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Biomedical subjects

K K Shung

Publications and source records attributed to K K Shung.

At least 55 records · Page 3Linked to original sources
PubMed1986

The effect of focusing on ultrasonic backscatter measurements.

In this paper, the effect of transducer focusing on the integrity of ultrasonic backscattering measurements is examined. The rationale for this study stems from our observation that the calculated values of backscattering coefficients from data obtained with nonfocused transducers are always substantially lower than those obtained with focused transducers when the standard substitution method is used for backscattering measurements. It is postulated that this discrepancy is caused by the extremely complicated beam behavior of a focused transducer. This hypothesis is verified experimentally. It is therefore concluded that focused transducer could yield misleading results when a standard substitution method is used for absolute backscattering measurements.

Erythrocytes↗
PubMed1985

Effects of atherosclerotic lesions on ultrasonic beam and CW Doppler signals.

Doppler ultrasound has been shown to be a useful clinical tool in the noninvasive detection of vascular stenoses, occlusion, or plaques. The presence of atherosclerotic lesions in blood vessel walls can distort the Doppler ultrasonic signal, producing inverted or biphasic tracings. This observation, in fact, has been used frequently as a criterion for the diagnosis of plaque formation and calcification of these lesions. To define the source of this distortion, we have examined the effects of various types of atherosclerotic lesions on the transmitted ultrasonic beam generated by a continuous wave (CW) Doppler ultrasonic probe. These results are compared to the Doppler flow tracings obtained by a CW ultrasonic Doppler flowmeter from blood vessels with overlaying lesions in a mock flow system. It is concluded that severe distortion in the form of beam refraction or diffraction can be produced by calcified lesions, resulting in biphasic or inverted flow signals.

Arteriosclerosis↗
PubMed1985

Ultrasonic characterization of biological tissues.

Ultrasonic imaging has become increasingly important as a diagnostic tool in medicine because it is noninvasive and it can provide valuable information otherwise unattainable. However, at present, clinical interpretation of an ultrasonic image still mostly relies on recognition of boundaries and positional relationship of anatomical structures and a subjective analysis of the distribution or texture of echo amplitudes. Other potentially useful information carried back by the echoes is completely discarded. The aim of ultrasonic tissue characterization research is to develop methods to extract additional information from the returned echoes so that tissue pathology or abnormality can be reliably identifed and severity of the pathology objectively assessed with quantitative criteria. A number of ultrasonic parameters including acoustic velocity, impedance, attentuation and scattering, have been utilized in attempting to achieve this goal. In this paper, recent progress in this research will be discussed and relevant results presented.

Acoustics↗
PubMed1985

Ultrasonic backscatter from mammalian tissues.

Ultrasonic B-mode images are formed from echoes backscattered from tissue structures in the body. Quantitative analysis of this signal from tissues may provide additional information about the tissues which may be valuable for clinical diagnosis. Results on measurements of backscatter properties of tissues such as heart, liver, and blood have been reported by a number of investigators. Data on other tissues such as spleen, kidney, and pancreas, however, are still very scanty. In this paper, results on ultrasonic backscattering properties of bovine heart, liver, kidney, spleen, pancreas, and rat myocardium, recently obtained in our laboratory utilizing a computerized system over the frequency range of 2-7 MHz, are presented. The results show that for all the tissues investigated, backscatter from liver is the highest, while that from spleen is the lowest. Liver and pancreas exhibit frequency dependence distinctively different from other tissues. Moreover, backscatter from bovine myocardium is found to be higher than that from rat myocardium. The significance of these findings in relation to the histological composition of these tissues is discussed.

Animals↗
PubMed1984

Effect of flow disturbance on ultrasonic backscatter from blood.

Due to the better resolution and performance provided by the new generation of real-time high resolution ultrasonic scanners, blood now becomes a tissue which can also be visualized ultrasonically. There is strong experimental evidence indicating that the echogenicity of blood is increased as a result of erythrocyte aggregation. In this paper, we will show that flow disturbance may also play a significant role in influencing blood ultrasonic backscatter or echogenicity. Our results indicate that the introduction of turbulent flow can cause ultrasonic backscatter from erythrocyte suspensions to increase appreciably for hematocrits greater than 10%. We will also show that this increase may be correlated to the turbulent intensity. Moreover, the scattering peak is observed to shift to lower hematocrits when turbulence is eliminated. Experimental results obtained for uniform flow are in excellent agreement with theoretical models for small spherical scatterers which predict a scattering maximum at a hematocrit of 13%.

Animals↗
PubMed1982

Further studies on acoustic impedance of major bovine blood vessel walls.

Data on ultrasound velocity and specific impedance of major bovine blood vessel walls are compared to structural protein content measured by hydroxypoline assay as well as total solid tissue content of these tissues. Results indicate that acoustic velocity in these tissues is determined largely by the collagen and elastin contents of the tissues. However, acoustic impedance, which is the product of density and velocity, shows a stronger dependence on the total tissue content, suggesting that other solid tissues, in particular, muscle in blood vessel walls, may also play a significant role in the determination of acoustic impedance.

Adipose Tissue↗
PubMed1982

Acoustic measurement of erythrocyte compressibility.

Adiabatic compressibility of red blood cells obtained from humans using a modified ultrasound velocity technique has been determined and correlated to the mean cellular hemoglobin concentration of the red blood cells. The ultrasound technique has an accuracy of better than 0.1% The results show a mean adiabatic compressibility of 34.814 X 10(-12) +/- 0.851 cm2/dyn for an average mean cellular hemoglobin concentration of 32.12 +/- 1.51 g%. The relationship between the MCHC and compressibility was investigated by suspending erythrocytes in saline of different NaCl concentrations. A correlation coefficient of 0.932 was obtained based on linear regression analysis.

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↗
PubMed1979

Effects of oxygen tension and pH on the ultrasonic absorption properties of sickle cells.

The ultrasonic absorption of sickle cells was compared with the morphological changes in these cells are produced by varying oxygen tensions and pH. A decrease in oxygen tension caused increased sickling and an increase in the ultrasonic absorption of the blood. An increase in pH reduced the ultrasonic absorption and decreased sickling. These findings indicate that ultrasonic absorption can detect changes in the aggregation state of sickle cell hemoglobin in situ within the red cell and that the method may be used to monitor the degree of sickling under various environmental conditions.

Adult↗
PubMed1978

Ultrasound velocity in major bovine blood vessel walls.

Data on ultrasound velocity, compressibility. and specific acoustic impedance in bovine aorta, pulmonary artery, vena cava, and myocardium are reported and analyzed based on amounts of structural proteins present in these tissues.

Animals↗