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Biomedical subjects

W D O'Brien

Publications and source records attributed to W D O'Brien.

At least 55 records · Page 3Linked to original sources
PubMed1989

Numerical study of higher-order diffraction tomography via the sinc basis moment method.

Behavior and limitations of the sinc basis method have been discovered during simulation studies. An iterative row-action method (ART) is compared with a full-matrix, least-squares solution (QR decomposition) and the problem of multiple solutions is discussed. Knowledge of the spatial distribution of scattered field energy can be used to speed up convergence. The first iteration is shown to be equivalent to the first Born solution. A fundamental limitation of present diffraction tomography algorithms, concerning phase shift through the scatterer, is found and related to clinical values. Effects of improvements on the initial guesses for the object function and internal field are studied. Lossy cylinder and contrived multicomponent reconstructions yield additional understanding of the phase shift problem. A sequence of simulations investigates estimated solution movement in hyperspace.

Humans↗
PubMed1988

Ultrasonic propagation properties (@ 100 MHz) in excessively fatty rat liver.

The effects on the ultrasonic propagation properties of livers of the addition of 1% orotic acid to rat diets were examined. In rats, dietary orotic acid exerts several effects on lipid metabolism; its overall consequence is that excessively high hepatic fat concentrations are built up over a short period of time, thus making this an ideal model to study the ultrasonic propagation properties as a function of sequential development of fatty liver. Over a 16-day period on the orotic acid diet, the supplemented rat liver lipid concentrations increased from a normal range of 2%-4% to the lower 20's%; hepatic water concentration decreased from a normal value of approximately 70% to approximately 50%; total protein concentration decreased slightly from a normal range of 17%-20% to 11%-16%; and rat liver weight increased from approximately 11 g to around 20 g. Ultrasonic attenuation coefficient and speed were assessed in liver tissue with the scanning laser acoustic microscope at 100 MHz. As hepatic lipid increased, ultrasonic attenuation at 100 MHz increased temporally from a normal range of 12-14 dB/mm to a maximum of 54 dB/mm and ultrasonic speed decreased from a normal range of 1553-1584 m/s to a minimum of 1507 m/s. Multivariant linear regression was used in the analysis of covariance to fit the least-squares estimates to the linear regression model. Strong correlates of ultrasonic speed with both water concentration and fat concentration in the liver were observed.

Animals↗
PubMed1986

Interlaboratory comparison of ultrasonic attenuation and speed measurements.

A set of test samples, all containing ultrasonically equivalent tissue-mimicking material, was produced and measurements of ultrasonic speed and ultrasonic attenuation coefficients were made at seven laboratories using various techniques. The ultrasonic speed values agree well with one another, having a spread of about 0.3 per cent; thus, speed values for tissue parenchyma appearing in the literature are likely to be accurate. Values of ultrasonic attenuation coefficients agree fairly well with one another, with differences between individual values and the group mean of generally less than 20 per cent of the group mean.

Humans↗
PubMed1985

Ultrasonic attenuation and velocity properties in rat liver as a function of fat concentration: a study at 100 MHz using a scanning laser acoustic microscope.

This study examines the extent to which ultrasonic attenuation coefficients and velocity properties change between normal and fatty rat liver. The view of this problem is toward the application in clinical medicine in the future. Fatty livers were produced in rats by feeding them alcohol diets in liquid form. The animals were sacrificed and the fat concentration of the liver specimens determined. The fat concentration varied from 2.5% to 16.8% wet weight. The ultrasonic attenuation coefficient and velocity properties in 28 specimens were measured at 100 MHz with the scanning laser acoustic microscope (SLAM). Regression analysis was applied to the liver's ultrasonic propagation properties as a function of fat concentration. The results show that the attenuation coefficient increases at a rate of 1.08 dB/mm/% fat and the velocity decreases at a rate of 2.3 m/s/% fat as the fat concentration increases.

Animals↗
PubMed1981

Dependence of the ultrasonic scatter coefficient on collagen concentration in mammalian tissues.

The difference between literature values of ultrasonic attenuation and absorption coefficients, defined as the scatter coefficient, was related to percent wet weight collagen concentration for brain, heart, liver, kidney, and tendon, in the range of 0.7 to 7 MHz. The comparison shows that as the ultrasonic frequency increases, the scatter coefficient increases, and the dependence of scattering upon collagen concentration decreases.

Acoustics↗
PubMed1981

Quantitative acoustical assessment of wound maturation with acoustic microscopy.

Preliminary results of the ultrasonic characterization of cutaneous wound tissue and surrounding margin, obtained with the scanning laser acoustic microscope, show an increase in the speed of sound and in the acoustic heterogeneity as function of wound age. As the wound age increased, the following results were noted: (1) The wound area, initially quite homogeneous in acoustic appearance, became more heterogeneous; (2) the acoustic appearance of the wound tended to become similar to that of the adjacent tissue; and (3) the ultrasonic velocity of the wound area increased from a range of 1540--1575 m/s at 7 days to a range of 1700--2000 m/s at 35 days.

Animals↗
PubMed1981

Ultrasonically induced, in vivo morphological damage in mouse testicular tissue.

Mouse testes were exposed in vivo to 1 MHz continuous wave ultrasonic energy for 30 sec at spatial peak intensities of either 2 or 5 W/cm2. Following exposure they were surgically removed at times ranging from immediate (within 60 sec) to 63 days, and histologically prepared for optical microscopy examination. The observed alterations can be classified according to the number and type of affected cell layers in the tubule. Leydig cells were unaffected, and some alterations differed from those previously seen at higher ultrasonic exposure intensities or at much longer exposure times.

Animals↗
PubMed1980

Modified assay for determination of hydroxyproline in a tissue hydrolyzate.

A modified assay for the determination of hydroxyproline in tissue is presented. The modifications greatly reduce the time required for analysis of excised tissue as first introduced by Stegemann and Stalder [1]. These modifications include a change in the technique for tissue hydrolysis and a change in the preparation of the hydroxyproline oxidizing agent. The analysis utilizes the standard addition technique, eliminating the need for correction of matrix effects between the specimen and standard. This paper attempts to give a complete detailed description of the assay such that the procedure may be repeated without requiring additional reference material.

Animals↗
PubMed1977

Effects of ultrasound on nucleic acid bases.

To understand the effects of ultrasound in biological systems at the molecular level, sonolysis of nucleic acid bases at sonic intensities less than or equal to 5 W/cm2 was studied. These sonoreactions were followed by UV-spectral decrease and by sonoproduct analysis. The order of reactivity was found to be thymine greater than uracil greater than cytosine greater than guanine greater than adenine. The extent of sonoreactions depends on the exposure time and the rate of the intensity. Aeration was necessary for maintenance of a reasonable reaction rate. "Threshold" intensities for uracil and thymine were observed at approximately 0.5 W/cm2. The effectiveness of the dissolved gases in producing sonoreactions was Ar greater than 02 greater than air greater than N2 greater than He greater than N2O, suggestive of free radicals mediating these reactions since N2O is an effective radical scavenger. Studies of the effects of substituents have shown that electronic rather than steric effects may have a greater influence. Preliminary identification indicates that cis- and trans-uracil glycols are the major products of uracil. Thus, a stepwise mechanism of pyrimidine sonolysis is proposed. Sonolysis of a dilute aqueous solution of uracil yielded pseudo-first-order kinetics in terms of [Ura] with a rate constant of 3.9 X 10(-2) min-1, implying that the rate-limiting step is the reaction of HO- with the base.

Adenine↗