The spatial variation in reflectance such as the blood-vessel pattern can be observed in the image of cerebral cortex. This spatial variation is mainly caused by the difference in concentrations of oxy- and deoxyhemoglobin in the tissue. We analyze the reflectance spectra obtained from multispectral images of pig cortex by principal component analysis to extract information that relates to physiological parameters such as the concentrations of oxy- and deoxyhemoglobin and physical parameters such as mean optical path length. The light propagation in a model of exposed pig cortex is predicted by Monte Carlo simulation to estimate the interpretation of physiological and physical meanings of the principal components. The spatial variance of reflectance spectra of the pig cortex can be approximately described by the first principal component. The first principal component reflects the spectrum of hemoglobin in the cortical tissue multiplied by the mean optical path length. These results imply that the wavelength dependence of mean optical path length can be experimentally estimated from the first principal component of the reflectance spectra obtained from multispectral image of cortical tissue.
Optical imaging derived from intrinsic signals such as blood volume and flow has enabled us to characterize the area of brain activation.
Multi-spectral imaging of the change in cortical reflectance allows the determination of the change in the oxy-hemoglobin concentration independent of the deoxy-haemoglobin concentration. The changes in blood volume and oxygenation are closely related to the cerebral blood flow, and hence the simultaneous measurement of blood volume and flow in the cortical tissue must be beneficial for investigation of functional brain activation. Laser speckle flowgraphy has also been developed to visualize the blood flow in tissue and has been applied to measure the blood flow in tissue. In this study, a functional imaging system has been designed and assembled for the simultaneous measurement of the change in blood volume and flow in
tissue. The optical systems of multi-spectral imaging and laser speckle flowgraphy are attached to the photo ports of the beam-splitter attachment of a stereo-microscope. The data of the multi-spectral image and speckle pattern of phantoms and finger are obtained for the initial experiments with the proposed system.