NMR Imaging in Solids

In vivo NMR spectra are often displayed in the normal fashion of signal versus frequency. However, an alternative method of displaying such chemical shift data is to select the frequency at the peak of a particular component and to show the 2D chemical shift image. Such a presentation is often useful in investigating the spatial variation in concentration of a particular substance. 

NMR imaging is increasingly used to study structures and processes in solid materials. In some instances, the material being imaged is a liquid that penetrates a solid substance—for example, water and oil in sandstone. Here the methods are similar to those that we have already described for imaging water in biological materials, with parameters adjusted according to the nature and size of the samples. 

Because NMR imaging constitutes a very broad area from human studies to animals, microscopy, and solids, there are many specialized books in the field. We mention two that include good discussions of many aspects of the techniques NMR in Physiology and Biomedicine edited by Robert Gillies134 and Principles of NMR Microscopy by Paul Callaghan.135 About 20% of the articles in the Encyclopedia of NMR relate to NMR imaging and to in vivo spectroscopy. All aspects of the technology, as well as many applications to biomedicine and to studies of solid materials, are included. 

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CONTINUOUS-WAVE NMR IMAGING IN THE SOLID STATE 117 number of harmonics of wm ... 

Many methods for improvements of the spatial resolution in NMR imaging of solid materials have been proposed with different impact on applications in polymer science [8, 9, 11-13, 21]. For the great variety of techniques only those are reviewed in Sections 5.1.3 and 5.1.4 below, which are being applied successfully to problems in polymer science. Depending on the dominating features, the techniques can be classified into frequency and phase encoding approaches. 

Ramanathan and Ackerman (1999) have shown that solid-state 31P NMR imaging can be used to measure quantitatively the mass of hydroxyapatite in the presence of bone hence to follow non-invasively the resorption and remodeling of calcium phosphate implants in vivo. A three-dimensional projection reconstruction technique has been used to record NMR images in the presence of a fixed amplitude field gradient, the direction of which was varied uniformly over the unit sphere. Chemical selection was achieved using differences in T1 relaxation time of neighbouring protons as the synthetic hydroxyapatite has a shorter T1 (1.8 s at 4.7 T) compared to bone (approximately 15 s at 4.7 T in vivo, 42 s ex vivo). The experimental results demonstrated that a linear relationship exists between image intensity and HAp density. 

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