456
H. M. Heise
and photon penetration depths. An interesting tutorial has recently been published
to which the readers are referred [36]. The mean optical pathlength for radiation
within mucosa tissue, as given for diffuse reflectance accessories, is wavenumber
dependent as illustrated above (see Fig. 20.10). Tissue optical properties are the
absorption and the scattering coefficients, μ a and μ s (in units of mm
−1 ), respectively,
and the anisotropy of scattering g (dimensionless). From the latter two parameters,
the reduced scattering coefficient μ s ’ = μ s (1 – g) can be calculated. From diffusion
theory for photon transport in tissues, an optical penetration depth can be estimated
based on these optical constants with δ = (3 μ a (μ a + μ s ’))
−1/2 [36].
In Fig. 20.12, experimentally derived optical constants from the upper skin layers
are shown, i.e., absorption and scattering coefficients; the inset in panel B shows also
Fig. 20.12 Optical constants of dermis and epidermis in the NIR spectral range including uncertainties (μ a absorption coefficient, μ s ’ reduced scattering coefficient with μ s ’ = (1 – g) μ s , which
is a property incorporating the scattering coefficient μ s and the anisotropy g; all data were from
Refs. [37–39]; note the significant differences in the scattering coefficients for the NIR region
H. M. Heise
and photon penetration depths. An interesting tutorial has recently been published
to which the readers are referred [36]. The mean optical pathlength for radiation
within mucosa tissue, as given for diffuse reflectance accessories, is wavenumber
dependent as illustrated above (see Fig. 20.10). Tissue optical properties are the
absorption and the scattering coefficients, μ a and μ s (in units of mm
−1 ), respectively,
and the anisotropy of scattering g (dimensionless). From the latter two parameters,
the reduced scattering coefficient μ s ’ = μ s (1 – g) can be calculated. From diffusion
theory for photon transport in tissues, an optical penetration depth can be estimated
based on these optical constants with δ = (3 μ a (μ a + μ s ’))
−1/2 [36].
In Fig. 20.12, experimentally derived optical constants from the upper skin layers
are shown, i.e., absorption and scattering coefficients; the inset in panel B shows also
Fig. 20.12 Optical constants of dermis and epidermis in the NIR spectral range including uncertainties (μ a absorption coefficient, μ s ’ reduced scattering coefficient with μ s ’ = (1 – g) μ s , which
is a property incorporating the scattering coefficient μ s and the anisotropy g; all data were from
Refs. [37–39]; note the significant differences in the scattering coefficients for the NIR region