The optical properties of human skin, subcutaneous adipose tissue and human mucosa were measured in the wavelength range 400–2000 nm. The measurements were carried out using a commercially available spectrophotometer with an integrating sphere. The inverse adding–doubling method was used to determine the absorption and reduced scattering coefficients from the measurements.

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Optical properties of human skin, subcutaneous and mucous tissues in the wavelength range from 400 to 2000 nm

Methods of applying laser light to the skin, and apparatus therefor, include methods for removing hair, for synchronizing hair growth, for stimulating hair growth, for treating Herpes virus, for reducing sweat and body odor, for in situ formation of a chromophore in hair ducts, for reducing light loss at the skin surface, for grafting of hair stem cells, and for removing keloid or hypertrophic scars. The hair removal methods include controlling the proportions of photomechanical and photothermal damage by selection of laser parameters, chromophore particle size and/or pulse duration, with optional dynamic skin cooling. Additional hair removal methods include infiltrating a photoactivated drug into hair ducts and exposing the skin to sunlight or administering an anti-proliferative agent into hair ducts, for example, by encapsulating the anti-proliferative agent in a slow release vehicle. The methods of treating Herpes virus, reducing sweat or body odor, and removing keloid or hypertrophic scars include infiltrating a light-absorbing contaminant into hair ducts or other openings in the skin and illuminating the contaminated skin section. The methods for stimulating hair growth include grafting of cloned auto hair stem cells, the hair ducts or administering methionine to a skin section to increase hair growth. Apparatus useful in performing these methods include devices for making a smooth optical boundary between skin and air or for dividing a light beam into a plurality of smaller light beams, and dressings for use before, during and after laser illumination.

Methods and devices for inhibiting hair growth and related skin treatments

The development of optical methods in modern medicine in the areas of diagnostics, therapy, and surgery has stimulated the investigation of optical properties of various biological tissues, since the efficacy of laser treatment depends on the photon propagation and fluence rate distribution within irradiated tissues. In this work, an overview of published absorption and scattering properties of skin and subcutaneous tissues measured in wide wavelength range is presented. Basic principles of measurements of the tissue optical properties and techniques used for processing of the measured data are outlined.

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Optical properties of skin, subcutaneous, and muscle tissues: a review

Background and Objective: A method to increase light transport deeply into target areas of tissue would enhance both therapeutic and diagnostic laser applications. The effects of a hyperosmotic agent on the scattering properties of rat and hamster skin were investigated. Study Design/Materials and Methods: A hyperosmotic agent, glycerol, was applied in vitro and in vivo to rat and hamster skin to assess the changes in tissue optical properties. Changes in the reduced scattering coefficient after application of the agent in vitro to rat skin and after the skin has been rehydrated were assessed to evaluate the effect of the agent on tissue. Results: Experimental results showed a transient change in the optical properties of in vitro rat skin. A 50% increase in transmittance and decrease in diffuse reflectance occurred within 5‐10 min after the introduction of anhydrous glycerol. In addition, reduction of light scattering with this technique increased depth of visibility with optical coherence tomography. Injection of glycerol under the skin allowed in vivo visualization of blood vessels. Conclusions: The application of the agent reduces the amount of refractive mismatch found in the tissue and markedly reduces random scattering, thereby making the skin less turbid for visible wavelengths for a controlled period of time. Lasers Surg. Med. 24:133‐141, 1999. © 1999 Wiley-Liss, Inc.

Use of an agent to reduce scattering in skin

A survey of the literature is presented that provides an analysis of the optical properties of human skin, with particular regard to their applications in medicine. Included is a description of the primary interactions of light with skin and how these are commonly estimated using radiative transfer theory (RTT). This is followed by analysis of measured RTT coefficients available in the literature. Orders of magnitude differences are found within published absorption and reduced-scattering coefficients. Causes for these discrepancies are discussed in detail, including contrasts between data acquired in vitro and in vivo. An analysis of the phase functions applied in skin optics, along with the remaining optical coefficients (anisotropy factors and refractive indices) is also included. The survey concludes that further work in the field is necessary to establish a definitive range of realistic coefficients for clinically normal skin.

https://www.spiedigitallibrary.org/journals/journal-of-biomedical-optics/volume-17/issue-9/090901/Optical-properties-of-human-skin/10.1117/1.JBO.17.9.090901.pdf

Optical properties of human skin.

Tissue optical properties are necessary parameters for prescribing light dosimetry in photomedicine. In many diagnostic or therapeutic applications where optical fiber probes are used, pressure is often applied to the tissue to reduce index mismatch and increase light transmittance. In this paper, we have measured in vitro optical properties as a function of pressure with a visible-IR spectrophotometer. A spectral range of 400-1800 mm with a spectral resolution of 5 nm was used for all measurements. Skin specimens of a Hispanic donor and two Caucasian donors were obtained from the tissue bank. Bovine aorta and sclera, and porcine sclera came from a local slaughter house. Each specimen, sandwiched between microscope slides, was compressed by a spring-loaded apparatus. Then diffuse reflectance and transmittance of each sample were measured at no load and at approximately 0.1, 1, and 2 kgf/cm/sup 2/. Under compression, tissue thicknesses were reduced up to 78%. Generally speaking, the reflectance decreased while the overall transmittance increased under compression. The absorption and reduced scattering coefficients were calculated using the inverse adding doubling method. Compared with the no-load controls, there was an increase in absorption and scattering coefficients among most of the compressed specimens.

Effects of compression on soft tissue optical properties

We investigated anomalies in the reflectance change of retinal lesions resulting from laser photocoagulation. These anomalies deviate from the predicted pattern and could cause misleading postoperative assessment of lesion depth and problems with proposed automated lesion control algorithms. We found that for certain irradiation parameters which produce super-threshold lesions, lesions exhibiting annular reflectance patterns are induced in an albumen eye phantom. The correlation between central reflectance and actual lesion depth thus becomes invalid for these anomalous lesions. Evidence of anomalous lesions in vivo was also found. Assumptions regarding retinal lesion formation must consider annular reflectance patterns. These patterns are produced by vaporization in the albumen eye phantom; vaporization may also play a role in anomalous retinal lesions along with the well known effect of minor retinal hemorrhage.

Anomalous reflectance of laser-induced retinal lesions

Optical characterization and coagulation performance of side-emitting fiber delivery systems for laser therapy of benign prostatic hyperplasia: A comparative study

We developed a 3D thermo-electrical model of RF tissue cutting that takes into account variations in electrical and thermal properties with temperature and water content, dynamics of water evaporation and thermal and electrical processes at the tissue-scalpel interface. The model predicts measurable parameters of the electric circuit (tissue impedance, ESU output RMS voltage and current) and tissue cutting rate. Results of numerical simulations suggest that high circuit impedance during electrosurgical cutting can result not only from tissue dehydration but from the configuration of the electric field as well. It appears that the area of tissue-scalpel electric contact is significantly smaller than the area of the scalpel itself but is large enough to rule out electric sparks as a major mechanism of electrosurgical cutting.

Thermoelectrical numerical model of electrosurgical rf cutting

Tissue optical properties are necessary parameters for prescribing light dosimetry in photomedicine. In many diagnostic or therapeutic applications where optical fiber probes are used, pressure is often applied to the tissue to reduce index mismatch and increase light transmittance. In this study, we have measured in vitro optical properties as a function of pressure with a visible-IR spectrophotometer. A spectral range of 400 - 1800 nm with a spectral resolution of 5 nm was used for all measurements. Skin specimens of two Hispanic donors and three caucasian donors were obtained from the tissue bank. Each specimen, sandwiched between microscope slides, was compressed by a spring-loaded apparatus. Then diffuse reflectance and transmittance of each sample were measured at no load and at approximately 0.1 and 1 kgf/cm2. Under compression, tissue thicknesses were reduced up to 78%. Generally, reflectance decreased while the overall transmittance increased under compression. The absorption and reduced scattering coefficients were calculated using the inverse adding doubling method. Compared with the no-load controls, there was an increase in the absorption and scattering coefficients among most of the compressed specimens.

Dmitry E. Protsenko

Papers

Effects of compression on soft tissue optical properties

Anomalous reflectance of laser-induced retinal lesions

Optical characterization and coagulation performance of side-emitting fiber delivery systems for laser therapy of benign prostatic hyperplasia: A comparative study

Thermoelectrical numerical model of electrosurgical rf cutting

Effects of compression on human skin optical properties