Abstract
There is a great variety of spin-coherence evolution experiments in the rotating frame which are quite analogous to laboratory-frame experiments. The far-reaching equivalence of experiments conducted in the laboratory and in the rotating frame has its origin in the fact that the equations of motion in both reference frames are formally identical (see Chap. 48.7). The basic phenomenon behind Hahn echoes is “Larmor precession” about the external magnetic field. The rotating-frame equivalent is “nutation” about the effective field. The first rotating-frame experiment which we draw attention to is the generation of rotary echoes [463].
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Notes
If the laboratory-frame coherences contributing to transverse magnetization are entirely spoiled by transverse relaxation or B0 inhomogeneities, the second RF pulse acts solely on the magnetization left over in the z direction. This appears analogous to the stimulated-echo experiment Fig. 2.2 where the third RF pulse under equivalent field or relaxation conditions merely affects the longitudinal magnetization. The rotary echo produced in this way may therefore be termed “stimulated rotary echo” [131].
Note that 〈ρ(r, 0+)〉 ≈ 0 because of the strong dependence of α on r. That is, no FID signal appears after the first pulse.
Note that the difference of the phase angles is not necessarily subject to an equipartition, especially if the evolution times approach each other.
Note that the mean trigonometric functions of the difference of the flip angles, 〈sin(α—β)〉r and 〈cos(α — β)〉 r, do not vanish if the argument is small enough to prevent equipartition of the argument.
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© 1997 Springer-Verlag Berlin Heidelberg
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Kimmich, R. (1997). Rotary Echoes. In: NMR. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-60582-6_3
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DOI: https://doi.org/10.1007/978-3-642-60582-6_3
Publisher Name: Springer, Berlin, Heidelberg
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