Improving the quality of QUS imaging using full angular spatial compounding

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., 360°) 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 μm and 25 μm, respectively. ASD estimates were obtained using radio frequency data at up to 128 angles of view. When using ROIs of size 16λ by 16λ, the use of multiple view data reduced the ASD standard deviations in the outer and inner cylinders from 7.4 μm and 14.4 μm to 1.5 mu;m and 2.5 μm, respectively. When using ROIs of size 8λ by 8λ, the use of multiple view data reduced the ASD standard deviations in the outer and inner cylinders from 13.7 μm and 19.6 μm to 2.5 μm and 3.7 μm, 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 μm and 53 μm. When using ROIs of size 10λ by 10λ and 32 angles of view, the ASD standard deviation was reduced from 24.6 μm to 4.8 μm. This value was below 10.4 μm, the ASD standard deviation obtained using single view data and ROIs of size 20λ by 20λ. 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 360°, e.g., a tomographic breast scanner.