Development of high-speed fluorescent X-ray CT system

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In recent biomedical research, the innovation of the new imaging techniques with high-contrast and high-spatial resolution is required for molecular imaging. Fluorescent x-ray technique used in the planar mode is one of the most sensitive methods for detecting trace elements of large atomic numbers in the order of picogram. However, the specimen must be cut into thin slices and be scanned with a beam perpendicular to its surface. Fluorescent x-ray CT (FXCT) method described here combines the sensitivity of fluorescence x-ray technique and the cross-sectional description of CT. Since FXCT can detect small amount of heavy atomic number element as iodine, our group has been developing FXCT system for molecular imaging. Here, we describe the development of high-speed FXCT system for in-vivo FXCT imaging.FXCT system consists of a silicon (220) double crystal monochromator, an x-ray slit system, a scanning table, highly purity germanium (HP-Ge) detector, and pin-diode detectors. To perform h … More igh-speed data detection, 3 channel-type HP-Ge detector was manufactured. The experiment was carried out at the bending-magnet beam line of the Tristan accumulation ring in Tsukuba, Japan. Monochromatic x-ray energy was set 37keV. The incident monochromatic x-ray was collimated into a pencil beam of 0.5 x 0.5mm^2 for the live objects, and less than 0.5 x 0.2 mm^2 for the phantom and pathological specimens, respectively. The data acquisition time was set 5 sec for each scanning step.In the fundamental phantom experiment, energy resolution of each channel was about 290-310 eV at the energy of 28keV. Using sheet beam exposure for phantom, energy spectrum of iodine was clearly separated from Compton scattering X-ray. 1-127 labeled IMP inside the brain of a live mouse was clearly imaged by FXCT at a 0.5 mm spatial resolution and a 0.5 mm slice thickness. Transmission x-ray CT that demonstrate geometrical structure of skull (skull bone, and surrounding soft tissue), can be simultaneously obtained with FXCT data. Then, the anatomical position corresponding functional changes can be understood easily. Now, this FXCT system is not sufficient to perform high speed FXCT imaging because high photon flux from object caused the significantly increased dead-time, and overflowed the electronics (ADC) of detector system. Less