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
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio wave ...
,
spatially selective spectroscopy and studies of
diffusion via diffusion ordered
nuclear magnetic resonance spectroscopy (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
In physics, the gyromagnetic ratio (also sometimes known as the magnetogyric ratio in other disciplines) of a particle or system is the ratio of its magnetic moment to its angular momentum, and it is often denoted by the symbol , gamma. Its SI u ...
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 Gradient enhanced NMR is a method for obtaining high resolution nuclear magnetic resonance spectra without the need for ''phase cycling''. Gradient methodology is used extensively for two purposes, either rephasing (selection) or dephasing (eliminat ...
References
Nuclear magnetic resonance
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