Neinvazina karakterizacija sipalnih lastnosti človeške kože

The objective of my doctoral research was the characterization of the scattering properties of the human skin and their changes due to aging and injury. In this thesis, I combined two non-invasive optical techniques to characterize the skin's optical properties: diffuse reflectance spectroscopy (DRS) and pulsed photothermal radiometry (PPTR). DRS measurements were made in the visible part of the spectrum, while PPTR involves measurements of mid-infrared emission from the sample surface after irradiating it with a light pulse. The two measurements are then fitted and compared with the predictions from a Monte Carlo model of light-tissue interaction. Using different types of skin models, I obtained a good match between the model and experimental data. Using a numerical forward model (inverse Monte Carlo, IMC) I iteratively got up to 14 sample model parameters. I showed that modification to the DRS measurements and additional corrections in the analysis have to be done to properly evaluate skin parameters. This was especially true with measurements of the tattooed skin, where I showed better results after corrections were made. In the context of a skin aging study, it was demonstrated that the scattering amplitude of the dermis decreases with the person’s age. However, no influence of the person’s age was observed on the thickness of the epidermis and dermis, nor on the scattering amplitude of the epidermis. I demonstrated that blood content influences the assessed scattering properties and that by eliminating the blood we can compensate for the smaller sample size in skin aging studies. I show that our method is effective in noninvasive measurements of burned skin. I show that the scattering properties of the skin change after a burn injury and that difference between severity of the burn can be seen. With this method we were able to measure the exact same part of the burns during the healing process. In the end, I also tried to validate the method using phantoms. While the assessed values of dye and scatterers concentrations were found to be proportional to the theoretical values, there was no absolute agreement. I found that many problems arise during validation, especially in the preparation of samples. The nanoparticles adhere to the walls of the containers, potentially forming aggregates, which could be a contributing factor to the observed discrepancies. All this reduces the accuracy of assessing scattering properties. In the case of absorption, the differences between assessed and theoretically predicted values are much smaller and consistent.