Prospective GIRF-based RF phase cycling to reduce eddy current-induced steady-state disruption in bSSFP imaging
Prospective GIRF-based RF phase cycling to reduce eddy current-induced steady-state disruption in bSSFP imaging
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DOI：
10.1002/mrm.28097
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发表时间：
2019-11-22
影响因子：
3.3
通讯作者：
Tijssen, Rob Hendrikus Nicolaas
中科院分区：
文献类型：
--
作者：
Bruijnen, Tom;Stemkens, Bjorn;Tijssen, Rob Hendrikus Nicolaas
目的提出一种明确的平衡稳态自由进动（bSSFP）信号模型，预测涡流引起的稳态扰动，并提供一种前瞻性、实用性和通用性的涡流补偿方法。理论与方法利用梯度脉冲响应函数（GIRF）模拟了重复块末端涡流引起的相位误差。这些相位误差被包括在bloch仿真中，以建立bSSFP信号模型来预测稳态中断及其相应的图像伪影。该信号模型被嵌入到MR系统中，并用于通过前瞻性地修改RF脉冲的相位循环方案来补偿相位误差。信号模型和涡流补偿方法在体模和体内实验中得到了验证。此外，信号模型用于分析现有的涡流缓解方法，如2D微小黄金角径向和3D成对相位编码笛卡尔采集。结果该信号模型预测了涡流引起的图像伪影，其中零阶GIRF是预测稳态破坏的主要因素。自动在线计算前瞻性射频相位循环方案，大大减少了涡流诱导的图像伪影。信号模型为k空间轨迹的平滑性提供了直接关系，这解释了相位编码配对和微小黄金角轨迹的有效性。结论所提出的信号模型可以准确预测bSSFP成像中涡流引起的稳态破坏。该信号模型可用于推导涡流感应相位误差，这是特定于磁阻的RF相位循环方案所需的，可大大减少涡流感应图像伪影。
Purpose To propose an explicit Balanced steady-state free precession (bSSFP) signal model that predicts eddy current-induced steady-state disruptions and to provide a prospective, practical, and general eddy current compensation method. Theory and Methods Gradient impulse response functions (GIRF) were used to simulate trajectory-specific eddy current-induced phase errors at the end of a repetition block. These phase errors were included in bloch simulations to establish a bSSFP signal model to predict steady-state disruptions and their corresponding image artifacts. The signal model was embedded in the MR system and used to compensate the phase errors by prospectively modifying the phase cycling scheme of the RF pulse. The signal model and eddy current compensation method were validated in phantom and in vivo experiments. In addition, the signal model was used to analyze pre-existing eddy current mitigation methods, such as 2D tiny golden angle radial and 3D paired phase encoded Cartesian acquisitions. Results The signal model predicted eddy current-induced image artifacts, with the zeroth-order GIRF being the primary factor to predict the steady-state disruption. Prospective RF phase cycling schemes were automatically computed online and considerably reduced eddy current-induced image artifacts. The signal model provides a direct relationship for the smoothness of k-space trajectories, which explains the effectiveness of phase encode pairing and tiny golden angle trajectory. Conclusions The proposed signal model can accurately predict eddy current-induced steady-state disruptions for bSSFP imaging. The signal model can be used to derive the eddy current-induced phase errors required for trajectory-specific RF phase cycling schemes, which considerably reduce eddy current-induced image artifacts.