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MRI Sequences

Sequence classification

by Denis Hoa

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There are two main sequence families, depending on the type of echo recorded:

  • spin echo sequences, characterized by the presence of a 180° rephasing RF pulse
  • gradient echo sequences

Numerous variations have been developed within each of these families, mainly to increase acquisition speed:

  • Fast spin echo sequences, Single shot FSE and Haste
  • Gradient echo sequences with spoiling of residual transverse magnetization (spoiled gradient echo and ultrafast gradient echo), a group of gradient echo sequences with steady state residual transverse magnetization (Steady state gradient echo) and its derivatives (Contrast enhanced steady state gradient echo) and with balanced gradients (Balanced steady state gradient echo), echoplanar (EPI).

Some sequences are hybrid, mixing spin echo and gradient echo (GRASE, SE-EPI).

Magnetic resonance angiography sequences (FBI, contrast-enhanced MRA, TOF, PC) perfusion imaging, diffusion imaging (DW) and MR spectroscopy will be dealt with in separate chapters in the second part.