Generic tissue optical properties

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 (µ_a [cm^-1]) and a reduced scattering coefficient (µ_s' [cm^-1]):

where
• B = blood volume fraction
• S = oxygen saturation of hemoglobin
• W = water volume fraction
• M = melanosome volume fraction
• F = fat volume fraction
• µ_s.500nm' = reduced scattering coeff. at 500 nm [cm^-1]
• f = fraction of scattering at 500 nm due to Rayleigh scattering
• 1-f = fraction of scattering at 500 nm due to Mie scattering
• b_mie = scattering power for Mie scattering

FOR EXAMPLE, skin dermis can be described:

• B = 0.002
• S = 0.70
• W = 0.65
• M = 0
• F = 0
• µ_s.500nm' = 43 cm^-1
• f = 0.64
• 1-f = 0.36
• b_mie = 0.91

The values of scattering beyond 1000 nm are extrapolated using the expression for µ_s', since measurements at these longer wavelengths are not available. Values of melanin absorption are extrapolated above 1100 nm, for lack of measurements.

Constituent properties for generic tissue

Blood

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
https://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.

Water

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).
https://omlc.org/spectra/water/data/hale73.txt

Melanin (absorption of melanosome interior)

The melanin content is described by the volume fraction (M_f) 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).

Fat

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.