Phase detection in acoustic microscopy.

The scanning laser acoustic microscope provides a relatively simple means by which speed of sound data can be collected from biological specimens. By employing a phase detection circuit, phase-contour lines can be superimposed on acoustic micrographs and digitized for direct speed of sound calculations. Because of the existence of mild field non-uniformities, the phase reference must be mathematically modeled. This is accomplished by employing a polynomial function and simple linear regression. Scattering can be studied by using a frequency-selective "dark field" approach. Speed of sound maps are readily produced from the phase data by applying the simple geometric relationships of wave propagation; however the theoretical limitations of the technique must be kept in mind. Using this approach, useful data have been obtained.