Hyperechoes - Hyperechoes with gradient echo sequences

Since the hyperecho technique is able to refocus any spoiled magnetization (at least if one knows how it was spoiled) it can also be applied to gradient echo sequences. Below is a simulation of the motion of M during a gradient echo hyperecho train. Seven 60° pulses have been used prior to the central 180° refocusing pulse, and again seven pulses. This finally ends with coherent magnetization in -z direction.

Relaxation (T1=20TR, T2=10TR) leads to a damping, and magnetization vectors are no longer on the unit sphere. The hyperecho is somewhat reduced compared to the previous example. Again, seven 60° pulses have been used prior to the central 180° refocusing pulse, and again seven pulses.



The flow of magnetization of the hyperecho- refocused gradient echo sequence can also be visualized in Fourier space, using the extended phase graph depiction. Left is a sequence with 30° flip angles. The phases of the excitation pulses were zero (most left), and quadratically increased (RF-spoiled 117°, left), both without relaxation.

 


 


Last updated: Monday, 18.04.2011