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1. (WO1992010140) MINIATURE ULTRASONIC TRANSDUCER FOR PLAQUE ABLATION AND CLOT DISSOLUTION
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WHAT IS CLAIMED IS:

1. Ultrasonic apparatus for clot dissolution and plaque ablation comprising:
radiator means for coupling ultrasonic waves into plaque;
piezoelectric crystal means, connected with said radiator means, for the intravascular generation of ultrasonic waves, said ultrasonic waves being propagated along a longitudinal axis of said piezoelectric crystal means and having an inertial node position within said piezoelectric crystal means, said radiator means and piezoelectric crystal means being sized for intravascular position; and
means, including means defining a piezoelectric crystal length, for preventing significant power loss caused by a shifting of the inertial node of the generated ultrasonic waves to a position exterior to said piezoelectric crystal means due to loading of the radiator means caused by the coupling of ultrasonic waves into the clot or plaque.

2. The apparatus of claim 1 further comprising amplifier means, interconnected between said radiator means and piezoelectric crystal means, for transmitting and amplifying mechanical vibration of an ultrasonic frequency from said piezoelectric crystal means to said radiator means.

3. The apparatus according to claim 2 wherein said radiator means includes a convex arcuate radiating surface subtended by a concave surface.

4. The apparatus according to claim 3 wherein said amplifier means comprises a cylindrical member having two regions of different cross-sectional area, a larger cross-sectional region attached to the piezoelectric crystal means and a smaller cross- sectional region attached to the radiator means.

5. The apparatus according to claim 4 wherein said amplifier means and radiator means are formed from a single piece of material.

6. The apparatus according to claim 5 wherein said amplifier means and radiator means include means defining a coaxial bore therein extending from said piezoelectric crystal means to said concave surface.

7. The apparatus according to claim 6 further comprising means for blocking ultrasonic frequency radiating from the cylindrical body portion and concave surface.

8. The apparatus according to claim 7 wherein said means for blocking comprises a low density foam material disposed over said cylindrical body portion and concave surface and extending from said arcuate surface edge to the amplifier means cylindrical member, said foam material having a density substantially less than a density of the cylindrical body portion.

9. The apparatus according to claim 2 wherein said amplifier means has two coaxial portions joined end to end, one substantially solid with free end attached to piezo, and the other having a coaxial hole bored through its length, and having its free end attached to the radiator.

10. The apparatus according to claim 9 wherein said amplifier means and radiator means are formed from a single piece of material.

11. Ultrasonic surgical apparatus for clot dissolution and plaque ablation comprising:
a catheter having at least one lumen therethrough and adapted for intravascular positioning;
an ultrasonic transducer disposed in the catheter lumen at a distal end thereof, said ultrasonic transducer comprising:
radiator means for coupling ultrasonic waves into plaque;
piezoelectric crystal means, connected with said radiator means, for generating ultrasonic waves, said ultrasonic waves being propagated along a longitudinal axis of said piezoelectric crystal means and having an inertial node position within said piezoelectric crystal means; and
means, including means defining a piezoelectric crystal length, for preventing power loss caused by a shifting of the inertial node of the generated ultrasonic waves to a position exterior to said piezoelectric crystal means due to loading of the radiator means caused by the coupling of ultrasonic waves into the clot or plaque; and
power source means, disposed exterior to a proximate end of said catheter and electrically connected to said ultrasonic transducer through said catheter lumen, for causing said piezoelectric crystal to generated ultrasonic waves.

12. The apparatus of claim 11 further comprising amplifier means, interconnected between said radiator means and piezoelectric crystal means, for transmitting and amplifying mechanical vibrations of an ultrasonic frequency from said piezoelectric crystal means to said radiator means.

13. The apparatus according to claim 12 wherein said radiator means includes an arcuate radiating surface subtended by a concave surface defined by a radius of curvature greater than that of the radiator means.

14. The apparatus according to claim 13 wherein said amplifier means comprises a cylindrical member having the regions of different cross-sectional area, a larger cross-sectional region attached to the piezoelectric crystal means and a smaller cross- sectional region attached to the radiator means.

15. The apparatus according to claim 16 wherein said amplifier means and radiator means are formed from a single piece of material.

16. The apparatus according to claim 14 wherein said amplifier means and radiator means include means defining a coaxial bore therein extending from said piezoelectric crystal means to said concave surface.

17. The apparatus according to claim 16 wherein said cylindrical body portions and radiator surface are disposed exterior to the catheter distal end.

18. The apparatus according to claim 17 further comprising means for blocking ultrasonic frequency radiation from the cylindrical body portion and concave surface.

19. The apparatus according to claim 18 wherein said means for blocking comprises a low density foam material disposed over said cylindrical body portion and concave surface and extending from said arcuate surface edge to the catheter distal end, said foam material having a density approaching that of air.

20. The apparatus according to claim 12 wherein said amplifer means has two coaxial portions joined end to end, one substantially solid with free end attached to piezo, and the other having a coaxial hole bored through its length, and having its free end attached to the radiator.

21. The apparatus according to claim 20 wherein said amplifier means and radiator means are formed from a single piece of material.

22. An ultrasonic transducer for clot dissolution and plaque ablation comprising:
radiator means for coupling ultrasonic waves into plaque; and
piezoelectric crystal means, interconnected with said radiator means and having a front and a rear face, for the intravascular generation of ultrasonic waves, said ultrasonic waves being propagated along a longitudinal axis of said piezoelectric crystal means extending between the front and rear faces thereof and having an inertial node positioned between the front and rear faces when the radiator means is not coupling ultrasonic waves into a clot or plaque, said front and rear faces being spaced apart from one another so that when the radiator means is coupling ultrasonic waves into plaque, the inertial node of the ultrasonic waves generated by the piezoelectric crystal means is positioned between the first and second faces.

23. Ultrasonic transducer apparatus for clot dissolution and plaque ablation comprising:
piezoelectric crystal means for generating ultrasonic waves;
radiator means for coupling ultrasonic waves into plaque;
mechanical amplifier means interconnected between said piezoelectric crystal means and said radiator means, for supplying ultrasonic waves to said radiator means of sufficient vibrational energy to disrupt and/or pulverize plaque and liquify clots; said piezoelectric crystal means, radiator means, and mechanical amplifier means being sized for intravascular positioning; and
means for enabling said piezoelectric crystal to sustain relatively constant ultrasonic vibration, without significant change in electrical power input, as the radiator means couples ultrasonic energy into the clot or plaque.

24. The apparatus according to claim 23 wherein said radiator means includes a cylindrical body portion and an arcuate radiating surface subtended by a concave surface defined by the surface of revolution of an arc extending from a surface of the cylindrical body portion to an edge of the arcuate radiating surface.

25. The apparatus according to claim 24 wherein said amplifier means comprises a cylindrical member having a diameter greater than the cylindrical body portion.

26. The apparatus according to claim 25 wherein said amplifier means and radiator means are formed from a single piece of material.

27. The apparatus according to claim 26 wherein said amplifier means and radiator means include means defining a coaxial base therein extending from said piezoelectric crystal means to said concave surface.

28. The apparatus according to claim 28 further comprising means for blocking ultrasonic frequency radiation from the cylindrical body portion and concave surface.

29. The apparatus according to claim 28 wherein said means for blocking comprises a low density foam material dispersed over said cylindrical body portion and concave surface and extending from said arcuate surface edge to the catheter distal end, said foam material having a density substantially less than a density of the cylindrical body portion.

30. The apparatus according to claim 23 wherein said radiator means comprises a hollow cylindrical body portion having a hemispherical surface disposed at a radiating end thereof.

31. The apparatus according to claim 30 wherein said amplifier means and radiator means are formed from a single piece of material.