A N Bashkatov

Optical Properties of the Subcutaneous Adipose Tissue in the Spectral Range 400-2500 nm

The optical characteristics of subcutaneous adipose tissue are studied in the wavelength range 400–2500 nm. The experiments are conducted in vitro using a Cary 2415 spectrophotometer. Based on the measured diffuse reflectance and total transmittance spectra, the spectra of the absorption and transport scattering coefficients are calculated in terms of the inverse adding-doubling method.

Optical Clearing of Human Dura Mater

The changes in the optical parameters of the human dura mater in the spectral range 400–700 nm caused by the action of an aqueous solution of mannitol with a concentration of 0.16 g/ml are studied in vitro. The diffusion of mannitol into the tissue leads to a partial matching between the refractive indices of the structure-forming elements (the collagen fibrils) and the base substance of the dura mater (the interstitial fluid). As a result, the light scattering by the biological tissue in the entire spectral range under study is decreased, on the average, by a factor of 1.5–2. The immersion of the biological tissue is shown to cause a decrease in the absorption of the dura mater in the range of the blood absorption bands by a factor of 1.2–1.6. The results presented may prove to be useful in the laser therapy and optical diagnostics of brain diseases.

Immersion clearing of human blood in the visible and near-infrared spectral regions

The possibility of the immersion clearing of human blood in the visible and near-IR spectral regions is considered and theoretically substantiated. On the basis of the model presented, the spectral behavior of the scattering and absorption characteristics of blood upon its immersion clearing by glucose is analyzed.

Optical properties of human sclera in spectral range 370-2500 nm

Optical characteristics of human sclera are experimentally studied. Experiments are performed in vitro on a Cary-2415 spectrophotometer in the spectral range 370–2500 nm. Based on the measured diffuse reflection and total transmission spectra, the absorption and transport scattering coefficient spectra are calculated by the inverse adding-doubling method.

Optical clearing of skin under action of glycerol: Ex vivo and in vivo investigations

The behavior of optical parameters of the skin of a laboratory rat under the action of an aqueous solution of glycerol is studied ex vivo and in vivo. It is found that the collimated transmission coefficient of ex vivo skin samples increases by a factor of 20–40-fold depending on the wavelength in the studied spectral range, and the diffuse reflection coefficient of skin in vivo decreases on the average by 16%. The results presented can be useful for many methods of laser therapy and optical diagnostics of skin diseases and localization of subcutaneous neoplasms.

Optical properties of mucous membrane in the spectral range 350-2000 nm

The optical characteristics of the mucous membrane from the human maxillary sinus are studied experimentally. The experiments were carried out in vitro in the spectral range 350–2000 nm. On the basis of the measured total transmittance and diffuse reflectance spectra, the absorption and transport scattering coefficients are calculated in the entire range in terms of the inverse adding-doubling method.

Effect of storage conditions of skin samples on their optical characteristics

The optical characteristics of skin samples are experimentally studied ex vivo and in vitro at different storage conditions. The experiments are performed on a Cary-2415 spectrophotometer in the spectral range 400–700 nm. Based on the measured diffuse reflectance and total transmittance spectra, the spectra of the absorption and reduced scattering coefficients are calculated in terms of the inverse adding-doubling method. It is shown that the method of storage of samples mainly affects the reduced scattering coefficient of biotissue. Thus, upon storage of skin in an isotonic solution and in its absence, the reduced scattering coefficient increases ∼1.5 and ∼2 times, respectively, compared to the value of this parameter for the intact sample. The differences in the absorption spectra of ex vivo samples and samples stored under different conditions are the most noticeable in the absorption range of blood and are significant above 600 nm.

Study of the epidermis ablation effect on the efficiency of optical clearing of skin in vivo

We present the results of a comparative analysis of optical immersion clearing of skin in laboratory animals in vivo with and without preliminary ablation of epidermis. Laser ablation is implemented using a setup based on a pulsed erbium laser (λ = 2940 nm). The size of the damaged region amounted to 6 × 6 mm, the depth being smaller than 50 μm. As an optical clearing agent (OCA), use is made of polyethylene glycol (PEG-300). Based on optical coherence tomography, we use the single scattering model to estimate the scattering coefficient in the process of optical clearing in 2 regions at depths of 50−170 μm and 150−400 μm. The results show that skin surface ablation leads to the local oedema of the affected region that increases the scattering coefficient. However, the intense evaporation of water from the ablation zone facilitates the optical clearing at the expense of tissue dehydration, particularly in the upper layers. The assessment of the optical clearing efficiency shows that the efficiency exceeding 30% can be achieved at a depth from 50 to 170 μm in 120 min after ablation, as well as after the same ablation with subsequent application of PEG-300, which increases the efficiency of the immersion method by almost 1.8 times. At a depth from 150 to 400 μm, dehydration of upper layers cannot completely compensate for an increase in light scattering by dermis after epidermis ablation. The additional effect of OCA enhances the optical clearing of skin at the expense of improving the refractive index matching between dermis components, but the maximal efficiency of optical clearing in 120 min does not exceed 6%.

Modeling of optimal conditions for oxyhemoglobin photodissociation in laser-irradiated biotissue

Based on the theory of radiation transfer and a model that describes the structure and optical properties of biotissues, we have found spectral conditions of irradiation of the skin surface that ensure efficient generation of molecular oxygen O2 in the dermis due to the photodissociation of blood oxyhemoglobin. We show that, for maximal local O2 formation at depths z ≤ 0.2 mm, 0.2 mm < z ≤ 0.9 mm, 0.9 mm < z ≤ 2.5 mm, and z > 2.5 mm, it is more effective to use wavelengths in the intervals 418 ± 5, 575 ± 5, 585 ± 5, and 600 ± 5 nm, respectively. Physical reasons for the shift of optimal wavelengths toward the red range of the spectrum are described. We show that they are based on the selectivity of optical properties of the skin biotissue, which acts as of a kind of spectral filter the transmission curve of which depends on the depth. It is found that irradiation at a wavelength near 575 nm is optimal for the generation of a maximal amount of O2 in the intire bulk of the dermis.

Comparative study of the physical, chemical, and multimodal approaches to enhancing nanoparticle transport in the skin with model dermatitis

This paper presents a comparative analysis of the combined and separate influence of ultrasound and DMSO on the transport of a gold nanoshell suspension in intact and injured skin from data on optical coherence tomography and histochemical analysis. Experimental allergic contact dermatitis was used to model injury to the stratum corneum during various pathological changes in the skin. The studies were performed on outbred laboratory rats. It is shown that the best method for enhancing transdermal transport of an immersion liquid is multimodal physical and chemical impact (a combination of DMSO and ultrasonophoresis); the effectiveness of optical clearing of the dermis both in the presence and absence of the stratum corneum is approximately the same. To enhance the transport of nanoparticles into the skin when it undergoes pathological changes related to injuries of the protective barrier, exposure to ultrasound is sufficient.