G. Gilgrass

Iseult/INUMAC Whole Body 11.7 T MRI Magnet Status

A Whole Body 11.7 T MRI Magnet is presently being developed at the CEA Saclay for the Iseult/Inumac project, a French-German initiative focused on very-high-magnetic-field molecular imaging to improve sensitivity, spatial, temporal, and spectral resolution for preclinical and/or clinical MR systems. The magnet will be installed at the Neurospin center, Saclay, in 2012. This actively shielded magnet system, with a stored energy of 338 MJ and an inductance of 308 H, has external dimensions of 5 m in diameter and 5.2 m in length. The magnet will operate at a homogeneous field level of 11.75 T within a 90 cm warm bore and at a current of 1483 A. The technological choice for the cryostable winding is a double pancake structure, using NbTi conductors cooled with a pressurized bath of Helium II at 1.8 K. In April 2009, the project passed an important milestone with the publication of the Technical Design Report, which defines the engineering parameters, design of the magnet, and establishes its engineering feasibility. In the paper, the status of the 11.7 T magnet is reviewed and the future developments are presented.

The Whole Body 11.7 T MRI Magnet for Iseult/INUMAC Project

Neurospin, a neuroscience research centre with very high field MRI equipments, just opened in November 2006 at Saclay by the CEA life science division. One of the imaging systems will require an 11.7 T magnet with a 900 mm warm bore. This magnet is currently under development at CEA Saclay, in collaboration with Siemens Medical Solutions and Alstom Magnets and Superconductors, within the framework of the French-German consortium Iseult/INUMAC (Imaging of Neuro disease Using high field. MAgnetic resonance and Contrastophores). The main aim of the consortium is to promote magnetic resonance and molecular imaging within high magnetic fields. The proposed magnet design is based on conservative options, but definitely unusual construction methods, for an MRI magnet (pancake winding, liquefier, stabilized power supply). These key design points therefore need to be assessed with several prototypes, integrated within a 5 years projected development plan, ending in 2011. The paper will present the objectives of the project as well as the main characteristics of the magnet and its development plan.

The Iseult/Inumac Whole Body 11.7 T MRI Magnet R&D Program

A neuroscience research center with very high field MRI equipments has been opened in November 2006 by the CEA life science division. One of the imaging systems will require a 11.75 T magnet with a 900 mm warm bore. Regarding the large aperture and field strength, this magnet is a real challenge when compared to the largest MRI systems ever built, it is being developed within an ambitious R&D program, Iseult, focused on high field MRI. The conservative MRI magnet design principles are not readily applicable, other concepts taken from high energy physics or fusion experiments, namely the Tore Supra tokamak magnet system, will be used. The coil will thus be made of a niobium-titanium conductor cooled by a He II bath at 1.8 K, permanently connected to a cryoplant. Due to the high level of stored energy, about 340 MJ, and a relatively high nominal current, about 1500 A, the magnet will be operated in a non-persistent mode with a conveniently stabilized power supply. In order to take advantage of superfluid helium properties and regarding the high electromagnetic stresses on the conductors, the winding will be made of wetted double pancakes meeting the Stekly criterion for cryostability. The magnet will be actively shielded to fulfill the specifications regarding the stray field. In order to develop the magnet design on an experimental basis, an ambitious R&D program has been set-up based on magnet prototypes, high field test facility (Seht) and stability experiments. The main results from these experiments and their impact on the Iseult magnet design will be discussed.

Manufacturing of the Iseult/INUMAC Whole Body 11.7 T MRI Magnet

As part the Iseult/Inumac project, a French-German initiative focused on very high magnetic-field molecular imaging, the Whole Body 11.7 T MRI Magnet currently under development is the worlds largest to-date. It is an actively shielded magnet system, manufactured from NbTi superconductor, with a homogeneous field level of 11.75 T within a 90 cm warm bore. It will operate at a current of 1483 A, in nonpersistent mode, in a bath of superfluid LHe at 1.8 K. The stored energy is 338 MJ and the inductance 308 H. The cryostat has external dimensions of 5 m in diameter and 5.2 m in length, the total weight of the magnet is 132 tons. The magnet is serviced by a separate cryogenic and electrical facility forming an integral part of the installation. It is currently being manufactured at Alstom Belfort under the supervision of CEA Saclay. Several reduced scale prototypes, each addressing a specific set of design and manufacturing risks, have been tested. Full-scale serial production of the 170 double pancakes that form the main coil has been finished by Alstom. The project plan includes finishing the cold mass and cryostat assembly in May 2014. Full tests and commissioning of the magnet at 1.8 K will be performed at the Neurospin center upon completion of assembly. The paper reviews the manufacturing status of the 11.7 T magnet and its dedicated equipment.

Latest Progress on the Iseult/INUMAC Whole Body 11.7 T MRI Magnet

The Whole Body 11.7 T MRI Magnet is an actively shielded magnet system, with a stored energy of 338 MJ and an inductance of 308 H. Operating at a homogeneous field level of 11.75 T within a 90 cm warm bore, the cryostat has external dimensions of 4.8 m in diameter and 5.0 m in length. It is part of the Iseult/Inumac project, a French-German initiative focused on very-high-magnetic-field molecular imaging to improve sensitivity, spatial, temporal, and spectral resolution for preclinical and/or clinical MR systems. After the qualification of two first unit lengths of 820 m, the NbTi conductor with a current of 1483 A is now being produced at Luvata Waterbury. Winding of the main coil, made of 170 double pancakes, is starting at Alstom Belfort. Several pieces of equipment have already been delivered to the Neurospin site, CEA Saclay,; including the main refrigerator produced by Air Liquide. Several prototypes have been tested and confirmed the soundness of the magnet design. This paper describes the 11.7 T magnet and the latest progress in its design and fabrication.

Iseult/INUMAC 11.7 T Conductor Production Status

The Iseult/INUMAC 11.7 T MRI magnet uses NbTi conductors larger than those typically used in conventional MRI magnets. The principal conductors are the main coil one, producing the magnetic field of 11.7 T and the conductor of the shielding coil that limits the fringe field. Both conductors are being produced by Luvata Waterbury Inc. The main coil conductor is a Rutherford cable in a copper channel (160 km) and carries 1500 A at 12 T and 2.8 K (2727 A at 9.5 T and 4.2 K). The shielding coil conductor is a wire in channel (60 km) and carries 2100 A at 5 T and 4.2 K. The conductor shape must be very precise with reproducible dimensions (tolerances below 15 microns) to enable good magnetic field homogeneity. They must also simultaneously exhibit a low electrical resistance (20 μΩ/m at 10 K and 12 T) and a high mechanical strength (σ0.2%>;250 MPa). Conductors of this industrial production are characterized by mechanical, electrical and geometrical measurements.

Expected Magnetic Field Quality From the Preliminary Measurements Performed During the Manufacturing of the Iseult/Inumac Whole-Body 11.7-T MRI Magnet

A new innovative whole-body 11.7-T MRI magnet is currently being manufactured at Alstom Belfort as part of the Iseult/Inumac project. The magnet will be installed by the end of the year in a neuroscience research center with other very high-field MRI equipment operating in France at CEA Saclay since November 2006. This actively shielded magnet system, which was manufactured from a NbTi superconductor, will generate a homogeneous magnetic field of 11.75 T within a 90-cm warm bore. This paper presents the geometrical controls performed on the Iseult/Inumac magnet during the different fabrication stages, and it compares them to the specifications. A FEM analysis taking into account magnet cooling down and energizing has also been performed, in order to estimate the final magnet homogeneity, taking into account load tests and geometrical measurement performed on the main coil. Measured field maps will be analyzed and compared to the field computation based on geometrical measurements.

Status of the Shielding Coil Fabrication for the Iseult/INUMAC Whole Body 11.75 T MRI Magnet

A neuroscience research center with a very high field magnetic resonance imaging (MRI) equipment was opened in November 2006 in the Neurospin site at CEA Saclay. One of the imaging systems requires a whole body 11.75 T MRI magnet with a 900 mm warm bore. Operating at a homogeneous field level of 11.75 T, the cryostat has external dimensions of 4.8 m in diameter and 5.0 m in length. With the large aperture and high field strength, this magnet represents a real challenge when compared to the largest MRI systems ever built. The coil is made from a copper-stabilized niobium-titanium conductor cooled by a superfluid helium bath at 1.8 K and permanently connected to a cryo-plant. The main coil is constructed from a stack of 170 double pancakes and the magnet is actively shielded by two large coils connected in series to fulfill the stray field specifications. The two shielding coils, each of about 4 m in diameter, are presently being manufactured by Alstom Power Systems STTG Magnets, Belfort. This paper describes the design of these coils and presents the latest progress of their fabrication. Details are given of the winding technique, impregnation method, and the first results of electrical and geometrical tests.

The Development of a Pulse Tube Cooler with More than 1 W at 4.2 K

A pulse tube cooler (PTR) for shield cooling and for re‐condensation of Helium in MRI magnets has been developed successfully by co‐operation of Forschungszentrum Karlsruhe (FZK) and Siemens Magnet Technology Ltd. (SMT, formerly Oxford Magnet Technology, OMT). Refrigeration power of 1.1 W at 4.2 K and 40 W at 45 K were achieved with less than 8 kW of compressor input power. The two‐stage PTR is of a ’4‐valve type on each stage. A special non‐wear rotary valve has been developed at SMT. The design of the cooler is based on investigations carried out at FZK on a test rig, which was versatile enough to allow many different experiments to be carried out. They have been accompanied by numeric studies. The code FZKPTR based on the thermoacoustic theory has proved a very helpful tool. This development work at FZK and SMT lead to a commercial PTR solution for MRI magnets. The industrial partner, SMT, defined the needs for his application, and has modified the FZK design according to these requirements and those o...

Iseult/INUMAC 11.7-T MRI Assembly Status

A new innovative whole-body 11.7-T MRI magnet is currently being manufactured at Alstom Belfort as part the Iseult/Inumac project, a French-German initiative focused on very high magnetic field molecular imaging. It will be installed at the end of year 2016 in a neuroscience research center with other very high field MRI equipment, operating in France at CEA Saclay since November 2006. The main coil constructed from a stack of 170 double pancakes of 2-m diameter, with a finished height of 4 m and 50 t in weight, has been completed within required tolerances. The two shielding coils, vacuum impregnated solenoids of 4 m in diameter and 10 t in weight, have been also completed within tolerances. A crack has been discovered inside the 2-m diameter mandrel of the cryogenic correction coils. A new mandrel has been manufactured, with delivery in July 2015. The main coil and the shielding coils have been integrated inside the helium vessel, and the assembly of thermal shield and vacuum vessel is due to start, with completion expected by the middle of 2016. The magnet will be serviced by a separate cryogenic and electrical facility; the installation of this external equipment will be completed by the end of 2015 when the first phase of the commissioning will start. Full tests and commissioning of the magnet at 1.8 K are expected at NeuroSpin at the beginning of 2017.