Improving the quality of QUS imaging using full angular spatial compounding

Abstract

Quantitative ultrasound (QUS) imaging techniques make use of information from backscattered echoes discarded in conventional B-mode imaging. Using scattering models and spectral fit methods, properties of tissue microstructure can be estimated. The variance of QUS estimates is usually reduced by processing data obtained from a region of interest (ROI) whose dimensions are larger than the resolution cell of B-mode imaging, which limits the spatial resolution of the technique. In this work, the use of full angular (i.e., 360deg) spatial compounding is proposed to extend the trade-off between estimate variance and spatial resolution of QUS. Simulations were performed using an f/4, 10-MHz transducer with 50% -6-dB bandwidth and a synthetic phantom consisting of two eccentric circular cylindrical regions. The inner and outer cylinders had radii of 7 mm and 12.5 mm, respectively, and nine scatterers per resolution cell. The average scatterer diameters (ASDs) for the outer and inner cylinders were 50 mum and 25 mum, respectively. ASD estimates were obtained using radio frequency data at up to 128 angles of view. When using ROIs of size 16lambda by 16lambda, the use of multiple view data reduced the ASD standard deviations in the outer and inner cylinders from 7.4 mum and 14.4 mum to 1.5 mum and 2.5 mum, respectively. When using ROIs of size 8lambda by 8lambda, the use of multiple view data reduced the ASD standard deviations in the outer and inner cylinders from 13.7 mum and 19.6 mum to 2.5 mum and 3.7 mum, respectively. Experimental validation was obtained using a 10 MHz, f/4 transducer to analyze a 2 cm diameter homogeneous agar phantom with embedded glass spheres of diameters between 45 mum and 53 mum. When using ROIs of size 10lambda by 10lambda and 32 angles of view, the ASD standard deviation was reduced from 24.6 mum to 4.8 mum. This value was below 10.4 mum, the ASD standard deviation obtained using single view data and ROIs of size 20lambda by 20lambda. Therefore, the use of full angular compounding was found to significantly improve the trade-off between spatial resolution in QUS imaging and precision of QUS estimates. These results suggest that QUS imaging can achieve optimal performance on a platform capable of producing views of an object from 360deg, e.g., a tomographic breast scanner.