Reflectance spectroscopy and fluorescein angiography applied to assess photodynamic response in healthy mouse skin treated with topical hexylaminolevulinate

SummaryBackgroundMeasurements of tissue oxygenation and blood supply are of vital importance during photodynamic therapy. The aim of this study was to measure photosensitization responses in healthy mouse skin using non-invasive reflectance spectroscopy and fluorescein angiography.MethodsHealthy mouse skin was treated topically with hexylaminolevulinate (HAL) for 3 h and then exposed to red light (632 nm).ResultsNon-invasive reflectance spectroscopy showed that the fraction of oxygenized haemoglobin decreased considerably after treatment with HAL and red light. This indicates reduced tissue oxygenation. Fluorescein angiography showed no vasoconstriction in the mouse skin after short (3 h) treatment with HAL and light, indicating that the oxygen concentration was high enough to give a photodynamic effect consistent with the skin damage (scar formation) observed for a few days after the treatment. However, longer treatment with HAL (17 h) resulted in complete vasoconstriction with oxygen depletion and no skin damage in the centre, while a circular (rim) wound was seen around the light exposed area. Skin damage was larger for the lowest fluence rate (20 mW/cm2) than for the highest one (100 mW/cm2) applied.ConclusionSkin treatment with topical HAL and red light in fluencies and fluence rates as applied here does not result in complete vasoconstriction. Haemoglobin oxygenation monitored by reflectance spectroscopy can be used as a rough measure of the resulting photodynamic response. However, haemoglobin oxygenation alone is not a complete predictive factor since reflectance spectroscopy did not reveal any differences in the status of haemoglobin oxygenation for different fluence rates.