Stephen W. Flax

Phase Aberration Measurements in Medical Ultrasound: Human Studies:

Using a modified real-time phased array sector scanner, phase aberrations and amplitude fluctuations across the imaging aperture have been measured in a number of human subjects. Data from these subjects were classified into two categories based on the quality of conventional longitudinal images of the liver. Measured phase aberrations were very small in all subjects exhibiting high quality images. In contrast, large phase aberrations were measured in subjects producing low quality images. However, there were no significant amplitude variations across the array for all subjects studied. These results suggest that the absence of significant phase aberrations is a necessary condition for high quality phased array imaging. If so, improvements in clinical image quality in such subjects may be possible.

Spectral Characterization and Attenuation Measurements in Ultrasound

Various means of characterizing ultrasonic attenuation in tissue are reviewed. A simple method for estimating frequency-dependent attenuation via measurement of the zero crossing density of the signal is presented and validated. Both the effects of the frequency dependence of scatter and stochastic variability of the measurement are considered and discussed. Results of measurements made in phantoms, animals and humans are presented and compared to the theoretical model. The technique is shown to be technically feasible.

Attenuation estimation in reflection: Progress and prospects

This monograph presents a tutorial review of the current state-of-the-art in ultrasonic attenuation estimation in reflection. Clinical indications which provide the motivation for attempting in vivo attenuation estimation are discussed. Frequency and time domain techniques and their respective tradeoffs and problems are presented. Finally, current clinical results obtained with the various techniques are summarized and further areas of study are suggested.

Textural variations in B-mode ultrasonography: A stochastic model

Analysis of textural patterns in gray-scale ultrasonography is frequently the basis for clinical diagnosis. It has been found, however, that texture is shaped not only by tissue microstructure but by characteristics of the imaging system as well. This paper describes computer and analytic models which give insight into the role of the imager in texture formation. It is shown that spatial resolution and texture granularity are not simply related, and that axial and lateral texture are determined by unrelated phenomena. Experimental results are given which confirm the modeling.

Method of estimating tissue attenuation using wideband ultrasonic pulse and apparatus for use therein

Tissue attenuation of ultrasound energy is determined by transmitting a wide band ultrasonic pulse into tissue and obtaining a measure of the average center frequency of the reflected pulse between two levels in the tissue. The log amplitude decay is estimated from a reflected pulse, and the attenuation coefficient is then obtained from the ratio of log amplitude decay to average center frequency between the two levels.