A Unified Method of Broad-Band Echo Characterization for Diagnostic Ultrasound

Blood flow can be described by a scattering function, i.e., by the expected distribution of Doppler shifts and delays that are introduced by a collection of moving point scatterers. An equivalent representation is the echo autocovariance function, measured for a sequence of echoes from different transmitted pulses. Tissue structure can be characterized by the frequency dependence of acoustic reflectivity for echoes from large acoustic discontinuities (highlight echoes), and by the "texture" of the echo from a distributed reflector. Highlight structure and frequency dependence of tissue reflectivity can be obtained from the signal-echo cross-ambiguity function, and texture differences are related to differences in echo power spectra and auto-covariance functions.