SignificanceA better understanding of diffusion reflection (DR) behavior may allow it to be used for more noninvasive applications, including the development of in vivo non-damaging techniques, especially for medical topical diagnosis and treatments.AimFor a bilayer opaque substance where the attenuation of the upper layer is larger than the attenuation of the lower layer, the DR crossover point (Cp) is location where the photons coming from the bottom layer start affecting the DR. We aim to study the dependency of the Cp on absorption changes in different layers for constant scattering and top layer thickness.ApproachMonolayer and bilayer optical tissue-like phantoms were prepared and measured using a DR system. The results were compared with Monte Carlo simulations.ResultsThere is an agreement between the experiments and the simulations. Cp correlates with the square root of the absorption coefficient ratio of the lower layer to the top layer.ConclusionThe experimental findings support and validate the theoretical prediction describing the dependency of the Cp on the square root of the ratio of the layers’ absorption coefficients. In addition, a secondary breaking point is suggested to be observed experimentally at the entrance to the noise area.
Experimental measurements of the reflected light intensity from two-layer phantoms are presented. We report, for the first time, an experimental observation of a typical reflected light intensity behavior for the two-layer structure characterized by two different slopes in the reflected light profile of the irradiated tissue. The point in which the first slope changes to the second slope, named as the crossover point, depends on the upper layer thickness as well as on the ratio between the absorption coefficients of the two layers. Since similar experiments from one-layer phantoms present a monotonic decay behavior, the existence and the location of the crossover point can be used as a diagnostic fingerprint for two-layer tissue structures. This pertains to two layers with greater absorptivity in the upper layer, which is the typical biological case in tissues like skin.
Light-tissue interaction is common in clinical treatments and medical researches, therefore investigation of light path in
irradiated tissues is of high importance. In this research, simulations and experimental measurements of the reflected
light intensity from one-layered lattices and phantoms are presented. Our results suggest that random walk simulations
fit well the photon migration model and enable the extraction of the lattice absorption parameter. The experimental
results present a partial fitting to the random walk model: while phantoms presenting different absorption coefficients
are distinguished by different reemitted light profiles, the model does not apply an adequate description for the phantom
absorption coefficient extraction. This calls for further investigation.
We study the optical detection of absorptive tumors in turbid tissues, using a random-walk model to describe the migration of photons in the tissue. We consider time-resolved transillumination measurements in slab-like tissues, and calculate the tranmsmitted intensity with and without the inclusion. The ratio of these quantities, defined as the measure of the detectability, is studied as a function of the inclusion size and absorption coefficient. The detectability is found to depend only on the difference between the absorptivities of the abnormality and the surrounding tissue. The nonmonotonic behavior in time of this ratio corresponds to the three different types of photon trajectories in the tissue, and its extremum points provide information which can be used to determine the optimal time window for best detection.
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