T. Douglas Mast
Robert C. Waag
Dept. of Elec. Eng., Univ. of Rochester, Rochester, NY 14627
Pulse-echo measurements of ultrasonic scattering are a useful technique for characterization of scatterer properties, since the spectra of a scatterer's spatial properties can be determined from the frequency-dependent backscatter coefficient. In such measurements, the spatial localization associated with transducer beam patterns and time gates causes an uncertainty in the measured spatial-frequency domain properties of the scatterer. This uncertainty is analyzed using an analytic and computational model for measurement system effects in backscatter measurements. The results indicate that wavespace resolution is limited in the direction of the scattering vector by the finite durations of the transmitted pulse and the detector time gate, being approximately proportional to the time gate durations. Resolution in the lateral direction depends mainly on the transducer aperture, increasing approximately in proportion to the aperture diameter. Smooth aperture apodization improves lateral resolution somewhat but has little effect on resolution in the direction of the scattering vector.