Measurement Of Microvascular Oxygen Saturation In Window Chamber By Diffuse Reflection Spectroscopy

Singlet oxygen (1O2) is a major phototoxic component during Type-II photochemical reaction of photodynamic therapy (PDT) and its generation is dependent on the availability of tissue oxygen. The feasibility of using diffuse reflection spectroscopy (DRS) to measure microvascular blood oxygen saturation (StO2) in dorsal skinfold window chamber was evaluated in this paper. The variation of StO2 and vascular morphology dependent on the irradiation power densities during vascular-targeted photodynamic therapy (V-PDT) were analyzed. The diffuse reflection spectra of microvascular in the range of 450nm-800nm were measured and fitted to obtain the StO2. The obtained StO2 were found in accord with that from photoacoustic imaging, which indicates that DRS can be used to measure microvascular StO2 in dorsal skinfold window chamber model. The effects of V-PDT on the StO2 and vasoconstriction under three different oxygen conditions (hypoxic, normoxic and hyperoxic) were further analyzed. It was found that both the average vasoconstriction and StO2 of normoxic and hyperoxic groups changed significantly while those of hypoxic group had no significant change. Moreover, under different irradiation power densities (50,100 and 200mW/cm2), there is no signification correlation between average diameter change of vessel and average StO2. However, the variation of average StO2 during V-PDT showed a positive correlated with irradiation power densities, indicating that a high power density resulted in a rapid decrease of StO2.