Pulsed field gradient

A Pulsed field gradient is a short, timed pulse with spatial dependent field intensity. Any gradient is identified by four characteristics: axis, strength, shape and duration.

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Pulsed field gradient (PFG) techniques are key to magnetic resonance imaging, spatially selective spectroscopy and studies of diffusion via NMR. PFG techniques are widely used as an alternative to phase cycling in modern NMR spectroscopy.

Common field gradients in NMR

The effect of a linear z-gradient on spin I, is considered to be a rotation around z-axis by an angle = γ_IGz; where G is the gradient strength and γ_I is the gyromagnetic ratio of spin I. It introduces a phase factor to the magnetizations:

Φ (z,τ) = γ_IzGτ

The time duration is usually 100s of µs or a few ms.

See also

• Gradient enhanced NMR spectroscopy