ABSTRACTS, ULTRASONIC IMAGING AND TISSUE CHARACTERIZATION SYMPOSIUM

COMPARISON OF SPECTRAL SHIFT, SPECTRAL DIFFERENCE AND ZERO-CROSSING TECHNIQUES FOR ASSESSING TISSUE ATTENUATION, M. Bodruzzaman, R. Price, G. Thieme, D. Pickens, A. Fleischer, J. Erickson and A.E. James, Jr., Division of Radiological Sciences, School of Medicine, Vanderbilt University, Nashville, TN 37232.

Our laboratory has reported previously on the description of a digital rf ultrasound system and our preliminary results in estimating parameters of tissue texture 111. The system utilizes a PDP-11/55 computer, a model 8100 Biomation waveform recorder (100 MHz, b-bit digitizer) and a computer-controlled rectilinear scanner. The system is used to produce both A- and B-mode digital scans.

Spectral-shift, spectral difference and zero-crossing techniques for estimating tissue attenuation have been implemented on the system. System calibration was performed using tissue-mimicking phantoms. Measurements from isolated liver tissues and from normal volunteers will be presented. [l] Horev., G., Price, R., Erickson, J., Fleischer, A., James, A.E., Radiology 145, 773-775 (1982).

STATISTICS OF SPECTRAL MOMENT ESTIMATES WITH APPLICATIONS TO SHORT-TIME FOURIER ANALYSIS FOR ATTENUATION ESTIMATION, R. Stern', A. Macovskily2and G. Sommer2, Departments of Electrical Engineering1 and Radiology2, Stanford University, Stanford, CA 94305.

Short-time Fourier analysis for estimation of the slope of the attenuation coefficient requires estimates of the mean frequency and variance of the propagating pulse spectrum as a function of the propagation distance.

A general expression for the joint probability of any number of spectral moments calculated from the periodogram of a section of data from a stationary random process has been derived. The joint and marginal densities of estimates of the mean frequency and variance provide the information necessary to calulate statistical properties of estimates of attenuation.

Least squares theory predicts that confidence intervals for the estimates are proportional to the ratio of the rms deviation of mean frequency estimates to the variance of the spectrum. This ratio can be used to compare the quality of the esimates of attenuation when spectra of different shapes and bandwidths are used.

Computer calculations of the ratio of rms deviation of mean frequency estimates to the spectrum variance for Gaussian and other spectral shapes will be presented. The results of these calculations have implications for the design of optimal spectral shapes and algorithms for attenuation estimation. A comparison of predicted confidence intervals for attenuation to confidence intervals calculated from phantom and from normal liver data is presented to validate the theoretical predictions.

This research was made possible by funding from the American Cancer Society (Grant #PDT-1881 and Diasonics, Inc.

A STATISTICAL ANALYSIS OF TIME FREQUENCY REPRESENTATION OF A PULSE-ECHO SIGNAL, J.F. Cardoso, F. Hottier and M. Fink, Laboratoires D'Electronique et de Physique Appliquee, Limeil-Brevannes, France.

At the last symposium 111, we have presented a study of the Wigner distribution WD which provides an instantaneous time-frequency representation of a pulse-echo signal. Compared to the short-time Fourier analysis (STFA) which is strongly dependent on the time window shape, the WD gives more accurate information on the scattering distribution. However, the WD computation is time consuming and a statistical analysis of the spectral moment of this representation is quite difficult.

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