一切权利归原作者所有。仅供学习交流使用，严禁用作商业用途。Book：《Handbook of MRI Pulse Sequences》原著：MATT A. BERNSTEIN, KEVIN F. KING, XIAOHONG JOE ZHOU,译注：蒋强盛SSFP-FID and SSFP-Echo SSFP-FID is a standard gradient-echo pulse sequence that provides greater signal than spoiled pulse sequences, but often at the cost of reduced contrast (Figure 14.4). It goes by a variety of commercial names (e.g., FISP) that are listed in Table 14.1. SSFP-echo is a less widely used pulse sequence, but is conceptually important for understanding the transverse steady state.SSFP-FID 与 SSFP-Echo
SSFP-FID 序列是标准的梯度回波序列，它的信号强度高于扰相梯度回波序列，但经常是以牺牲图像对比为代价（图 14.4）。它也被冠以各种商业名称（比如 FISP），见表 14.1。SSFP-echo 序列使用不太广泛，但它对于从概念上理解横向磁化矢量的稳态具有重要帮助。  If the RF excitation pulses in the θ-TR-θ-TR-θ-TR... sequence are phase coherent and TR is less than or on the order of T2, then an SSFP (Carr 1958; Ernst and Anderson 1966) is established. In this context, phase coherent means that the RF pulses all have the same phase in the rotating frame, (i.e., θx-TR-θx-TR-θx...) or else a simple phase cycle such as sign alternation (θx-TR-θ(-x)-TR-θx-TR-θ(-x)-...). A further condition to avoid spoiling the steady state is that the phase accumulated by the transverse magnetization be the same in each TR interval. This condition requires that the gradient area in each TR interval be the same, so, for example, a phase-encoding rewinder lobe must be applied.在序列 θ-TR-θ-TR-θ-TR... 中，如果射频激发脉冲的相位一致且 TR 小于 T2 量级或与 T2 量级相当，那么稳态自由进动 steady-state free precession SSFP（Carr 1958; Ernst and Anderson 1966）就建立了。此处，相位一致表示所有射频脉冲在旋转坐标系中拥有相同的相位（即 θx-TR-θx-TR-θx...），或拥有一简单的相位周期，比如正负交替（θx-TR-θ(-x)-TR-θx-TR-θ(-x)-...）。进一步避免稳态的扰乱就是在每个 TR 间期内横向磁化矢量累积的相位保持一致。那么这就需要每个 TR 间期内梯度的面积保持一致，例如，必须施加相位卷绕梯度。%%%%%%%%%%%%%%%【译者注1】TR is less than or on the order of T2要想获得横向磁化矢量的稳态，那么 TR 不能太长，太长的话，横向磁化矢量消散了，就不能被后续的 RF 进行回聚了，此也为一种扰相的方法（前面有提过）。那么为了不让横向磁化矢量消散，TR 必须要与 T2 保持一个量级，或者比 T2 的量级还要短。换句话说，就是如果组织的 T2 值约 100ms，那么 TR 也要是 100ms 左右，或者小于 100ms，比如 10ms、20ms 等。另外，每一个 RF，在梯度回波序列中，0 |