We will measure quantitative scattering parameters for biological tissues. These data will be useful to improve utility of diagnostic procedures using reflected or scattered ultrasound in two ways. First, knowledge of the factors which govern the strength of the observed echoes will be useful in the design of clinical apparatus. Second, knowledge of scattering parameters will be useful in differential diagnosis and the identification of particular tissues if the scattered echoes are found to characterize particular tissues. We will initially measure the phase and amplitude in detail of waves scattered by model random scatterers and biological tissue. The data will be processed to yield correlation functions and phase variance. Phase-cancellation artifact magnitude will be calculated for uniform, focussed and shaded apertures. When we can demonstrate that measurements can be taken under conditions which are free of the artifact our measuring program will be resumed. Backscattering cross-sections will be measured as a function of frequency for various tissues, including muscle, myocardium, endocardium, heart valves, blood vessel walls and plaque. Auxilliary studies will involve velocity and adsorption in thin-layered structures. Other studies will concern identification of the mechanisms of scattering through correlations between theory, model measurements and computer simulations of multiple scattering. Fourier optical techniques will be used to obtain from our measurements strict farfield radiation conditions for comparison with theory. Fourier techniques will be used to project the waveforms back into the scattering object to attempt to image the actual scattering sources. We will investigate the feasibility of this technique for medical imaging as well.