Reconstruction of absorption distribution in diffuse medium using backscattered light

Near-infrared light at 700-1200 nm has high transmission through the human body. However, there is strong scattering in the body tissue and it is difficult to obtain an image of the internal structure of our body. There has been an increasing interest in the study of light propagation in dense random media to realize optical CT. With optical CT, physiological information such as hemoglobin oxygenation in the body can be obtained as a cross-sectional image noninvasively. In optical CT, two types of light-detection schemes have been used. One detects the transmitted or forwardly scattered light, and another the backwardly scattered light (here we call it as backscattered light). Using transmitted light, we can have the whole cross-sectional image of the subject. But the thickness of the subject has to be thin enough to get transmitted light. Using backscattered light, we can obtain the cross-sectional image of only a certain part near the surface of the subject. However, the applicability of this technique is not restricted by the thickness of the subject. In the combination with optical fibers, it is particularly useful in the clinical applications, such as the imaging of inner walls of digestive tracts, blood vessels and heart chambers. We have developed a new technique to reconstruct the cross-sectional image of a diffuse medium using backscattered light. This paper presents the basic idea of this technique and some results of a computer simulation to examine the capability of this technique