Ilya V. Yaroslavsky

Micro-fractional ablative skin resurfacing with two novel erbium laser systems

Fractional ablation offers the potential benefits of full‐surface ablative skin resurfacing while minimizing adverse effects. The purpose of this study was to evaluate the safety, damage profile, and efficacy of erbium fractional lasers.

Tissue optics, light distribution, and spectroscopy

A model of multilayered tissue is considered. The Monte Carlo simulation technique is used to study laser beam transport through tissues with varying optical properties for each layer (absorption, scattering, scattering anisotropy factor, and refractive index). Calculations are performed for some models of the human skin and adjacent tissues for visible and UV wavelength ranges. New technology for human epidermis optical parameters determination is presented. This technology includes epidermis upper layers glue stripping; in vitro measurements of total transmission, diffuse reflection, and angular scattering of stripping samples; and using an inverse calculation technique based on four-flux approximation of radiation transport theory. The technology was successfully used for depth dependence monitoring of epidermis optical parameters. An inverse Monte Carlo technique for determining the optical properties of tissues based on spectrophotometric measurements is developed. This technique takes into account the 2-D geometry of the experiment, finite sizes of incident beam and integrating sphere ports, boundary conditions, and sideways losses of light.

Inverse hybrid technique for determining the optical properties of turbid media from integrating-sphere measurements

We have combined the Monte Carlo method with the small-angle approximation of the radiative transfer theory to derive the optical properties (the absorption coefficient, the scattering coefficient, and the anisotropy factor) of turbid materials from integrating-sphere measurements (the total transmittance and the diffuse reflectance) and the collimated transmittance. Unlike one-dimensional models, the technique accounts for the side losses of light at the edges of the sample. In addition, it enables the correction of the measured collimated signal for the contribution of multiply scattered light. On the other hand, the hybrid technique allows a significant reduction in calculation time compared with inverse methods based on a pure Monte Carlo technique. Numerical tests and experimental results from a phantom material (milk) as well as samples of biological tissue (porcine myocardium) confirmed the feasibility of applying this technique to the determination of the optical properties of turbid media.

Optical properties of blood in the near-infrared spectral range

We determine the optical properties of whole blood samples in the near infrared spectral range from double integrating sphere measurements using an inverse Monte Carlo technique. The measured values included the diffuse reflectance, the total transmittance, and the collimated transmittance. From these data, the absorption coefficient, the scattering coefficient, and the anisotropy factor were derived. The spectral range investigated extended from 700 nm to 1200 nm. It was found that the optical properties of blood were substantially different from the respective data for other relevant human tissues known so far. In addition, we analyzed the effect of the scattering phase function approximation on the resulting estimates of the optical properties. The Henyev-Greenstein and the Gegenbauer kernel phase functions were considered. The calculated angular distributions of scattered light were compared with goniophotometric measurements performed at the wavelength of 633 nm. The data presented in this study prove that the variations of the employed scattering phase function approximation can cause large discrepancies in the derived optical properties. This leads to the conclusion that the exact knowledge of the scattering phase function is required for the precise determination of the optical constants from the double integrating sphere measurements.

Low level light effects on inflammatory cytokine production by rheumatoid arthritis synoviocytes

Low level light therapy (LLLT) is being evaluated for treating chronic and acute pain associated with rheumatoid arthritis (RA) and other inflammatory diseases. The mechanisms underlying the effectiveness of LLLT for pain relief in RA are not clear. The objectives of this study were to determine whether LLLT decreased production of pro‐inflammatory cytokines by cells from RA joints, and, if so, to identify cellular mechanisms.

Optical clearing of human skin: comparative study of permeability and dehydration of intact and photothermally perforated skin

Accelerated diffusion of water and hyperosmotic optical clearing agents is studied as a result of enhanced epidermal permeability. A lattice of microzones (islets) of damage in stratum corneum is induced using a flash-lamp applique system. An optical clearing agent composed of 88% glycerol in aqueous solution is used for all experiments. Research of skin dehydration and glycerol delivery through epidermis at both intact and perforated stratum corneum is presented. The dehydration process induced by both stimuli of evaporation and osmotic agent action is studied by weight measurements. Dynamics of refractive index alteration of both glycerol solution and water during their interaction with skin samples is monitored. The amounts of water escaping from skin through the stratum corneum, due to hyperosmotic-agent action, and glycerol penetrating through the skin sample, are estimated. The results show that the proposed method allows for effective transepidermal water loss and delivery of optical clearing agents.

Effect of the scattering delay on time-dependent photon migration in turbid media

We modified the diffusion approximation of the time-dependent radiative transfer equation to account for a finite scattering delay time. Under the usual assumptions of the diffusion approximation, the effect of the scattering delay leads to a simple renormalization of the light velocity that appears in the diffusion equation. Accuracy of the model was evaluated by comparison with Monte Carlo simulations in the frequency domain for a semi-infinite geometry. A good agreement is demonstrated for both matched and mismatched boundary conditions when the distance from the source is sufficiently large. The modified diffusion model predicts that the neglect of the scattering delay when the optical properties of the turbid material are derived from normalized frequency- or time-domain measurements should result in an underestimation of the absorption coefficient and an overestimation of the transport coefficient. These observations are consistent with the published experimental data.

Transcutaneous delivery of micro- and nanoparticles with laser microporation

Abstract. Fractional laser ablation is one of the relatively safe and minimally invasive methods used to administer micro- and nanoparticles into the skin at sufficiently large depth. In this article, we present the results of delivery of TiO2 nanoparticles and Al2O3 microparticles into skin. Fractional laser microablation of skin was provided by a system based on a pulsed Er:YAG laser with the following parameters: the wavelength 2940 nm, the pulse energy 3.0 J, and the pulse duration 20 ms. Ex vivo and in vivo human skin was used in the study. The suspensions of titanium dioxide and alumina powder in polyethylene glycol with particle size of about 100 nm and 27 μm, respectively, were used. In the ex vivo experiments, reflectance spectra of skin samples with administered particles were measured and histological sections of the samples were made. In the in vivo experiment, reflectance spectroscopy, optical coherence tomography, and clinical photography were used to monitor the skin status during one month after suspension administering. It is shown that particles can be delivered into dermis up to the depth 230 μm and distributed uniformly in the tissue. Spectral measurements confirm that the particles stay in the dermis longer than 1 month.

Different phase-function approximations to determine optical properties of blood: a comparison

We investigated the impact of the scattering phase function approximation on the optical properties of whole human blood determined from integrating sphere measurements using an inverse Monte Carlo technique. The diffuse reflectance Rd and the total transmittance Tt ((lambda) equals 633nm) of the whole blood samples were measured with a double integrating sphere equipment. The experimental scattering phase functions of the highly diluted blood samples were measured with a goniophotometer. We approximated the experimental scattering phase function with Mie, Gegenbauer kernel (GKPF), and Henyey-Green (HGPF) phase functions to pre-set the anisotropy factor (mu) for the inverse problem. We have employed HGPF, GKPF, and MPF approximations in the inverse Monte Carlo procedure to derive the absorption coefficient (mu) a and the scattering coefficient (mu) s. The results show significant difference in the final estimates of (mu) s. 12

Semi-Automated method of analysis of horizontal histological sections of skin for objective evaluation of fractional devices.

The treatment of skin with fractional devices creates columns of micro‐ablation or micro‐denaturation depending on the device. Since the geometric profiles of thermal damage depend on the treatment parameters or physical properties of the treated tissue, the size of these columns may vary from a few microns to a few millimeters. For objective evaluation of the damage profiles generated by fractional devices, this report describes an innovative and efficient method of processing and evaluating horizontal sections of skin using a novel software program.