Superconducting magnets are effective for obtaining a highly stable, strong magnetic field for magnetic resonance imaging (MRI). Current MRI superconducting magnets require cooling in liquid helium at 4.2 K in order to use NbTi superconducting wire. The development of a high-temperature superconducting (HTS) coil that can be used without liquid helium cooling is greatly desired. In order to develop liquid helium-free MRI magnets using a high-temperature superconductor, the author has prototyped a model magnet that is able to generate extremely uniform, highly stable magnetic fields. This particular development includes such subjects as developing a coil structure where the superconducting characteristics do not deteriorate, working on a method of producing precision coils, designing coils that generate extremely uniform magnetic fields, and having high-temperature superconducting coils generate highly stable magnetic fields. MR imaging was carried out to verify the uniformity and stability of the magnetic fields.
A project for developing of RE1Ba2Cu3O7-δ (REBCO) magnets to be utilized in ultrahigh-field magnetic resonance imaging (MRI) was started in 2013. Our final targets are 9.4 T MRI systems for whole-body and brain imaging. In this project, two different development approaches towards the final target were planned. One is a small REBCO coil that can generate 10 Tclass magnetic fields, which is the same level as the target magnetic field. The other is a conduction-cooled 1.5 T REBCO MRI magnet that has a room-temperature bore of 396 mm, which is as large as those of mid-sized model magnets. These results were reflected in the design of a conduction-cooled 9.4 T REBCO magnet for whole-body MRI systems.