Speaker
Description
We have been developed the compact NMR magnets consisted of the stacked high temperature superconducting (HTS) bulks trapped by a field cooling (FC) method. The HTS bulk annuli magnet for compact NMR relaxometry operating in liquid nitrogen was analytically designed and experimentally demonstrated. On the other hand, the high-quality magnetic resonance imaging (MRI) techniques can provide precise anatomical details of small extremities such as hands and feet. The low temperature superconducting (LTS) magnets cooled by liquid helium are used as conventional MRI systems and these MRI systems occupy a large amount of space. Therefore, we have been developing a compact and high-performance desktop finger MRI system using HTS bulks. The proposed HTS magnet is cooled by cryocooler and will be operated from 20 K to 40 K. The target values for magnetic field strength and field homogeneity in a cylindrical measurement space 20 mm in diameter and 10 mm in height without other magnetic field compensation methods are 3 T and 100ppm/cm2, respectively. Therefore, in this study, the structure and field properties of the HTS bulk magnets were designed and analytically calculated by the 3-D FEM. A face-to-face type HTS bulk magnet was proposed as the basic structure for the compact MRI magnet due to the limitation of the HTS bulk size. The minimum distance between the HTS bulks was set to 70 mm, and the shape of the HTS bulks and the characteristics of the critical current density were used as parameters. It was possible to improve the magnetic field homogeneity of the proposed HTS bulk magnet by assembling several bulks having different critical current densities. The designed structure of HTS bulk magnet for compact MRI and its calculated field performances will be presented.