Ultrasonic catheter power control

1. A method of treating an occlusion at a treatment site within a patient's vasculature comprising:

providing an ultrasonic catheter having a distal region, a proximal region opposite the distal region, a fluid delivery lumen having at least one opening in the distal region, and an ultrasound radiating member positioned within the distal region;

positioning the ultrasonic catheter at the treatment site, such that at least a portion of the distal region is within the occlusion;

passing a therapeutic compound through the fluid delivery lumen such that the therapeutic compound is delivered to the treatment site; and

emitting ultrasonic energy from the ultrasound radiating member, wherein the emitted ultrasonic energy has

an amplitude that is periodically varied between a low amplitude and a high amplitude,

a high amplitude pulse duration of between approximately 1 millisecond and approximately 50 milliseconds, and

a high amplitude pulse repetition rate of between approximately 5 hertz and approximately 150 hertz, and

an in situ intensity at an energy radiating surface of between approximately 20 watts in −2 and approximately 90 watts in −2 .

2. The method of claim 1 , wherein the emitted ultrasonic energy has a time average power inclusive of the low amplitude and the high amplitude periods of between approximately 0.1 watts and approximately 2.0 watts.

3. The method of claim 2 , wherein the emitted ultrasonic energy has a time average power inclusive of the low amplitude and the high amplitude periods of between approximately 0.6 watts and approximately 1.2 watts.

4. The method of claim 1 , wherein the emitted ultrasonic energy has a pulse average power exclusive of the low amplitude periods of between approximately 0.01 watts and approximately 20 watts.

5. The method of claim 1 , wherein the emitted ultrasonic energy has a duty cycle of between approximately 1% and approximately 50%.

6. The method of claim 5 , wherein the duty cycle is between approximately 7.5% and approximately 15%.

7. The method of claim 1 , wherein the emitted ultrasonic energy has a high amplitude pulse duration of between approximately 2.5 milliseconds and approximately 5 milliseconds.

8. The method of claim 1 , wherein the ultrasound radiating member is a PZT transducer.

9. The method of claim 1 , further comprising monitoring a temperature at the treatment site.

10. The method of claim 9 , further comprising adjusting a time average power inclusive of the low amplitude and the high amplitude periods in response to the temperature measured at the treatment site.

11. A method comprising:

providing a catheter having an ultrasound radiating member positioned in a catheter distal region, wherein the catheter has an outer diameter of less than about 5 French for advancement through a small blood vessel, and wherein the ultrasound radiating member has a hollow central region;

delivering a therapeutic compound through the catheter to the small blood vessel, such that the therapeutic compound passes through the ultrasound radiating member hollow central region; and

passing an electrical driving signal through the catheter to the ultrasound radiating member, such that the ultrasound radiating member periodically delivers pulses of ultrasonic energy having an in situ intensity at an energy radiating surface of between approximately 20 watts in −2 and approximately 90 watts in −2 to the small blood vessel, the pulses of ultrasonic energy having a pulse duration.

12. The method of claim 11 , wherein the ultrasound radiating member comprises a PZT transducer.

13. The method of claim 11 , further comprising monitoring a temperature in the small blood vessel.

14. The method of claim 13 , further comprising adjusting a pulse average power in response to the temperature measured in the small blood vessel.

15. The method of claim 11 , wherein the pulse duration is between approximately 1 millisecond and approximately 50 milliseconds.

16. The method of claim 15 , wherein the pulse duration is between approximately 2.5 milliseconds and approximately 5 milliseconds.

17. The method of claim 11 , wherein the pulses of ultrasonic energy further have a pulse average power.

18. The method of claim 17 , wherein the pulse average power is between approximately 0.1 watts and approximately 20 watts.

19. The method of claim 18 , wherein the pulse average power is between approximately 8 watts and approximately 16 watts.

20. The method of claim 11 , wherein the pulses of ultrasonic energy are delivered to the small blood vessel at a frequency of between approximately 5 hertz and approximately 150 hertz.