  The modified Beer-Lambert law (MBL) and the spatially resolved spectroscopy
are used to measure the tissue oxidation in muscles and brains by the
continuous wave near-infrared spectroscopy. The spatially resolved spectroscopy
predicts the change in the concentration of the absorber by measuring the slope
of attenuation data according to the separation and calculating the absorption
coefficients of tissue on the basis of the slop in attenuation at the
separation distance satisfying the linearity of this slop. This study analyzed
the appropriate source-detector separation distance by using the diffuse
approximation resolution for photon migration when predicting the absorption
coefficient by the spatially resolved spectroscopy on the basis of the
reflective image of the tissue. We imagine the 3 dimensional attenuation image
with the absorption coefficient, reduced scattering coefficient and separation
distance as its axes and obtained the attenuation data cube by calculating the
attenuation on a certain interval of coordinate on the basis of the diffuse
approximation expression. We predicted the separation distance appropriate for
the application of the spatially resolved spectroscopy by calculating and
analyzing the first derivatives and second derivatives of attenuation with
respect to the coordinates and also doing the differential pathlength factors
and first derivatives of the attenuation with respect to the absorption
coefficient from the attenuation data cube. When analyzing the hemoglobin
derivatives in tissues, the appropriate separation distances are 3-5cm and the
value of its corresponding differential pathlength factors are from 3.5 to 5.
These data agree with the preceding experimental data.
