Magic echo sequence

Fig. 24. Top Magic-echo sequence, TREV-16TS, for solid-state imaging with (a) ideally pulsed (b) nonideally pulsed and (c) sinusoidal field gradients. On-resonance RF irradiations along x and — x are sandwiched by 90° pulses (magic sandwich). The hatched magic sandwich consists of four magic sandwiches. Bottom Projections of the one-dimensional test sample (admantane powder) obtained with the TREV-16TS sequence (r = 30 ps) and the field gradients shown in Fig. 18. The RF field was set at 100 kHz. (Adapted from Matsui et al.296 with permission.)...

In order to preserve the effect of the gradients on the evolution of magnetization in a time-suspension sequence, the gradient pulses must be applied with alternating polarity in successive free-evolution windows of the magic-echo sequence. In this case, the evolution of the density operator can be expressed similar to (8.8.2),... 

The cw-NMR is orthodox and sufficiently reliable if the signal-to-noise ratio of the spectrum is high enough to estimate its baseline precisely. In the pulse NMR case, on the other hand, since the short-time behaviour immediately after the intense radio-frequency (rf) pulse irradiation is important, as expected from (6.2), recovery time or dead time of the experimental equipment after the pulse, causes a serious limitation of reliability for the estimated moments. To overcome this weak point the improvements in technique, the magic echo sequence [26-29] and in analysis, the functional forms of fitting [30-32] were applied to recover the FID signal at r = 0. Details are described in [2]. 

Unified spin echo and magic echo USEME Spin-echo and magic-echo sequences are applied to recover the dipolar interaction (Fujiwara T, Ramamoorthy A, Nagayama K, Flioka K and Fujito T (1993) Dipolar HOFIAHA under MAS conditions for solid-state NMR. Chemical Physics Letters 212 81-84). 

It has been pointed in many investigations [43, 64, 65, 68] that off-resonance sequences like LG- and FSLG-CP are very sensitive to the choice of the H carrier frequency. Therefore, it may be difficult to obtain accurate dipolar couplings for multiple sites in the molecule due to the H chemical shift dispersion. To remedy this problem, combining CP with an on-resonance magic-echo sequence in H... 

Mastui et al.29S proposed a new version of the magic echo (ME) sequence, called tetrahedral magic echo (TME), which uses the so-called tetrahedral angle 0=109.5° instead of 90° in the ME or modified ME (MME). This is substantially superior to ME or MME line narrowing for solids where heteronuclear dipolar interaction between protons and the other nuclear species is comparable to the homonuclear proton-proton interaction. 

Fig. 3.4.3 Pulse sequence for generation of the magic echo. The magnetization dephases for a time 2r by free precession before and after refocussing by the magic sandwich of length At.

Fig. 7.3.2 Magic-echo pulse sequences for spectroscopic imaging and imaging of moments.

Multi-pulse sequences based on magic echoes... 

Multi-pulse sequences for line narrowing based on magic echoes represent another possibility to realize time-suspension. Such sequences are less difficult to implement than pulse sequences based on solid echoes and consequently, appear to be more popular for use in imaging. Therefore, they are treated separately in Section 8.8. 

For spectroscopic imaging with magic echoes the space encoding sequence can be appended by an MREV8 sequence for frequency encoding of the spectrum in the absence... 

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