In Sec. 2, we expressed the tissue reflectance [Eq. (3)] using three parameters, $StO2$, $cHb/\sigma $, and $\beta $, by assuming a semi-infinite homogeneous tissue model, and showed that the $StO2$ value can be obtained using the numerical correspondence of the ratios and $StO2$ in the 3-D space of the three signal ratios $(x,y,z)$ as defined in Eq. (5). Here, the parameter $\beta $ is the wavelength exponent of reduced scattering coefficient $\mu s\u2032(\lambda )$ [Eq. (2)], which determines the degree of decrease of $\mu s\u2032(\lambda )$ as the wavelength increases. According to some models based on the theory of Mie scattering, the exponent $\beta $ is closely related to the scatterer size in tissue.^{29}^{–}^{32} The value of $\beta $ is restricted theoretically and semiempirically in the range of $0.20<\beta <4.0$. Scatterers of large sizes compared with the wavelength (e.g., cells and nuclei) give small values of $\beta $, while smaller scatterers give large $\beta $. The upper limit of $\beta =4.0$ corresponds to the case of Rayleigh scattering, where the scatter size is typically smaller than the wavelength of light by one order of magnitude (e.g., collagen and elastin fibrils). Therefore, different tissue structures or components can lead to different values of $\beta $. Presently, we are going to apply our $StO2$ imaging technique to endoscopy of the esophagus, stomach, and colorectum. The tissue of the stomach and colorectum is glandular epithelium, where single-layer epithelial cells align along the intricate glandular pitted structure and cover the collagen-rich lamina propria, while the esophageal tissue is stratified squamous epithelium, where a thick flat layer of stratified epithelial cells covers the lamina propria. Considering the differences in structure and components of these organs, the value of $\beta $ should be changed depending on the tissue being observed. Our method may provide an appropriate value of $\beta $ for each organ by making use of the four spectral band signals.