Magic-echo

Hafner S, Demco D E and Kimmich R 1996 Magic echoes and NMR imaging of solids Solid State Nucl. Magn. Reson. 6 275-93... 

As increasing the time interval between the single-shot DNP operation and the aH NMR measurement, the intensity of the magic echo was found to decrease. Instead, the intensity of the 1H Hahn echo grew up, as demonstrated in Figure 19B-D). The fact that the inhomogeneous character in the aH spectra increased with time shows that the spin polarization had been transferred to the place where the H spins were dilute, that is surrounded by the 2H spins in the heavily deuterated host material. 

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. 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.)...

The basic symmetric magic-echo sandwich can be represented by... 

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.

In terms of instrumentation the less demanding approach is multi-pulse excitation for averaging of the homonuclear dipolar interaction by trains of repetitive magic echoes during space encoding and acquisition of the spectroscopic response. Two such magic-echo... 

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

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