The use of varying phase or timing of the RF pulses to prevent setting up a condition of steady state free precession, e.g. in rapid excitation MR imaging.

See also Spoiler Gradient Pulse and Rapid Excitation Magnetic Resonance Imaging.

(RE MRI) There are several approaches to speeding up the MRI data acquisition process by repeating the excitation by RF pulses in times short compared to T1, typically using small flip angles and gradient echo refocusing. When TR is also on the order of or shorter than T2, the repeated RF pulses will tend to refocus transverse magnetization remaining from prior excitations, setting up a condition of steady state free precession, and a dependence of signal strength (and image contrast) on both T1 and T2.
This can be modified in various ways, particularly:
1) to spoil the tendency to build up a steady state by reducing coherence between excitations, e.g. by variation of the phase or timing of consecutive RF pulses or of the strength of spoiler gradient pulses, thus increasing the relative dependence of signal strength on T1 or
2) acquire the signal when it is refocusing immediately prior to the next RF pulse, thus increasing the relative dependence of signal strength on T2.

See also Ultrafast Gradient Echo Sequence.

Refocused GRE sequences use a refocusing gradient in the phase encoding direction during the end module to maximize (refocus) remaining xy- (transverse) magnetization at the time when the next excitation is due, while the other two gradients are, in any case, balanced.
When the next excitation pulse is sent into the system with an opposed phase, it tilts the magnetization in the α direction. As a result the z-magnetization is again partly tilted into the xy-plane, while the remaining xy-magnetization is tilted partly into the z-direction.
Companies use different acronyms to describe certain techniques.

Different terms for these gradient echo pulse sequences
R-GRE Refocused Gradient Echo,
FAST Fourier Acquired Steady State,
FFE Fast Field echo,
FISP Fast Imaging with Steady State Precession,
F-SHORT SHORT Repetition Technique Based on Free Induction Decay,
GFEC Gradient Field Echo with Contrast,
GRASS Gradient Recalled Acquisition in Steady State,
ROAST Resonant Offset Averaging in the Steady State,
SSFP Steady State Free Precession.
STERF Steady State Technique with Refocused FID
In this context, 'contrast' refers to the pulse sequence, it does not mean enhancement with a contrast agent.

(ROAST) A gradient echo sequence.
See Refocused Gradient Echo Sequence and Steady State Free Precession.

(E-SHORT) A gradient echo sequence in which a non-zero steady state develops for transverse and longitudinal magnetization. The TR is shorter than the T1 and T2 times of the tissue.
See Gradient Echo Sequence and Steady State Free Precession.