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The relationship between center frequency downshift and transmitted bandwidth was investigated for a pulse with Gaussian amplitude spectrum propagating through a lossy medium with power law frequency dependence of attenuation. Tissue equivalent material was characterized by multiple narrowband attenuation measurements, via a substitution method. Power law curves were fitted to the data. The parameters of the curves were used to predict the behavior of the center frequency downshift vs. transmitted bandwidth obtained from a second experiment. The results confirm the mathematical model.

In applications requiring a liquid which is acoustically well matched to biological tissues, it is often difficult to find a material which is matched well in terms of both the acoustic impedance and speed of sound propagation in it; changing one parameter invariably affects the other. A three component liquid system is described, which allows independent adjustment of these two acoustic parameters over a wide range. This range encompasses the soft tissues of the body. Results of parameter measurements are presented in the form which allows simple determination of the mixture required to match any combination of acoustic impedance and speed of sound propagation over a given range.

A novel ultrasonic ring transducer and special control electronics have been developed for scattering and imaging studies. The transducer contains 2048 rectangular elements with a center frequency of 2.4 MHz and a −6-dB bandwidth of 70%. At the center frequency, the element size is 0.29 wavelength ×40 wavelength and the spacing is 0.37 wavelength. A multiplexer provides access to any contiguous 128 elements for transmission and any contiguous 16 elements for simultaneous reception. The transmit electronics have independently programmable waveforms. The receive electronics have time-varied gain functions independently programmable over the range 15–55 dB. Each receive channel includes a 20-MHz, 12-bit A/D converter. The electronics permit synthesis of arbitrary transmit and receive apertures. A novel ultrasonic wavefront design method has been implemented to determine element excitations using backpropagation of a user-specified field pattern. Pulse-echo compound images using constant f/1.0 transmit and receive apertures have been obtained for model scattering objects and an anthropomorphic breast phantom. Scattering measurements have been analyzed to obtain frequency- and angle-dependent average differential scattering cross sections of random media. The system is a useful facility for measurements of ultrasonic scattering for characterization of tissue, development of adaptive beam-formation techniques, and implementation of quantitative image reconstruction methods.