Optical Characterization of Biological Tissues Based on Fluorescence, Absorption, and Scattering Properties

Optical diagnostics methods are significantly appealing in biological applications since they are non-destructive, safe, and minimally invasive. Laser-induced fluorescence is a promising optical spectrochemical analytical technique widely employed for tissue classification through molecular analysis of the studied samples after excitation with appropriate short-wavelength laser light. On the other hand, diffuse optics techniques are used for tissue monitoring and differentiation based on their absorption and scattering characteristics in the red to the near-infrared spectra. Therefore, it is strongly foreseen to obtain promising results by combining these techniques. In the present work, tissues under different conditions (hydrated/dry skin and native/boiled adipose fat) were distinguished according to their fluorescence emission, absorption, and scattering properties. The selected tissues' optical absorption and scattering parameters were determined via Kubelka-Munk mathematical model according to the experimental tissue reflectance and transmittance measurements. Such measurements were obtained using an optical configuration of integrating sphere and spectrometer at different laser wavelengths (808, 830, and 980 nm). Moreover, the diffusion equation was solved for the fluence rate at the sample surface using the finite element method. Furthermore, the accuracy of the obtained spectroscopic measurements was evaluated using partial least squares regression statistical analysis with 0.87 and 0.89 R-squared values for skin and adipose fat, respectively.

Radiation mode and tissue thickness impact on singlet oxygen dosimetry methods for antimicrobial photodynamic therapy

The target of the presented study is to evaluate the performances of illumination modes on Photodynamic therapy (PDT) for different tissue depths. For this purpose, radiation-based super pulse and pulse illumination modes were investigated for antimicrobial PDT (AmPDT). Singlet oxygen luminescence level was measured from two different points. The first one was to appraise the light penetration depth effect on singlet oxygen luminescence level for various radiation modes. The second one explored the singlet oxygen luminescence dosimetry (SOLD) method from deeper photosensitizer accumulated tissue levels. Two main experiments were performed in this study. The singlet oxygen concentration was calculated with singlet oxygen explicit dosimetry (SOED) and SOLD methods for various tissue depths in these experiments. According to the results of the experiments, super pulse mode (SPM) provided relatively high Staphylococcus Aureus (S. aureus) cell death by 5-12%. The penetration depth was increased between 0.2 mm and 0.7 mm during the experiments. SOLD-based singlet oxygen detection system was utilized to detect singlet oxygen production levels from various tissue thicknesses to evaluate the system's usefulness for deeper infected tissues. It was observed that SPM was more effective than pulse mode radiation after a certain tissue depth (≤ 2 mm).