ABSTRACT
Over the last two decades, considerable advances have been made toward modeling light propagation in tissue. ™ese advances have been mainly driven by the development of optical tomographic imaging techniques, which rely on accurate modeling of light-tissue interactions in biomedical tissue. ™ese techniques employ near-infrared (NIR) light in the wavelength range of 600-900 nm, to probe biological tissue and image physiological functions (Gibson et al. 2005, Nissilä et al. 2005, Gibson and Dehghani 2009). ™e propagation of light in the NIR is governed by the spatial distribution of the tissue’s scattering and absorption coeŸcients, given by μs and μa, respectively. ™e scattering coeŸcient takes on values in the range of μs = 20, …, 200 cm−1 (Cheong et al. 1990, Cheong 1995, Collier et al. 2005). Also, o²en used to describe optical properties of tissue is the reduced scattering coeŸcient, μ′s = (1 − g)μs, which is a scaled scattering coeŸcient that takes into account the mean scattering cosine g (anisotropy factor) of a single scattering event. Typical values of g in tissue are between 0.8 and 0.98. Dižerence in the refractive index (RI) between intracellular and extracellular ¦uids, and various subcellular components, such as mitochondria or nuclei, as well as varying tissue densities give rise to dižerences in scattering coeŸcient and g-factors (Mourant et al. 1998, 2000). A multitude of chromophores inside tissue cause absorption at various wavelengths. ™e absorption coeŸcient covers a wide range of values from μa = 0.01 to 0.5 cm−1, for NIR (Utzinger
et al. 2001, Culver et al. 2003, Drezek et al. 2003, Srinivasan et al. 2003). Endogenous chromophores are, for example, hemoglobin, cytochrome, ¦avins, and porphyrins. Dižerences in chromophore content and concentration lead to dižerent absorption coeŸcients μa(r).
