Power parameters for ultrasonic catheter

1. A method of operating an ultrasonic catheter comprising:

advancing a catheter with at least one ultrasonic element to a treatment site in a patient's vascular system or tissue;

driving the at least one ultrasonic element to generate ultrasonic energy, wherein the ultrasonic energy may be characterized by a plurality of power parameters including a frequency, a pulse, a duty cycle, a time average power, and a peak power, wherein during a pulse the at least one ultrasonic element is driven at the frequency, the duty cycle is defined as a ratio of a time of one pulse to a time between an initiation of one pulse and an initiation of a second sequential pulse, the peak power is a peak power achieved during a pulse and the time average power is an average of power during a full cycle between the initiation of one pulse and the initiation of the second sequential pulse;

delivering a therapeutic compound to the treatment site through the catheter; and

varying a power parameter and a physiological parameter of the ultrasonic element, wherein varying the power parameter and the physiological parameter comprises:

repeatedly ramping the peak power between a first maximum value and a first minimum value; and

repeatedly ramping the physiological parameter between a second minimum value and a second maximum value.

2. The method of claim 1 , wherein the peak power and the physiological parameter are ramped up- and down-wards in a linear manner.

3. The method of claim 1 , wherein the peak power and the physiological parameter are ramped up- and down-wards in a non-linear or pseudo-linear manner.

4. The method of claim 1 , wherein ramping the peak power comprises moving through discrete peak power values, and ramping the physiological parameter comprises moving through discrete physiological parameter values.

5. The method of claim 1 , wherein ramping the peak power is independent of any temperature measurement.