Expansion:
Three Dimensional Gradient Recalled Echo
Technique:
3D volume acquisition has the advantages of improved slice and spatial resolution, increased SNR, with the penalty of increased sca Color n time and sensitivity to motion. A slab of tissue is excited and secondary phase encoding is performed in the slice select direction along with the primary phase encoding in the phase direction prior to collecting a gradient echo. GRE techniques are usually used to offset the time penalty of 3D imaging, as opposed to using a SE sequence. Both steady state (GRASS) and spoiled steady state (SPGR) sequences can be performed.
Typical Parameters:
flip angle: 5 to 45 degrees
TR: 10 to 50 msec
Reference:
All You Really Need to Know About MR Physics, 8-4.
Contributor:
Related Sequences/Terms:
GRE, SPGR, GRASS, MRA
Comments:
| scan time in 3D sequences: TR * # of primary phase encoding steps * # of secondary phase encoding steps * number of signal averages |
| increased sensitivity to motion |
| increased signal to noise |
| 2-4 slices from each end of the excited slab are discarded to reduce wrap |
Pulse Sequence Diagram:
