Fast Gradient Echo: Function

Imaging Sequence Type:

  • FSPGR (GE), FLASH (Siemens), T1 FFE (Philips), Field Echo (Toshiba)
  • Images are typically generated over several heartbeats during a breathhold

Acquisition Mode: Usually single slice, multiphase (i.e. a cine at one slice location is acquired per breathhold)

Image Contrast:

  • Bright blood
  • Does not require intravenous gadolinium contrast
  • T1-weighted

Imaging Options:

  • Fat suppression can be performed using fat saturation
  • TE can be set to in-phase or out-of phase which also can be helpful for identifying fat
  • Can be used with velocity-encoding to generate phase-contrast images for flow quantification

Clinical Utility:

  • Once was the mainstay sequence for functional imaging before it was largely supplanted by steady-state free precession (SSFP)
  • Fast gradient echo sequences usually have a longer TE than SSFP sequences, so they are more sensitive for detecting turbulent flow from valve disease, shunts, and LVOT obstruction. For example, in the video above, an eccentric jet of mitral regurgitation can be seen travelling along the lateral wall of the left atrium up to the origin of the left superior pulmonary vein. The jet is less well visualized in the SSFP video shown at the bottom of this page.
  • Less sensitive than SSFP to off-resonance artifacts. This can be an advantage in some patients with implanted ferromagnetic devices (e.g. Harrington rods, intravascular coils, etc.)
  • Typically, uses a lower flip angle than SSFP, so less energy deposition. This can be an advantage in special situations where it may be important to limit energy deposition (e.g. patients with implanted pacemakers or defibrillators)
  • Bright blood is dependent on blood flow, so image contrast is worse in patients with poor systolic function, and in regions of the heart where blood flow is generally low (e.g. LV apex, LA appendage).
  • Images are usually acquired without intravenous gadolinium contrast. Because the images are T1-weighted, it is possible to acquire images before and after the administration of gadolinium contrast to assess for contrast enhancement. However, perfusion and late gadolinium enhancement (LGE) sequences are better for this application.

 

Steady State Free Precession: