Atomic and nuclear radiation has been used to develop a large variety of medical imaging modalities for the benefit of humankind over the past fifty years. Diffraction Enhanced Imaging (DEI) is a new x-ray radiographic imaging modality using monochromatic x-rays to produce very clear digital radiographs of objects by virtually eliminating the detection of scattered photons and exploiting the refraction properties of the object. Being free of scatter DEI images have shown dramatically improved contrast over standard radiographs of the same object. The main objective of this work was to apply DEI to computed tomography (CT) and obtain three-dimensional tomographic images. Two sets of experiments on Lucite phantoms were performed at the X15A beamline of National Synchrotron Light Source. The first experiment was performed to evaluate previous work related to this work. The second experiment was performed to obtain threedimensional CT data. Three-dimensional images were successfully obtained and the apparent absorption and refraction images obtained from DEI showed information unavailable in conventional radiograph in computed tomography. There are two interesting findings in this research. One is that subtraction method for calculating refraction images which we suggested is found to be relatively free from contamination from the absorption component. The other is that the procedural orders of manipulation of taking logarithm and subtraction/addition seriously affect the quality of image. If one mixes this order, the result shows a hump-like artifact in both the absorption and refraction images. For further improvements, an experimental method for preventing drifting of the rocking curve during the data acquisition and for fully separating the absorption and refraction components of the DEI data need further study. Also, it is recommended that an algorithm for automatically correcting for the off-axis rotation should be developed.