We introduce a portable hand-held hyperspectral imaging system for the functional diagnostics of skin and vascular system. Hyperspectral image analysis aided by artificial neural networks (ANN) allows to reconstruct major physiological parameters of human skin nearly in real-time. The developed device provides spatial distribution of blood volume fraction, oxygenation and melanin content within skin. Special attention has been paid on the system validation and calibration using specially developed skin mimicking phantoms with confirmed optical properties.
The device was built on the basis of unique hyperspectral snapshot camera utilizing a micro Fabry-Perot filter providing real spectral response in each pixel (no interpolation is used in image formation). A broadband illumination unit combined with the camera is based on the fiber-optic illuminator providing uniform distribution of light intensity and utilizes halogen lamp.
The specially developed ANN algorithm was used to perform the inverse problem solution for quantitative assessment of major parameters of skin based on the measured hyperspectral images. A set of diffuse reflectance spectra of human skin imitated by the Monte Carlo method developed in-house has been used extensively for the training of ANN. The volume fraction of blood, oxygen saturation, melanin content and thickness of the epidermal layer were used variable parameters in the utilized seven-layer Monte Carlo-based skin model. The total training set contained 45,198 spectra in the range of 505–800 nm simulated with a step of 5 nm. The developed imaging system has been successfully used to perform the occlusion test measurements with healthy volunteers.
Employment of chlorin-based photosensitizers (PSs) provides additional advantages to photodynamic therapy (PDT) due to absorption peak around 405 nm allowing for superficial impact and efficient antimicrobial therapy. We report on the morphological and clinical study of the efficiency of PDT at 405 nm employing chlorin-based PS. Numerical studies demonstrated difference in the distribution of absorbed dose at 405 nm in comparison with traditionally employed wavelength of 660 nm and difference in the in-depth absorbed dose distribution for skin and mucous tissues. Morphological study was performed at the inner surface of rabbit ear with histological examinations at different periods after PDT procedure. Animal study revealed tissue reaction to PDT consisting in edema manifested most in 3 days after the procedure and neoangiogenesis. OCT diagnostics was confirmed by histological examination. Clinical study included antimicrobial PDT of pharynx chronic inflammatory diseases. It revealed no side effects or complications of the PDT procedure. Pharyngoscopy indicated reduction of inflammatory manifestations, and, in particular cases, hypervascularization was observed. Morphological changes were also detected in the course of monitoring, which are in agreement with pharyngoscopy results. Microbiologic study after PDT revealed no pathogenic bacteria; however, in particular cases, saprophytic flora was detected.
In this work we studied the efficiency of spatially modulated illumination in optical diffuse reflectometry (ODR) and analyzed various probing patterns. The optimal illumination pattern was determined from the series of Monte Carlo numerical experiments on structured illumination and comparison of the parameters of fluence distribution within tissue. We considered the following illumination profiles: sinusoidal patterns with different spatial frequencies k (1 - 2.5 mm-1); piecewise constant patterns with the fixed duty cycle w = 2 and various strip width (0.2 – 1 mm); piecewise constant patterns with the fixed strip width (0.1 mm) and various duty cycle (3 – 11). Assuming the same total incident intensity for all patterns, we observed the growth in intensity at depth with decreasing value of spatial frequency for sinusoidal pattern, the similar tendency of intensity distribution was for piecewise constant patterns with the fixed strip width (or duty cycle) and duty cycle increase (or increase of a strip width, respectively). The intensity distributions within the sample are almost identical for sinusoidal and piecewise constant patterns with matching peaks and lows. However, probing by piecewise constant profile of illumination provide more local information about sample’s properties. A prototype of an ODR system for probing with the structured illumination was designed. The system consists of PC-controlled optical projection system, polarization filters and a CCD camera. The approbation of the system was carried out on the optical phantoms with optical properties close to those of biological tissues and on skin of human volunteers.