Multi-quantum filtering

Depending on the strength of the dipole-dipole interaction, the multi-quantum filtered signals are generated with different intensity (Figure 7.9d). Strongly coupled protons are... 

The selectivity of multi-quantum filters is demonstrated in Fig. 7.2.28 by spectra recorded for poly(isoprene) (PI) with the multi-quantum filter from Fig. 7.2.26(d) [Schl 1, Schl2, Schl3]. The conventional single-quantum H NMR spectrum of PI shows a broad line with little to no chemical-shift resolution. But the double- and triple-quantum filtered spectrum of the material exhibit peaks at different chemical shifts which can be assigned primarily to the signals from CH2 and CH3 groups, respectively. At longer... 

Fio. 7,2.30 [Sch 13 Multi-quantum filtered images of a phantom made from Pt samples with different cross-link densities. The cross-link density varies from left to right according to medium, high and low. The top image is a conventional spin-echo image for reference. 

Fig. 7.2.31 Filters for homonuclear coherent magnetization transfer. All filters start from and end with longitudinal magnetization, (a) Selective excitation and reconversion of coherences with a nonselective mixing period, (b) Realization of a nonselective mixing period in a z filter via longitudinal magnetization, (c) Nonselective excitation and reconversion of coherences with a selective mixing period, (d) Realization of a selective mixing period by a multi-quantum filter, (e) Selective exchange of transverse magnetization within the multiplets of coupled homonuclear spin pairs by a homonuclear version of the INEPT method.

The use of multi-quantum imaging inherently includes a multi-quantum contrast filter in the sequence. Such multi-quantum filters (cf. Section 7.2.10) can also be combined with single-quantum space encoding techniques. They are used to discriminate coupled spins i from uncoupled spins in liquids and signals from ordered materials from those of disordered materials. 

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