Quasi monochromatic and coherent X-ray beams for medical diagnostics and radiation therapy

by Prof. Alberto Bravin (European Synchrotron Radiation Facility, Grenoble, France)

Tuesday 20 Dec 2011, 11:00 → 13:00 Europe/Rome

131 (INFN Edicifio C)

The limitations of X-ray tube based imaging techniques, arise mostly from insufficient spatial or time resolution and contrast, and the possibility of obtaining precise quantitative information on the tissues. These limitations are related to several characteristics including the intrinsic wide energy spread of the emitted radiation, and to the poor source coherence. The reference X-ray source for monochromatic and coherent beams is synchrotron radiation, presently available at large facilities. In the past twenty years, several imaging techniques with monochromatic X-rays have been developed at such sources. Two widely used methods in preclinical research are the (K-edge) energy subtraction and the temporal subtraction imaging. Tunable monochromatic beams of a few hundreds of eV bandwidth are relatively easily obtainable at such sources and used in combination with injection of contrast agents like iodine, gadolinium, gold nano-particles, or the inhalation of barely reacting gases like Xenon. In energy subtraction, two simultaneous images are taken at using two beams of different energies, and the map of the distribution of the contrast agent is extracted by the combination of the two images. These techniques have been used in preclinical, and pioneer clinical research programs, for brain perfusion and functional lung ventilation imaging. Absorption-based X-ray imaging techniques are often unsuitable for soft tissues like breast and articular cartilage, because the elemental composition of these samples is almost uniform and the variations of X-ray absorption (and therefore the image contrast) are small. Phase contrast imaging, which exploits phase variations of X-rays passing through non-uniform matter, has been demonstrated as an extremely powerful method for overcoming these difficulties in imaging soft tissues. Several phase-based techniques have been developed at SR sources all over the word and being applied to various fields like mammography, early signs of osteoarthritis visualization, brain imaging and others, obtaining very promising diagnostic tools, presently applied only in in-vitro or in small animal models. Recently, intense quasi monochromatic beams have been used for two new applications: in combination with a chemotherapic drugs or contrast agents containing a high Z element, to develop treatments targeting high grade glioma, and when the radiation is spatially fractionated in an array of submillimetric beams, to develop basic and applied research in the treatment of drug-resistant epileptic foci in the eloquent cortex, or in studying in vivo the bystander effect. If synchrotron radiation sources are perfect for developing fundamental science, for setting up models and technique and for performing preclinical research, severe limitations remains in the access to large clinical trials or clinical diagnostic routine and therapy. Compact X-ray quasi monochromatic sources