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Chapter 7: Gradient Echo Imaging Methods

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1 Chapter 7: Gradient Echo Imaging Methods
Mark D. Herbst, MD, PhD

2 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)

3 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 (GRASE=gradient and spin echo)

4 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

5 Spin Echo

6 Gradient Echo

7 Gradient Echo

8 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.

9 GRASS and Spoiled GRASS

10 Spin Echo

11 Effect of Flip Angle on Signal

12 Effect of Flip Angle on Net Magnetization Vector

13 Effect of Flip Angle on Longitudinal and Transverse Magnetization

14 Effect of Flip Angle on Contrast

15 Effect of TR on M


17 Spin Echo Planar Imaging (EPI)

18 Gradient Echo Planar Imaging (EPI)

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