We have developed X-ray refraction based computed tomography (CT) which is able to visualize soft tissue in
between hard tissue. The experimental system consists of Si(220) diffraction double-crystals called the DEI (diffraction-enhanced
imaging) method, object locating in between them and a CCD camera to acquire data of 900 x-ray images.
The x-ray energy used was 17.5 keV. The algorithm used to reconstruct CT images has been invented by A.
Maksimenko et al.. We successfully visualized calcification and distribution of breast cancer nest which are the inner
structure. It has much higher contrast which in comparison with the conventional absorption based CT system.
X-ray dark-field imaging (DFI) due to refraction is under development with intension of its clinical application. In this system we have adopted an asymmetric-cut monochro-collimator (<i>M</i>) and an angular analyzer (<i>A</i>) of Si 440 diffraction at 35 keV of X-rays. By choosing an appropriate thickness T of <i>A</i> that satisfies the condition T = ΛN where Λ is the extinction distance and N integer the transmissivity in the region of |<i>W</i>| (angular parameter) < 1 should be theoretically almost zero and |<i>W</i>| > 1 should be approximately 70-80%. This has been experimentally proven. Under this condition the X-rays whose propagation direction may not change such as those receiving only absorption will not go into the forward diffraction direction after <i>A</i> but go into the diffraction direction, while the X-rays refracted by object may go into the forward diffraction direction after <i>A</i>. We have settled two targets of clinical views: soft tissues at joints and early check of breast cancer. A first clear image of articular cartilage of small joint was successfully obtained using a proximal interphalangeal joint that was amputated from a cadaver. Since larger view field is needed for clinical use the size of approximately 90 mm in square has been successfully achieved. Using this beam articular cartilage of knee and shoulder joints from the same cadaver have been successfully visualized. Further visibility test by the DFI is under way for a phantom of breast cancer, paraffin fixed sliced breast samples containing micro-calcification, tumor and excised breast tissue.