A quantitative approach to partially coherent processing of ultrasonic data via the random phase transducer

The use of random-phase transducers has been suggested as a technique for incoherent processing of ultrasonic data aiming at speckle reduction. The spatial coherence of the transducer is controlled by moving a random-phase screen (RPS) across the ultrasonic beam. It is shown that the spatial coherence of the transmitted beam depends on the transmittance autocorrelation function of the RPS. The rate of speckle change has been measured as a function of the partial coherence of the random-phase transducer. A description is given of the tradeoff of resolution degradation versus SNR (signal-to-noise ratio) improvement encountered with incoherent or partially coherent processing. New possibilities of random-phase transducers are derived from these results. Totally incoherent transducers can be used in applications such as tissue characterization which require high SNR improvement. In the case of partially coherent transducers, nonnegligible SNR improvement can be reached with a very limited loss of resolution. Such transducers might be useful in echocardiographic imaging.<>