A simple numerical model is proposed to describe the process of OCT signal formation in a scattering medium
(biological tissue) under the conditions of immersion chemical agent diffusion. Due to optical clearing of the tissue the
shape of the OCT A-scan becomes time-dependent, thus providing information about the diffusion rate. The model
includes the numerical solution of the diffusion equation, the relation between the concentration of clearing agent and the
scattering coefficient, and, finally, the description of the OCT signal formation given the material parameters and with
the probe beam geometry taken into account. The test calculations qualitatively reproduce the experimentally observed
time behavior of A-scans in samples of human tooth dentine, caused by diffusion of different chemical agents. In
particular, it is shown that the non-monotonic A-scans having a maximum can be explained by assuming that the
backscattering coefficient giving rise to the OCT signal is, at least partially, subject to optical clearing alongside with the
scattering coefficient responsible for the signal attenuation.
Morphological changes of the adipose tissue at phototreatment are studied in vitro using optical coherence tomography. The 200 to 600 μm fat tissue slices are used in the experiments. The observed change in the tissue structure was associated with fat cell lipolysis and destruction caused by the photodynamic effect. It is found that overall heating of a sample from room to physiological temperature leads to deeper and faster morphology tissue changes if other processing conditions are kept constant. These data support the hypothesis that photodynamic/photothermal treatment induces fat cell lipolysis during some period after treatment.
Penetration of nanoparticles into tooth tissues is of significant interest in solving problems related to reduction of tooth
sensitivity, enamel strengthening and restoration and cosmetic bleaching. In this work we demonstrate two-photonexcited
autofluorescence and second-harmonic generation microscopy for visualization of penetration of TiO2 and ZnO
nanoparticles into tooth tissues.
Measurements of optical properties of fingernail and underlying tissues using OCT are presented. Review and
measurements of Raman spectra of tissue and phantom compounds were done. Updating of modeling algorithm for
scattering coefficient calculation on the basis of integrating sphere measurements accounting for particle size-distribution
was also done. The adequate fingernail and underlying tissue optical model at 830 nm was evaluation. Tissue phantoms
potentially suitable for calibration of Raman instrumentation for glucose sensing were designed and tested on the basis of
epoxy resin, TiO2-nanoparticles and micron-sized silica particles with the capillary net-work.
KEYWORDS: Diffusion, Optical coherence tomography, Teeth, Liquids, Tissues, Signal processing, Tissue optics, Signal attenuation, Data processing, Water
In our previous work optical coherence tomography (OCT) has been proved to be a useful tool for monitoring of
diffusion of chemical agents (water, glycerol) within human tooth dentine. Such diffusion studies are interesting for tooth
therapy (diffusion of medicinal preparations) and cosmetics (chemical whitening agents). Here we compare different
wetting schemes in which the sample is either merged in the liquid agent so that the probe beam is to pass through a layer
of liquid, or subjected to wetting through a special window from the back side. In spite of certain difference revealed, the
order of magnitude of the diffusion time constant and the permeability coefficient are shown to be the same in both
cases.
Monitoring of agent diffusion within tooth tissues is important in a wide context of tooth therapy (diffusion of medicinal preparations) and cosmetics (chemical whitening agents). We report here the results of optical coherence tomography (OCT) monitoring of diffusion of water and glycerol as clearing agents in samples of human tooth tissue. The diffusion process is analyzed by monitoring the changes in the OCT signal slope and the depth-resolved amplitude of OCT signal from a sample. Slow temporal kinetics of the mean attenuation coefficient was measured to monitor a saturable optical clearing due to the diffusion of the agent. The average permeability coefficient was estimated by dividing the measured thickness of the selected region by the time it took for the agent to diffuse through. The experimental results demonstrate that OCT can be an efficient tool in the study of agent diffusion through hard tissues.
Dentinal permeation is of interest in a wide context of tooth care and treatment, in particular, tooth color improvement using combination of chemical whitening agents and light activation. A simple model of dentinal permeation accounting for the morphology of human tooth dentine and including dentinal tubules, more dense and homogeneous peritubular dentine, and less dense and less homogeneous intertubular dentin is proposed. Calculation of permeability of dentine layer is carried out for H2O and H2O2 versus the tubule diameter and tubule density taken from the microphotograph analysis. This opens the possibility to calculate the distribution of permeability over the tooth surface taking into account the variations of tubule diameter and density as well as those of the diffusion coefficients and layer thickness
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