Review on high temperature superconducting magnet technology for its development for ultra-high-field MRI

Abstract MR researchers pursue higher and higher B0 field for new discoveries in medical sciences. High temperature superconducting (HTS) magnet has the potential advantages of compactness, cryogen-free operation and ultra-high field (UHF) performance for being applied as the key component in the UHF-MRI system. Intensive researches on the HTS magnets are being conducted in recent years. This review reports the up-to-date HTS magnet techniques and their problems and solutions for the potential application in the UHF-MRI magnet. Two commercial HTS tapes of Bi2223 and REBCO are discussed with their application cases in MRI/NMR magnets and other UHF magnets. The technical problems, especially for the REBCO magnet with the screening current effect, small radial tensile strength, tape uncertainty, etc. are introduced with the potential solutions. No-insulation technique with quench transient behaviour is also introduced. Since there is not an UHF-MRI magnet by HTS in the world by the time of formulating this review, the achievements of some other large-scale UHF-magnet projects by HTS are investigated. Sequential engineering phases with two prototype magnets are thus proposed for developing the UHF-MRI magnet by HTS. The detailed development cost is estimated with a decent price range. Besides, for the development of a first-in-kind UHF-MRI system by HTS magnet, the insight is provided that the UHF-magnet development is a make-or-break component and due a primary and independent project from the entire UHF-MRI system project. . 
Apart from the introduction and the conclusion, this review paper is organized with 8 other sections. The beginning of each section/sub-section is more geared at the UHF-MR researchers with introduction to the basic magnet knowledge, and the remaining and major part is presented with more professional review for the UHF-magnet researchers.