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Profiles of paint layer samples obtained in the fringe field of a high field magnet by means of very short broadband frequency modulated pulses
Magnetic Resonance in Chemistry ( IF 1.9 ) Pub Date : 2020-07-20 , DOI: 10.1002/mrc.5038
Pierre Taugeron 1 , Sullivan Bricaud 1 , Cindie Kehlet 2 , Jens Dittmer 1
Affiliation  

In this article we describe the acquisition of depth profiles, in particular of paint layers, in the static gradient of a high field magnet, providing a superior sensitivity. The main objective are reference profiles that help to understand scans made with non-invasive unilateral NMR, which often suffers from poor signal-to-noise ratio when working with real samples. Various technical aspects like the coil geometry and the limit of resolution are investigated. A major advancement is the use of frequency modulated pulses that are very broadband and at the same time very short (25 μs). The latter is necessary to allow the acquisition of a CPMG echo train of old, rigid paint material. Despite being far from adiabatic, they provide uniform excitation and refocusing over 1 MHz, which corresponds to about 400 μm with the used gradient. We show that the uniformity is even sufficient to obtain biexponential relaxation profiles. With these tools a paint sample from a restoration campaign is analyzed with different contrast criteria: the original and two layers from former restoration attempts can be visualized, and furthermore the relaxation profiles allow to study the migration of plasticizing molecules.

中文翻译:

通过非常短的宽带频率调制脉冲在高场磁体的边缘场中获得的涂料层样品的轮廓

在本文中,我们描述了在高磁场磁铁的静态梯度中获取深度剖面,特别是油漆层,提供了卓越的灵敏度。主要目标是参考轮廓,有助于理解使用非侵入性单边 NMR 进行的扫描,在处理真实样本时,这种扫描通常会受到较差的信噪比的影响。研究了线圈几何形状和分辨率限制等各种技术方面。一个主要的进步是使用非常宽带同时非常短 (25 μs) 的调频脉冲。后者对于获取旧的刚性涂料材料的 CPMG 回波序列是必要的。尽管远非绝热,但它们提供了超过 1 MHz 的均匀激发和重新聚焦,这对应于使用梯度的约 400 μm。我们表明均匀性甚至足以获得双指数弛豫曲线。使用这些工具,可以使用不同的对比标准分析修复活动中的油漆样品:可以显示原始层和之前修复尝试的两层,此外,松弛曲线还可以研究增塑分子的迁移。
更新日期:2020-07-20
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