X-ray phase contrast imaging

by Docent lecture (Biomedical and X-Ray Physics, KTH, AlbaNova), Dr Ulrich Vogt (Biomedical and X-Ray Physics, KTH, AlbaNova)

Thursday 29 May 2008, 10:15 → 11:00 Europe/Stockholm

FD5 (Svedberg Hall)

Ever since the discovery of x-ray radiation by Wilhelm Conrad Röntgen in 1895 the penetrating power of x-rays has been used to uncover the hidden inner structure of matter. Today, x-ray imaging is an essential tool in a variety of fields including research, medicine as well as industrial applications. The contrast in x-ray images is normally generated by the difference in x-ray absorption for different materials. However, the x-ray absorption coefficient is roughly proportional to the fourth power of the atomic number Z, making the imaging of objects consisting of low-Z elements like carbon, nitrogen and oxygen difficult. As an example, soft tissues in a body give very low contrast in medical x-ray imaging when no contrast enhancing media are used. In order to overcome this problem, the use of the x-ray phase information for imaging has attracted increasing attention in the recent past. For nearly all elements the real part d of the complex index of refraction n (n = 1 – d + ib) in the x-ray region is larger than the imaginary part b. As a consequence, the phase shift of any object is stronger than the absorption, and the difference between d and b becomes larger with increasing energy. Phase-sensitive imaging techniques, as known for a long time in optical microscopy, can access the phase shifting, real part d of the object for the creation of phase contrast in the image. This seminar will give a background on x-ray phase contrast imaging and will present state-of-the-art phase contrast imaging techniques. It will be shown that phase contrast has lead to a renaissance in x-ray imaging more than 110 years after the discovery of Röntgen.