Constant field gradients

Hence, a series of measurements with several Tcp values will provide a data set with variable decays due to both diffusion and relaxation. Numerical inversion can be applied to such data set to obtain the diffusion-relaxation correlation spectrum [44— 46]. However, this type of experiment is different from the 2D experiments, such as T,-T2. For example, the diffusion and relaxation effects are mixed and not separated as in the PFG-CPMG experiment Eq. (2.7.6). Furthermore, as the diffusion decay of CPMG is not a single exponential in a constant field gradient [41, 42], the above kernel is only an approximation. It is possible that the diffusion resolution may be compromised. 

Fig. 8.1.1 [Mal3] Principle of STRAFl imaging. The STRAFl plane is defined by a region of constant field gradient in the fringe field outside the magnet. The plane can be shifted through the sample by energizing sweep coils, or the sample is moved through the STRAFl plane for pointwise acquisition of projections.

The acquisition of projections in constant field gradients is the principle of the back-projection method [4]. Here, the spatial resolution is limited by the signal decay in a homogeneous field. But, for liquid samples, the final limit... 

With commercial samples, the range of measurement may be considerably enhanced by applying a large constant field gradient in addition to the pulsed field gradients. It has been shown (ID that in this case by the nmr tracer desorption technique a time constant t is... 

Under the influence of a constant field gradient go in addition to the pulsed ones, the spin echo attenuation in the PFG NMR experiments is given by the relation... 

Bq = magnetic flux density D = dipolar coupling constant D = effective dipolar coupling constant h = Planck s constant I = spin- nucleus / = coupling constant = field gradient tensor Q = nuclear quadrupole moment s = doublet splitting ... 

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