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When the Higgs boson was discovered in 2012, Paul Lecoq was one of the physicists who made it possible. Now, as principal investigator in the EU-funded TICAL project, he has been applying his expertise in building particle detectors to problems concerning medical imaging.
‘From the very beginning, I had the intuition that the technology I was proposing to improve the performance of our particle physics detectors would have a strong impact in medical physics,’ he says.
Until recently, Lecoq worked at CERN, the European Laboratory for Particle Physics, as technical coordinator for one of the detectors for the Large Hadron Collider. Known as a ‘calorimeter’, the detector uses dense crystalline blocks, called scintillators, to catch particles as they pass through. The energy of the particle appears as flash of light which is picked up by sensitive photodetectors.
In practice, a high-energy particle will produce a shower of other particles in the scintillator but the response of the scintillator is just too slow to record the complexity of the shower.
Nanocrystals
With funding for the TICAL project from the European Research Council, Lecoq set out to devise a new kind of scintillator that could more precisely record the position and timing of events within the shower. ‘What I want is a reconstruction of the spatial development of the shower and also the time – I want to know the dynamics of it.’
His solution was to use nanocrystals – tiny crystals of scintillator material that are small enough for quantum effects to dominate and for a captured particle to emit a much sharper flash of light. By sandwiching thin layers of nanocrystals between sheets of conventional scintillator, Lecoq’s ‘meta-scintillator’ allows the particle shower to be tracked more accurately.
Meta-scintillators could greatly improve the particle detectors at CERN – but that is not the whole story.
For many years, Lecoq focused on PET (Positron Emission Tomography) scanners, the imaging machines used to probe the interior of the human body, especially for cancer diagnosis. They rely on detecting gamma rays using much the same principles as CERN’s particle detectors.
‘I used to say that the 100-tonne calorimeter, the construction of which I was responsible for at the Large Hadron Collider, is nothing but a gigantic PET scanner,’ he jokes.
Ten picosecond challenge
At present, the best PET scanners can time the arrival of a gamma ray to better than 500 picoseconds. With the TICAL meta-scintillators ultimately capable of a precision of 10 picoseconds – 50 times better – Lecoq envisages future PET scanners able to produce much sharper images. They would also require much less radioactive material and potentially have wider applications in medicine.
Lecoq is currently seeking sponsors for a ‘Ten picosecond challenge’ to design and build gamma-ray detectors for PET applications capable of this higher time resolution.
TICAL finished at the end of 2018 but Lecoq, retired from CERN, is now co-CEO of Multiwave Metacrystal, a company created to commercialise the work of the project. It is setting up a laboratory in collaboration with the Polytechnic University of Valencia to develop meta-scintillators. Initially, they would be for PET scanners although they also have potential for other industrial and security applications.
Lecoq sees the project as a classic example of how European funding can allow ‘a completely crazy idea’ to mature to the point where it can be commercialised for the good of society. ‘For me, the ERC grant was fantastic. The European Commission has really played the role it should play.’