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.
Pulsed field gradient techniques are key to magnetic resonance imaging, spatially selective spectroscopy and studies of diffusion via diffusion ordered nuclear [magnetic resonance spectroscopy]. 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 = γIGz; where Gz is the gradient magnitude and γI is the gyromagnetic ratio of spin I. It introduces a phase factor to the magnetizations:Φ =
The time duration τ is in the order of milliseconds.