Tissue optical properties

M. S. Patterson, B. Chance, and B. C. Wilson. Time resolved reflectance and transmittance for the non-invasive measurement of tissue optical properties. Applied Optics, 28(12) 2331-2336, 1989. 

Farrell TJ, Patterson MS, Wilson B. A diffusion-theory model of spatially resolved, steady-state diffuse reflectance for the noninvasive determination of tissue optical properties in vivo. Medical Physics 1992, 19, 879-888. 

Sample variability is a critical issue in prospective application. For optical technologies, variations in tissue optical properties such as absorption and scattering coefficients can create distortions in measured spectra. This section provides a brief overview of techniques to correct turbidity-induced spectral and intensity distortions in fluorescence and Raman spectroscopy, respectively. In particular, photon migration... 

Dam JS, Pedersen CB, Dalgaard T, Fabricius PE, Aruna P, Andersson-Engels S. Fiberoptic probe for noninvasive real-time determination of tissue optical properties at multiple wavelengths. Applied Optics 2001, 40, 1155-1164. 

Doornbos RMP, Lang R, Aalders MC, Cross FW, Sterenborg HJCM. The determination of in vivo human tissue optical properties and absolute chromophore concentrations using spatially resolved steady-state diffuse reflectance spectroscopy. Physics in Medicine and Biology 1999, 44, 967-981. 

For interstitial treatments there is an analogous dependence of the spatial distribution of the light on the tissue optical properties. However, geometric spreading of the light causes an additional decrease in the fluence with radial distance, r, from the outer surface of the source. In the case of a point isotropic source (equal in all directions), the fluence distribution is of the form ... 

There are several possible solutions to this problem. One option is to measure the tissue optical properties at the excitation and emission wavelengths and correct the signal for the attenuation. A variation on this is to normalize the measured fluorescence signal, F, to some other measurement, such as the diffuse reflectance, R, that also depends on the tissue optical properties, so that there is partial cancellation of the attenuation effects in the ratio, F /R (this is illustrated in Figure 17(b-d)). A third method is to make the measurement in such a way that it is (relatively) independent of the optical properties. This can be done either by using very small optical fibers that both deliver the excitation light and collect the fluorescence so that the measurement is confined to a very small tissue volume within which the attenuation is minimal, or to separate the excitation and detector fibers at a specific distance where the effects of scatter and absorption roughly cancel each other. 

The output from LDF is measured not in easily interpretable units of flow but rather in hertz. It would be ideal to define a single calibration factor that could be used in all tissues to convert laser output to flow in absolute units. Unfortunately, the calibration to determine an absolute flow is limited by the lack of a comparable standard and the lack of preset controlled conditions. This may be due to varying tissue optical properties affected by tissue density (Obeid et al., 1990). Further, LDF signals can be affect by movement of the probe relative to the tissue. 

J. Farrell and M. S. Patterson, A Diffusion Theory Model of Spatially Resolved, Steady-State Diffuse Reflectance for the Noninvasive Determination of Tissue Optical Properties In Tvo, Med. Phys., 19(4), 879 (1992). 

B. C. Wilson, Measurement of Tissue Optical Properties Methods and Theories, in Optical-Thermal Response of Laser-Irradiated Tissue, ed. A. J. Welch and M. J. C. van Gemert, Plenum Press, New York, 1995, p. 233. 

H. Liu, B. Beauvoit, M. Kimura, and B. Chance, Dependence of tissue optical properties on solute -induced changes in refractive index and osmolarity. Journal of Biomedical Optics 1 (1996), 200-211. 

V.V. Tuchin, Controlling of Tissue Optical Properties, Proc. SPIE 4001, 2000, pp. 30-53. 

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