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Biomedical subjects

J F Greenleaf

Publications and source records attributed to J F Greenleaf.

At least 73 records · Page 4Linked to original sources
PubMed1990

Ultrasonic imaging of the nonlinear parameter B/A: simulation studies to evaluate phase and frequency modulation methods.

This paper presents a method for imaging the nonlinear parameter B/A. It is based on measuring phase shift and frequency shift of a high frequency acoustic probe wave by a low frequency acoustic pump wave. These measurements yield the real and the imaginary parts of the Fourier component of the distribution B/A at the wave number of the pump wave. We also derive the necessary set of wave numbers of the pump wave which must be employed to accurately image the B/A parameter. We show that these wave numbers are a function of sampling period and sampling number. Simulations of the imaging method show that the proposed method in this paper leads to more accurate imaging of B/A than the earlier method.

Animals↗
PubMed1990

A theoretical model of acoustoelectric transducer with a nonuniform distribution of piezoelectric coefficient: application to transducer optimization.

A general equation is derived that describes the behavior of a piezoelectric transducer with a nonuniform distribution of piezoelectric coefficient within its bulk, when submitted to an arbitrary distribution of acoustic pressure. Based on this equation, an expression for the receiving transfer function of the transducer is calculated. The results demonstrate the dependence of the transfer function on the distribution of piezoelectric coefficient, and that it is possible to benefit from a nonuniform distribution to optimize the transfer function. The general equation also describes the influence of the external electric circuit loading the transducer, which leads to another independent means of optimizing the transfer function. The proposed model combines effects of piezoelectric material characteristics, acoustic backing, and electric loading, without resorting to Mason or other equivalent circuits for the transducer.

Models, Theoretical↗
PubMed1988

Measurement of ultrasonic nonlinear parameter in excised fat tissues.

This paper reports sound speed co, adiabatic acoustic nonlinear parameter B/A, and isothermal nonlinear parameter (B/A)' of 33 samples of excised human and animal fats and some simple mixtures, e.g., skim milk and powdered milk. Tissues were obtained from different parts of the body and the measurements were made in the temperature range of 20 degrees C to 37 degrees C. All the fats were highly nonlinear. Although there was a considerable overlap in the values of acoustic nonlinearity of different body fats, in general their values followed the order: mesenteric fat greater than subcutaneous fat greater than omentum fat greater than breast fat. Temperature coefficients of co and B/A, and the difference between adiabatic and isothermal nonlinearity, correlated highly with water/fat content of tissues. A reciprocal relationship between B/A and co, similar to that proposed for liquids, was observed for soft tissues but not for solutions of powdered milk in skim milk. No significant correlation was observed between acoustic measurements and the age of human subjects from which fat tissues were obtained.

Adipose Tissue↗
PubMed1987

Dependence of ultrasonic nonlinear parameter B/A on fat.

This study deals with the relationship between the magnitude of acoustic nonlinearity, sound speed of tissues and the amount of fat present in them. A two-component model, i.e., nonfat and fat, has been assumed and equations that relate the nonlinear parameter (B/A) of a medium to the properties of its components have been derived for two cases. In the first case, the density and sound speed are the same for the two components; B/A is a linear function of fat concentration. To represent this case, mixtures of egg white and yolk were studied. Even though the differences in density and sound speed of the two egg components were within 1 percent of each other, B/A showed a deviation from linearity. In the second case, i.e., when the density and sound speed of the two components are not equal, a quadratic equation has been derived using mixture laws. Livers, fats, egg mixtures, and oil data were used to represent this case. B/A increased quadratically with fat concentration. The presence of proteins on the binary aqueous/fat mixtures modified the quadratic rule.

Adipose Tissue↗
PubMed1986

Correlative study of properties of water in biological systems using ultrasound and magnetic resonance.

Ultrasonic and nuclear magnetic resonance properties of media rich in water are investigated. The chemical shift of the water proton in pure water, aqueous solutions of tertiary butanol, and sodium chloride is shown to be linearly correlated to the reciprocal of sound speed in these media. A new method of determining the self-diffusion coefficient of water by using acoustic nonlinearity and sound speed is proposed. The method is tested on a variety of media that include pure water, aqueous solutions of glycerol, serum albumin, egg constituents, plant tissues, frog muscle and liver, and excised human tissues. In all the cases the results are found to compare closely to diffusion coefficients measured by magnetic resonance. The results presented here indicate that the acoustic and magnetic resonance modalities, though inherently different in their origin, can provide closely related information on the properties of water.

Animals↗
PubMed1986

Measurement and use of acoustic nonlinearity and sound speed to estimate composition of excised livers.

The acoustic nonlinearity parameter B/A and sound speed c have been determined for excised normal and abnormal human livers at 20-37 degrees C. These values are compared with analytic measurements of fat and water content of tissues. The results show that normal liver containing 71.0% water and 2.9% fat by weight has a B/A value of 6.75 and sound speed of 1592 m/s at 37 degrees C. Both these parameters increase at an average rate of 0.026 degrees C and 1.5 m/s/degrees C, respectively, as the temperature is raised from 20 to 37 degrees C. Fatty liver (24% fat by weight) exhibits highest B/A (9.12) and lowest c (1522 m/s) of all the livers studied. In contrast to normal livers sound speed in such a liver was found to decrease with temperature. Based on the acoustic and composition measurements, quantitative correlations of B/A and c with fat-water composition have been developed. Inversion of these relationships provide a simple method to determine composition of a tissue sample from B/A and c measurements.

Body Composition↗
PubMed1986

Echocardiographic visualization of acute myocardial ischemia--in vitro study.

To evaluate whether myocardial texture changes resulting from acute ischemia can be visualized with satisfactory spatial resolution, short axis compound echo images (CEI) (B-scan) were obtained from 12 excised canine hearts in vitro. Seven had myocardial ischemia produced by open chest ligation of the left anterior descending coronary artery (LAD) for 15-30 min prior to excision. The CEI were constructed by compounding 60 simple linear B-scans. Hearts were sectioned after scanning, and gross morphological changes were recorded. Microscopic comparison between grossly abnormal and normal regions were recorded. The CEI from the ischemic group revealed altered myocardial texture seen as bright coarsely granular echoes in the regions normally perfused by the ligated LAD artery. Corresponding anatomic sections revealed increased redness in these regions. Microscopically these regions revealed interstitial and intercellular edema as compared to the normal regions. Acute myocardial ischemia can be visualized in CEI and these regions have significantly increased backscatter, decreased attenuation, and decreased speed of ultrasound relative to normal regions in the same hearts. Myocardial edema is probably responsible for these changes.

Animals↗
PubMed1986

A graphical description of scattering.

The relationship between Fourier transforms of the refractive index of objects and the Fourier transform of the scattered ultrasonic waves are reviewed. Both the Born and Rytov approximations in the first order are used to linearize the Helmholtz wave equation. Both forward and backward scatter geometries are illustrated. The relationship between these coherent wave considerations and the clinically used echo and transmission modalities is discussed.

Fourier Analysis↗
PubMed1986

Application of stochastic analysis to ultrasonic echoes--estimation of attenuation and tissue heterogeneity from peaks of echo envelope.

A study of the statistics of ultrasound speckle indicates that the noise-to-signal ratio (NSR) of the echo envelope peaks (EEP) in a B scan is monotonically related to the variance of the mean power of the backscattered echoes. If it is assumed that the backscattered echoes all have the same mean power, the NSR of the EEP's in a B scan will be expected to reach a theoretical minimum value NSR0 (0.40 approximately 0.42). In practical situations, the variance of the mean power of the echoes is increased due to the presence of both attenuation (including beam spreading) and the spatial variation in the backscattering cross section (BCS) of the tissue. Accordingly, the measured value of the NSR of the EEP's is expected to be greater than the NSR0. In principle, the effects of beam pattern and the attenuation can be compensated for by system calibration and a depth-related gain function, respectively. The attenuation coefficient of the tissue may then be obtained by adjusting the gain function to minimize the NSR of the EEP's. Due to the random nature of the heterogeneity of diseased tissue, the effect of the variation in the BCS, however, cannot be compensated for by the depth-related gain function. Therefore, the minimum value of the NSR indicates the spatial variation in the BCS and may finally correlate to the disease state of the tissue.

Humans↗
PubMed1986

Ultrasonic nonlinear parameters and sound speed of alcohol-water mixtures.

Changes in the nonlinear parameter B/A caused by the addition of monohydric alcohols to water have been investigated. The measurements, made by using an aqueous solution of n-propanol, isopropanol, and t-butanol, show that as the alcohol concentration is increased, B/A decreases to a minimum at approximately 10% concentration (by volume). Further increase in alcohol concentration raises B/A rapidly to a maximum at about 80% by volume. This complex variation in B/A is attributed to solute-solvent interaction which is believed to be due to an enhancement of water structure in the water-rich region. These results suggest that the magnitude of B/A may be closely related to the quasilattice structure of water, which to a first approximation can be expressed by relative amounts of bound and unbound water.

Acoustics↗
PubMed1986

The scattering of ultrasound by cylinders: implications for diffraction tomography.

The validity of wave equations employed as system models in acoustical diffraction tomography is investigated using simulations and measurements of the scattering of plane ultrasound waves by cylinders. It is demonstrated by simulation and experiment that it can be appropriate to neglect density fluctuations and shear waves, implying that the commonly used form of the wave equation suitably describes scattering by fluctuations of acoustic speed and absorption. Diffraction tomographic reconstructions of simulated data reveal the importance of absorption, the behavior of the real and imaginary parts of the reconstructed refractive index, and the relative advantages and limitations of the Born and Rytov approximate transformations.

1-Propanol↗
PubMed1986

Attenuation estimation on phantoms--a stability test.

Global and local attenuation coefficient estimates were calculated using three methods: the envelope peak method, the central-frequency-downshift method, and the zero-crossing method. The results show that for each method the error of the local estimate with respect to the global estimate is increased as the sample volume is decreased. While the performances of the latter two methods are comparable, the performance of the envelope peak method is significantly superior.

Humans↗
PubMed1984

Measurement of the acoustic nonlinearity parameter B/A in human tissues by a thermodynamic method.

A thermodynamic method for measuring the acoustic nonlinearity parameter B/A in tissues is presented. It is based on the measurement of change in phase velocity as a function of time as the hydrostatic pressure of the sample is quickly reduced from a known value. This technique circumvents the effect of the attenuation in the medium and does not require a prior knowledge of the thermodynamic parameters of the tissues. The method is used to estimate nonlinearity parameters for normal and malignant tissues in the temperature range 20 degrees to 37 degrees C. The values and the temperature dependence of these parameters are found to vary with the nature of the tissues.

Adipose Tissue↗
PubMed1984

Ultrasound transmission computed tomography of the breast.

A preliminary clinical study of ultrasound transmission computed tomography of the breast (UTCTB) was undertaken to evaluate its capacity in the detection of breast abnormalities and to establish criteria for distinguishing benign from malignant lesions. Only patients with palpable and/or mammographically evident lesions were selected for study; complete analysis was accomplished in 78 cases. Visual and computer interpretations of reconstructed UTCTB scans were based on changes in speed of sound wave transmission and attenuation between the suspicious area and the surrounding tissue. In the computer-aided classification, discriminant functions were derived to predict the presence or absence of carcinoma. Visual analysis was subject to a low sensitivity. The presence of high speed transmission within a lesion usually indicated malignancy, although the converse was not true. Computer-aided preliminary screening of UTCTB scans by a trained technician may have the potential of contributing to interpretation accuracy; however, this finding must be highly qualified, given the methodologic constraints of the study.

Adult↗
PubMed1984

Scattering of ultrasound by tissues.

Scattering of ultrasound by biological tissues (continuous-inhomogeneous media) is discussed. An analytical expression for the attenuation due to scattering (alpha Tsc) and backscatter coefficients (sigma T) of tissues are obtained. The results explain the variation of alpha Tsc and sigma T with frequency for a number of tissues. The study also provides two statistical parameters, velocity fluctuation coefficient and correlation length, in terms of which the scattering of tissues can be defined quantitatively.

Animals↗
PubMed1982

Anthropomorphic breast phantoms for assessing ultrasonic imaging system performance and for training ultrasonographers: part I.

Three prototype anthropomorphic breast phantoms are discussed. The phantoms were constructed using ultrasonically tissue-mimicking materials; these materials mimic various tissue parenchymae in terms of attenuation, speed of sound, density, and scatter level. Realistic artifacts related to refraction and reflection at interfaces between different simulated parenchymae are produced. The phantoms represent premenopausal breasts, and they complement one another. Two of them represent the dense breasts of women under 30 years of age, and one represents that of a woman between 35 and 40 years of age. Of the former two, one produces what is apparently above-average refraction effects in the region of the peripheral fat layer; the other produces more typical refraction effects. Simulated tumors, cysts, and calcifications of various sizes are suspended in the glandular regions. Such phantoms are valuable for use in developmental testing of state-of-the-art ultrasound machines, quality assurance testing of clinical machines, and training of sonographers in breast imaging.

Adult↗
PubMed1982

Anthropomorphic breast phantoms for assessing ultrasonic imaging system performance and for training ultrasonographers: part II.

Three prototype anthropomorphic breast phantoms are discussed. The phantoms were constructed using ultrasonically tissue-mimicking materials; these materials mimic various tissue parenchymae in terms of attenuation, speed of sound, density, and scatter level. Realistic artifacts related to refraction and reflection at interfaces between different simulated parenchymae are produced. The phantoms represent premenopausal breasts, and they complement one another. Two of them represent the dense breasts of women under 30 years of age, and one represents that of a woman between 35 and 40 years of age. Of the former two, one produces what is apparently above-average refraction effects in the region of the peripheral fat layer; the other produces more typical refraction effects. Simulated tumors, cysts, and calcifications of various sizes are suspended in the glandular regions. Such phantoms are valuable for use in developmental testing of state-of-the-art ultrasound machines, quality assurance testing of clinical machines, and training of sonographers in breast imaging.

Adult↗