Expansion:
Spin-Echo Imaging
also called RF-ECHO
Technique:
Initial 90 degree radiofrequency pulse is applied. At time TE/2, 180 degree refocussing pulse (with same bandwidth as 90 degree pulse) is applied in order to rephase spins that have dephased from T2* mechanisms. At time TE, rephasing has occurred and spin echo is formed. Sequence is repeated after time TR.
Typical Parameters:
TR: 200-800 msec (T1-weighting), 2000-6000 (PD and T2-weighting)
TE: <15 msec (T1-weighting), <20 msec (PD), >80 msec (T2)
Reference:
Contributor:
Related Sequences/Terms:
T1, T2, Proton-density, Spin-density
Comment
| --> multiple 180 degree refocussing pulses can be applied and additional echoes formed (see FSE imaging), until no signal is left from true T2 decay |
| --> higher SNR than GRE images because of rephasing of T2* decay |
| --> Multi-slice imaging can be performed by exciting multiple slices (utilizing a frequency offset with slice select gradient) during one TR period |
Pulse Sequence Diagrams:
