Temperature induced changes in the optical properties of skin in vivo

Abstract

Knowledge of temperature-induced changes of skin optical properties is required for accurate dosimetry of photothermal treatments. We determined and compared in vivo optical properties of mouse ear skin at different temperatures. The diffuse reflectance, total and diffuse transmittance were measured in the spectral range from 400 to 1650 nm using an integrating sphere spectrometer at the temperatures of 25 °C, 36 °C and 60 °C. Target temperatures were attained and maintained using an automated heater equipped with a sensor for feed-back and control. Temperature and temperature induced morphological changes of skin were monitored using an infrared thermal camera and reflectance confocal microscopy, respectively. An inverse Monte Carlo technique was utilized to determine absorption, scattering, and anisotropy factors from the measured quantities. Our results indicate significant differences between the optical properties of skin at different temperatures. Absorption and scattering coefficients increased, whereas anisotropy factors decreased with increasing temperature. Changes in absorption coefficients indicate deoxygenation of hemoglobin, and a blue shift of water absorption bands. Confocal imaging confirmed that our observations can be explained by temperature induced protein denaturation and blood coagulation. Monitoring spectral responses of treated tissue may become a valuable tool for accurate dosimetry of light treatments.

Utilizing the spatial frequency domain imaging to investigate change in optical parameters of skin exposed to thermal‐hydrotherapy: Ex‐vivo study

“…Several studies have been proposed to investigate the changes that occur in skin following the increase in its temperature based on studying the change of the optical absorption and scattering properties. [54][55][56] All these studies recorded increasing in tissue scattering and absorption coefficients at tissue temperature between 20 C and 40 C. According to the literature, rising tissue temperature causes decrease in transmittance and increasing in reflectance due to the increase of tissue's scattering coefficient, 57,58 which agrees with our obtained results. As presented in Figure 7, the measured reflectance of the skin samples decreases by increasing the temperature of the immersing water, while the transmittance increases.…”

“…In addition to, modifications in lipids membrane, blood vessel walls, and collagen bundles in the dermis layer. 55 While, the increase in the absorption coefficient is mainly related to the hemoglobin content (oxygenated and deoxygenated) of the examined sample, which controls tissue absorption at our studied wavelength (650 nm). 32 However, at that specific wavelength, the temperature-induced change in the absorption coefficient is nominal, which agrees with our findings.…”

“…32 However, at that specific wavelength, the temperature-induced change in the absorption coefficient is nominal, which agrees with our findings. 55 Despite the wide use of animal models in skin research, there is no universal animal skin model as human skin consists of layers with different compositions. Therefore, the obtained results using chicken's skin cannot be directly translated to human applications.…”

Numerical Simulation of Enhancement of Superficial Tumor Laser Hyperthermia with Silicon Nanoparticles

“…According to Ref. [69], the value of dµ a /dT for biotissues does not exceed 0.02 cm −1 K −1 . Considering the typical temperature increase in the treated biotissues and their absorption coefficients (see Tables 1 and 2), the possible relative variation in absorption is estimated to not exceed 7% for tumor with embedded 1 mg/mL of eSiNPs and an order of magnitude smaller for tumor with 7 mg/mL wSiNPs.…”

Photothermal and Photodynamic Therapy of Tumors with Plasmonic Nanoparticles: Challenges and Prospects

“…Until now, this problem remains insufficiently studied. The changes in the optical parameters of biological tissues under the influence of temperature have been presented in a lot of works, for example, for blood [235], brain [236,237], skin [238,239], prostate [240], liver [241,242], etc. However, changes in the optical parameters of tumors during PPT require detailed research.…”