MEDRADSC 1C03 Lecture 12: MRI
1 Dec 2016
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Document Summary
Consider proton spinning- property called angular momentum (given by h1/2) Angular momentum leads to magnetic dipole moment. Y is called the gyromagnetic ratio and for a proton: e/2m. Protons in our body don"t experience an external magnetic field providing we ignore the earth"s very weak magnetic field. Dipole moments with each proton are randomly orientated. However, if subjected to an external magnetic field of strength b0, then the dipoles acting like magnets will try to align themselves with the field direction. One state has a higher energy state than the other. A small majority go into the lower of the two energy states. The opposite dipoles cancel each other out. Lower energy states are slightly more populated than the higher energy spin states. The lower energy states are precessing about their field or in the z direction. The higher energy states are precessing around the negative z direction.
