Biomedical subjects

Stephen J Matcher

Publications and source records attributed to Stephen J Matcher.

4 recordsLinked to original sources

PubMed2006

Three-dimensional optic axis determination using variable-incidence-angle polarization-optical coherence tomography.

Polarization optical coherence tomography (PSOCT) is a powerful technique to nondestructively map the retardance and fast-axis orientation of birefringent biological tissues. Previous studies have concentrated on the case where the optic axis lies on the plane of the surface. We describe a method to determine the polar angle of the optic axis of a uniaxial birefringent tissue by making PSOCT measurements with a number of incident illumination directions. The method is validated on equine flexor tendon, yielding a variability of 4% for the true birefringence and 3% for the polar angle. We use the method to map the polar angle of fibers in the transitional region of equine cartilage.

Animals↗

PubMed2004

The collagen structure of bovine intervertebral disc studied using polarization-sensitive optical coherence tomography.

Polarization-sensitive optical coherence tomography (PS-OCT) is used to measure the birefringence properties of bovine intervertebral disc and equine flexor tendon. For equine tendon the birefringence delta n is (6.0 +/- 0.2) x 10(-3) at a wavelength of 1.3 microm. This is somewhat larger than the values reported for bovine tendon. The surface region of the annulus fibrosus of a freshly excised intact bovine intervertebral disc displays an identical value of birefringence, delta n = (6.0 +/- 0.6) x 10(-3) at 1.3 microm. The nucleus pulposus does not display birefringence, the measured apparent value of delta n = (0.39 +/- 0.01) x 10(-3) being indistinguishable from the effects of depolarization due to multiple scattering. A clear difference is found between the depth-resolved retardance of equine tendon and that of bovine intervertebral disc. This apparently relates to the lamellar structure of the latter tissue, in which the collagen fibre orientation alternates between successive lamellae. A semi-empirical model based on Jones calculus shows that the measurements are in reasonable agreement with previous optical and x-ray data. These results imply that PS-OCT could be a useful tool to study collagen organization within the intervertebral disc in vitro and possibly in vivo and its variation with applied load and disease.

Animals↗

PubMed2002

Quantitative assessment of skin layers absorption and skin reflectance spectra simulation in the visible and near-infrared spectral regions.

We have simulated diffuse reflectance spectra of skin by assuming a wavelength-independent scattering coefficient for the different skin tissues and using the known wavelength dependence of the absorption coefficient of oxy- and deoxyhaemoglobin and water. A stochastic Monte Carlo method is used to convert the wavelength-dependent absorption coefficient and wavelength-independent scattering coefficient into reflected intensity. The absorption properties of skin tissues in the visible and near-infrared spectral regions are estimated by taking into account the spatial distribution of blood vessels, water and melanin content within distinct anatomical layers. The geometrical peculiarities of skin histological structure, degree of blood oxygenation and the haematocrit index are also taken into account. We demonstrate that when the model is supplied with reasonable physical and structural parameters of skin, the results of the simulation agree reasonably well with the results of in vivo measurements of skin spectra.

Absorption↗

PubMedDate not supplied

Measuring red blood cell flow dynamics in a glass capillary using Doppler optical coherence tomography and Doppler amplitude optical coherence tomography.

Blood, being a suspension of deformable red cells suspended in plasma, displays flow dynamics considerably more complicated than those of an ideal Newtonian fluid. Flow dynamics in blood capillaries of a few hundred micrometers in diameter are investigated using Doppler optical coherence tomography (DOCT) and Doppler amplitude optical coherence tomography (DAOCT), a novel extension of DOCT. Velocity profiles and concentration distributions of normal and rigidified in vitro red blood cell suspensions are shown to vary as functions of mean flow velocity, cell concentration, and cell rigidity. Deviation from the parabolic velocity profile expected for Pouseille flow is observed for both rigid and normal cells at low flow rates. Axial red cell migration both toward and away from the tube axis is observed for both rigid and normal cells as a function of flow velocity. Good agreement is found between our measurements, and theoretical expectations.

Blood Flow Velocity↗