From Ohm

Measuring Spins Not Density

As opposed to regular computer tomography, where the scanned object remains passive, the MRI (Magnetic Resonance Imaging) technique activates the object in a sense that an external strong magnetic field aligns the spin of hydrogene atoms.

Principle of MRI: When the magnetically aligned spins of hydrogene atoms are misaligned by another electromagnetic field, the response of each atom during its swing back can be measured.

Thus, MRI does not measure a density function, it measures the various spins of hydrogene atoms in the examined object.

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Page last modified on October 14, 2013, at 08:29 AM