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Beginner MRI Training Tutorials

Alignment in Magnetic Fields

Zero Net Magnetization

Although each spin creates a tiny magnetic field on a microscopic view, the net magnetization or macroscopic magnetization is usually zero because all the individual spins are oriented randomly and cancel each other's fields. An example of this can be shown in the picture of the un-aligned spins below.

Un-aligned spins

Alignment in a large external magnetic field

When particles are placed in a large external magnetic field (B) their spins will align with the magnetic field. Most of the spins will align with the magnetic field (parallel), as that is the lower-energy option. However, a few will align against the external field (anti-parallel) if they are at a higher energy. When large groups of spins have aligned, either parallel or anti-parallel, a net magnetization is present.

Aligned spins

Further Reading

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