Gradient Echo Sequences - One pulse


After excitation the magnetization is first dephased by a negative gradient lobe, then rephased by a positive gradient to form the gradient echo. At the end of the gradient lobe the magnetization is dephased within the x-y plane.
 
Motion of magnetization during RF pulse, dephasing, and rephasing (initial M = (0,0,1), T1=20TR, T2=10TR, α=60°)

There exists no possibility to spoil the residual, dephased magnetization at the end of the one-pulse experiment. Additional spoiler gradients just increase the amount of dephasing. Only T2 relaxation can reduce or cancel residual transverse magnetization.
In order to describe multi-pulse experiments it is thus not important to know the exact gradient pattern switched between excitation pulses. Just the total amount of dephasing between excitation pulses determines the flow of magnetization.

The one-pulse experiment will thus be simplified to a simple excitation-dephasing experiment.
 
Motion of magnetization during RF pulse and dephasing (initial M = (0,0,1), T1 = 20TR, T2=10TR, α=50°)

Last updated: Montag, 18.04.2011