Introduction

Abstract

X-ray based imaging techniques are already the subject of active research for almost 130 years starting right after the discovery of X-rays by Wilhelm Conrad Röntgen in 1895 (Roentgen 1895a, Roentgen 1895b) up to the present. The nature of X-rays to penetrate the object which has been used to visualize the inner structures of opaque objects have changed the world in medical and non-medical application fields. It opened new opportunities in recognition and understanding of human diseases without surgical intervention and in non-destructive material testing (NDT). Although the human body is “transparent” for X-rays and can be visualized using X-rays, a single X-ray image contains only the projective overlap of all structures in the body. The three-dimensional information about the structure locations can be recovered only by using the principle of tomography. For this, a set of X-ray images from different sides must be measured and the inverse problem of image reconstruction must be solved.