Spoiled gradient echo sequences

Type of sequence	Philips	Siemens	GE	Hitachi	Toshiba
Spoiled GE	T₁-FFE	FLASH	SPGR MPSPGR	RSSG	RF-spoiled FE

Principles

In certain cases, the steady state can be detrimental, namely for obtaining T₁ weighted sequences. To resolve this problem, gradients and/or RF pulses (spoilers) are used to eliminate residual transverse magnetization.
In this type of echo gradient sequence, image weighting will depend on:

the flip angle for T₁ weighting (the greater the angle, the more T₁ weighting)
the TE for T₂^* weighting (the shorter the TE, the more T₂^* deweighting)

These sequences allows for fast 3D imaging during short apnea (10 to 20 seconds). They are used in angiography after gadolinium injection, possibly completed by a prior acquisition to allow subtraction. This type of sequence is also used in intra-voxel water-fat mixture imaging, by choosing in phase and out of phase TEs (cf. Chemical shift artifact of the second type). Like all other gradient echo sequences, these are also sensitive to magnetic susceptibility artifacts.

Advanced topics

Spoiling gradients and RF pulses

The spoiing RF pulse consists in randomly varying the excitation pulse phase at each repetition.
A spoiling gradient has 2 components:

A constant component, consisting of prolonging the readout gradient
A variable component, changing randomly at each repetition, in the direction of the slice selection gradient

Ernst angle and TR in gradient echo sequences

For a given flip angle and relaxation time T₁, there is an optimal TR to obtain the maximum signal after a series of excitation pulse . The relationship between flip angle and optimal TR follows the Ernst angle formula:

Summary

MRI sequences

Spoiled gradient echo sequences

Principles

Advanced topics

Spoiling gradients and RF pulses

Ernst angle and TR in gradient echo sequences