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While NMR is of immense use in identifying structure, it has perhaps found more important day-to-day application in the field of medical imaging. You might be aware that modern medicine makes use of "magnetic resonance imaging" or MRI to generate detailed cutaway views of the inside of a patient's body. It's a particularly useful tool for imaging soft tissues, where X-ray scans are of more limited use. The technique does not intrinsically rely on chemical shift per se (other than selecting the right nucleus). And of the likely candidate nuclei (1H, 13C, 31P, 19F, 15N, 17O), only protons are abundant enough to be of much use, and most of those are in the water that composes >70% of our body. However, as it turns out, the NMR characteristics of that waster vary based on where the water is. The environment affects "relaxation time" of the hydrogen nucleus, and essentially, different relaxation times can be detected. See the Wikipedia page for details. |
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| One of the chemical strategies involved in MRI is to use a contrast agent. These are typically paramagnetic complexes of rare earth elements, such as the gadoliunium complex shown to the left. The paramagnetism usually causes the relaxation time of surrounding nuclei to drop dramatically, thus changing the NMR behavior. These comtrast agents are effective because they build up concentration in the blood before they get absorbed into specific tissues, allowing the operators to screen out the signal from water in blood versus that in tissue. And these things can be designed to selectively absorb to specific kinds of tissues. | |
| An exciting new technique is called "Functional MRI" or fMRI. This looks at the time dependence of the MRI image as a function of physiological change. Researchers are currently exploring neurochemistry with this in a variety of ways, the most exciting is testing whether we can associate specific thought patterns with fMRI images of the brain. See Wikipedia for a start into this field. | |