Figure 4
Quantitative assessment of the progressive changes in the shape and location of the vaporization fields. (A) There is a logarithmic relationship between the length of the lateral axis and the PSNE concentration for a given acoustic intensity (R2 ≥ 0.94, p < 0.001, linear regression on log scale), demonstrating that most of the change occurs in the lower PSNE concentration range. (B) Change in the area-to-perimeter ratio reflects changes in the microbubble cloud shape (distortion). (C) Prefocal displacement of the centroid (center shift) as a function of PSNE concentration. The first PSNE concentration for a given intensity to demonstrate a statistically significant increase in distortion compared to the previous concentration (p ≤ 0.01 by Student's t test) corresponded with the first concentration to demonstrate a statistically significant center shift (p ≤ 0.03 by Student's t test). These are the points of early tadpole transformation and occurred at PSNE concentrations of 5 × 105, 2.5 × 106, and 1 × 107 ND per milliliter using intensities of 650, 390, and 140 W/cm2 (PNP = 4, 3, and 2 MPa), respectively. (n ≥ 4, mean ± S.D.). The arrowed bracket identifies this transformation point for an acoustic intensity of 140 W/cm2.