CPMG - more refocusing pulses

For ideal 90° excitation and 180° refocusing pulses each refocusing period during the multi-echo train is identical, except for T1 and T2 relaxation. A more and more complicate situation is generated with refocusing pulses below 180°.
 
Below is the motion of M during excitation, dephasing, and 6 refocusing periods. The rapid relaxation chosen here gives a rapid T2-related signal decay. Shown is the dephased magnetization before the next 180° excitation pulse  (initial M = (0,0,1), T1=5TR, T2=3TR, 90°-180° ...)
 

Same simulation as before, but with 100° refocusing pulses. Again, relaxation is rapid resulting in deformed echoes. Below is the motion of M during excitation, dephasing, and 6 refocusing periods, with initial M = (0,0,1), T1=5TR, T2=3TR, 90°-100 ...
 
 

More symmetrical echoes can be observed without relaxation. The distribution of the magnetization is located on a sphere (as for all other sequences without relaxation) Same simulation as before, with 100° refocusing pulses, but without relaxation. Below is the motion of M during excitation, dephasing, and 8 refocusing, with initial M = (0,0,1), no relaxation, 90°-100°...

Magnetization is more spoiled on the unit disk for smaller refocusing pulses. As a result, echo amplitudes are reduced, and oscillations can be observed before the pseudo steady state (echo amplitude steady state without relaxation) has been reached. Below is the motion of M during excitation, dephasing, and 8 refocusing periods (initial M = (0,0,1), no relaxation, 90°-50° ...)
 

Last updated: Monday, 18.04.2011