Scheffler Klaus, Hennig Jürgen
Section of Medical Physics, Department of Diagnostic Radiology, University of Freiburg, Freiburg, Germany.
Magn Reson Med. 2003 Feb;49(2):395-7. doi: 10.1002/mrm.10351.
It is commonly accepted that TrueFISP (balanced FFE, FIESTA) belongs to the class of gradient-echo (GRE) sequences. GRE sequences are sensitive to dephasing effects of the transverse magnetization between the excitation pulse and echo acquisition, and phase coherence is only established directly after and before excitation pulses. However, an analysis of the phase evolution of transverse magnetization in a TrueFISP experiment shows very close similarities to the echo formation of a spin-echo (SE) experiment. If dephasing between excitation pulses is below +/-pi, TrueFISP exhibits a nearly complete refocusing of transverse magnetization at TE = TR/2. Only signals acquired before and after TR/2 show an additional T*2 sensitivity.
人们普遍认为,稳态自由进动序列(平衡快速场回波序列,快速成像稳态进动序列)属于梯度回波(GRE)序列类别。GRE序列对激发脉冲与回波采集之间横向磁化的失相效应敏感,并且仅在激发脉冲前后直接建立相位相干性。然而,对稳态自由进动实验中横向磁化相位演变的分析表明,其与自旋回波(SE)实验的回波形成非常相似。如果激发脉冲之间的失相低于+/-π,稳态自由进动序列在TE = TR/2时表现出横向磁化几乎完全重聚焦。仅在TR/2之前和之后采集的信号显示出额外的T*2敏感性。