自旋回讯

自旋回波，是磁共振现象中的一种信号来源，相对于第一个射频脉冲（RF pulse）激发后立刻出现的自由感应衰减（FID），自旋回讯是透过第二个射频脉冲之后，将失相的磁化矢量重新聚焦（refocus）而长回来的信号。「自旋回讯」是项历史名词，若从意义上来看，称之为射频回讯（RF echo）可能更为贴切，以其为射频聚焦造成的回讯，相对于利用梯度反转达成聚焦的梯度回讯（gradient echo）。

词汇	Spin echo
分类	英语词汇英语翻译词典
释义	Spin echo 中文百科自旋回讯自旋回波，是磁共振现象中的一种信号来源，相对于第一个射频脉冲（RF pulse）激发后立刻出现的自由感应衰减（FID），自旋回讯是透过第二个射频脉冲之后，将失相的磁化矢量重新聚焦（refocus）而长回来的信号。「自旋回讯」是项历史名词，若从意义上来看，称之为射频回讯（RF echo）可能更为贴切，以其为射频聚焦造成的回讯，相对于利用梯度反转达成聚焦的梯度回讯（gradient echo）。英语百科 Spin echo 自旋回讯 In magnetic resonance, a spin echo is the refocusing of spin magnetisation by a pulse of resonant electromagnetic radiation. Modern nuclear magnetic resonance (NMR) and magnetic resonance imaging make use of this effect. The NMR signal observed following an initial excitation pulse decays with time due to both spin relaxation and any inhomogeneous effects which cause different spins in the sample to precess at different rates. The first of these, relaxation, leads to an irreversible loss of magnetisation. However, the inhomogeneous dephasing can be removed by applying a 180° inversion pulse that inverts the magnetisation vectors. Examples of inhomogeneous effects include a magnetic field gradient and a distribution of chemical shifts. If the inversion pulse is applied after a period t of dephasing, the inhomogeneous evolution will rephase to form an echo at time 2t. In simple cases, the intensity of the echo relative to the initial signal is given by e where T₂ is the time constant for spin-spin relaxation.
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Spin echo

自旋回讯

Spin echo 自旋回讯