Hyperechoes - Hyperechoes with CPMG sequences

During the spin zoo tour numerous images and videos have been presented that depict sequences that basically scramble the single initial magnetization vector into some weird distribution. Recently, Jürgen Hennig presented a method to disentangle these scrambled magnetization vectors, and to bring them back again into a totally coherent state. The hyper echo mechanism gives the receipt how this disentanglement procedure has to be performed. Below is an example of a CPMG sequence with six 60° refocusing pulses, the central 180° pulse, and again six 60° refocusing pulses (with opposite phase), and the final 90° flip back pulse. Without relaxation the full initial magnetization can be restored.

Since relaxation (and diffusion) cannot be reversed a reduced hyperecho has to be expected. Below is the same simulation as before, but with relaxation times of T1=30TR and T2=20TR.

Last updated: Monday, 18.04.2011