abstract
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An integrating sphere system has been developed to study the optical properties of biological tissues non-invasively, over a broad spectral range with the ultimate goal of quantifying erythema resulting from external beam radiotherapy. An empirical model was defined to calculate the absorption coefficient, μa, from the normalized integrating sphere signal, R *, and the reduced scattering coefficient, μ's As erythema is associated with an increase in the apparent concentration of oxygenated haemoglobin in the skin, the potential of the technique in quantifying erythema was assessed using measurements made in homogenous tissue simulating phantoms containing whole horse blood. After system validation in this simple model, a two-layer model was investigated. Whole blood from a horse was added to the bottom layer, while the top layer was fixed at an optical thickness simulating the epidermis. Reflectance measurements were made through the top layer while the bottom layer was deoxygenated using yeast. The retrieved concentrations of oxy- and deoxygenated haemoglobin were used to calculate the total haemoglobin concentration and the haemoglobin oxygen saturation. Errors in estimating the total haemoglobin concentration ranged from 3-12%; decreasing as a broadband absorber was added to the top layer. Preliminary in vivo measurements were also performed on areas of erythema induced by a topical anesthetic. For regions of erythema there was an increase in the apparent haemoglobin oxygenation which correlates to values of the erythema index calculated from the definition established by Dawson et al. These results demonstrate that the apparent haemoglobin oxygenation has the potential to be used as a surrogate in quantifying erythema.