Monitoring blood volume fraction and oxygen saturation in port-wine stains during vascular targeted photodynamic therapy with diffuse reflectance spectroscopy: Results of a preliminary case study

Objective: Monitoring dynamic changes during vascular targeted photodynamic therapy (V-PDT) for port-wine stains (PWS) is crucial for achieving an optimal therapeutic outcome. The present investigation is a preliminary research study designed to quantify and monitor the vascular parameters, e.g., blood volume fraction (BVF) and oxygen saturation (StO₂), of a PWS lesion by using diffuse reflectance spectroscopy (DRS) before and during V-PDT. Material and methods: A portable DRS detection system was developed with an appropriate source-detector distance of 520 μm for fiber-optic probe. The diffuse reflectance spectra from 450 to 800 nm in specific regions of interest (ROIs) within a PWS lesion were recorded before and 3, 5, 10, 15, and 20 min during V-PDT. In order to extract the optical properties and vascular parameters of the PWS lesion, a modified well-known diffusion theory model with a correction factor for the vessel package effect was employed to analyze the steady state-diffuse reflectance spectra. Results: The corrected reflectance spectra of the PWS lesion can be fitted very well with the modified diffusion theory model. Differences in pretreatment values of BVF and StO₂ as well as changes in these parameters were observed between two ROIs during V-PDT. Conclusion: The ability of using DRS for quantifying and monitoring the BVF and StO₂ of a PWS lesion has been assessed. The preliminary data suggest that the clinical V-PDT efficiency is affected by the heterogeneity of the PWS lesion. DRS may have the potential to characterize the PWS lesion and to monitor V-PDT response.