Apparatus and methods for ultrasonically enhanced intraluminal therapy

An ultrasonic catheter comprises a catheter body having a resonantly vibrating assembly at its distal end. The resonantly vibrating assembly comprises a tail mass, an interface member, and a spring element which connects the tail mass to the interface member. An interface surface is formed on the interface member and is forwardly disposed at the distal end of the catheter. A longitudinally oscillating driver is disposed between the tail mass and the interface member, and the catheter can be connected to a suitable power supply to induce oscillations in the driver. The driver is typically a piezoelectric device, such as a tubular piezoelectric transducer or a piezoelectric stack. The characteristics of the interface member, spring element, and longitudinally oscillating driver are selected so that the interface member may be resonantly vibrated at an ultrasonic frequency. The catheter is useful for treating luminal conditions, such as vascular clot and plaque. Optionally, a therapeutic agent may be delivered through the catheter simultaneously with the application of ultrasonic energy.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to medical devices and methods. 
More particularly, the present invention relates to apparatus and methods 
for the localized delivery of therapeutic ultrasound energy within the 
vasculature and other body lumens. 
Despite the growing sophistication of medical technology, vascular (blood 
vessel) diseases, such as acute myocardial infarction (heart attack) and 
peripheral arterial thrombosis (blood clots in leg arteries), remain a 
frequent, costly, and very serious problem in health care. Current methods 
of treatment, often expensive, are not always effective. In the U.S. 
alone, the cost of treatment and support and the loss of productivity due 
to vascular diseases together exceed $40 billion per year. 
The core of the problem is that diseased sites within the blood vessels 
narrow and eventually become completely blocked as a result of the 
deposition of fatty materials, cellular debris, calcium, and/or blood 
clots, thereby blocking the vital flow of blood. Current treatments 
include drugs, interventional devices, and/or bypass surgery. High doses 
of thrombolytics (clot-dissolving drugs) are frequently used in an effort 
to dissolve the blood clots. Even with such aggressive therapy, 
thrombolytics fail to restore blood flow in the affected vessel in about 
30% of patients. In addition, these drugs can also dissolve beneficial 
clots or injure healthy tissue causing potentially fatal bleeding 
complications. 
While a variety of interventional devices are available, including 
angioplasty, atherectomy, and laser ablation catheters, the use of such 
devices to remove obstructing deposits may leave behind a wound that heals 
by forming a scar. The scar itself may eventually become a serious 
obstruction in the blood vessel (a process known as restenosis). Also, 
diseased blood vessels being treated with interventional devices sometimes 
develop vasoconstriction (elastic recoil), a process by which spasms or 
abrupt reclosures of the vessel occur, thereby restricting the flow of 
blood and necessitating further intervention. Approximately 40% of treated 
patients require additional treatment for restenosis resulting from scar 
formation occurring over a relatively long period, typically 4 to 12 
months, while approximately 1-in-20 patients require treatment for 
vasoconstriction, which typically occurs from 4 to 72 hours after the 
initial treatment. 
Bypass surgery can redirect blood around the obstructed artery resulting in 
improved blood flow. However, the resulting bypass grafts can themselves 
develop scar tissue and new blood clots in five to ten years resulting in 
blockage and the need for further treatment. In summary, all current 
therapies have limited long term success. 
The use of ultrasonic energy has been proposed both to mechanically disrupt 
clot and to enhance the intravascular delivery of drugs to dissolve clot 
and inhibit restenosis. Ultrasonic energy may be delivered intravascularly 
using specialized catheters having an ultrasonically vibrating surface at 
or near their distal ends. One type of ultrasonic catheter employs a wire 
or other axial transmission element to deliver energy from an ultrasonic 
energy vibration source located outside the patient, through the catheter, 
and to the ultrasonically vibrating surface. While such systems can 
deliver relatively large amounts of energy, the need to transmit that 
energy through the entire length of the catheter presents a substantial 
risk to the patient. 
Moreover, such catheters are typically rigid and cannot easily traverse 
narrow, tortuous arteries, such as the coronary arteries which frequently 
need to be treated. Because of their rigidity and inability to follow the 
vascular lumen, these catheters present a serious risk of vascular wall 
perforation. 
In order to avoid the use of ultrasonic transmission members, catheters 
having ultrasonic transducers mounted directly on their distal ends have 
also been proposed. See, for example, U.S. Pat. Nos. 5,362,309; 5,318,014; 
5,315,998; 5,269,291; and 5,197,946. By providing the transducer within 
the catheter itself, there is no need to employ a transmission element 
along the entire length of the catheter. While such catheter designs offer 
enhanced safety, they suffer from a limited ability to generate large 
amounts of ultrasonic energy. Even though certain of these designs, such 
as that described in U.S. Pat. No. 5,362,309, employ "amplifiers" which 
enhance the delivery of ultrasonic energy, such designs are still 
problematic. In particular, the catheters of the '309 patent have 
relatively long, rigid transducers and are not amenable to receiving 
guidewires, both of which features make it difficult to position the 
catheters within the vasculature, particularly the coronary vasculature. 
For these reasons, it would be desirable to provide improved ultrasonic 
catheter designs overcoming at least some of the problems discussed above. 
In particular, it would be desirable to provide ultrasonic catheters 
having ultrasonic transducers at their distal ends, where the transducers 
are capable of driving interface surfaces with relatively high energy and 
amplitude. It would further be desirable to provide transducer and driver 
designs which are highly efficient and which minimize the production of 
heat within the vascular or other luminal environment. It would be still 
further desirable to provide methods for the intraluminal delivery of 
ultrasonic energy, where the ultrasonic energy is useful for a variety of 
purposes, including the direct mechanical disruption of clot, the 
enhancement of thrombolytic activity of agents to dissolve clot, and the 
enhancement of pharmacologic agents to prevent restenosis of vascular 
sites previously treated by angioplasty or other interventional methods. 
2. Description of the Background Art 
Catheters having ultrasonic elements with the capability of delivering 
thrombolytic and other liquid agents are described in U.S. Pat. Nos. 
5,362,309; 5,318,014; 5,315,998; 5,197,946; 5,397,301; 5,380,273; 
5,344,395; 5,342,292; 5,324,255; 5,304,115; 5,279,546; 5,269,297; 
5,267,954; 4,870,953; 4,808,153; 4,692,139; and 3,565,062; in WO 90/01300; 
and in Tachibana (1992) JVIR 3:299-303. A rigid ultrasonic probe intended 
for treating vascular plaque and having fluid delivery means is described 
in U.S. Pat. No. 3,433,226. An ultrasonic transmission wire intended for 
intravascular treatment is described in U.S. Pat. No. 5,163,421 and 
Rosenschein et al. (1990) JACC 15:711-717. Ultrasonically assisted 
atherectomy catheters are described in U.S. Pat. No. 5,085,662 and EP 
189329. Ultrasonic enhancement of systemic and localized drug delivery is 
described in U.S. Pat. Nos. 5,286,254; 5,282,785; 5,267,985; and 
4,948,587; in WO 94/05361 and WO 91/19529; in JP 3-63041; and Yumita et 
al. (1990) JPN. J. CANCER RES. 81:304-308. An electrosurgical angioplasty 
catheter having ultrasonic enhancement is described in U.S. Pat. No. 
4,936,281. An infusion and drainage catheter having an ultrasonic cleaning 
mechanism is described in U.S. Pat. No. 4,698,058. A drug delivery 
catheter having a pair of spaced-apart balloons to produce an isolated 
region around arterial plaque is described in U.S. Pat. No. 4,636,195. 
SUMMARY OF THE INVENTION 
According to the present invention, a catheter for the intraluminal 
delivery of ultrasonic energy comprises a catheter body having a proximal 
end and a distal end. A tail mass is attached to the catheter body, 
typically at its distal end, and a longitudinally oscillating driver 
engages and extends distally from the tail mass. An interface member is 
disposed to engage a distally forward surface of the oscillating driver, 
and the mass of the interface member is much less than that of the tail 
mass. The tail mass and interface member are connected to each other by a 
spring element so that a resonant system is formed for driving the 
interface member. By employing a relatively large tail mass, the resonant 
frequency of the interface member, spring element, and oscillating driver 
is independent of the tail mass and defined primarily by the mass of the 
interface member and the elastic modulus of the spring element, and the 
oscillating driver. By properly choosing the operating frequency of the 
longitudinally oscillating driver, the resonant system defined by the 
interface member, the spring element, and the oscillating driver can be 
resonantly driven to enhance both the displacement amplitude of an 
interface surface on the interface member and increase the efficiency of 
operation, i.e., the conversion of electrical energy to mechanical energy. 
The longitudinally oscillating member may take any conventional form for an 
ultrasonic transducer, typically being a tubular piezoelectric transducer, 
a piezoelectric stack, or the like. An exemplary tubular piezoelectric 
transducer comprises a hollow piezoelectric cylinder having an inner 
cylindrical electrode and an outer cylindrical electrode. Application of a 
driving current to the electrodes causes axial and radial expansion and 
contraction of the piezoelectric transducer. The axial expansion and 
contraction allow the piezoelectric cylinder to resonantly drive the 
interface member in the longitudinal direction. An exemplary piezoelectric 
stack comprises a plurality of ceramic disks having electrodes 
therebetween. 
The spring element will comprise an axial member capable of mechanically 
coupling the interface member to the tail mass with sufficient space 
therebetween to receive the longitudinal driver. Typically, the spring 
element will comprise at least one rod secured at a proximal end to the 
tail mass and at a distal end to the interface member. The rod may 
optionally be tubular to provide the path for a guidewire, infusion of 
therapeutic agent, or the like. A single rod will usually be disposed 
coaxially within the catheter. Multiple rods may be disposed symmetrically 
about the axis of the catheter body. Alternatively, the spring element may 
comprise a thin-walled cylindrical member secured to the tail mass and the 
interface member and enclosing the longitudinally oscillating member in a 
concentric manner. 
The interface member will usually include a distally disposed interface 
surface which forwardly transmits longitudinal oscillations into the 
environment surrounding the distal end of the catheter. The interface 
surface will typically be convex, although it could be flat, concave, or 
irregular. 
A method according to the present invention for treating intraluminal 
lesions comprises providing a catheter having an interface member at its 
distal end. A forwardly disposed surface of the interface member is 
advanced to a region near the intraluminal lesion, typically to a region 
of vascular stenosis within a patient's vasculature, and the interface 
member is resonantly driven relative to a tail mass mounted proximally of 
the interface member. In this way, ultrasonic energy is efficiently 
delivered into the regions surrounding the distal end of the catheter. The 
interface member is typically driven at a frequency in the range from 10 
kHz to 300 kHz, and will have a longitudinal amplitude in the range from 
about 0.05 .mu.m to 20 .mu.m, under typical mass loading conditions of a 
vascular lumen. The forwardly disposed surface of the interface member 
will typically have an area in the range from 0.5 mm.sup.2 to 20 mm.sup.2, 
and the catheter may be used in a variety of specific therapeutic 
protocols. 
In a first such protocol, the interface member will be engaged directly 
against a vascular obstruction and used to ablate the structure or 
optionally to dissolve the structure with the simultaneous delivery of a 
thrombolytic or fibrinolytic agent. Alternatively, the catheter can be 
used to deliver ultrasonic energy into an environment where a thrombolytic 
or fibrinolytic agent has been delivered, where the catheter need not be 
directly engaged against clot or other stenoses. In such cases, the 
ultrasonic energy will enhance the activity of the therapeutic agent, 
typically by improving penetration of the agent into the clot. In a third 
exemplary protocol, the catheter may be used to deliver an anti-thrombotic 
agent to a previously treated vascular site to inhibit restenosis. Again, 
the ultrasonic energy will typically provide for enhanced delivery and 
penetration of the anti-thrombotic agent into the blood vessel wall. In a 
fourth exemplary protocol, the catheter may be used to dissolve the clot, 
without the adjunct benefit of thrombolytic agents.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS 
The present invention provides apparatus and methods for the treatment of 
luminal conditions, particularly for the treatment of diseases of the 
coronary and peripheral vasculature. Specific conditions include coronary 
and peripheral arterial disease and thrombosis. The apparatus and methods 
are useful for primary treatment of such diseases, where the purpose is to 
ablate, dissolve, or otherwise disrupt the clot, plaque, or other stenotic 
lesions which are responsible for the disease. For example, catheters 
constructed according to the principles of the present invention can be 
used to directly engage and transmit ultrasonic energy into the stenotic 
material in order to mechanically disrupt the material to open the 
associated blood vessel lumen. Such mechanical disruption can be 
accomplished with or without the simultaneous administration of 
pharmacologic and therapeutic agents. The apparatus and methods of the 
present invention are also useful to enhance the administration of 
therapeutic agents, where the therapeutic agents are primarily responsible 
for the disruption of the stenotic material. In such cases, the catheter 
may be engaged against the stenotic material, or alternatively may be 
maintained a short distance away from the stenotic material. The 
ultrasonic energy will be relied on to agitate and promote the penetration 
of the therapeutic agent into the stenotic material. Suitable therapeutic 
agents include known thrombolytic and fibrinolytic drugs, such as heparin, 
tissue plasminogen activator (tPA), urokinase, streptokinase, and the 
like. The catheters and methods of the present invention are still further 
useful for the treatment of vascular sites which have been previously 
treated by other interventional techniques, such as angioplasty, 
atherectomy, laser ablation, and the like. In such cases, the catheters 
will be used to agitate and promote the penetration of anti-thrombogenic 
agents into the vascular or other luminal wall to inhibit restenosis. 
Suitable anti-thrombogenic agents include hirudin, hirulog, heparin, tPA, 
urokinase, streptokinase, and the like. In addition to treatment of the 
vascular system, the present invention may also be used for systemic and 
localized delivery of drugs within other body lumens, such as the ureter, 
the urethra, fallopian tubes, and the like. The present invention may 
further be used for the systemic and localized delivery of drugs within 
the vascular system for treatment of non-vascular diseases, e.g., for the 
treatment of tumors by the localized delivery of drugs to the vasculature 
supporting the tumor. 
The catheter of the present invention will comprise a catheter body having 
a proximal end and distal end. The catheter body will have dimensions and 
physical characteristics selected for the particular use. For vascular 
applications, the length of the catheter body will typically be from 50 cm 
to 200 cm, usually being from 75 cm to 150 cm, and the diameter will be 
from 1 mm to 5 mm, usually being from 2 mm to 4 mm. The diameter of the 
catheter body may vary over its length, and different portions of the 
length may be formed from different materials. In the exemplary 
embodiment, the catheter body will comprise a single extrusion having at 
least one lumen therethrough. The lumen will usually be capable of 
receiving a guidewire, and may also be capable of delivering therapeutic 
agents and/or carrying electrical wires for connection from the proximal 
end of the catheter body to the distal end. Alternatively, the catheter 
body may include separate lumens for delivering therapeutic agent(s), 
routing electrical wires for connection to the ultrasonic transducer, or 
other purposes. The catheter body may be reinforced over all or a portion 
of its length. Conventional reinforcement materials include wire braids, 
wire meshes, wire coils, and the like. When employed with a guidewire for 
placement within the vasculature, the catheter body may have an 
"over-the-wire" design or a "rapid exchange" design. In the former case, 
the guidewire lumen will extend substantially through the entire length of 
the catheter body. In the latter case, the guidewire lumen will terminate 
in a proximal guidewire port located relatively near the distal end of the 
catheter body, usually within 50 cm, more usually within 30 cm, and often 
within 25 cm or less. Usually, a proximal housing will be secured to the 
proximal end of the catheter body, where the housing includes a guidewire 
port, a therapeutic agent infusion port, and the like. 
A resonantly vibrating assembly is secured at or near the distal end of the 
catheter body. The assembly will include an interface member which is 
resonantly vibrated at the desired ultrasonic frequency and which includes 
at least one interface surface for transmitting the ultrasonic vibrations 
to the fluid environment surrounding the distal end of the catheter. The 
resonantly vibrating assembly will usually be attached directly to the 
distal end of the catheter body but also could be disposed partially or 
totally within the distal end of the catheter body. Usually, the 
resonantly vibrating assembly will have a relatively short length, usually 
being below 2 cm, preferably being below 1 cm, and typically being in the 
range from about 0.4 cm to 1.5 cm, more usually in the range from about 
0.6 cm to 1 cm. The assembly will preferably have a low profile to 
facilitate vascular or other intraluminal introductions, typically having 
a diameter below 6 mm, usually in the range from 1 mm to 5 mm, more 
usually in the range from 2 mm to 4 mm. 
In the exemplary embodiment of the present invention, the interface surface 
will be forwardly disposed so that the surface may engage intraluminal 
obstructions as the catheter is advanced through the body lumen, such as a 
blood vessel. Such forwardly disposed vibrating surfaces will also be 
useful for projecting ultrasonic energy forwardly to agitate and promote 
absorption of a liquid therapeutic agent, which agent is usually delivered 
by the same catheter. In alternative embodiments, which are described in 
detail in copending application Ser. No. 08/566,739 (Attorney Docket no. 
17148-000600) now pending, the interface surfaces may be laterally 
disposed to radiate ultrasonic energy radially outward from the catheter 
body. 
The resonantly vibrating assembly of the present invention will further 
comprise a tail mass, a spring element connecting the interface member to 
the tail mass, and a longitudinally oscillating driver disposed between 
the tail mass and the interface member. The mass of the tail mass will be 
substantially greater than that of the interface member, typically being 
at least four-fold greater, and usually being at least eight-fold greater. 
Usually, the mass of the tail mass will be in the range from about 0.1 gm 
to 10 gm, more usually in the range from about 0.2 gm to 4 gm. The mass of 
the interface member will be in the range from 0.01 gm to 1 gm, more 
usually in the range from 0.03 gm to 0.1 gm. In this way, the tail mass 
will remain substantially stationary or immobilized while the 
longitudinally oscillating driver imparts longitudinal (axial) movement to 
the interface member. The mass of the interface member and the spring 
constant of the spring element will be selected so that the resonantly 
vibrating assembly resonates at a particular ultrasonic frequency, 
typically in the range from 10 kHz to 300 kHz, preferably from 20 kHz to 
80 kHz. The longitudinally oscillating driver will also be selected to 
operate (when electronically driven) at the same ultrasonic frequency. In 
this way, the longitudinally oscillating driver will drive the resonantly 
vibrating assembly at its resonant frequency, thus enhancing the 
efficiency of energy transfer and increasing the amplitude of vibration 
(displacement) of the interface member. Preferably, the interface member 
will operate with a displacement (under loaded conditions) of at least 
about 0.5 .mu.m, preferably in the range from 0.05 .mu.m to 20 .mu.m, and 
more preferably in the range from 0.5 .mu.m to 2 .mu.m. 
The tail mass will usually be formed separately from the catheter body and 
other components of the vibratory assembly, but optionally could be formed 
as part of the catheter body or alternatively as an integral unit with the 
spring element and/or interface member. The dimensions and shape of the 
tail mass will usually be selected to conform to the dimensions of the 
catheter body, i.e., usually being a short cylinder having a diameter 
which is the same as or slightly smaller than that of the distal end of 
the catheter body. 
The interface member will usually form the distal-most tip of the catheter, 
and will usually have a forwardly disposed convex surface which defines 
the interface surface. The interface surface, however, need not be convex, 
and could alternatively be concave, flat, irregular, or have any other 
geometry capable of radiating ultrasonic energy forwardly as the interface 
member is vibrated. Typically, the interface surface will have an area in 
the range from 0.5 mm.sup.2 to 20 mm.sup.2, preferably from 3 mm.sup.2 to 
12 mm.sup.2. 
The spring element may comprise a single rod or tube extending distally 
from the tail mass and attached to the proximal surface of the interface 
member. Usually, the single spring element will be disposed coaxially 
within the catheter. Alternatively, the spring element may comprise 
multiple rods or shafts, in which case they will usually be disposed 
symmetrically about the axis of the catheter. 
One or more axial passages may be formed through the resonantly vibrating 
assembly, typically for passage of a guidewire, delivery of therapeutic 
agents, or the like. To provide such lumens, it will be necessary to form 
holes through both the tail mass and the interface member. Such holes can 
be aligned and joined by one or more axial components of the spring 
element, typically in the form of hollow tubes to provide a continuous 
lumen through the assembly. 
The longitudinally oscillating driver can take any conventional form of 
ultrasonic transducer capable of converting electrical energy to 
mechanical ultrasonic vibrations. Exemplary transducers include 
piezoelectric elements, such as hollow piezoelectric cylinders, 
piezoelectric stacks, and the like. Suitable piezoelectric cylinders will 
be composed of a suitable piezoelectric material, such as a lead zirconate 
titinate (e.g., PZT-8), have a length in the range from 2 mm to 2 cm, an 
outer diameter in the range from 1 mm to 4 mm, and a wall thickness in the 
range from 0.1 mm to 0.5 mm. Piezoelectric stacks will comprise a 
plurality of ceramic disks, typically from 10 to 60 disks, having 
electrodes of alternate polarity disposed between the disks. Other 
suitable ultrasonic transducers include magnetostrictive elements, such as 
those described in copending application Ser. No. 08/566,740 (Attorney 
Docket no. 17148-000500) pending, the full disclosure of which is 
incorporated herein by reference. 
The spring element which joins the interface member to the tail mass may 
comprise a single component, e.g., a single solid rod or hollow tube 
disposed along the longitudinal axis of the catheter or a cylindrical 
shell either within or external to the longitudinally oscillating driver. 
Alternatively, the spring element may comprise a plurality of components, 
such as a plurality of rods or tubes disposed symmetrically about the 
longitudinal axis of the catheter. The spring element may be composed of 
any of a wide variety of materials, most typically being a stainless 
steel, such as a hardened stainless steel having a Rockwell stiffness of 
at least about 35. The cross-sectional area of the spring element(s) shall 
be sufficient to provide a maximum tension of approximately 20% of the 
tensile strength of the material, typically about 25,000 PSI, at the time 
when the spring experiences its maximum deformation, i.e., the time of 
maximum forward displacement of the interface member. The assembly of the 
tail mass, interface member, and longitudinally oscillating driver is 
compressed by the spring mass with a static force sufficient to present 
continuing compressive forces at the time when the assembly shrinks to its 
minimum longitudinal displacement. The interface member and spring element 
shall have a mass and stiffness which together assure that the spring 
element retains compressive force on the interface member at the time of 
maximum reverse acceleration in order to prevent the interface member from 
separating from the oscillating driver. The time of maximum reverse 
acceleration occurs at the time of maximum forward displacement. 
Referring now to FIG. 1, a catheter system 10 comprising a catheter 12 
constructed in accordance with the principles of the present invention and 
an ultrasonic power supply 14 is illustrated. The catheter 12 includes a 
catheter body 16 having a distal end 18 and a proximal end 20, a proximal 
housing 22 having a fluid infusion port 24, and a guidewire port 26. The 
catheter 12 includes at least a single lumen 28 extending from the 
proximal end 20 to the distal end 18 and connected to both the fluid 
infusion port 24 and the guidewire port 26. A cable 30 extends from the 
proximal end 20 of the catheter body 16 (typically through the lumen 28) 
and includes a connector 32 which may be removably attached to the power 
supply 14. The power supply 14 may be selected to drive the ultrasonic 
transducer (described below) at about a preselected frequency. The power 
supply 14 will typically comprise a conventional signal generator, such as 
those that are commercially available from suppliers such as 
Hewlett-Packard, Palo Alto, Calif., and Tektronics, Portland, Oreg., and a 
power amplifier, such as those commercially available from suppliers such 
as ENI, Rochester, N.Y., and Krohn-Hite, Avon, Mass. Alternatively, the 
power supply may comprise custom signal generator and power amplifier 
circuits with tracking circuits to keep the driving frequency at the 
resonant frequency of the ultrasonic driver in the catheter tip as this 
resonant frequency drifts due to thermally induced material variations. 
Referring now to FIGS. 2-4, a resonantly vibrating assembly 40 is mounted 
within the distal end of the catheter body 16. The resonantly vibrating 
assembly 40 comprises a tail mass 42, an interface member 44, and a spring 
element 46 in the form of a tube having a lumen 48 therethrough. The 
tubular spring element 46 is connected at its distal end to the interface 
member 44 and at its proximal end to the tail mass 42. Attachment of these 
components can be achieved in conventional ways, such as threaded 
attachment joints, the use of adhesives such as epoxy, solder joints, 
welded joints, and the like. 
A longitudinally oscillating driver 50 is mounted between the tail mass 42 
and the interface member 44. The driver 50 is a tubular piezoelectric 
transducer, as best illustrated in FIGS. 3 and 4. The tubular transducer 
includes a piezoelectric tube 52 formed from a suitable material, as 
described above, sandwiched between an outer electrode 54 and inner 
electrode 56. Often, a small annular gap will be left between the driver 
50 and the inner wall of the catheter body 16 and/or the outer wall of the 
spring element 46, although the gap is not shown in FIG. 2. Application of 
a suitable driving voltage to the electrodes 54 and 56 will cause the 
tubular transducer to oscillate both longitudinally and radially. A 
suitable driving voltage will be from 10 V to 200 V. The resulting axial 
displacement is best observed in FIG. 5, where displacements in the range 
from 0.05 .mu.m to 20 .mu.m, usually from 0.5 .mu.m to 2 .mu.m, may be 
achieved. 
A lumen 60 is formed through the tail mass and a second lumen 62 is formed 
through the interface member. The lumens 60 and 62 are aligned with the 
lumen 48 through the driver 50. In this way, a continuous lumen is 
provided from the lumen 28 of the catheter body through the distal tip of 
the catheter. This lumen is suitable for introducing the catheter over the 
guidewire and/or delivering therapeutic agents through the catheter and 
releasing said agents from the distal tip. 
An alternative resonantly vibrating assembly 70 is illustrated in FIGS. 6 
and 7. Catheter body 12, tail mass 42, and interface member 44 may all be 
identical to those described in connection with FIGS. 1-5. The spring 
element, however, comprises a pair of radially offset shafts 72 which are 
disposed symmetrically about the axis of the catheter. A longitudinally 
oscillating driver 74 comprises a stack of piezoelectric disks 76 which 
are sandwiched between electrode plates 78, as best illustrated in FIG. 7. 
The electrodes 78 will be connected to positive and negative terminals of 
the power supply 14 in order to induce longitudinal vibrations in the 
piezoelectric stack. The stack may be machined to include opposed channels 
80 to accommodate the rods 72 as well as a central lumen 82 for 
accommodating a guidewire and/or the delivery of fluids. 
Referring now to FIG. 8, use of the catheter 12 for directly engaging a 
region of thrombus T in a diseased blood vessel BV having a region of 
plaque P is illustrated. The forwardly disposed interface surface of 
interface member 44 is advanced through the lumen of the blood vessel in a 
conventional manner until it engages the thrombus T. The resonantly 
vibrating assembly will then be activated to cause ultrasonic vibration of 
the interface member 44. The interface surface of the interface member, in 
turn, will transmit the ultrasonic vibrations directly into the thrombus 
T, resulting in mechanical disruption of the thrombus and clot. 
Optionally, a thrombolytic or fibrinolytic agent may be delivered through 
the catheter 12 and released into a region proximal to the thrombus T, 
either before, during or after the mechanical disruption. Preferably, the 
ultrasonic energy will be transmitted while the treatment agent is being 
released to enhance penetration of the agent into the thrombus T. 
An alternative treatment method is illustrated in FIG. 9. There, a sleeve 
catheter 90 is disposed over the catheter 12 of the present invention. An 
anti-thrombogenic treatment agent is delivered through the sleeve catheter 
90 to a target site TS within a blood vessel BV. The interface member 44 
is ultrasonically vibrated, as described previously. The ultrasonic 
vibration will enhance penetration of the agent into the wall of the blood 
vessel BV. This method would be equally suitable for delivering drugs into 
other body lumens. Use of the sleeve catheter 90 for delivering drugs is 
illustrated as an alternative to delivering the drugs through the lumen of 
the catheter 12 itself. It will be appreciated that the sleeve catheter 90 
could have been used in the method of FIG. 8. Conversely, the lumen of 
catheter 12 could have been used to deliver the anti-thrombogenic agent in 
the method of FIG. 9. 
While the above is a complete description of the preferred embodiments of 
the invention, various alternatives, modifications, and equivalents may be 
used. Therefore, the above description should not be taken as limiting the 
scope of the invention which is defined by the appended claims.