AC Loss Measurement in Nb3Sn Coil for a New Fast Switching-Field MR Concept Magnet

The ability to perform magnetic resonance (MR) imaging or spectroscopy at significantly different magnetic field strengths during scanning holds great potential for expanding the range of contrast parameter options and obtaining high “superthermal” spin polarization for increased signal-to-noise ratio (SNR) or measuring certain spins at what would otherwise be impractically highRFfrequencies. Enablingmeasurements at multiple field strengths heretofore has required either rapidly altering the strength of a resistive magnet with pulsed currents or shuttling the specimen between two field regions. We propose a novel approach to switching-fieldMR that we expect to be practical for live animal and ultimately human imaging. In this paper we propose the design of a liquid-helium-free fast switching-field MR magnet that can change the field very quickly in time (≤1 s) between significantly different field strengths. For this magnet, two types of Nb3Sn wire are selected, and AC loss is measured by electrical method, and characteristics are analyzed.

在扫描过程中，能够在显著不同的磁场强度下开展磁共振（Magnetic Resonance, MR）成像或波谱学研究，对拓展对比参数可选范围、获取高“超热”自旋极化以提升信噪比（Signal-to-Noise Ratio, SNR），或是在原本难以企及的高射频频段下测量特定自旋，均具有重大应用前景。此前，要实现多场强下的测量，要么需通过脉冲电流快速调节阻性磁体的场强，要么需将样品在两个磁场区域间往复转运。我们提出了一种全新的切换场磁共振（Switching-Field MR）方案，预期可应用于活体动物成像，并最终推广至人类成像领域。本文中，我们设计了一款无液氦快速切换场磁共振磁体，其可在显著不同的场强之间以≤1秒的极快速度完成磁场切换。针对该磁体，我们选用了两种类型的铌三锡（Nb3Sn）导线，并通过电学方法测量了其交流损耗，同时对相关特性展开了分析。