梯度回波成象技术分析

当今磁共振快速成象技术大多是建立在梯度回波脉冲序更的基础上，这种序列采用小的射频（ＲＦ）偏转角、短重复时间（ＴＲ）。当ＴＲ小到自与自旋－自旋驰豫时间Ｔ２同数量组或更短时，序列上的细微差异将引起图象对比上的较大变化，从而产生了多种多样的梯度回波序列，它们在结构上大致相似，但通过一些细微的差异保留各自的特色。梯度回波的物理基础是磁共振波谱学中早期发展的稳态自由进动即ＳＳＦＰ技术，本文从这一基本理论出发

Analysis of Gradient Recalled Echo Imaging Techniques

Current MR fast imaging techniques are based on gradient recalled echo (GRE) sequences with reduced RF flip angle and very short repetition times (TR). When TR is reduced to be of the order of spin-spin relax T2 or even shorter, a subtle difference between the sequences may lead to a different image contrast. Thus a great variety of GRE sequences are presented. Their structures are alike but they retain their own characteristics by subtle differences. GRE are based on SSFP (Steady-State Free Procession) which developed from early MR spectrum. According to this theory, several GRE imaging sequences are systematically analyzed in this paper,Two methods are presented to modify the ideal GRE sequence to reduce its actual problem. Then image strength and contrast formulas are obtained from different sequences. Finally a classification and summary are proposed for these GRE sequences.