Joel Lecture Series | And yet it bends - 25 years of reflections on (X-ray) refraction скачать в хорошем качестве

Joel Lecture Series | And yet it bends - 25 years of reflections on (X-ray) refraction

Röntgen discovered x-rays in 1895, for which he was awarded the first Nobel Prize. X-rays caused a huge revolution in science, medicine and society in general, and still to this day the vast majority of diagnostic imaging examinations are x-ray based. X-ray images exploit the different attenuation to x-rays of different materials – different tissues if we are referring to medical images: bones absorb more x-rays than muscles, which is why they appeared white in old radiographic films. This is the source of x-rays notorious “low soft tissue sensitivity”: most soft tissues absorb x-rays in a similar way, hence for a soft tissue examination your doctor would probably prescribe an MRI instead. However, x-rays are waves, and as such they not only get absorbed by matter, but also refracted. Röntgen stated that he "could not demonstrate that the X-rays were refracted, but if they did it would be to a minimal degree”, and in a sense he was right (as Nobel Laureates tend to be): x-ray refraction does exist, but it occurs at incredibly small angles – of the order of 0.0001 degrees, which is the angle subtended by a millimetre if you place it a kilometre away. However, it turns out that x-ray images created by using refraction look much better than those originating from absorption, to the extent that they give x-rays that elusive “soft tissue sensitivity” they have been missing since Röntgen’s discovery. X-ray imaging using refraction started at very specialized facilities called synchrotrons, of which there are about 50 in the world. Work from pioneering groups including UCL’s Advanced X-Ray Imaging (AXIm) group adapted the concept so that it could be exploited with conventional x-ray sources, which in turn allowed its deployment into the first pre-commercial prototypes. This talk will take you on that journey. The Joel Chair is the oldest established Chair in Medical Physics in the world. It is currently held by Prof Robert Speller of UCL Medical Physics & Biomedical Engineering.