Synchrotron radiation in radiology: novel X-ray sources

X-rays, the key ingredient of radiology, are still primarily produced with the mechanism discovered by Röntgen over one century ago. A different approach, however, is becoming increasingly important: the use of synchrotron sources based on fast-moving electrons and on their relativistic properties. We discuss the elements of this new strategy, its practical implementation, and some new types of synchrotron sources under development. The present and potential impact on radiology of different classes of synchrotron sources is briefly and realistically analyzed.