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At least 109 records · Page 6Linked to original sources
PubMed2002

New data on histology and physico-mechanical properties of human tooth tissue obtained with acoustic microscopy.

Quantitative evaluation of human tooth structural elements, revealed in acoustic images, has been carried out. It has been shown that tissue elements with different acoustic impedances differed in acoustic images by intensity of grey color, and also feature with different longitudinal sound velocities (C(L)). In the layer of mantle dentin, C(L) is 7% to 8% lower than in bulk dentin, and in the layer of dentin around the pulp chamber, C(L) is 15% lower. In carious enamel and dentin, C(L) decreases up to 7% to 17%. In pathologic teeth, dentin areas with higher density can be revealed; they feature higher C(L); in transparent dentin C(L) can be 15% to 20% higher than in bulk dentin. Results of the present study show that acoustic images reflect internal biomechanical properties of tooth tissue microstructure that can be evaluated quantitatively by means of longitudinal sound velocity determination.

Acoustics↗
PubMed2004

Frequency and resolution dependence of the anisotropic impedance estimation in cortical bone using time-resolved scanning acoustic microscopy.

The influences of frequency and spatial resolution on the anisotropic impedance estimation of cortical bone was investigated in the frequency range 25-100 MHz. A set of spherically focused transducers provided a spatial resolution in the range from 150 down to about 20 mum. Four embedded cortical bone samples (two male, two female, two donors aged <30 years, two donors aged >70 years) were cut with different orientations relative to the long axis of the femur (0-90 degrees ). From each section, impedance maps were acquired in the C-scan mode. Histogram evaluations showed a similar angular dependence with a characteristic off-axis maximum of the estimated impedance for all samples and frequencies. The impedance values obtained with the 25-MHz transducer were significantly lower than those obtained with the 50- and 100-MHz transducers. Morphological parameters of the macrostructure, for example, size and distribution of the haversian channels and the resulting porosity, were estimated from the high-resolution acoustic images. These structures appeared to have a significant influence on the measured properties of the bone matrix for the low-frequency and low-aperture measurements.

Adult↗
PubMed1991

Acoustic microscopy of cultured cells. Distribution of forces and cytoskeletal elements.

The scanning acoustic microscope (SAM) allows one to measure mechanical parameters of living cells with high lateral resolution. By analyzing single acoustic images' sound attenuation and sound velocity, the latter corresponding to stiffness (elasticity) of the cortical cytoplasm can be determined. In this study, measurements of stiffness distribution in XTH-2 cells were compared with the organization of F-actin and microtubules. Single XTH-2 cells exhibit relatively high stiffness at the free margins; toward the cell center this value decreases and reaches a sudden minimum where the slope of the surface topography enlargens at the margin of the dome-shaped cell center. The steepness of the increase in slope is linearly related to the decrease in sound velocity at this site. Thus, a significant determinant of cell shape is paralleled by an alteration of stiffness. In the most central parts, no interferences could be distinguished, therefore, this region had to be excluded from the calculations. Stiffness distribution roughly coincided with the distribution of F-actin, but no correlation to microtubule arrangement was found. Following the treatment of XTH-2 cells with ionomycin in the presence of calcium (in the culture medium), the cell cortex first contracted as indicated by shape changes and by a marked increase in stiffness (deduced from sound velocity). This contraction phase was followed by a phase of microtubule and F-actin disassembly. Concomittantly, sound velocity decreased considerably, indicating the loss of elasticity in the cell cortex. No structural equivalent to sound attenuation has been identified.

Acoustics↗
PubMed1989

Acoustic microscopy applied to nonlinear characterization of biological media.

The use of an acoustic microscope as a method for nonlinear characterization of biological media is evaluated. The method consists of measuring the second harmonic signal generated in a sample located at the focus of the acoustic lens. Two experimental configurations were compared: The first is the simple case where the sample is a liquid mixture filling the space between the lens cavity and the receiver; in the second case, the liquid mixture is confined to a thin layer at the focal plane, in order to simulate a real tissue layer. Aqueous solutions of ethylene glycol and methanol were used as liquid samples. Simple theoretical models are presented for each configuration and the predictions show good qualitative agreement with experimental measurements. These results confirm our belief that the acoustic microscope is potentially a good tool for nonlinear B/A imaging of biological systems.

Acoustic Stimulation↗
PubMed1997

Scanning Acoustic Microscopy of human and canine cortical bone microstructure at high frequencies.

An Olympus UH3 Scanning Acoustic Microscope (Tokyo, Japan) has been used in the burst mode at 400 and 600 MHz to study the elastic properties of osteons and osteonic lamellae in both canine and human compact cortical bone. The nominal resolution at each frequency is within the width of an individual lamella. Three important new observations have been made regarding the acoustic properties of individual lamellae. Firstly, the acoustic impedance, as measured by shade of gray levels, of the outer most lamellae of adjacent osteons interdigitate (blend) although the structures, as determined by backscatter scanning electron microscopy, are seen to be quite separate. Secondly, in almost every osteon observed in this study, the shade of gray level for individual lamellae appear to alternate-dark, light etc.-translating to alternating compliant, stiff lamellar units respectively. Thirdly, the outermost lamella of each osteon appears to be the most compliant (darkest gray level). A preliminary SAM study of sheep femoral trabecular bone has shown the some alternation of lamellar gray levels as observed in osteonic lamellae.

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↗
PubMed1975

Recent advances in acoustical microscopy.

One cannot be involved in research in universities, government establishments and industry for 35 years without becoming aware of a number of misconceptions about pure science, applied science, engineering and technology in the mind of the public and also in the very places where research is carried out. There is confusion about the aims of research and development. There is uncertainty about the proper roles of universities, research establishments and industry. There is the question whether science is intrinsically good or not. The author illuminates some of these issues by relating milestones in the development of microscopy--optical as well as electron--and gives a snapshot picture of the recent work at Stanford University on the acoustic microscope as a felicitous instance of physics applied to the ever-present desire of mankind: to explore the unknown and to understand nature. Experiments with a mechanically scanning type of acoustic microscope have shown that a resolution limited only by diffraction can be attained and using a sonic frequency of 1-2 GHz, objects of less than 1 mum diameter can in principle be resolved. Various biological tissues have been explored and it appears that the acoustical images contain information substantially different from that obtained optically or electron-optically. Images have also been obtained using the harmonic radiation generated within the object and this mode of operation promises to open up yet another dimension of information. When, in due course, the full power, and the limitations, of the acoustic microscope are appreciated, its use may well lead to advances in science and technology comparable to those brought about by the introduction of the electron microscope.

Acoustics↗
PubMed1995

[Ultrasonic tissue characterization of diseased myocardium by scanning acoustic microscopy].

Ultrasonic tissue characterization of the myocardium has become very important because the requirement for evaluating local cardiac function has increased. In the present study, the acoustic properties of the tissue elements in myocardial infarction were measured by a specially developed scanning acoustic microscope (SAM) system, and the echo intensity of the infarcted myocardium was assessed. Ten samples of infarcted myocardium obtained at autopsy were formalin-fixed, paraffin-embedded and cut into 10 microns thick slices. The SAM system was operated in the frequency range of 100 to 200 MHz. The values of the attenuation constant and sound speed were measured in five tissue elements, normal myocardium, degenerated myocardium, fibrosis, granulation, and hemorrhage by comparing the optical microscopic image and acoustic images. The density of each tissue element was measured by the CuSO4 method, and the specific acoustic impedance was calculated by multiplying the sound speed and the density of each tissue element. The specific acoustic impedance was 1.75 x 10(6) Ns/m3 in normal myocardium, 1.69 x 10(6) Ns/m3 in degenerated myocardium, and 1.85 x 10(6) Ns/m3 in fibrosis. The intensity of the reflected ultrasound at the interface between two different tissue elements was calculated by the difference of specific acoustic impedance. Using the sensitivity changing method in clinical echocardiography, the intensity of myocardial scar was -15 dB compared to the pericardial echo. The corrected ideal ultrasonic reflection between degenerated myocardium and fibrosis was calculated as -15.4 dB. The results suggest that measurement of acoustic properties is very important to provide basic data for ultrasonic characterization of myocardium tissue.

Acoustics↗
PubMed1997

Cellular motility in vitro as revealed by scanning acoustic microscopy depends on cell-cell contacts.

A new method is described for observing and quantifying an aspect of contact inhibition of cell movement that is sometimes called "contact paralysis". Based on the scanning acoustic microscope (SAM), the method can detect changes in the mechanical properties of cells, as well as changes in their motility and may therefore be more sensitive to some dynamic changes than methods based on optical microscopy. With this method intracellular motility of normal and transformed cells of epithelial and fibroblastic origin was investigated. By subtraction of SAM images patterns of motility, domains were detected that changed in a characteristic way among various cell lines. Wave-like and nucleating domains could be distinguished; they were also used for the quantification of motility. Like migration intracellular motility is influenced by cell-cell contacts. In zones where a cell touches its neighbours motility domains change or disappear depending on the cell type. In immortalized epithelial cells (XTH-2 cells) large quiescent zones developed in the region where contact with neighbouring cells was established, whereas in fibroblastic (3T3) cells motility was reduced less and did not change in domain pattern. Epithelial and fibroblastic cells were less motile when in contact with other cells or in confluent cultures than when solitary, i.e. their motility was contact inhibited. Transformed (SV40 3T3) cells, however, did not reduce their motility when in contact to or enclosed by other cells. The molecular basis for motility domains remains to be investigated.

3T3 Cells↗
PubMed1990

Measurements of cells in culture by scanning acoustic microscopy.

A novel method allowing the determination of thickness, attenuation and impedance of both living and fixed cells in culture using a single image recorded with a scanning acoustic microscope is described. The method is based on the recording of the image data locating the surface of the cell far below the geometric focus. In this way only the normal incident acoustic wave is used for image formation. Higher values of impedance and attenuation coefficients were found in the cell periphery than in the central part of the cell. This phenomenon is suggested to be due to the different organization of cytoskeletal elements.

Animals↗
PubMed2000

Texture measurement of shaped material by impulse acoustic microscopy

All the microstructural parameters involved in metallurgical processes are difficult to determine directly on a shaped material. The aim of this paper is to use an impulse line-focus acoustic microscope (LFAM) as a non-destructive alternative to X-ray diffraction for measuring texture of slightly anisotropic materials. We apply it to characterize the rolling and annealing texture for tantalum sheets.

Journal Article↗
PubMed1997

Acoustic properties of dialysed kidney by scanning acoustic microscopy.

BACKGROUND: A correlation between acquired renal cysts in the dialysed kidney and renal cancer has long been debated, but no changes in the physical properties of kidneys at the microscopic level have been reported. The purpose of the present study was to classify the physical properties of the kidneys of patients undergoing haemodialysis at several stages of pathology by use of the scanning acoustic microscope. METHODS: Sixteen surgically excised kidneys of dialysis patients were investigated. Tissues were fixed in 10% formalin, frozen in acetone, and cut 10 microns thick on a cryostat. We used a scanning acoustic microscope operated in the frequency range of 100-200 MHz. Attenuation constant and sound speed were measured on a two-dimensional distribution. RESULTS: The attenuation constant for inflammatory granulation tissue was significantly higher than that for hyaline degeneration tissue (P < 0.001). Sound speed was high for granulation tissue, but tended to diminish gradually for hyaline degeneration. Sound speed increased again with progression to cystic degeneration (P < 0.001), but the attenuation constant remained low. When a cystic kidney contained a malignant lesion, the previously low attenuation constant rose at that site (P < 0.001), and the previously high sound speed was diminished (P < 0.001). CONCLUSION: Our data suggest that the physical properties of dialysed kidneys at different stages of pathology can be classified by their acoustic properties. Simultaneous evaluation of attenuation constant and sound speed is considered applicable to determining whether tissues contain malignant elements.

Acoustics↗
PubMed2000

Evaluation of the inner-surface morphology of an artificial heart by acoustic microscopy.

The total artificial heart (TAH) is being developed for permanent replacement of the natural heart instead of heart transplantation. The need for detecting the material fatigue in the TAH is increasing in order to guarantee long-term use. In this study, the inner surface morphology of the TAH was evaluated by a specially developed scanning acoustic microscope (SAM) system operating in the frequency range of 100-200 MHz. The inner sac of our TAH consisted of polyvinylchloride coated with polyurethane, and the SAM investigations were performed before and after the implantations in goats. The amplitude images of the SAM demonstrated protein adhesion on the inner surface of the TAH after the animal experiment, and the phase images showed distortion of the wall with spatial resolution of 0.2 microm. These results suggest the feasibility of a high-frequency ultrasound for evaluating the material fatigue of TAH.

Animals↗
PubMed1998

[Mitral valve tissue characterization using acoustic microscopy].

Mitral valve hardness in the rough and clear zones was evaluated by measuring the propagation velocity (m/sec) of ultrasound through the valve, based on the hypothesis that harder tissues will have larger ultrasonic velocity values passing through the tissue. Mitral valve specimens were obtained from 16 normal subjects (age, 15-72 years) at autopsy. An acoustic microscope, operating at 450 MHz, was used to measure the ultrasonic velocity through the three layers of the valve: the atrialis; the spongiosa; and the fibrosa. Furthermore, the mean ultrasonic velocity through the three layers was measured. These measurements were conducted in the rough and clear zones of the valve. In the rough zone, the ultrasonic velocities were 1,634 +/- 71 in the atrialis, 1,574 +/- 37 in the spongiosa, and 1,726 +/- 97 m/sec in the fibrosa. In the clear zone, the ultrasonic velocities were 1,691 +/- 117 in the atrialis, 1,575 +/- 44 in the spongiosa, and 1,909 +/- 131 m/sec in the fibrosa. There were significant differences between velocities in the three layers in both the rough and clear zones. Furthermore, the mean ultrasonic velocity in the three layers in the clear zone (1,887 +/- 138 m/sec) was higher than that in the rough zone (1,642 +/- 53 m/sec; p < 0.001). These findings show that fibrosa, which is rich in collagen fibers, is harder than atrialis, which is rich in elastic fibers, and the spongiosa, which is poor in connective tissues, is the softest. The higher mean ultrasonic velocity in the clear zone than in the rough zone indicates that the clear zone is harder than the rough zone, although the clear zone is thinner than the rough zone.

Adolescent↗