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首页> 外文期刊>Journal of Physics, D. Applied Physics: A Europhysics Journal >The emergence of the propagation wave vector in high field NMR: analysis and implications
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The emergence of the propagation wave vector in high field NMR: analysis and implications

机译：高场核磁共振中传播波矢量的出现：分析与启示

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摘要

At ultra high field strength (> 4 T), the RF-wavelength relative to the dimension of the human body leads to significant excitation field ( B-1) inhomogeneity arising out of wave propagation effects. The excitation field is thus spatio-temporal and in conjunction with the increase in tissue conductivity, wave propagation phenomena can no longer be ignored. We thus find the propagation of radiation at ultra high fields new phenomena commonly observed in quantum optics but traditionally negligible in NMR such as spatio-temporal phase modulation of the excitation field such that the identity between pulse area and flip angle is no longer valid. In this paper, the emergence of field propagation phenomena in NMR experiments is analytically and experimentally demonstrated. It is shown that in addition to the well-studied dielectric resonance phenomena at high magnetic fields, propagation effects transform the excitation pulse into an adiabatic excitation. The high field strength also means that nonlinear effects such as self-induced transparency, propagation phenomena such as transient four wave mixing, are now possible in NMR experiments. It is shown and experimentally demonstrated at 7 T that additional constraints due to phase matching considerations are imposed on the formation of echoes in high field NMR.
机译：在超高场强（> 4 T）下，相对于人体尺寸的RF波长会由于波传播效应而导致明显的激发场（B-1）不均匀性。因此，激发场是时空的，并且随着组织电导率的增加，波传播现象不再被忽略。因此，我们发现了辐射在超高场的传播，这种新现象通常在量子光学中观察到，但在NMR中传统上可以忽略不计，例如激发场的时空相位调制，使得脉冲面积和翻转角之间的标识不再有效。本文通过分析和实验证明了NMR实验中场传播现象的出现。结果表明，除了在高磁场下已充分研究的介电共振现象外，传播效应还将激发脉冲转换为绝热激发。高的场强还意味着，在NMR实验中，非线性效应（例如自感应透明性），传播现象（例如瞬态四波混合）现在已成为可能。结果表明，并在7 T处进行了实验证明，由于相位匹配的考虑，在高场NMR中回波的形成受到了其他限制。

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