1Chapter 7: Gradient Echo Imaging Methods Mark D. Herbst, MD, PhD
2Two 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-spaceGradient Echo – uses gradient pulse to form the echoGradient Echo – abbreviated GE, or GRE for Gradient Recalled Echo, or FFE for Fast Field Echo, or SAGE (small angle GE)
3Advantages of GE Methods Faster than SE (spin echo) because of short TRs and short TEsShows flowing blood as bright good for MRAGood for functional MRIGood for subtle hemorrhage (microhemorrhage technique or magnetic susceptibility technique)Can be combined with SE to produce very fast images (GRASE=gradient and spin echo)
4Disadvantages of GE Methods Can have too much metal artifactGE gives T2*-weighted images (“T-two-star”) instead of T2WINeed to be aware of fat and water being in-phase or out-of-phase at interfaces between water and fat
8Spoiled 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.