Basic study for non-invasive measurement of internal function of animal body with light

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A fundamental study has been conducted for the development of the measurement technique to visualize the functional information in an animal body. Through theoretical and experimental studies, the following results were obtained.[ Trans-body imaging of functional information ](1) It was found that the wavelength in the range of 700-900 nm is appropriate for the trans-body imaging.(2) Trans-body imaging system was developed with Ti-Sapphire laser and high sensitivity CCD camera. It enables us to get the transillumination image of the internal organ in a mouse abdomen. In the multi-wavelength measurement, the oxygenation change in a kidney was visualized successfully.(3) In the transillumination imaging of a rat brain, the change in blood volume caused by the occlusion of a carotid artery was measured successfully.[ Scattering suppression and CT imaging ](4) A technique to suppress the scattered component in transmitted light has been devised. This technique is based on a spatial collimation of laser light and a differential principle in light detection. The effectiveness of this technique was verified in the measurement using a model phantom.(5) The above technique turned out to be inapplicable to a living animal body. The cause was found to be the refraction and reflection of light at an air-body boundary. A technique to overcome this problem was newly devised.(6) An experimental system was developed which enables us to utilize above two techniques simultaneously. Using this system, the CT images of a mouse abdomen were obtained. The existence of a liver and kidneys were observed in the images.(7) A new technique was developed which uses scattered light instead of the weak nonscattered light which is usually difficult to measure. In a computer simulation, the feasibility to obtain a CT image using this technique was verified.