Chapter 7: Gradient Echo Imaging Methods

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Chapter 7 Gradient Echo Imaging Methods

• Mark D. Herbst, MD, PhD

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Two Main Imaging Methods

• Spin Echo uses 180 degree refocusing RF pulse
  to refocus spins and form an echo that is
  captured and put into k-space
• Gradient Echo uses gradient pulse to form the
  echo
• Gradient Echo abbreviated GE, or GRE for
  Gradient Recalled Echo, or FFE for Fast Field
  Echo, or SAGE (small angle GE)

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Advantages of GE Methods

• Faster than SE (spin echo) because of short TRs
  and short TEs
• Shows flowing blood as bright? good for MRA
• Good for functional MRI
• Good for subtle hemorrhage (microhemorrhage
  technique or magnetic susceptibility technique)
• Can be combined with SE to produce very fast
  images (GRASEgradient and spin echo)

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Disadvantages of GE Methods

• Can have too much metal artifact
• GE gives T2-weighted images (T-two-star)
  instead of T2WI
• Need to be aware of fat and water being in-phase
  or out-of-phase at interfaces between water and
  fat

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Spin Echo
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Gradient Echo
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Gradient Echo
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Spoiled Gradient Echo

• Spoiling refers to the destruction of any T2
  contrast in the image, leaving you with a fast
  way of getting a T1WI using a gradient technique.
  The spoiler pulse completely dephases the spins
  in the xy plane, removing any evidence of T2 or
  T2 contrast.

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GRASS and Spoiled GRASS
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Spin Echo
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Effect of Flip Angle on Signal
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Effect of Flip Angle on Net Magnetization Vector
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Effect of Flip Angle on Longitudinal and
Transverse Magnetization
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Effect of Flip Angle on Contrast
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Effect of TR on M
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GRASE
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Spin Echo Planar Imaging (EPI)
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Gradient Echo Planar Imaging (EPI)