Expansion:
Fast Spin Echo
Rapid Acquisition with Refocussed Echoes
Turbo Spin Echo™ (GE)
Fast Acquistion Spin Echo
Technique:
As in routine spin-echo imaging, a 90 degree RF pulse is followed by a single 180 degree refocussing pulse. However, in fast spin echo (FSE) imaging, multiple 180 degree refocussing pulses are performed with multiple resulting spin-echoes. Each echo has a different phase encoding value and is assigned to a different k-space line. As the number of echoes acquired after a 90 degree excitation increases, scan time decreases but signal to noise also decreases and T2 blurring increases. Maximum ETL is limited by true T2 decay.
Typical Paramaters:
TR: >3000 msec (for T2-weighted images)
TE: Effective TE is time when the central k-space views are acquired (which determine image contrast).
ETL: Echo Train Length - generally between 4 and 16
Reference:
All You Really Need to Know About MR Physics, 8-1
Contributor:
Related Sequences/Terms:
RARE, SE, Turbo Spin Echo (GE)
Comments:
| ETL is number of echoes obtained following single 90 degree RF pulse |
| As ETL increases scan time decreases |
| fat appears abnormally bright on T2 FSE images (due to J-coupling) |
| some proteinaceous tissue appears darker due to magnetization transfer |
Pulse Sequence Diagram:
Fast Spin Echo (FSE/RARE) sequence