11.7 teslas: The world-record magnetic field generated by a human MRI magnet

The Iseult project magnet being installed at Neurospin (CEA Paris-Saclay) reached a nominal magnetic field of 11.7 teslas (T) on July 18, 2019. This is a world record for a whole-body magnetic resonance imager (MRI) magnet, the culmination of years of R&D and at the forefront of innovation in the field of superconducting magnets. Over the coming months, the equipment required for neuroimaging will be installed around the magnet and in its central tube to create a human MRI scanner capable of examining the brain more accurately than ever before, in the interest of fundamental research, cognitive sciences and diagnosing neurodegenerative diseases.

In the process of being installed at the CEA Paris-Saclay site since July 2017, the colossal magnet weighing 132 tons is now fully operational. To do this, the teams had to meet the many challenges involved in setting up such equipment:

· Connecting the magnet to auxiliary equipment already installed and tested (cryogenic plant, electrical power supplies, instrumentation and control system);

· Reaching a stable temperature of 1.8 K: the magnet must be cooled to 1.8 K (- 271°C), at which temperature helium, its “cooling liquid”, is in a special physical state known as superfluid. At this temperature level, the conductor that forms the magnet (niobium-titanium alloy) has no resistance to the electric current passing through it, thereby preventing any power dissipation or temperature rise: it is in a superconducting state;

· Ramping-up to reach 11.7 T1: once the conductor has cooled to its nominal temperature, current was gradually injected into the magnet to reach the target magnetic field of 11.7 T. This “ramp-up” was performed in several stages, with numerous electrical and magnetic tests, as well as tests of emergency shutdown procedures. In total, 1,300 procedures intended to detect any potential defects were tested.

To reach its nominal magnetic field, the magnet is supplied with a current of 1,500 amperes and the conductor coils are cooled constantly by 7,000 liters of superfluid helium. With a magnetic field of 11.7 T, this is a world record in the field of MRI for a whole-body system and an all-time record with this type of superconducting material. Manufacturing this 132-tonne prototype – measuring 5 m in length with an outer diameter of 5 m and an inner diameter of 90 cm – will have taken six years of development in Alstom (now General Electric, GE) factories in Belfort and nearly two years of installation and testing before it is commissioned.

Over the following months, numerous items of equipment will be added to the magnet to transform it into an MRI machine capable of producing images of volunteers’ brains: gradient coils, radiofrequency coils, patient table, outer casing, etc.

About the Iseult project
Neuroscientists wanted to acquire an 11.7-tesla MRI scanner in order to examine the human brain with an observation quality never before achieved, whether in terms of spatial or temporal resolution, or in terms of the accuracy of the images obtained. The Iseult project was started at the turn of the 21st century with the ambitious goal of developing a giant magnet (90-cm diameter opening) that could generate a magnetic field of 11.7 T. The project was jointly led by neuroscience researchers and CEA physicists specialized in magnets at the Institute of Research into the Fundamental Laws of the Universe (IRFU) and specialized in MRI at the Frédéric Joliot Institute for Life Sciences. The researchers and their partners, both academic and industrial, set out to design and manufacture the magnet, the core of the MRI scanner, which was delivered to Neurospin, on the CEA Paris-Saclay site, in May 2017.

The Iseult development is part of a larger Franco-German project initiated in 2006. It is the fruit of collaboration between:

· industrial partners (Siemens Healthineers, Bruker Biospin, Alstom – now part of General Electric – and Guerbet);

· academic partners (University of Freiburg, CEA’s Fundamental Research Division);

· with partial financial support from public agencies (in France: Bpifrance; in Germany: the German Federal Ministry of Education and Research).

Source: http://www.cea.fr/

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