Flow compensation in balanced SSFP sequences
Flow compensation in balanced SSFP sequences
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DOI：
10.1002/mrm.20619
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发表时间：
2005-10-01
影响因子：
3.3
通讯作者：
Scheffler, K
中科院分区：
文献类型：
--
作者：
Bieri, O;Scheffler, K
在平衡稳态自由进动 (b-SSFP) 序列中，编码梯度的未补偿一阶矩会引起激励序列内移动自旋的非恒定相位演化，从而导致信号丢失和图像伪影。为了恢复这些与流量相关的相位扰动，将连续相位编码 (PE) 步骤的“配对”与使用沿所有三个编码方向的补偿梯度波形的完全流量补偿序列进行比较。在志愿者研究中，无论用于数据采集的所选视图排序方案如何，通过“配对”技术获取的图像质量与通过完全流量补偿技术获取的图像质量相当。然而，模型实验的结果表明，当流速超过大约 0.5-1 m/s 时，配对技术就会变得无效。因此，在流量补偿的 b-SSFP 序列中消除第一梯度矩所需的额外扫描时间使得“配对”技术更适合于预期慢到中等流速的应用。
In balanced steady-state free precession (b-SSFP) sequences, uncompensated first-order moments of encoding gradients induce a nonconstant phase evolution for moving spins within the excitation train, resulting in signal loss and image artifacts. To restore these flow-related phase perturbations, "pairing" of consecutive phase-encoding (PE) steps is compared with a fully flow-compensated sequence using compensating gradient waveforms along all three encoding directions. In volunteer studies, the quality of images acquired with the "pairing" technique was comparable to that of images obtained with the fully flow-compensated technique, regardless of the selected view-ordering scheme used for data acquisition. Nevertheless, the results of phantom experiments indicate that the pairing technique becomes ineffective at flow velocities exceeding roughly 0.5-1 m/s. Consequently, the additional scan time required to null the first gradient moments in a flow-compensated b-SSFP sequence makes the "pairing" technique preferable for applications in which slow to moderate flow velocities can be expected.