Ultra High Field MRI Magnets: Present Situation and Future Perspectives

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1 SA-8-INV Ultra High Field MRI Magnets: Present Situation and Future Perspectives Pierre Vedrine (CEA Saclay, DSM/Irfu/SACM, Universite Paris Saclay, Gif sur Yvette Cedex, France) Magnetic resonance imaging (MRI) is a diagnostic and research tool used in the neurosciences and to observe deep organs totally non-invasively. MRI is based on the magnetic properties of the nuclei of atoms. It uses a magnet with a high and homogenous magnetic field, as well as specialized electronic and computer equipment. The stronger the magnetic field is, the higher the sensitivity and the spatial or temporal resolution that can be achieved are important, in order to see more details. Today, standard MRI magnets in clinical use for human imaging operate at 1.5 T; the high-field systems operate at 3.0 T. There are a few ultra-high field systems operating at 7 T and 9.4 T, and systems at 10.5 T, T and 14 T are being installed or are in the development stages in Minnesota, NIH, Saclay (France), Japan and in Korea. The proposed new systems should provide unprecedented resolution and play a significant role in decoding the mysteries of the human brain. For human applications, the design of magnets capable of the utmost field intensity, beyond 10 T, on diameters close to 1 m remains a technological challenge. Today the generation of strong magnetic fields for MRI is made with superconducting magnets using NbTi superconductors cooled to the temperature of liquid helium but the use of new superconducting materials is foreseen for the future. We will describe first the present situation and the state of the art in the high field MRI magnets, stopping at some examples and then we will address the future challenges in the field, as the new innovative Iseult Whole Body 11.7 T- 90 cm MRI magnet which will be commissioned in 2016 at the CEA Saclay or the new ideas developed at the NHMFL in Tallahassee targeting a 20T magnetic field in a 68 cm bore along with an intermediate magnet of 14 T in 68 cm. Figure 1. The Iseult actively shielded 11.7T Whole Body MRI magnet.

2 SA-9-INV Research and Development of the Very Stable Magnetic Field HTS Coil System Fundamental Technology for MRI Shoichi Yokoyama *,1, Jiwon Lee 1, Takeshi Imura 1, Tetsuya Matsuda 1, Tatsuya Inoue 1, Ryo Eguchi 1, Toshinari Ngahiro 1, Hajime Tanabe 1, Shinji Sato 1, Taketsune Nakamura 2, Yasuyuki Shirai 2, Daisuke Miyagi 3, Makoto Tsuda 3 ( 1 Mitsubishi Electric Corporation, 2 Kyoto University, 3 Tohoku University) The characteristic of the medical Magnetic Resonance Imaging (MRI) are not radiation exposure and can observe the bloodstream for imaging using the internal proton magnetic resonance by a magnetic field. In addition, f-mri is provided with many functions for a medical. The superconducting magnet is effective to get a very stable and high magnetic field for MRI. The current MRI superconducting magnet needed cooling in the liquid helium (4.2K) to use NbTi superconducting wire. For these several years, a price of the liquid helium rise and acquisition-related difficulty become the problem. Therefore the development of a high-tc superconducting (HTS) coil dispensing with liquid helium cooling advances. The research and development project of the very stable magnetic field HTS coil system fundamental technology that started from the latter half of 2013 develops a HTS coil for 3T-MRI superconducting magnets and carries out that I get a prospect of the practical use as the final aim. In this project, we will produce a HTS test coil of 300mm bore experimentally and evaluate the magnetic field. Specifications of the HTS test coil of 300mm bore are shown in Table 1. Figure of constitution that is shown in Figure 1. This coil is cooled in less than 20K by a G-M refrigerator. A Coil load factor for minimum critical current of HTS wire at the rating current is 61% by critical current calculation of field characteristics at 20K.We are going to make MR imaging used by the HTS coil field to evaluate the uniformity and stability of the magnetic field. This research is supported by Development of Medical Devices and Systems for Advanced Medical Services form the ministry of economy, trade and industry (METI) and Japan Agency for Medical Research and development (AMED). Table 1 Specifications of the HTS test coil of 300mm bore. Inner Diameter 320mm Outer Diameter 420mm Axial Length 450mm Central Field 2.9T Maximum Field 4.2T Critical Current of wire at field 351A(20K)/4.1T(36 ) Ampere Turn 1.5MA Current Density of coil 139A/mm2 Field Uniformity 1.72ppm/100mmVrms Leak Field Domain (5 gauss) R3.2m Z4.0m Figure 1. The HTS test coil of 300mm bore.

3 Magnetic field SA-10-INV R&D Progress of HTS Magnet Project for Ultra-high Field MRI Taizo Tosaka *1, Hiroshi Miyazaki 1, Sadanori Iwai 1, Yasumi Otani 1, Masahiko Takahashi 1, Kenji Tasaki 1, Shunji Nomura 1, Tsutomu Kurusu 1, Hiroshi Ueda 2,4, So Noguchi 3,4, Atsushi Ishiyama 4, Shinichi Urayama 5, Hidenao Fukuyama 5 ( 1 Toshiba corporation, 2 Osaka University, 3 Hokkaido University, 4 Waseda University 5 Kyoto University) As the magnetic field become higher above 7 T, the nuclear magnetic resonance (NMR) signals from, for example, carbon, phosphorous, nitrogen and oxygen may become easier to detect. Therefore ultra-high field magnetic resonance imaging (MRI) system is expected as a novel diagnostic equipment. For ultra-high field MRI systems (RE) Ba 2Cu 3O 7 (REBCO; RE = rear earth) wires are promising components because of their superior superconducting and mechanical properties. Against this background the R&D project of high temperature superconducting (HTS) magnet using REBCO wires is started from In this year as the final year of the project, a small test coil to demonstrate generating a high magnetic fields and a model magnet to demonstrate MRI imaging are manufactured and tested for establishing the magnet technologies. The small test coil has the inner diameter of 50 mm, and is planned to generate the magnetic field of 9.4 T. The model magnet has the inner diameter of 500 mm, and is planned to generate a homogeneous magnetic field within the 200 mm diameter spherical volume (DSV). The knowledge gained through the development of these coil and magnet is reflected in the design of 9.4 T MRI magnets for brain imaging and whole body. 9.4 T Small test coil MRI magnet for brain imaging and whole body imaging Design and simulation 1.5 T Model magnet Φ500mm Φ1m Inner diameter of coil Figure 1. Test coil and model magnet in the R&D project

4 SA-11 Spatial Field Homogeneity for 2G HTS NMR/MRI Magnet Using External Shim Coils Y. G. Kim*, Y. H. Choi, D. G. Yang, S. G. Kim, and H. G. Lee Department of Materials Science and Engineering, Korea University, Korea Magnetic field homogeneity within a target volume is one of the major requirements for the development of nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) magnets. In order to achieve high spatial field homogeneity, conventional NMR/MRI magnets employing the low temperature superconductor (LTS) are equipped with their own shim coils located at the outside of the magnets. However, it has been recently reported that the spatial homogeneity of high temperature superconducting (HTS) magnets can barely be improved using external shim coils because of the screening current-induced field (SCF) limiting the effect of the external shim coils on the center field. Therefore, it is essential to eliminate the SCF caused by external shim coils. In this study, Z1 and Z2 external shim coils were designed and fabricated to enhance the field homogeneity of a prototype 10-MHz NI NMR magnet. In order to eliminate the effect of the SCF on the magnetic field by shim coils, we investigated the strength of each shim coil with and without applying the CSR technique. Furthermore, harmonic analyses were performed to validate the proposed approach by confirming the field gradients when each shim coil was charged with the CSR charging scenario. <Acknowledgment> This work was supported by the Materials and Components Technology Development Program of KEIT [ , Development of MgB 2 wire and coil with high critical current and long length for superconducting medical electric power equipment].

5 SA-12 Publicly available codes for estimating the critical current of superconducting devices using a stationary model approach V. Zermeno 1, S. Quaiyum 1, F. Grilli 1,* ( 1 Karlsruhe Institute of Technology, Germany) The high current capacity of superconducting wires has made them candidates of choice for designing compact and light cables and coils that can be used in large scale power applications. However, their performance is often limited by their critical current and the AC losses they experience. In general, these characteristics are determined by several factors, including the conductor's material properties, the electromagnetic environment and the geometric layout of the device. Therefore, the estimation of the Ic and AC losses in a particular device often requires a detailed analysis that considers the aforementioned factors. While several design and simulation tools have already been developed to estimate both the Ic and AC losses, these tools remain often kept as a secret sauce and in most cases only a mathematical description of the modeling technique is made available. In this work, we present in detail the implementations of a recently proposed stationary model used to estimate the critical current of superconducting devices. Said implementations are made in different programming environments, both commercial an open-source. A comparison of the accuracy and calculation speed of the different implementations of the model is carried out for the case of a Roebel cable. Although the model is primarily developed with the purpose of calculating the critical current of HTS devices, its applicability for a simple way of approximately estimating the AC losses is discussed. The numerical codes, two of which are open-source, are made freely available to interested users.