Multi-modal assessment of light transport through biological tissue

The doctoral thesis discusses four individual studies, linked through either their methods or applications. Specifically, the biological tissues that light interacts with are skin and its layers, muscle, bone and blood. Skin-safe lasers are used in the studies to interact with participants through simulations and experiments. Through the course of this research, I investigate the optical compatibility of human skin with synthetic skin samples known as human skin equivalents (HSEs)1. The result is a novel assessment combining tissue engineering and biomedical optics. Secondly, a simulated analysis of light interaction with a two-layer model was subsequently analysed in a study to look for anaemic blood condition markers in the reflectance and fluence of photons. This study resulted in a unique assessment of light transport through two-layer models. The models accommodate melanin and haemoglobin concentrations in the layers of the skin, thereby accounting for all skin types and healthy and anaemic blood perfusion in the dermal layer. In a third study, the understanding and consideration of the influence of melanin and haemoglobin in the skin layers are extended to developing full-finger models. The full-finger models are based on high-frequency ultrasound image data. The optical models were assessed in visible and near-infrared wavelengths using Monte Carlo simulations. This provides a method to assess tissue damage before treatments such as photodynamic therapy. Finally, an image-processing exercise to identify and monitor vascular activity was undertaken in the fourth study of this thesis. The vascular activity was imaged and monitored using a simple transmission-based experimental strategy and off-the-shelf equipment. Vascular activity analogous to heart rate was successfully monitored for the participants of the study, accounting for the motion of the finger in a non-contact experimental and processing workflow.