In this study we have established a new approach to more accurately map
acoustic wave speed (which is a measure of stiffness) within soft biological
tissues at micrometer length scales using scanning acoustic microscopy. By
using thin (5 μm thick) histological sections of human skin and porcine
cartilage, this method exploits the phase information preserved in the
interference between acoustic waves reflected from the substrate surface as
well as internal reflections from the acoustic lens. A stack of images were
taken with the focus point of acoustic lens positioned at or above the
substrate surface, and processed pixel by pixel using custom software
developed with LABVIEW and IMAQ (National Instruments) to extract phase
information. Scanning parameters, such as acoustic wave frequency and gate
position were optimized to get reasonable phase and lateral resolution. The
contribution from substrate inclination or uneven scanning surface was
removed prior to further processing. The wave attenuation was also obtained
from these images.