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Biomedical subjects

G A Briggs

Publications and source records attributed to G A Briggs.

11 recordsLinked to original sources
PubMed2001

Monte Carlo simulation of growth of porous SiOx by vapor deposition.

A random network model containing defects has been developed and applied to the deposition of amorphous SiOx films on a flat substrate. A new Monte Carlo procedure enables dangling bonds to migrate and annihilate. The degree of porosity in the films is found to increase with oxygen content. As the oxygen content increases a larger fraction of pore surfaces is covered with oxygen, and the density of dangling bonds on pore surfaces decreases. Oxygen plays the role of a surfactant, lowering the energies of pore surfaces and enhancing the porosity of amorphous SiO2 compared to amorphous Si.

Journal Article↗
PubMed2001

Biomechanical measurements in microscopically thin stratum comeum using acoustics.

BACKGROUND/AIMS: This study investigated whether a scanning acoustic microscope (SAM) could be developed to measure changes in the mechanical properties of the microscopically thin external layer of skin, the stratum corneum. The adapted microscope was used to determine the effects of various aqueous reagents, as compared with water, on the thickness, density, compression wave velocity and elastic constant, using 10 microm thin sections of human skin. METHODS: Specimens were exposed to aqueous solutions of glycerol, sodium chloride and alpha-hydroxy caprylic acid (HCA) to investigate permeation and to investigate the effect of these solutions on the above physical properties for signal transmission at a centre frequency of approximately 650 MHz in a path parallel to the epidermal layers. RESULTS: The system of measurement was found to give repeatable results and to provide a reliable indicator of the change in mechanical properties of the stratum corneum that arise from imbibition with different substances. Acoustic measurements of untreated specimen thickness and density agreed well with optical measurements and with previously published measurements, respectively. The trend in change of elastic moduli, however, was not in agreement with the results of the large-scale extensibility tests of Takahashi et al. and Hall & Hill, which used thicker specimens that contained additional epidermal or dermal layers. CONCLUSION: Disparate trends in elastic moduli were believed to be due to the strain rate dependence of the tissues and the different rates of loading applied during testing.

Acoustics↗
PubMed2001

Small intestine wall distribution of elastic stiffness measured with 500 MHz scanning acoustic microscopy.

Obtaining data relating intestinal mechanical properties and histology is a step towards the next level in the hierarchy of structure of living tissue, and may provide new insight into the mechanisms of intestinal function and disease such as obstruction. Due to lack of methodology, however, such data are currently sparse. Scanning acoustic microscopy (SAM) can measure the propagation speed of sound (C) and the acoustic impedance (Z) with micrometer resolution in tissue. By use of elementary theory of elasticity, the elastic stiffness (c11) can be computed from C and Z. We used 5-microm-thick transverse sections of ethanol treated guinea pig small intestine as the experimental model and measured the distribution of C and Z across the intestinal wall using SAM at 500 MHz. The individual layers mucosa, submucosa, and circular and longitudinal muscle were discerned with ease in the images and varied significantly with respect to both C and Z in most cases. The measured values (median values) of C ranged from 1550 to 1669 m s(-1), and Z ranged from 2.10 to 2.60 MPa s m(-1). c11 differed between all layers ranging from 3.25 to 4.27 GPa with the following sequence of magnitude: circular muscle >submucosa>mucosa>longitudinal muscle (p<0.001). In conclusion, we provided the first microscale mechanical data relating to the histological layers of the small intestine.

Acoustics↗
PubMed2000

Microscopy of Metal Oxide Surfaces.

Elevated temperature scanning tunneling microscopy is used to study oxides that are room temperature insulators but become sufficiently electrically conducting at higher temperatures to allow imaging to be performed. Atomic resolution images of NiO, CoO, and UO(2) have been obtained in this fashion which allow surface structure and defect determination. To complement the experiments, modeling of the electronic surface structure reveals which atomic sites give rise to the contrast observed in the images. Low voltage scanning electron microscopy is used to image small equilibrium pores in UO(2) single crystals to evaluate the surface energy ratio of the (111) to (001) surfaces.

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↗
PubMed1992

Acoustic microscope study of the elastic properties of fluorapatite and hydroxyapatite, tooth enamel and bone.

Measurements of Rayleigh velocity and attenuation were taken in single mineral crystals of hydroxyapatite and fluorapatite at angular intervals relative to their c axes, using an acoustic microscope. These results are compared with the values that were calculated using the elastic constants of apatite from Yoon and Newnham [(1969) Am. Miner. 54, 1193-1197.] and Katz and Ukraincik [(1971) J. Biomechanics 4, 221-227.]. The slowness curves of various wave modes are plotted and discussed in relation to cross-coupling effects that were found to cause instability in measurements of attenuation for the c axes direction. Velocity measurements were taken in specimens of tooth enamel and bone. Here comparisons are made with the values that were calculated by modelling the 'z' scan response of the microscope, using published data for the elastic and acoustic properties. Comparisons are also made with the measurements on single crystals, since apatite is a major component of enamel and bone.

Animals↗
PubMed1989

The elastic microstructure of various tissues.

Previous work has indicated that a modified Quate-Lemons scanning acoustic microscope (SAM) is capable of measuring the acoustic propagation properties of sections of biological tissue. The lens is excited by an impulse, rather than a tone burst, and the undemodulated returning signal from the tissue is recorded. The variations in received signal with time are used to deduce the sound speed, attenuation, impedance, and section thickness. In this article, the technique is applied to various types of tissue, and the variations in acoustic propagation properties are computed. Conventional tone burst SAM images at 425 MHz are compared with the time resolved data in order to elucidate the contrast mechanisms. The effects of varying the frequency and position of the focal plane on the tone burst images are interpreted in the light of the broadband results.

Acoustics↗
PubMed1989

Frequency dependence of tissue attenuation measured by acoustic microscopy.

Broadband scanning acoustic microscopy (SAM) has been used to investigate the mechanical properties of sections of tissue with a resolution of around 8 microns. The work reported here extends these results by reporting the frequency dependence of the attenuation coefficient from 100-500 MHz. A discussion of the theory of the measurements is presented. The scanning laser acoustic microscope (SLAM) is used to characterize similar tissue sections at 100 MHz. The data obtained with the two forms of acoustic microscopy are compared with results from the literature.

Acoustics↗
PubMed1989

Studies on sound and carious enamel with the quantitative acoustic microscope.

The scanning acoustic microscope gives strong contrast from small caries lesions in sections of human enamel. The uniqueness of the acoustic microscope lies in its ability to image elastic properties. In addition to revealing the extent and the shape of lesions, the microscope may also be used to measure the elastic properties point by point across an area of interest. Since enamel is anisotropic, measurements of the Rayleigh velocity and attenuation were made as a function of direction on a section of sound enamel. The velocity was greatest parallel to the prism axis, and the attenuation was least in this direction. Measurements of V(z) across a section through a lesion are presented. The variation of attenuation can be interpreted in terms of the development of demineralization, initially along prism boundaries and then along cross-striations. The variation of velocity indicates a substantial reduction of elastic stiffness in the lesion.

Dental Caries↗