Fig. 4

Example of PAM image magnitude (mean of pixel values) vs. commonly reported measures of cavitation activity (arbitrary units) for a 10 W and 80 W, 30-second phantom sonication. The tight correlation suggests PAM image magnitude is equivalent to variance and broadband noise as a proxy for cavitation activity. Each point is computed from a single ultrasound acquisition, and the full set of 600 acquisitions is shown for 10 W and 80 W. Channel variance is the sum of raw channel variances (proportional to receive volts-squared). Broad-band noise level is the total amplitude of the frequency spectrum (proportional to volts), once harmonic and ultra-harmonics have been filtered out. In both plots the x-axis values were computed per channel and then summed. The color saturation gradient represents sonication time, as is shown in the color bar on the right. The most saturated color is at time 0, and the least saturated is at 30 s. Quantities remained correlated even after bubble depletion in the first several seconds