Using resolution enhancement compression to reduce variance of scatterer size estimates from ultrasonic backscattered signals

Quantitative ultrasound (QUS) imaging techniques based on ultrasonic backscatter have been used successfully to diagnose and monitor disease. A method for improving the contrast and axial resolution of QUS parametric images by using the resolution enhancement compression (REC) technique is proposed. REC is a coded excitation and pulse compression technique that improves the axial resolution and enhances the -6-dB bandwidth of an ultrasonic imaging system. In this study, the improvements in variance of average scatterer diameter (ASD) estimates by using REC-QUS were quantified. Furthermore, REC-QUS was used to extend the tradeoff between estimate variance and the spatial resolution of QUS parametric imaging using ASD estimates. Simulations and experimental measurements were conducted with a single-element transducer (174) having a center frequency of 10 MHz and a -6-dB bandwidth of 80%. Using REC, the -6-dB bandwidth was enhanced to 155%. In simulations, to monitor the improvements in contrast a software phantom with a cylindrical lesion was evaluated. In experimental measurements, a tissue mimicking phantom that contained glass spheres with different scatterer diameters was evaluated. Estimates of ASD in the simulations and experiments were obtained by comparing the normalized backscattered power spectra to theory. Improvements in REC-QUS over conventional QUS were quantified through estimate bias and variance, contrast-to-noise ratio and histogram analysis of QUS parametric images. Overall, a 51% increase in contrast and an 80% decrease in the variance of ASD estimates were obtained during simulations, while a reduction 93% was obtained in the variance of ASD for the experimental results.