Figure 2

Schematic representation of the changing shape of vaporization fields (microbubble clouds) with increasing PFC concentrations and acoustic energies. (A) The desired shape is a cigar (prolate ellipsoid) centered at the acoustic focal point (white dot). (B) Tadpole lesions (asymmetric ellipsoids) occur as vaporization begins to concentrate in prefocal regions. (C) Eventually, the microbubble clouds flatten (oblate ellipsoids) and mass along the frontal phantom surface. These shape changes (distortion) can be appreciated qualitatively and can also be assessed quantitatively by measuring the length of the lateral axis (horizontal white line), the area-to-perimeter ratio, and the displacement of the centroid off of the focal plane (center shift).