Acoustic microscopy: a study of contrast in fresh tissue

The scanning laser acoustic microscope (SLAM), which exhibits a resolution of about 15 /spl mu/m in biological materials, was operated at a frequency of 100 MHz to evaluate the source of image contrast. Specifically, the SLAM´s quantitative capabilities yielded the ultrasonic propagation properties of attenuation coefficient and propagation speed of rat brain tissue (white versus gray matter) and these properties mere correlated with tissue constituents and image contrast. The SLAM´s image contrast between the two brain layers in both fresh and fixed specimens was analyzed subjectively by an experienced microscopist. It was determined that ethanol fixation decreased the image contrast between the brain layers. Additionally, the propagation speed was the least affected property in the fresh tissue specimens yet increased in both brain layers after fixation whereas the attenuation coefficient of white matter in unfixed brain tissue was higher than that of gray matter. These results indicate that the SLAM´s acoustic image contrast is a direct reflection of the difference in attenuation coefficient whereas the propagation speed is not a significant contributor to the image contrast.<>