抄録
Fluorescent X-ray induced by monochromatic synchrotron X-ray is quite useful to describe the distribution of non-radioactive target materials in the body with high sensitivity. The target material emits characteristic fluorescent X-ray by the excitation. From the detected fluorescence, we can estimate the amount of target material in the crossing volume between excitation beam and observed area. Thus, by scanning both excitation beam and observation area, we can reconstruct the tomographic image of target material distribution. To estimate the amount of target material, we must detect both excitation and fluorescent X-ray intensity with proper correction for their attenuation in the object. However, the structure of the object itself is just under examination. Here an algorithm is developed to correct the absorption of incident X-ray and induced fluorescence respectively along the optical path in the object. From observed spectrum, we can discriminate target material and tissue, then the characteristic of observed volume area in the object is estimated, and the absorption corrections and exact estimations are done sequentially along scanning sequence. An experimental scanning fluorescent X-ray tomography system with monochromatic SR X-ray is constructed. Reconstructed images for phantom with iodine demonstrate usefulness of above procedure. The minimum detectable density of target material was 50μg/ml in this experiment. Here quantization procedure for spectrum measurement is also prepared and the linear relationship between the fluorescent intensity and the amount of target material is confirmed experimentally. Finally, further improvements to realize practical system are discussed on detecting system, reconstruction algorithm, etc. and optimum energy spectrum of incident X-ray.
