3D sequence

Another approach to obtain spatially selective chemical shift information is, instead of obtaining the entire image, to select only the voxel of interest of the sample and record a spectrum. This method called Volume Selective spectroscopY (VOSY) is a ID NMR method and is accordingly fast compared with a 3D sequence such as the CSI method displayed in Figure 1.25(a). In Figure 1.25(b), a VOSY sequence based on a stimulated echo sequence is displayed, where three slice selective pulses excite coherences only inside the voxel of interest. The offset frequency of the slice selective pulse defines the location of the voxel. Along the receiver axis (rx) all echoes created by a stimulated echo sequence are displayed. The echoes V2, VI, L2 and L3 can be utilized, where such multiple echoes can be employed for signal accumulation. 

Syvitski et al43 reported a 3D sequence which uses TPPI to separate the spectra of different coherence orders. The pulse sequence employs a non-selective 2D excitation sequence (as in Fig. 2) but also systematically increments the phase of the first two pulses in the excitation sequence by A

) in the experiment is arbitrary but needs to be at least 2TV+ 1, where TV is the number of spins in the spin system. The 3D interferogram is then a function of t, Fourier transformation over these dimensions6,30,44 affords MQ spectra of various orders cleanly separated in the pseudo-frequency ... 

It is also a more subtle effect, which is why Goppert-Mayer (1941) had difficulty computing it by using the Thomas-Fermi model. Griffin et al. (1971) in their numerical study foimd that the mean radius of the 4s electron in the 3d sequence lies very close to the knee between the two wells. Thus adding a 4s electron has a profound effect on the 3d effective potential, which accoimts for the otherwise mysterious effect known as competition between the filling of the d and s subshells. 

NRL 3D Sequence-structure databases http //laguerre.psc.edu/general/soft- ware/packages/nrl 3d/... 

In heteronuclear correlation experiments, magnetization transfer between protons and heteronuclei can be via either heteronuclear single quantum coherence (HSQC) or heteronuclear multiple quantum coherence (HMQC) pathways. The HSQC sequence gives rise to narrower lines, but uses more pulses and requires a longer phase cycle than the HMQC. Thus, HSQC is used for 2D experiments where the highest resolution is required and HMQC is preferred for 3D sequences in which the experimental time is limited. 

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