Abstract
We have seen that variations in the external field B contribute to dephasing of the dipoles. These extrinsic variations are constant in time and space and can therefore be neutralized. All we have to do is reverse the direction of spin precession, without affecting the precession rate. This is accomplished with an RF pulse of 180°, called the refocusing pulse. After the activation of such a pulse all spins are instantaneously shifted into mirror-image positions with respect to the z-axis (Fig. 20).
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© 2009 Springer-Verlag Berlin Heidelberg
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(2009). Spin Echo. In: Clinical MR Imaging and Physics. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-78023-6_13
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DOI: https://doi.org/10.1007/978-3-540-78023-6_13
Publisher Name: Springer, Berlin, Heidelberg
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