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Depending on a developed micro-CT prototype system,propagation-based phase-contrast imaging has been investigated by using thin plastic sheet and insect samples.The system mainly includes an open type microfocus x-ray tube with nominal focal spot size less 2 μ m and a cooled x-ray CCD detector with pixel size of 24 μ m.Edge-enhancement effect can be observed clearly in the images.Based on a 1 mm thickness plastic edge phantom,the effects of x-ray tube parameters (focal spot size,target current and tube voltage) and imaging geometry on the phase-contrast imaging were investigated,also quantitative upstroke index (UI),downstroke index (DI) and edge-enhancement index (EEI) were calculated.Results showed that a smaller focal spot size is helpful for phase-contrast imaging and the focal spot sizes less than 15 μ m can be used in phase-contrast imaging well.A larger target current (or tube current) can decrease phase-contrast effect by the variation of focal spot size and the effect is different for different microfocus x-ray tube.Phase-contrast effect has a slight drop with the increasing of tube voltage and the edge enhancement at the high voltage of 150 kVp is still obvious.Geometric distance can affect the phase-contrast effect greatly and a middle range of R1 (or R2) values make the edge enhancement maximum.The optimal distance is independent of tube voltage and has a small dependence on focal spot size.