Theoretical evaluation of some related methods for reducing acoustic speckle

The authors present the theory underlying a set of previously reported procedures that reduce speckle degradation in ultrasound B-scans. These methods range from intensity detection of individual phased array elements to the use of simulation of multiple random-phase screens across the transmit and/or receive apertures. An advantage inherent in each is the cancellation of effects due to random-phase distortions that might be created by propagation medium inhomogeneities arising near the apertures. The methods also cancel to various degrees the quadratic phase distortions present outside the transducer focal zone, and they yield similar improvements in detectability of large speckle-generating targets, achieving a performance level that lies approximately midway between conventional processing and the theoretical limit imposed by the properties of the imaging system. However, the methods differ in their responses to specular reflectors and single large scatterers. The authors derive and compare analytic expressions for both the speckle signal-to-noise ratio and imaging system impulse response of each method.