Gradient Echo Sequences - More pulses

With increasing number of excitation pulses and dephasing periods the distribution of magnetization as a function of its dephasing Φ between excitation pulses becomes more and more complicated, and more interesting.
 
Motion of magnetization during ten RF pulses and ten dephasing periods (initial M = (0,0,1), T1=20TR, T2=10TR, α=50°, Φ= ±10π)

Just for fun it is also possible to take a complete image instead of a single magnetization vector as an initial configuration, and then to apply to rotation matrices for the multi-pulse experiment. Below is the motion of a (MR) head during fife RF pulses and fife dephasing periods (initial M = MR head, no relaxation, α=40°)
 

Sometimes it is practical to vary the phase of the excitation pulses. For example T1-weigted gradient echoes can be produced by a quadratic increase of the RF phase (RF spoiling). Below is the motion of magnetization during 12 RF pulse and 12 dephasing periods (initial M = (0,0,1), T1=50TR, T2=25TR, α=50°/50°**2)

Last updated: Montag, 18.04.2011