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Magalie Quet - 28/06/2017

At Saclay, researchers will be able to study the brain in very high resolution

L'aimant IRM du centre de recherche NeuroSpin du CEA Saclay (Essonne) pèse 130 tonnes et produit un champ magnétique de 11,7 teslas. - CEA

At the end of May, after six years in construction and over 14 days being transported, the largest human MRI scanner[i] - the Iseult project - arrived at the Neurospin research centre in Saclay. Equipped with the most powerful magnet in the world, generating a record magnetic field of 11.7 teslas[ii], this MRI will be able to explore the human brain with a hitherto unparalleled level of precision. The Parietal project team from the Inria Saclay - Île-de-France centre, a joint team with the CEA[iii] and located at the NeuroSpin research centre will, a few months from now, be able to work on this behemoth of technologies and push their studies of the brain even further.

Discovering the brain with Parietal

The Parietal project team is working on the modelling of the structure, functioning and variability of the brain using high-field MRI. In other words, the team's researchers focus on “the study of the brain through the image of the brain” explains  Bertrand Thirion, the team leader.

For this, part of Parietal is working on functional MRIs. Unlike an anatomical MRI, that enables the visualisation of the structure of the brain - which evolves very slowly, over some years – a functional MRI allows for the study of the oxygenation of the blood in the brain, over time, on a subject given a cognitive task (reading, writing, speaking...). In the areas activated by the task, a slight increase in oxygen consumption by the neurons is overcompensated by an increase in blood flow. Functional MRI enables the recording of these flow modifications: this data can be processed, have the noise removed and reconstructed thanks to software developed by the Parietal team, making it possible to visualise neural activity in the different stimulated areas.

Improving the resolution and processing of the image

With the technologies currently available to the team it is possible, for example, to acquire 1 image every 2 seconds at a resolution level of 1,500 microns [i] (1.5 millimetres), which generates over a million points to cover the entire brain. Parietal is working on high-field imagers that rely on a magnetic field of 3 and even 7 teslas, however very high-level imaging remains too costly in terms of acquisition time and lack of sensitivity. Part of the team, led by Philippe Ciuciu, CEA, is currently carrying out cutting-edge research on compressed sensing, a technique enabling the reconstruction of the same images but from fewer measurements , and therefore much more quickly.

In concrete terms, this technique consists in only obtaining certain points of the image and reconstituting all of the measurements thanks to the points acquired. Compressed sensing requires work to be done on the choice of acquisition and reconstruction parameters in order to best sample the measurement space and reconstruct the images as accurately as possible.

In this way, the team has demonstrated that it is “possible to acquire 10 times less data whilst still ending up with the same image quality” , Bertrand Thirion explains.

Coming soon, the brain in very high resolution

The higher the magnetic field of an MRI, the greater the resolution of the images. Capable of generating a magnetic field of 11.7 teslas - which is a world record - the Iseult project's new ultra-powerful imager will enable the acquisition of images of the brain in very high resolution . And the work of the Parietal team on compressed sensing techniques aims to make the reconstruction of these images possible by retaining their high level of quality, using relatively few measurements and in a reasonably short time.

“With these new cutting-edge technologies and the advances of our research, we should probably be able, within around 10 years, to visualise the brain at a resolution level of 200 to 500 microns, which would allow us to get close to the size of the cortical column - a group of neurons found in the cerebral cortex and which form a kind of functional unit” , Bertrand Thirion explains. 

Even though the magnet has taken its place in one of the arches of the NeuroSpin building, specially built to house it, installing the complete MRI and obtaining the first images will no doubt take several more months. The magnetic field of the magnet should progressively increase from September onwards. The first human acquisition will only be carried out following a test phase lasting several months.

 

[i]  IRM – Imagerie à Résonnance Magnétique

[ii] Tesla (T) – Unité de mesure du champ magnétique. Sur la Terre, le champ magnétique est de 31 µT à l'équateur (latitude de 0°).

[iii] CEA – Commissariat à l’énergie atomique et aux énergies alternatives

[iv] Micron – Unité de mesure correspondant à 0,001 millimètre

Keywords: Neurospin Inria Saclay - Île-de-France CEA Parietal

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