Double pulsed field gradient spin-echo

OPPOSE double pulsed field gradient spin echo... 

The double pulsed field gradient spin echo (DPFGSE) pulse sequence has been used to improve the measurement of proton-proton nuclear Overhauser effect (NOE) [28]. The DPFGSE NOE does not rely on difference spectroscopy and very small NOEs can be measured. This technique has been used to determine the structure of organosilicon compounds [28]. 

Figure 6-41 The double pulse field gradient spin echo (DPFGSE) NOE experiment with llp-hydroxyproges-terone (a) the unirradiated spectrum (b)-(g) spectra with irradiation at selected frequencies. (Reproduced with permission from K. Stott,...

Figure 7-5 The double pulsed field gradient spin echo-NOE pulse sequence. The relative strengths of gradients Gi, G2, and Gm are 16,7, and 13 G cm, respectively. The mixing time is 650 ms.

The most robust experiment to date [34] (Fig. 8.39b) is based upon the double pulsed field gradient spin-echo (DPFGSE) sequence as a means of selecting a target resonance from which the NOEs ultimately develop. This... 

Figure 9.18. Selective excitation sequences based on (a) a single and (b) a double pulsed field gradient spin-echo. The element S represents any selective 180° inversion pulse or pulse sequence.

Figure 9.19. Clean selective excitation with the double pulsed field gradient spin-echo sequence using a 40 ms Gaussian 180° pulse and gradients of 0.07 0.07 0.03 0.03 Tm- .

Figure 9. Experimental excitation profiles for the double pulsed field gradient spin-echo excitation sequences in which the element S is a 180° Gaussian pulse (truncated at 1%) of the duration shown.

OPPOSE Double pulsed field gradient spin-echo (selective excitation) 9.3.3... 

The mathematical results of the double pulsed field gradient spin echoes can also be formulated as a set of rules [2.54] ... 

It can be concluded [2.53] A double pulsed field gradient spin echo of any pulse sequence S returns any transverse magnetization to its original position, attenuated by the square of the probability that a spin is flipped by the sequence S. 

DPFGSE Double Pulsed Field Gradient Spin Echo... 

The traditional nuclear Overhauser difference spectroscopy can be replaced by DPFGSE-NOE (Double Pulsed Field Gradient Spin Echo method-NOE spectrometry) experiment. The desired NOE effects can be recorded without interference from other signals and without phase distortion [66]. 

Fig. 8.33 Pulse sequence schematic for the gradient ID NOESY experiment. The double pulsed field gradient spin echo (DPFGSE) refocuses only for that resonance subject to the selective pulse. All other magnetization is left defocused in the xy-plane. Ultimately, a NOESY spectrum is recorded only for the selected re-...

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