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Biomedical subjects

S W Flax

Publications and source records attributed to S W Flax.

13 recordsLinked to original sources
PubMed1988

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.

Humans↗
PubMed1984

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.

Female↗
PubMed1983

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.

Animals↗
PubMed1983

Spectral variations in tissues and phantoms.

This paper is concerned with the characterization of attenuation in tissue. A simple method for measuring frequency dependent attenuation is demonstrated. The effects of frequency dependent scatter on the measurement of attenuation are also considered in order to determine the theoretical and practical ramifications of this interfering effect. Finally, a means of placing definitive error bounds on the statistical reliability of the measurement is discussed.

Animals↗
PubMed1981

Renal preservation resistance: evidence against myogenic vasoactive factors.

Vasoconstriction is believed to be a dominant cause of high perfusion resistance during kidney preservation at low temperatures. An experiment was performed to study the effects of hypothermia on vasoactivity. Measurements were made on an apparatus that permitted perfusion resistance to be compared simultaneously in two isolated kidneys at different temperatures. With perfusion temperature serving as the variable, the vascular responses to several vasoactive agents were measured. Hypothermia diminished or altered the vascular responses to the agents. For example, no vasoconstriction was observed with Angiotensin II, dopamine, acetylcholine, or BaCl2 and no vasodilation was observed with papaverine or bradykinin in the hypothermic kidney. A significantly altered response was observed with norepinephrine. The responses were reversible upon return to normothermia. From these data, we conclude that myogenic vasoconstriction plays a questionable role in producing the elevated perfusion resistance observed in some hypothermic kidneys.

Acetylcholine↗
PubMed1979

A microprocessor-based aid for training autistic children.

This paper describes a unique application of microprocessor technology to training autistic children. Such training presents problems in data collection and reduction. The system described is a training session monitor which accumulates data from a session. The system also generates prompt data and controls the end of a session based on five possible criteria. The accumulated data are then automatically reduced and printed. The evolution of this training session monitor and recorder is reviewed. A description of the hardware and software realization of the final system is presented. The tools and techniques used in the development of the system are discussed. Possibilities for future additional training aids are explored, and improved development tools and techniques are suggested.

Autistic Disorder↗
PubMed1978

Pressure-flow relationships and pathological changes during renal preservation.

The renal pedicle of one kidney from each of four dogs was ligated for one hour. The contralateral kidney served as a control. Both kidneys were removed and perfused using the "Belzer" technique. Pressure-flow relationships were determined and biopsy samples taken. The vasculature was then injected with silicone rubber. Perfusion resistance, vascular filling with silicone rubber and observations made by electron microscopy were compared.

Animals↗