Refractive index imaging by computed tomography using an X-ray shearing interferometer

In the conventional X-ray imaging such as radiography or computed tomography, we measure intensity distribution of X-rays. It reflects the distribution of absorption coefficient inside the object. However, absorption becomes low for materials of low atomic number and for hard X-rays. An alternative way is to measure distribution of refractive index for X-rays. Spatial variation of refractive index causes spatial variation in. the phase of the transmitted X-rays. To detect the phase X-ray interferometers can be used. In this paper we shall describe an X-ray shearing interferometer and discuss the method of reconstructing the refractive index distribution from the obtained phase data with the method of computed tomography. Reconstruction is made from data obtained in a simple experiment with plastics as objects.