Alexander P. Sviridov

Intensity profiles of linearly polarized light backscattered from skin and tissue-like phantoms

Anisotropy of mouse and human skin is investigated in vivo using polarized videoreflectometry. An incident beam (linearly polarized, wavelength 650 nm) is focused at the sample surface. Two types of tissuelike media are used as controls to verify the technique: isotropic delrin and highly anisotropic demineralized bone with a priori knowledge of preferential orientation of collagen fibers. Equi-intensity profiles of light, backscattered from the sample, are fitted with ellipses that appear to follow the orientation of the collagen fibers. The ratio of the ellipse semiaxes is well correlated with the ratio of reduced scattering coefficients obtained from radial intensity distributions. Variation of equi-intensity profiles with distance from the incident beam is analyzed for different initial polarization states of the light and the relative orientation of polarization filters for incident and backscattered light. For the anisotropic media (demineralized bone and human and mouse skin), a qualitative difference between intensity distributions for cross- and co-polarized orientations of the polarization analyzer is observed up to a distance of 1.5 to 2.5 mm from the entry point. The polarized videoreflectometry of the skin may be a useful tool to assess skin fibrosis resulting from radiation treatment.

Visualization of biological texture using correlation coefficient images.

Subsurface structural features of biological tissue are visualized using polarized light images. The technique of Pearson correlation coefficient analysis is used to reduce blurring of these features by unpolarized backscattered light and to visualize the regions of high statistical similarities within the noisy tissue images. It is shown that under certain conditions, such correlation coefficient maps are determined by the textural character of tissues and not by the chosen region of interest, providing information on tissue structure. As an example, the subsurface texture of a demineralized tooth sample is enhanced from a noisy polarized light image.

Enhancement of hidden structures of early skin fibrosis using polarization degree patterns and Pearson correlation analysis

The skin of athymic nude mice is irradiated with a single dose of x-ray irradiation that initiated fibrosis. Digital photographs of the irradiated mice are taken by illuminating the mouse skin with linearly polarized probe light of 650 nm. The specific pattern of the surface distribution of the degree of polarization enables the detection of initial skin fibrosis structures that were not visually apparent. Data processing of the raw spatial distributions of the degree of polarization based on Fourier filtering of the high-frequency noise improves subjective perception of the revealed structure in the images. In addition, Pearson correlation analysis provides information about skin structural size and directionality.

Statistics of light deflection by randomly oriented interfaces in the geometric optics approximation

The statistics of light deflection by interfaces between two media is analytically related with the angular probability density between the normal to the interface and the incident beam. In the proposed model all reflection and refraction events are considered as independent with statistical weights equal to Fresnel intensity coefficients. The calculus of phase matrixes of light deflection resulting in the interaction with the randomly oriented interface is proposed. The balance of integrated probabilities of reflected and refracted photons from both sides of the interface allowed quantitative estimates of the probability of photons to be situated in different phases of inhomogeneous media.

Influence of tissue anisotropy on photon migration

Some recent advances in the optical analysis of anisotropic media, especially those, related with work of our group at National Institutes of Health, are presented. Comparison of theoretical formulas, obtained from random walk theory with available time-resolved (transmission mode) and polarization CW (reflectance mode) experimental data is discussed.

Analysis of Biological Tissue Textures Using Measurements of Backscattered Polarized Light

To enhance visibility of hidden anisotropic structures of biological tissues, geometry of sample illumination was optimized. Imaging of Pearson correlation coefficient of the degree of polarization was used to determine regions of statistical similarities.

Potentials of skin diagnostic with digital photometric patterning of backscattered linearly polarized light

Potentials of two modalities of skin diagnostic with focused and expanded linearly polarized probe light are studied. For the focused beam (wavelength 650 nm) the photometric patterns of light backscattered from skin and collagenous tissue phantoms were recorded using digital camera. It is shown that equiintensity contours are well fitted with ellipses that appeared to follow the orientation of collagen fibers. In the peripheral zone from the entry point of the probe beam the ratio of the ellipses semi-axes is correlated with the ratio ofreduced scattering coefficients obtained from intensity profiles. In the vicinity of the entry point it depends on the mutual orientation of polarization vector and collagen fibers. For the expanded probe beam the digital mapping of the residual polarization degree of backscattered linearly polarized light allowed visualization of the hidden structure of earlier fibrosis of the mouse skin arisen from X-ray treatment. The structure of the skin fibrosis was enhanced using Fourier transform filtering of polarization degree pattern. The pattern scanning with Pearson correlation coefficient was developed to determine the orientation and characteristic size of hidden structure. Both modalities may be potentially used for diagnostic ofskin abnormalities, such as fibrosis.

Photometry of skin and collagenous tissue phantoms with focused linearly polarized light

Equi-intensity contours of photometric patterns of backscattered focused linearly polarized light were fitted with ellipses. The orientation and ratio of semi-axes lengths revealed correlation with collagen fiber orientation. Optical anisotropy parameters were measured.