Chemical Sciences: A Manual for CSIR-UGC National Eligibility Test for Lectureship and JRF/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 (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 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 G is the gradient magnitude and γI is the gyromagnetic ratio of spin I. It introduces a phase factor to the magnetizations:

Φ (z,τ) = γIzGτ

The time duration τ is of order ms.