Pulsed field gradient
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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.
Pulsed field gradient (PFG) techniques are used in multiple quantum filtering and diffusion experiments as well as in magnetic resonance imaging and spatially selective spectroscopy. In NMR spectroscopy, PFG can act as an alternative to phase cycling.
[edit] 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 = γIGz; where G is the gradient strength and γI is the gyromagnetic ratio of spin I. It introduces a phase factor to the magnetizations:
Φ (z,τ) = γIzGτ
The time duration is usually 100s of µs or a few ms.
