ESTIMATING THE SPATIAL AUTOCORRELATION FUNCTION FOR ULTRASOUND SCATTERERS IN ISOTROPIC MEDIA

The autocorrelation function pertaining to spatial distributions of ul trasonic scatterers in soft tissue is believed to contain useful infor mation related to tissue morphology. A simple processing method applie d to radio-frequency echo signals estimates this function for a sample having isotropic scattering conditions. It utilizes backscattered ech o signals from the sample and echo signals from a reference object hav ing defined scattering properties. The ratio of the echo signal power spectrum from the sample to the echo signal power spectrum from the re ference object is obtained, and corrected for attenuation differences between the two media. This yields a ''form factor'' for the sample, w hose inverse Fourier transform is the autocorrelation function. The me thod was tested using tissue-mimicking samples for which spatial autoc orrelation functions could be modeled from the dimensions of embedded scatterers. The shapes of the measured autocorrelation functions were in reasonable agreement with those estimated, although measured functi ons overestimated the function at small lag distances. Scatterer diame ters estimated from the zeros of the autocorrelation function agreed t o within 6% of expected values when the measurement system bandwidth s atisfied minimal criteria. (C) 1998 American Association of Physicists in Medicine.