Spatial Coherence and Beamformer Gain

Many acoustical imaging systems rely upon the assumption that received backscattered waves are perfectly coherent. Poor performance of such systems results as a consequence of poor spatial coherence. The spatial coherence of the backscattered field is influenced by system-, target-, and propagation-dependent factors, such as the transmit beam, scattering properties, and aberration and attenuation, respectively (Goodman, 1985; Liu and Waag, 1995; Mallart and Fink, 1991). This paper demonstrates the relationship between imaging performance and spatial coherence in medical pulse-echo imaging. Performance is quantified here in terms of the gain attained by a conventional delay and sum beamformer. The results are intended for applications such as aperture design, beamformer development, and aberration compensation.