Tissue characterization from ultrasonic scattering

Abstract

Scattering provides a basis for tissue characterization that is being developed to extend the diagnostic usefulness of ultrasound. Tissue architecture can be related to scattering by a model which expresses a weakly scattered wave as a volume integral involving variations in sound speed and tissue density, transducer fields, and intervening paths. Assumptions of plane wave illumination, farfield reception, distortionless paths, and negligible density variations reduce the integral description of the scattered wave to a Fourier transform of the refractive index variations. When the scattering medium is also weakly homogeneous, an analogous relation exists between average scattered intensity and the correlation function of the refractive index variations. Backscatter measurements by a number of investigators show the feasibility of differentiating tissues and determining spacings. Regular and random model scattering as functions of frequency and angle have agreed with theory. Similar in vitro measurements of scattering by liver show qualitative agreement with architecture observed optically. The results indicate the promise of scattering measurements for tissue characterization but more development is required to identify diseases about which scattering provides information.