Frequency-dependent angle scattering of ultrasound by liver.

Ultrasonic scattering by one specimen of normal pig liver and two specimens of abnormal human liver has been measured as a function of angle and frequency at each angular position of transmit and receive transducers which were rotated in equal and opposite directions about the axis of a cylindrically shaped tissue sample. Mean data values were determined by averaging points at like frequencies and angular positions in scans made at intervals along the axis of the specimen. Sections of the specimens were obtained throughout its length and stained to emphasize structures containing collagen and connective tissue shown by acoustic microscopy to produce sound speed variations which are known to cause scattering. Using the stained sections as diffraction screens, calculations of scattering were carried out via Fourier transforms on a scale comparable to that in the acoustic studies for comparison with the acoustic data. In all specimens studied, mean acoustic scattering exhibited a general decrease in level with increasing scattering angle. The rate of decrease in acoustic scattering with angle agreed qualitatively with the calculations of average angular falloff of scattering by the stained sections. Lower rates of decrease were observed in tissues with more closely spaced collagen containing structures. Although the data derived from the few substantially different specimens studied is not intended to be representative of all liver, the results show a qualitative correspondence between acoustic scattering and visual appearance which depends on tissue components and their arrangement.