The optical properties of a tissue are dependent on the properties of the tissue's constituents (water, oxy-hemoglobin, deoxy-hemgolobin, melanin, fat and scattering).
These generic constituent properties can be mixed to mimic any tissue type. A "generic" tissue will be described by an absorption coefficitnt (µa [cm-1]) and a reduced scattering coefficient (µs' [cm-1]):
FOR EXAMPLE, skin dermis can be described:
The values of scattering beyond 1000 nm are extrapolated using the expression for µs', since measurements at these longer wavelengths are not available. Values of melanin absorption are extrapolated above 1100 nm, for lack of measurements.
The blood spectra for oxy- and deoxy- whole blood (150 g hemoglobin/liter) are based on Graetzer & Kollias, as cited by Prahl (300-1000 nm).
W. B. Gratzer, Med. Res. Council Labs, Holly Hill, London N. Kollias, Wellman Laboratories, Harvard Medical School, Boston http://omlc.org/spectra/hemoglobin/summary.html
Also shown are the spectra of H. Suzaki between 1000-1300 nm.
H. Suzaki (2006) Proceedings of the 28th IEEE EMBS Annual International Conference New York City, USA, Aug 30-Sept 3, 2006 (Suzaki data was adjusted to match the Graetzer/Kollias data at 1000 nm.) bloodSuzaki.dat
which illustrates how the absorption of blood falls below the absorption of water at longer wavelengths.
The water absorption of Hale and Querry 1971 is used.
G. M. Hale and M. R. Querry, "Optical constants of water in the 200nm to 200µm wavelength region," Appl. Opt., 12, 555--563, (1973). http://omlc.org/spectra/water/data/hale73.dat
The melanin content is described by the volume fraction (Mf) of a standard cutaneous melanosome in the epidermis. The absorption coefficient of the interior of a melanosome was estimated by the threshold pulsed laser radiant exposure required to explode a cutaneous melanosome:
Jacques SL, DJ McAuliffe, (1991) The melanosome: threshold temperature for explosive vaporization and internal absorption coefficient during pulsed laser irradiation Photochem Photobiol 53:769-776 JacquesMcAuliffe1991.pdf
which is described by the expression:
This expression is for eumelanin. Pheomelanin is slightly different (see Extinction coefficient of melanin).
The absorption coefficient of fat is based on two reports: (1) a study of purified pig fat by Van Veen et al.
R.L.P. van Veen and H.J.C.M. Sterenborg, A. Pifferi, A. Torricelli and R. Cubeddu (2004) Determination of VIS- NIR absorption coefficients of mammalian fat, with time- and spatially resolved diffuse reflectance and transmission spectroscopy OSA Annual BIOMED Topical Meeting, 2004. (Prepared by Scott Prahl.) pigfatVanVeen.m
and (2) a study of human fat by Anderson.
Anderson R R et al. (2006) Selective photothermolysis of lipid-rich tissues: A free electron laser study. Laser Surg. Med. 38 913–19 AndersonFat.m
Prepared Feb. 24, 2015, by SL Jacques.