Calculating Ultrasound Pressure and Power Intensity.

The output pressures were measured using a calibrated hydrophone (Onda, model HNR-0500). The hydrophone measurements were performed at the position of peak spatial pressure. When converting the measured voltages into pressures, we accounted for the hydrophone capacitance according to the manufacturer’s calibration. Using the appropriate conversion factor listed under the Pascals-per-volt column on the look-up table that was supplied with the calibrated hydrophone, the hydrophone voltage-trace waveform was transformed into an acoustic-pressure waveform measured in MPa.

We calculated the ultrasound power intensity in Watts/square centimeter (W/cm²) with the following equation:

where P is effective ultrasound pressure (calculated as 0.707 multiplied by peak amplitude of the pressure wave) and Z is the acoustic impedance (1.48 × 10⁶ kg ⋅ m⁻² ⋅ s⁻¹ was used).