Preliminary study of monochromatic X-ray CT with synchrotron radiation

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From 1990, a biomedical SR-CT to detect tracer material up to a few mug iodine/ml is being developed for functional evaluations of regional blood flow and metabolism of the organs corresponding to their anatomical structures. The feasibility test of our SR-CT system is performed on phantom and rats.[Methods and material] SR-CT system consists of a rotating X-ray shutter, a silicon (111) channel-cut monochromator, a sample rotating system, X-ray slits and a detector system. Energy of monochromatic X-rays is set at 33.28 keV.Exposure time of each projection is set at 25 msec. The number of projection is 90. Experiment beam line is BLNE 5A of Tristan Accumulation Ring in Tsukuba. Imaging plate(IP) is used as the X-ray detector. The IP data is read by laser beam and digitized by 10 bit analog-to-digital converter (BAS-2000). The spot size of laser is 100 mum^2 with a 10 bit depth. CT image is reconstructed by the post-processing computer(HP 9000). Objects are small rod and brain phantom filled with an iodine, and rats.[Results] The image of above iodine K-edge shows the hole and ditch of phantom filled with iodine clearly. The 44.8 mum/ml iodine can be detected faintly. This concentration corresponds well to the theoretical value (59.7 mug/ml iodine). But this detectable dose of iodine is about 10 times larger than that of our purpose (5 mug/ml iodine). Main reason is poor dynamic range of laser reading system of IP.So to improve the system for detecting very low contrast agent, the sensor with wide dynamic range(50000) is needed.CT image of rat skull with 100 mum spatial resolution showed fine structures of nose, mandibular bone and skull. Final goal of this SR-CT is to detect 5 mug/ml iodine and to obtain less than 5 mm spatial resolution of the brain image like a PET study.