Magnetic Resonance Imaging

Perturbing the Net Magnetization

The net magnetization can be perturbed by other magnetic fields.

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DC in coil of wire wrapped around the X axis...

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AC in coil of wire wrapped around the X axis...

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In rotaing frame...

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Pulsed Magnetic Fields

q = 2p g t B₁.

where:

q = rotation angle
g = gyromagnetic ratio
t = duration of RF field << T₁ and T₂
B₁ = RF magnetic field

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Rotion Examples

90^o rotation in rotating frame

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90^o rotation in lab frame

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A 180^o rotation

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Other examples ...

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The location of a magnetization vector after a B₁ pulse can be determined by the rotation matrix.

where:

[X', Y', Z] = initial location of the vector
[X", Y", Z"] = location after the rotation

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Copyright © 2000 J.P. Hornak.
All Rights Reserved.