Linking theoretical predictions of backscatter from biological media with experimental estimates

Abstract

Medical ultrasonic imaging is based on scattering processes that arise because of the inhomogeneous nature of biological media. In laboratory-based investigations, reduction of experimental rf data to the true backscatter coefficient is accomplished by compensating for measurement system, attenuation, and diffraction effects. In clinical imaging, image brightness is qualitatively related to local values of the backscatter coefficient after operator-adjusted compensation for attenuation (Time Gain Compensation). Clinical backscatter-based approaches to tissue characterization typically provide semi-quantitative data in regions-of-interest somewhat larger than the resolution cell of the image. This spatial averaging can improve the stability of the backscatter estimates. In addition, averaging over a range of frequencies can also improve the signal-to-noise ratio, as in the case of Integrated Backscatter. The sophisticated post-processing of backscattered data to form images poses an additional layer of complexity in compensating clinical data for imaging system-dependent effects. The objective of this talk is to address some approaches, and the corresponding approximations and compromises required, for comparing the results of laboratory and clinical estimates of backscatter with theoretical predictions of the backscatter coefficient (i.e., the differential scattering cross section per unit volume at 180 degrees). [Work supported in part by R37HL40302.]