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Les plus puissantes machines IRM du monde repoussent les limites de l’imagerie humaine (en anglais)

Les dernières machines IRM développées aux États-Unis et en France, conçues pour fonctionner sous des champs magnétiques de très forte intensité grâce à des aimants supraconducteurs géants, devraient notamment permettre des progrès considérables de la compréhension des maladies neurologiques.

Magnetic Resonance Imaging (MRI) requires the use of magnetic field strengths in excess of 1 Tesla (T). This can only be achieved practically through the use of superconducting magnets. In most of MRI magnets, the superconducting coil is enclosed in a helium tank containing liquid helium at less than 4K (-269°C).1


Today, hospitals routinely use machines with field strengths of 1.5?T or 3?T. But ultra-high-field scanners are on the rise. There are already dozens of 7-T machines in research labs around the world and in December 2017, US scientists at the Center for Magnetic Resonance Research, University of Minnesota became the first in the world to perform magnetic resonance imaging of the human body at 10.5 T. 2 The CMRR team spent years preparing the 110-ton magnet for operation, including cooling the conductors below liquid helium temperature, configuring its complex electronics, and conducting animal studies to ensure safety for human use.3


In addition to the University of Minnesota’s machine, researchers are readying two 11.7-T devices for their first tests on people: a gargantuan one for whole-body scanning at the NeuroSpin Centre at CEA Saclay outside Paris, and a smaller one for head scans at the US National Institutes of Health (NIH) in Bethesda, Maryland. Germany, China and South Korea are considering building 14-T human scanners.2


The development of the high magnetic field imager for the Neurospin platform is part of the ISEULT Franco-German project. The coil consists of 182 kilometers of niobium-titanium superconducting wire wound in double pancake coils and carrying a current of 1483 A. The 132-ton magnet is maintained at a very low temperature of 1.8 K by means of 5000 liters of superfluid helium isolated from the exterior by series of insulating enclosures. The use of this magnet in molecular imaging, together with new pharmaceutical contrast agents, is expected to enable a deeper understanding of the brain by improving the images by a factor of ten. 4,5 The first images obtained at 11.7 T are expected to be produced during the course of 2022.


The appeal of ultra-high-field scanners is clear. The stronger the magnetic field, the greater the signal-to-noise ratio, which means the body can be imaged either at greater resolution, or at the same resolution, but faster. At 3?T, MRI machines can resolve details of the brain as small as 1?millimetre. That resolution can be as fine as 0.5?millimetres in a 7-T machine — enough to discern the functional units inside the human cortex and perhaps see for the first time how information flows between collections of neurons in a live human brain. Scanners with even higher field strengths are expected to have resolving power of at least twice that of the 7-T devices.2


1 https://www.europhysicsnews.org/articles/epn/pdf/2012/04/epn2012434p26.pdf

2 https://www.nature.com/articles/d41586-018-07182-7

3 https://research.umn.edu/inquiry/post/u-scientists-scan-worlds-first-105-tesla-human-mri-image

4 http://irfu.cea.fr/en/Phocea/Vie_des_labos/Ast/ast_visu.php?id_ast=3377

5 http://www.cea.fr/presse/Documents/DP/2017/dossier-presse-iseult-aimant-cea.pdf (in French)