Integrating sphere-based spectrally constrained total diffuse reflectance for in vivo quantification of hemoglobin in skin

Abstract

The ability to monitor changes in skin redness through the hemoglobin concentration in skin has the potential to personalize patient care by providing a quantitative objective way of monitoring patient response to interventions such as radiation therapy and plastic surgery. Currently available commercial systems for monitoring skin redness rely on total diffuse reflectance spectroscopy and can only accurately measure hemoglobin changes relative to a baseline measurement when all other skin chromophores, such as melanin, remain constant. This work investigates the application of a spectrally-constrained diffusion theory model for analyzing total diffuse reflectance spectra obtained with an integrating sphere-based system. A low cost integrating sphere-based system was designed, constructed, and characterized to yield accurate total diffuse reflectance spectra. The system was first used with an absorbance-based erythema index to investigate the time to maximal effect of epinephrine – a vasoconstrictor used in plastic surgery. A spectrally-constrained diffusion theory model was developed to improve the interpretation of the reflectance spectra obtained with the integrating sphere-based system. Correction factors necessary to apply the developed model to the obtained spectra were determined through Monte Carlo simulations, and then confirmed with tissue-simulating liquid phantoms. The model was tested for sensitivity and specificity, as well as how it responded to variations in the experimental parameters. The system and model were then used to monitor radiation-induced erythema in head and neck intensity modulated radiation therapy patients. Analysis of the results enabled earlier detection of erythema by 1-19 days compared to visual assessment. The work completed in this thesis illustrates a cost-effective, user-friendly diffuse reflectance spectroscopy system which has potential applications in a number of clinical settings.