Gradient localized spectroscopy

Often the information on NMR relaxation parameters carried by image contrast is insufficient to address a particular problem. We can then look to the rich information content of the spectrum itself. Generally, spectroscopy of the entire body is not of much value, and in vivo spectroscopy is usually carried out as localized spectroscopy, that is, over a part of the body. There are various ways of restricting the operation of the spectrometer to a particular region, and they fall into two broad classes those that depend on the physical dimensions of the rf coil and those that use field gradients in the pulse sequences. Often these approaches are combined. At this time, the use of spectroscopic examinations has not become part of the repertoire of clinical practice, despite a history of in vivo spectroscopy almost as old as MRI itself. In vivo spectroscopy has had a number of landmark successes in solving problems in metabolism research in both animals and humans, but there have been no spectroscopic applications that have been demonstrated to be more effective than other methods for the routine diagnosis of disease. 

Another productive area would be in situ imaging and/or spatially localized spectroscopy of model How reactors. Pulsed-field gradient measurements could conceivably be used to characterize diffusion and pore blockage due to coking while the reaction is in progress. Xe might be similarly useful. This technique has already been used to probe adsorbate distributions in catalyst beds 1108]. 

Pulsed magnetic field gradients are essential for MR imaging and localized spectroscopy applications. However, besides the desired linear field... 

Conventionally, all imaging procedures acquire data in the presence of a gradient, depending on Equation [5]. In spatially localized spectroscopy, data are frequently measured in the absence of any gradient field and this approach could also, in theory, be useful in microscopy experiments, though in this case to minimize the impact of diffusion. 

Spatially localized NMR spectroscopy was performed using a sample composed of a monoolein-D20 dispersion forming a cubic liquid-crystalline phase [41]. The spectra were selected from a slice of 300-pm thickness. The direction of the gradient was along the spinning axis. A spectral resolution was obtained that had never been observed before when selecting the whole volume of the sample. 

Fig. 5.5.8 The volume selective spectroscopy rf pulse sequence used to acquire the data shown in Figures 5.5.9-5.5.11. Magnetic field gradients applied alongthex, y and zdirections enable localized spectra to be recorded from...

Fig. 9 A volume-selective spectroscopy r.f. pulse sequence. Magnetic field gradients applied along x-, y-, and z-directions enable recording of localized spectra from pre-defined local volume elements within the sample.

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