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MRI
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by Cless Alvein
on 2006-04-04 17:38:03
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I'm not hoping for much, but maybe someone will post a Wikipedia article that can answer this question? (The main one doesn't really explain it) When a magnetic field B0 is applied to a protonated sample, the protons start precessing with a net magnetic moment pointing in the direction of the z-axis. When an 90-degree rf field B1 is applied, the protons start precessing in phase, and the net magnetic moment pointing in the direction of the z-axis is lost. Instead, we have, over time, a gyrating net magnetic moment that will eventually become circular and entirely in the xy plane. Is this due to the protons' individual "flattening" of their magnetic moments into the xy plane or do they keep their current orientations, with some force cancelling out the net magnetic moment in the z-axis? Here is a flash animation to better show what I mean: http://www.physics.utoronto.ca/%7Ekey/PHY138/Flash/MRI%20-%20the%20Movie.swf |