Ultrasound Imaging Using the Coherence of Estimated Channel Data

This article introduces a novel method to estimate the coherence of ultrasound channel data from beamformed radio frequency (RF) data. Estimates of ultrasound channel data are obtained by spatially filtering acquired RF data in the frequency domain. The frequency response of the spatial filters yields outputs similar to frequency domain representations of individual channel signals. This technique performs multiple normalized cross-correlations from the outputs of multiple spatial filters. The coefficients are summed together for each pixel in the coherence-based image. Simulation results using a 64 element 2.5-MHz phased array showed an improvement in contrast-to-noise ratio (CNR) of 67%–93% and a 125%–183% improvement in speckle signal-to-noise ratio (SNR) compared with standard beamformed data. Experimental CNR using a tissue-mimicking phantom showed improvement of 43%–58%, and experimentalSNR improvement was 23%–154%. Comparisons to a previously coherence method, short-lag spatial coherence, are also presented. Preliminary
in vivo
images of the heart and gall bladder are also shown. This method improves CNR enabling improved visualization of anechoic regions such as cyst and blood vessels.