Double-quantum imaging

Figure 7.11 Double-quantum images of a strained rubber band with a cut (a) image, (b) 2H image of deuterated spy molecules incorporated into the rubber network by swelling, (c) finite element simulation of the stress distribution...

Fig. 8.4.4 [KM i double-quantum imaging of deuterated spy molecules in strained rubber bands with a cut on each side, (a) Pulse sequence. A 180 pulse in the preparation period refocusses the chemical shift and off-resonance interactions, (b) Spin-echo image, (c) Hi double-quantum image. The contrast is determined by the doubic-qiianium coherence uiiipliludc weighted by the spin density.

Double-quantum imaging of static strain distributions... 

Fig. 10.2.3 Stress images of rubber bunds wiih a cut after correction tor spin density and relaxation effects, (a) H douhle-quantum (iltcrcd image ol poly(isopicnc) Sch6). (b) H double-quantum image at zi = I..1 of deulerated butadiene oligomers incorporated into a rubber band by swelling, (c) l-FM calculation of stress in a sample similar to (h) lKli2. ...

The fact that multiple quantum coherences can only be measured indirectly by their influence on the amplitude and phase of a subsequently acquired single quantum signal makes this technique a phase-encoding method. The necessity to acquire the spatial information in time-consuming extra dimensions is a penalty in all phase-encoding techniques. However, in the case of double quantum imaging of quadrupolar nuclei like, e.g., H, the wideline information of the single quantum spectrum can be utilized for contrast, because the quadrupolar interaction usually dominates all other spectral features and is a sensitive probe for molecular dynamics and orientations [80-83]. 

Efficient suppression of water signals is a side benefit of heteronuclear coherence transfer schemes. The heteronuclear multi-quantum coherence (HMQC) method (Fig. 7.3.4(b)) is a broad-band version of the HYCAT experiment of proton detected C imaging (cf. Fig. 7.2.30(a)) [Knii4]. The initial 90° pulse on is used for slice selection. For a heteronuclear AX system, single-quantum proton magnetization is transferred into heteronuclear zero- and double-quantum magnetization by a 90° C pulse after... 

Because H linewidths in many elastomers are of the order of 3 kHz or less, spin-echo and gradient-echo imaging techniques can be applied. Contrast is introduced by suitable filters like Ti and double-quantum filters or by use of the spectroscopic dimension. Parameter images of T2, the double-quantum signal intensity, or the quadrupolar coupling strength are evaluated and rescaled according to theory or experimental calibration data (cf. Section 7.1.6). 

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