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T₂-enhanced steady-state gradient echo

In T₂-enhanced steady-state gradient echo sequences:

• residual transverse magnetization is conserved
• the sequence is inverted in time, compared to the preceding sequences
• only the echo corresponding to the Hahn echo, dependent on T₂ but weaker tthan spin echo, is recorded

The fact that the sequence is reversed in relation to standard gradient echo sequences creates a Hahn echo after two excitation pulses (separated by TR). The amplitude of this echo will depend on the relaxation time T₂. It is weaker than that of a true spin echo. The T₂ image weighting is linked to double TR (since the Hahn echo will not occur during the repetition corresponding to the first excitation pulse, but in the following one, after a second excitation pulse).
The weak intensity of the Hahn echo, produces a low signal to noise ratio in T₂-enhanced steady state gradient echo sequences. This type of sequence is rarely used in clinical practice.