Localized spectroscopy

In 1982 Hall and Sukumar118 demonstrated the ability to select species processing distinct chemical shifts in images, where the chemical shifts do not overlap, using capillaries of water, acetone, benzene and methylene chloride. Since then, volume-localized spectroscopy and chemical-shift imaging have been applied to a number of medical and non-medical problems. Most of these studies, however, are focused on the H and 31P nucleides, especially those investigations which are clinically oriented119,120. 

However, the theorem of reciprocity is a wave optical argument that does not consider intensities where we easily find the differences. For example, if one thinks of a STEM as an inverted HRTEM one would not detect any intensity in an image since it is an inherent property of a point detector to collect no intensity. On the other extreme side, the ability to form an intense and focused probe is a valuable ability that boosts local spectroscopy. Obviously, the best choice of tools cannot be a matter of exclusion but must relate to the problem at hand that needs solving . 

Fig. 16.10. Topograph and local spectroscopy of Si(lll) with oxygen. Left, the STM image of a region of the oxygen-exposed Si( 111 )-7 X 7 surface. Right, the local tunneling spectra at different sites. Spectra A, B, and C are those of unreacted restatom, corner atom, and center adatom, respectively. Spectra D, E, and F are obtained over oxygen-induced dark, bright, and perturbed (gray) adatom sites, respectively. (Reproduced from Avouris, Lyo, and Bozso, 1991, with permission.)...

Ramaprasad S, Newton JEO, Cardwell D, et al In vivo li NMR imaging and localized spectroscopy of rat brain. Magn Reson Med 25 308-318, 1992 Rampello L, Nicoletti G, Raffaele R Dopaminergic hypothesis for retarded depression a symptom profile for predicting therapeutic responses. Acta Psychiatr Scand 84 552-554, 1991... 

A. I. Schmid, M. Chmelik, J. Szendroedi, M. Krssak, A. Brehm, E. Moser and M. Roden, Quantitative ATP synthesis in human liver measured by localized spectroscopy using the magnetization transfer experiment. NMR Biomed., 2008, 21,437- 43. 

Charles HC, Lazeyras, AQ Krishnan KRR, et al. Brain choline in depression in vivo detection of potential pharmacodynamic effects of antidepressant therapy using hydrogen localized spectroscopy. Prog Neuropsychopharmacol Biol Psychiatry 1994 18 1121 -1127. 

The crystallization kinetics of bulk triglycerides and oil-in-water emulsions has been characterized by both NMR imaging and localized spectroscopy. The rate of lipid crystallization in an oil-in-water emulsion was affected by the addition of a second homopolymer (addition of trilaurin to trimyristin in this case). The addition of the second homopolymer of higher chain length was observed to slow the rate of crystallization [26]. 

Localized NMR spectroscopy, which is often called as MRS in comparison with MRI, is not so familiar technique in food science, because a specific pulse sequence such as ISIS and a facility which can precisely follow the pulse sequence without any contamination from other position is needed for localization of position. The localized NMR is usually used together with NMR imaging. The study of solid/liquid ratios, fat structure and polymorphism and the kinetics of fat crystallization was reviewed [24], The potential of applications in food process development and control was offered. The localized spectra of sausages in areas of 0.3 mm X 0.05 mm (thickness of sample =1.5 mm) were obtained by the spin echo 2DFT method [113], in which the difference in the tissue structure was discussed with relation to the process and original materials. McCarthy et al. determined mobility of water in foams by using a localized spectroscopy [114]. T2 relaxation time varies in the foam as function of diameter and its variation was analyzed by the classic 2-state fast exchange model. 

As with UV-visible spectroscopy in the bulk, such techniques do not yield chemical identification, so that combining other local spectroscopies with STM is typically necessary to identify the atoms and molecules present. Specialized approaches have been developed for this, such as STM photoemission spectroscopy (PESTM) and inelastic electron tunneling spectroscopy to yield vibrational and other information. This area is extremely promising for further work in combining any number of spectroscopies with the exquisite spatial resolution of STM. 

The development of NMR spectroscopy has been propelled not only by improved instrumentation but also by the introduction of new and powerful techniques. A detailed description of these techniques is beyond the scope of this chapter. However, we have selected a few techniques which have been, or are likely to be, the most important in the area of NMR studies of cellular metabolism. We exclude NMR imaging and localized spectroscopy techniques which are not directly relevant to studies on isolated cells. The reader is referred to chapter 14 by Huang in this book and detailed discussions elsewhere (Mansfield and Morris, 1982 Leach, 1988 Koretsky and Williams, 1992). 

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. 

Chapter 14 NMR Imaging and Spatially Localized Spectroscopy Relaxation Times... 

Komoroski, R., Newton, J. E., Cardwell, D., et al. (1994) In vivo 19F spin relaxation and localized spectroscopy of fluoxetine in human brain. Magnetic Resonance in Medicine, 31, 204-211. 

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