NMR Micro-imaging

NMR micro-imaging is a powerful tool for examining the chemical composition of samples in a non-invasive way. It is one of the techniques available with the Varian UNITY spectrometer system. This is a high-performance research tool that is completely modular and fully integrated. UNITY NMR spectrometers enable spectroscopists to switch easily from micro-imaging liquids to solids and back, depending on the scope of their work. 

The use of horizontal back imaging has extended this technique to small samples at high magnetic field strength. Because the field of micro-imaging is evolving so rapidly, Varian built modularity into its UNITY NMR spectrometers, giving the spectroscopist the ability to add new experimental capabilities as they are introduced. 

Uses of this technique include the examination of microscopic changes of the physical state of polymeric materials, the distribution and binding of water in polymers, diffusion experiments of liquids in polymers, structural integrity investigations, and material homogeneity, porosity, and pore size. 

Gussoni and co-workers [2] used proton NMR imaging techniques to characterise a silicone rubber. The effect of the polymerisation on the silicone properties and of the dispersion of a guest polymer inside the host matrix was investigated. Any source of inhomogeneities such as air bubbles or defects was localised and measured. The occurrence of an in situ polymerisation reaction was proved by IR spectroscopy. 

---

Bertram, H.C., Whittaker, A.K., Shorthose, W.R., Andersen, H.J., and Kalsson, A.H. 2004. Water characteristics in cooked beef as influenced by ageing and high-pressure treatment—an NMR micro imaging study. Meat Sci. 66, 301-306. 

Pope J.M., Yao S., and Fane A.G., Quantitative measurements of the concentration polarization layer thickness in membrane filtration of oil-water emulsions using NMR micro-imaging. Journal of Membrane Science 118 1996 247-257. 

Olt et al. introduced Na NMR micro imaging to map the sodium distribution in living plants. The experiments were performed at 11.71 T with a double resonant Na- H probe-head. The Na micro imaging promises great potential for physiological studies of the consequences of salt stress on the macroscopic level and thus may become a unique tool for characterizing plants with respect to salt tolerance and salt sensitivity. 

HUls, B. P., NMR Micro-imaging studies of water diffusivity in saturated microporous systems. In Eood Colloids and Polymers Stability and Mechanical Properties, Dickenson, E. and Walstra, P., Eds., The Royal Society of Chemistry, Cambridge, U.K., pp. 235-242, 1993. 

Impurity inclusions and surface defects are a cause of many difficulties to the polymer producer and user. Equipment used for studying these phenomena discussed in Chapter 4 include electron microprobe x-ray emission/spectroscopy, NMR micro-imaging, various forms of surface infrared spectroscopy, e.g., diffusion reflection FTIR, ATR, also photoacoustic spectroscopy and x-ray diffraction - infrared microscopy of individual polymer fibres. Newer techniques such as scanning electron microscopy (SECM), transmission electron microscopy, time of flight secondary ion mass spectrometry (TOFSIMS), laser induced photoelectron ionisation with laser desorption, atomic force microscopy and microthermal analysis are discussed. 

Figure 8. Wetting and diffusion of LMGS (MCH and TBME) between ice particles at atmospheric condition observed by i I micro-imaging NMR. (Reprinted from J. Phys. Chem. B (Susilo et al., 2006), Copy right (2006) with permission from American Chemical Society).

Figure 5 Distribution ofLMGSs and diffusion of LMGS (MCH and TBME) between ice particles at atmospheric condition obset ved by H micro-imaging NMR...

Plate 38 a and b Black and white colourscale diffusion weighted spin echo magnetic resonance images of postmortem human cervical spinal cord using a micro-imaging probe at 600 MHz observation frequency. See NMR Microscopy. Reproduced with permission from Doty Scientific Inc. 

For a manufacturer the difficulty is to estimate future developments or trends in NMR microscopy. Based on dedicated laboratory-made hardware developed by the NMR microscopy users and on their requests for new commercial hardware and software, the following topics could become more important micro-coil applications, multiple receiver systems and multi-coil arrangements, NMR microscopy at very high magnetic fields, MAS imaging and localized 1H MAS spectroscopy and localized single-shot 2D spectroscopy. There are no clear-cut distinctions between most of the individual topics, as will be discussed in the following sections. 

---