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 key to
magnetic resonance imaging,
spatially selective spectroscopy and studies of
diffusion
Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemica ...
via diffusion ordered
nuclear magnetic resonance spectroscopy
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique to observe local magnetic fields around atomic nuclei. The sample is placed in a magnetic fie ...
(DOSY).
[ ] PFG techniques are widely used as an alternative to phase cycling in modern NMR spectroscopy.
Common field gradients in NMR
The effect of a uniform magnetic field gradient in the z-direction on spin I, is considered to be a rotation around z-axis by an angle = γ
IGz; where Gz is the gradient magnitude (along the z-direction) and γ
I is the
gyromagnetic ratio of spin I. It introduces a phase factor to the magnetizations:
''Φ (z,τ) = (γ
I)(Gz)(τ)''
The time duration τ is in the order of milliseconds.
See also
*
Gradient enhanced NMR spectroscopy
References
Nuclear magnetic resonance
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