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PubMed2005

[Application of the method of acoustic microscopy for the study of eye tissues].

The paper describes the results of evaluation of potentialities of the application of scanning acoustic microscopy, which is still relatively new and as yet uncommon method of biological research, for the supravital study of animal eye structure in species with different eyeball size. Using the eyes of a goat, quail embryo (in situ) and frog tadpole (in vivo) as the examples, it was shown that non-destructive nature of the method used allows for the study of peculiarities of major morphologic structures in the state that is close to the natural one. Some acoustic images are presented showing eye structural elements along with the results of quantitative characteristic of the cornea, sclera and iris.

Animals↗

PubMed2006

The study of guided waves in surfaces and thin supported films using surface Brillouin scattering and acoustic microscopy.

This paper reviews the use of surface Brillouin scattering (SBS) and acoustic microscopy (AM) in studying the surface dynamics of solids in order to obtain information about the near-surface elastic properties of solids and thin supported films. The vibrational modes that are probed by these means include Rayleigh surface and pseudo-surface acoustic waves, longitudinal lateral waves (surface skimming bulk longitudinal waves) and various thin film guided modes, such as Sezawa and Love waves. SBS is the inelastic scattering of light, mediated by thermodynamic fluctuations in the surface elevation and near surface elastic strains. The scattering cross-section is conveniently expressed in terms of Fourier domain elastodynamic Green's functions. AM depends on the insonification of a surface through a coupling fluid, and the resulting excitation and subsequent decay of the various surface modes. The complex reflectivity of the fluid-loaded surface, and the line and point force surface Green's functions are invoked in the interpretation of different modalities of AM, yielding much the same information about the surface dynamics. The focus in this paper is on the Green's function approach. A number of illustrative examples, drawn from the authors' research, are provided.

Journal Article↗

PubMed2006

Elastic properties of composites: periodical homogenisation technique and experimental comparison using acoustic microscopy and resonant ultrasonic spectroscopy.

The macroscopic elastic properties of two composites (Duralumin/air and Duralumin/tungsten carbide (WC)) have been calculated using periodical homogenisation methods and the elastic properties of each phase (measured by high frequency acoustic microscopy). In order to check the validity of such an approach, acoustical resonant spectroscopy has also been applied. Thanks to the comparison between the resonant frequencies predicted and measured, two major conclusions have been obtained: the homogenisation method is very accurate for the composite Duralumin/air, but not for the Duralumin/WC sample: the experimental results are not in very good agreement with the simulation. This result can be then explained by the major role of interfacial state between Duralumin and tungsten carbide.

Computer Simulation↗

PubMed1990

Phase detection in acoustic microscopy.

The scanning laser acoustic microscope provides a relatively simple means by which speed of sound data can be collected from biological specimens. By employing a phase detection circuit, phase-contour lines can be superimposed on acoustic micrographs and digitized for direct speed of sound calculations. Because of the existence of mild field non-uniformities, the phase reference must be mathematically modeled. This is accomplished by employing a polynomial function and simple linear regression. Scattering can be studied by using a frequency-selective "dark field" approach. Speed of sound maps are readily produced from the phase data by applying the simple geometric relationships of wave propagation; however the theoretical limitations of the technique must be kept in mind. Using this approach, useful data have been obtained.

Acoustics↗

PubMed2000

A new approach for glomerular lesions: evaluation of scanning acoustic microscopy (SAM) for experimental glomerular disease in rats.

Most pathological evaluations using ordinary optical microscopy are usually qualitative and subjective. The beneficial properties of scanning acoustic microscopy (SAM) include not only observation of microstructure but also quantitative measurement of acoustic propagation speed, indicating the tissue elasticity. In this study, we examined the capability of SAM to evaluate pathological findings in glomeruli using anti-Thy.1 glomerulonephritis. Light microscopic observations of the glomeruli showed severe cell proliferation and mesangial matrix expansion at 10 days after induction of glomerulonephritis and, yet, to a lower extent at day 21 with onset of healing. C-mode scanning of SAM enabled imaging of glomerular structure compatible to findings of ordinary light microscopy. In addition, glomerular propagation speed in nephritic rats was significantly increased at day 10, and then decreased at day 21. These results indicate that SAM evaluation may be a new, useful technique for quantitative evaluation of proliferative glomerular lesions.

Animals↗

PubMed2004

Phase-sensitive acoustic microscopy of polymer thin films.

The three-dimensional images obtained by scanning acoustic microscopy with vector contrast (PSAM), contain significant qualitative and quantitative information that is not easily obtainable by other methods. We employ this technique to examine homopolymer and polymer blend thin films. The complex V(z) functions derived from the images, and the results obtained by image processing and meticulous analysis are employed to render the morphology, composition and micro-mechanical properties of the polymer films. In addition, ways by which the information inherent in the phase images can be extracted are examined. This is highly desirable, as the phase images contain very useful additional information.

Journal Article↗

PubMed1993

Quantitative acoustic microscopy of individual living human cells.

The elastic properties of cells can be measured with microscopic resolution by acoustic microscopy. By measuring the waveform of very short pulses, the thickness, and the acoustic velocity, impedance and attenuation can be determined from the two separate signals reflected from the top and the bottom of the cell.

Acoustics↗

PubMed1997

Ultrasonic tissue characterization of infarcted myocardium by scanning acoustic microscopy.

The purpose of this study was to ultrasonically characterize infarcted human myocardial tissue at the microscopic level by scanning acoustic microscopy. Infarcted myocardial specimens from ten cases with acute myocardial infarction were studied. Specimens were formalin fixed, paraffin embedded and sectioned to 10-micron thickness. A specially developed scanning acoustic microscope system, operating in the 100- to 200-MHz ultrasound frequency range, was used for the measurements. The values of the attenuation constant were 0.94 +/- 0.04 dB/mm/MHz in normal myocardium, 0.71 +/- 0.12 dB/mm/MHz in degenerated myocardium, 0.88 +/- 0.47 dB/mm/MHz in granulation tissue and 1.75 +/- 0.11 dB/mm/MHz in fibrosis. The values of sound speed were 1620.2 +/- 8.2 m/s in normal myocardium, 1572.4 +/- 10.6 m/s in degenerated myocardium, 1590.2 +/- 32.5 m/s in granulation tissue and 1690.3 +/- 9.1 m/s in fibrosis. The ultrasonic properties of the diseased myocardium at the microscopic level will provide important information for ultrasonic tissue characterization at the macroscopic level.

Acoustics↗

PubMed2005

Quantitative scanning acoustic microscopy compared to microradiography for assessment of new bone formation.

Recently, it has been shown that quantitative scanning acoustic microscopy (SAM) is a powerful tool to image the acoustic impedance of even inhomogeneous materials like bone. Therefore, the aim of our study was to compare SAM to conventional microradiography with respect to histomorphometrical assessment of undecalcified sections of newly formed bone. Forty specimens were harvested 12 weeks after implantation of either autogenous cancellous bone graft or 5.0 mg of Osteogenic Protein-1 (BMP-7) in a critical-sized defect model in sheep. Undecalcified transverse bone sections of 500 microm thickness were investigated with conventional microradiography and SAM. Linear regression analysis was carried out to compare the measurements of the area of new bone formation within the defect sites. Both methods allowed for good discrimination between newly formed bone and cortical bone at the edges of the former defect. Images obtained with SAM revealed a better resolution and sharpness compared to that of microradiographs since SAM imaging unlike microradiography does not depend on the thickness of bone sections. The results of quantitative histomorphometric analysis obtained by both methods showed no significant differences, and it was possible to predict 90% of the variability of each method (coefficient of determination r2 = 0.90; P < 0.0001). In conclusion, SAM offers comparable quantitative histomorphometric information with a better spatial resolution than conventional microradiography. Thus, SAM is a promising new micro-visualizing technique for basic bone research.

Animals↗

PubMed2006

Application of pulse acoustic microscopy technique for 3D imaging bulk microstructure of carbon fiber-reinforced composites.

Impulse acoustic microscopy technique is applied for 3D imaging of bulk microstructure of composite materials. Short pulses of focused high-frequency ultrasound have been employed for layer-by-layer imaging of internal microstructure of carbon fiber-reinforced composite (CFRC) laminates. The method provides spatial resolution of 60 microm and in-depth resolution of 80 microm, approximately. Echo signals reflected from structural units--plies, fiber bundles; and microflaws form acoustic images of microstructure at different depth inside samples. The images make it possible to see ply arrays, packing of bundles in plies; binding material distribution over the specimen body. They reveal failure of interply adhesion, buckling of single plies and fiber bundles, internal defoliations and disbonds, voids in the specimen body. The series of successive images offer outstanding possibilities to reconstruct the bulk structure, to estimate local variations of properties, topological and geometrical characteristics of structural components. The imaging technique has been applied to study different types of fiber packing--unidirectional, cross-ply and woven laminates. Mechanisms of ultrasonic contrast for diverse elements in acoustic images of CFRC laminate bulk microstructure and structural defects are discussed.

Journal Article↗

PubMed2006

Prediction of biomechanical stability after callus distraction by high resolution scanning acoustic microscopy.

Accurate clinical prediction of the resistance to fracture after callus distraction requires a detailed understanding of structural and elastic properties of the newly formed bone. We investigated 26 sheep that underwent middiaphyseal callus distraction at a rate of 0.5 mm every 12 h for 30 d using a standard unilateral fixator system. The sample population included four groups undergoing different treatments to improve bone healing, including bone grafting and the local application of growth factors. All animals were sacrificed eight weeks after the end of distraction. The fracture forces of the lengthened tibia and the contralateral control tibia from each animal were evaluated by biomechanical (four-point bending) testing. The microstructure and anisotropic acoustic impedance distributions were assessed by quantitative 50-MHz scanning acoustic microscopy. The relationships between resistance to fracture, structural properties and acoustic impedance of the newly formed callus tissue and adjacent cortical tissue were investigated. A significant linear multivariate regression model was developed that predicts the fracture force with a high accuracy (RMSE = 248 N, R(2) = 0.86, p < 0.0001).

Acoustic Impedance Tests↗

PubMed1995

Elastic properties of osteoporotic bone measured by scanning acoustic microscopy.

A combination of low bone mass and decreased bone quality underlies osteoporotic fracture. We used scanning acoustic microscopy, a nondestructive method for assessing bone elasticity at a resolution of about 60 microns, to estimate the quality of biopsied iliac bones. We compared the acoustic velocities and bone volumes among premenopausal normal (n = 10), osteoporotic (n = 20), and postmenopausal normal (n = 10) subjects, the latter age-matched to the osteoporotic subjects. The acoustic measurements were highly reproducible (coefficient of variation = 0.32%). Bone volume of osteoporotic subjects (BV/TV = 13.3%) was lower than that of premenopausal and age-matched normals (BV/TV = 22.8%, p = 0.0007; BV/TV = 24.8%, p = 0.0004, respectively). Acoustic velocity of osteoporotic bone was 6.2% lower than that of age-matched normal bone (p < 0.02), but 3.4% higher than that of bone from premenopausal normal women. The lower acoustic velocity of osteoporotic bone than that of age-matched normal subjects implies that osteoporosis involves altered tissue elasticity. However, the lowest acoustic velocities were measured in premenopausal normal subjects. This unexpected result may indicate a complex relationship between tissue level properties and fragility in bone.

Aged↗

PubMed2006

Preservation of microelastic properties of dentin and tooth enamel in vitro--a scanning acoustic microscopy study.

OBJECTIVES: The aim of this study was to examine the influence of storage media on the elastic properties of dentin and tooth enamel with respect to the storage period. Several reports suggest that saline and other aqueous solutions may induce chemical reactions and the dissolution of minerals, which in turn may cause alterations of elastic tissue properties. METHODS: Three non-erupted human wisdom teeth were extracted and divided in three slices. Sections were stored in three different media for a maximum period of 21 days. During this time all sections were inspected by time-resolved 50-MHz scanning acoustic microscopy. RESULTS: Storage in saline solution resulted in a progressive decrease of the acoustic impedance up to 70% in dentin but not in enamel tissue. Hank's balanced salts solution and artificial saliva appeared to maintain the elastic properties of dentin and enamel during the entire time of storage. The measurements of surface wave velocities did not show significant differences. High resolution (900 MHz) inspection of sections cut perpendicular to the surface exposed to the storage media for 21 days revealed a progressive increase of impedance in dentin up to the initial values at a depth of approximately 300 microm. SIGNIFICANCE: These findings suggest that quantitative SAM is a suitable tool for assessing surface and sub-superficial elastic properties of tooth tissue.

Dental Enamel↗

PubMed2000

Integration of modeling and acoustic microscopy measurements for thin films

A model for measuring the V(z) curve by line-focus acoustic microscopy contains the reflectance function of the specimen as a principal component. In this paper the reflectance function has been analyzed for multilayered thin films on a substrate for both fast-on-slow and slow-on-fast systems. The phase velocities of modes of surface acoustic wave propagation and their associated mode reflection coefficients can be obtained from the reflectance function. This information can be used together with estimates of the elastic constants to determine suitable frequency ranges for measuring the V(z) curve. Minimization of the difference between phase velocities obtained from measured and calculated V(z) curves is used to determine the elastic constants. Results are presented for TiN films on M2 high-speed steel substrates.

Journal Article↗

PubMed1993

Quantification of ventricular remodeling in the tight-skin mouse cardiomyopathy with acoustic microscopy.

To determine the role of ultrasonic tissue characterization for the detection of changes in myocardial architecture associated with cardiomyopathy, acoustic microscopy was performed on the hearts of 4- to 6-month-old tight-skin mice [TSK/+, C57-B10.D2 (58B)/SN strain], a model of cardiomyopathy characterized by diffuse interstitial fibrosis. Ultrasonic backscatter was measured from excised segments of left ventricular free walls of five TSK mice and five sex- and age-matched normal controls with a 50 MHz broad band focused piezoelectric transducer operated in a saline-filled water tank at room temperature. Forty-nine radio frequency (RF) lines were digitized from each specimen at 2 ns/sample. Power spectral analysis of RF data was performed and mean integrated backscatter (IB) computed. The TSK group demonstrated greater IB (-53.6 +/- 0.6 dB, n = 5) than did the control group (-56.6 +/- 0.7 dB, n = 5; p < 0.02). Myocardial collagen content determined by hydroxyproline assay increased by 11% in the TSK group (2.54 +/- 0.08 microgram/mg dry wt, n = 5) over that in controls (2.28 +/- 0.07 microgram/mg dry wt, n = 5; p < 0.05). A significant linear relationship was observed between myocardial hydroxyproline concentration and IB (r = 0.74; p < 0.02). Thus, ultrasonic tissue characterization permits sensitive detection of modest changes in the extent of interstitial fibrosis that accompany tissue remodeling in the early stages of cardiomyopathy.

Acoustics↗

PubMed1988

Transmission acoustic microscopy of tissue sections (1 GHz). Histoacoustics and acoustic staining.

The acoustic microstructure of mouse small intestine has been studied with a transmission acoustic microscope working at 1 GHz and the influence of the histologic processing on the microacoustic pattern has been tested. Unstained thin sections provide pictures rich in details and highly contrasted. Gelatin has been used as hydrosoluble embedding medium and has been compared to paraffin. The former embedding procedure retained the viscoelastic properties of the specimen far more and provided the most detailed pictures. Osmiun tetroxide has been used to demonstrate acoustic staining.

Animals↗

PubMed1998

Physical and mechanical properties of ePTFE stretch vascular grafts determined by time-resolved scanning acoustic microscopy.

OBJECTIVES: Determination of physical and mechanical characteristics and properties of thin-walled (0.39 mm) expanded polytetrafluoroethylene stretch vascular prostheses by time-resolved scanning acoustic microscopy (TR-SAM). MATERIALS AND METHODS: Samples of Stretch Gore-Tex were mounted on polymethylmethaacrylate substrate, and ethyl alcohol was used as acoustic couplant. A 10 MHz ultrasound transducer mounted on a SAM50 scanning acoustic microscope generated short, pulsed sound waves. Reflected signals were used for imaging and for computer analysis of time resolved wave forms acquired by a digital sampling oscilloscope to calculate physical and mechanical characteristics of the material. RESULTS: Graft wall thickness: 0.395 (0.352/0.401) mm; graft wall sound wave penetration velocity: 1111 (1083/1129) ms-1; acoustic impedance: 3.685 (2.975/4.370) 10(6) kg m-3s-1; attenuation coefficient: 0.144 (0.096/0.229) dB mm-1 MHz-1; material density: 3360 (2712/3982) kg m-3; elastic stiffness: 4.06 (3.35/4.83) GPa (median and (25/75) percentiles; n = 8 samples, 10 measurements spaced 100 microns apart in each sample). CONCLUSIONS: TR-SAM can effectively quantify ePTFE graft wall properties, and new data on graft properties have been provided. The acoustic impedance and elastic stiffness of the ePTFE graft wall are 2.2 and 1.6 times higher, respectively, than in human coronary arteries, and it is highly reflective of ultrasound.

Acoustics↗

PubMed1997

Multiple-transducer scheme for scanning tomographic acoustic microscopy using transverse waves.

We propose a new type of multiple-transducer scheme with functions of multiple-angle and multiple-frequency tomography for scanning tomographic acoustic microscopy (STAM) using transverse waves. We review the data acquisition system and mode conversion of the acoustic waves for STAM and the multiple-angle and multiple-frequency tomography. Our multiple-transducer scheme has three insonification angles and three resonance frequencies in order to operate, in the transverse wave mode, multiple-angle and multiple frequency tomography for STAM. In order to evaluate the performance of our transducer scheme, we have simulated tomographic reconstruction with a back-and-forth propagation algorithm. Simulation results show that our multiple-transducer scheme is capable of obtaining good resolution with transverse wave mode and multiple-frequency tomography. We also show that our multiple-transducer scheme is an efficient rotation tool for a number of projections.

Microscopy↗