  at the cylindrical distal end capable of accommodating the one of the symmetrically tapered ends  110  of the collet. QAD base component  120  further comprises a thread assembly  132  located along its outer circumference proximal to its distal end, that is capable of engaging complementary threads in the QAD compression housing component  115 . The proximal end  136  of the base component contains a thread assembly  134  along the outer circumference that is capable of engaging and attaching to the horn assembly (not shown) of the invention. As seen in FIG. 12C, QAD compression housing component  115  comprises a hollow cylindrical segment with a proximal end  117  and a circular bore  114  (shown in FIG. 11) tapered distal end  119  capable of slideably receiving the proximal end of the elongated probe. The inner diameter at the proximal end of the QCD compression housing component  115  is chosen so as to accommodate the symmetrically tapered terminal end  110  of collet  105  that is distal to the base component, and further comprises a thread assembly  118  that enables compression housing component to engage with complementary threading  132  on the distal end of QAD base component  120 . The proximal end of the elongated probe of the invention is inserted through the circular bore  114  at proximal end of compression housing component  115  and the inserted symmetrically tapered end  110  of collet  105  in a manner so as to occupy the entire length of cylindrical slot  108  in collet  105 . The other symmetric end  110  distal to the compression housing  115  is then placed inside conical pocket  130  of base component  120 , following which threads  118  of the compression housing is engaged with the complementary threads  132  in QAD base component  120  by applying a torque so as to render the collet  105  to be non-removably retained inside the coupled base-compression housing assembly, thereby restraining the inserted elongated probe rigidly and non-removably within the coupling assembly. Additionally, the mode of restraint provided by the coupling assembly of the embodiment enables the probe to maintain intimate contact with said assembly and in turn the horn assembly (not shown) of the invention attached to the coupling assembly by engaging thread  134  in QAD base component  120  with complementary threading in the horn assembly. Ultrasound energy transmitted from the horn is therefore communicated to the probe via the coupling assembly. The elongated probe is detached by disassembling the coupling assembly, thereby allowing the probe to be withdrawn from collet  105  and compression housing component  115 .  
         [0073]    The device of the invention upon being activated causes the ultrasound generator component to transmit ultrasonic energy to the horn component. The transmitted energy is amplified by the horn component, which in turn, due to it&#39;s intimate and proximal contact with the elongated probe, transmits the amplified energy to the said probe. Transverse vibration modes on the elongated probe that fall within the horn resonance are therefore, excited. The “coupling” between the elongated probe and the horn is configured so to as to present a relatively large impedance mismatch. The coupling is located at an anti-node of the horn. Longitudinal waves impinging on the coupling will be either reflected back inside the horn, or transmitted outward to the elongated probe proportionally to the degree of the impedance mismatch at the coupling interface. In a preferred embodiment, the coupling is arranged in a manner so as to cause reflection of a substantial portion of ultrasound energy back into the horn. Under these conditions, the horn essentially functions as an energy storage device or reservoir, thereby allowing for a substantial increase in drive amplitude.  
         [0074]    The ultrasonic device of the present invention provides several advantages for tissue ablation within narrow arteries over convention devices. The transverse energy is transmitted extremely efficiently, and therefore the required force to cause cavitation is low. The transverse probe vibration provides sufficient cavitation energy at a substantially low power (˜1 watt). Because transverse cavitation occurs over a significantly greater i.e. along the entire probe longitudinal axis that comes in contact with the tissue, the rates of endovascular materials that can be removed are both significantly greater and faster than conventional devices. The transverse vibrational mode of the elongated probe of the invention and its attachable/detachable coupling mode to the horn assembly allows for the bending of the probe without causing probe heating as heat in the probe.  
         [0075]    Another advantage offered by the device of the invention is that the mechanism for probe attachment and detachment by means of a lateral wall compression and decompression provided by the coupling assembly. The probe can therefore, be rapidly attached to and detached from the coupling assembly without necessitating its “screwing” or “torquing” that are utilized conventional modes of attachment of ultrasonic probes to the probe handle. This feature facilitates ease of manipulation of the probe within narrow and torturous venal cavities, and its positioning at the occlusion site in a manner substantially similar to narrow lumen catheters prior to and after device use.