In this paper, we describe the development and performance evaluation of a 3-dimentional (3-D) high-resolution x-ray microtomography (micro-CT) system. Unlike a conventional micro-CT, the developed system uses a flat-panel detector as a digital x-ray imager. The detector is a CsI:Tl (thallium-doped cesium iodide) scintillator coupled to an active-matrix photodiode array with a pixel pitch of 50 [µm]. Without geometric magnification, the spatial resolution of the detector is 7 [lp/mm] at 10 [%] of MTF (modulation-transfer function). The overall efficiency of the detector for the input x-ray signal-to-noise ratio (SNR) has been measured to be about 50 [%] with the x-ray source operating at 60 [kVp] and 1-mm-thick Al filtration. For fast 3-D cone-beam image reconstruction, the Feldkamp algorithm has been realized in a distributed parallel processing system composed of multiple personal computers. The signal and noise properties in tomograms have been measured with quantitative phantoms and the measurement results are found to conform well to the theoretical models. From the measurements, it has been also found that the spatial resolution in a tomogram is almost determined by the detector resolving power. Some high-resolution imaging results are shown to demonstrate the capability of the developed system in bio-medical and industrial applications.
The gas electron multiplier (GEM), placed in the drift volume of a conventional gas detector, is a conceptually simple device for producing a large gas gain by concentrating the drift electric field over a very short distance to the point that electron avalanching occurs. This device consists of a thin insulating foil of several tens of μm in thickness, covered on each side with a thin metal layer, with tiny holes, usually 100 μm or less in diameter, and with a spacing of 100-200 μm through the entire foil, perforated by using chemical etching or high-powered laser beam technique. In this study, we have investigated its operating properties with various experimental conditions and demonstrated the possibility of using this device as a digital X-ray imaging sensor, by acquiring X-ray images based upon the scintillation lights of the GEM with a standard CCD camera.
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