A review of in-vivo optical properties of human tissues and its impact on PDT.

A thorough understanding of optical properties of biological tissues is critical to effective treatment planning for therapies such as photodynamic therapy (PDT). In the last two decades, new technologies, such as broadband diffuse spectroscopy, have been developed to obtain in vivo data in humans that was not possible before. We found that the in vivo optical properties generally vary in the ranges μ(a) = 0.03-1.6 cm⁻¹ and μ'(s) = 1.2-40 cm⁻¹, although the actual range is tissue-type dependent. We have also examined the overall trend of the absorption spectra (for μ(a) and μ'(s)) as a function of wavelength within a 95% confidence interval for various tissues in vivo. The impact of optical properties on light fluence rate is also discussed for various light application geometries including superficial, interstitial, and within a cavity.