Joel Lecture: 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.

• 17:30 - 17:40: Introduction by Professor Robert Speller
• 17:40 - 18:30: Joel Lecture by Professor Sandro Olivo
• 18:30 - 18:35: Closing remarks by Professor Andy Nisbet
• 18:35 - 20:00: Evening reception

This will be an in-person event and open to the public, if you are unable to attend the UCL campus, please register for the online stream via Zoom.

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.

The Joel Lecture Series is free to attend and open to all. You don't have to be a UCL staff member or student to come along.

Lectures begin at 17:30 and are typically one hour long. A drinks reception will follow, to which everyone is welcome to join. We look forward to meeting you at one of our events!

Please note photographs and recordings taken at this event may be included in future publications, on our website and on social media. You will have the opportunity to opt out at the event. If you have any questions, please contact [email protected]

Register your details to reserve a place at the lecture. Your personal information will only be used to administer your event attendance.

Event Venue & Nearby Stays

Sir Ambrose Fleming Lecture Theatre, Gower Street, London, United Kingdom