Diffusion imaging with stimulated echoes: signal models and experiment design
Diffusion imaging with stimulated echoes: signal models and experiment design
复制标题
受激回波的扩散成像：信号模型和实验设计
DOI：
--
复制
发表时间：
2013
期刊：
影响因子：
--
通讯作者：
T. Dyrby
中科院分区：
文献类型：
--
作者：
D. Alexander;T. Dyrby
目的：与脉冲梯度自旋回波（PGSE）相比，刺激回波采集模式（STEAM）弥散MRI的弥散时间较长， 两美元。因此，对于7T及以上的生物医学扩散成像应用， 2美元是短的。然而，STEAM序列中的成像梯度比PGSE中的扩散加权大得多，但在后处理期间通常被忽略。我们在这里证明，这可能会严重偏倚参数估计。
方法：我们提出了模型的蒸汽信号的自由和限制扩散，考虑破碎机和切片选择（蝴蝶）梯度，以避免这种偏见。蝶形梯度也会破坏实验设计，通常是通过使梯度向量向切片方向倾斜。我们提出了一个简单的补偿扩散梯度矢量指定的扫描仪，抵消蝴蝶梯度，以保持预期的实验设计。
结果如下：从猴脑实验中固定的高场数据表明，对于扩散张量成像和ActiveAx轴突直径指数映射，需要在采集期间进行补偿并在后处理期间进行正确建模。模拟支持的结果，并表明在体内人体应用程序中的类似需求。
结论：正确的建模和补偿对于STEAM扩散MRI的实际应用具有重要意义。
Purpose: Stimulated echo acquisition mode (STEAM) diffusion MRI can be advantageous over pulsed-gradient spin-echo (PGSE) for diffusion times that are long compared to $ two$. It is important therefore for biomedical diffusion imaging applications at 7T and above where $ two$ is short. However, imaging gradients in the STEAM sequence contribute much greater diffusion weighting than in PGSE, but are often ignored during post-processing. We demonstrate here that this can severely bias parameter estimates.
Method: We present models for the STEAM signal for free and restricted diffusion that account for crusher and slice-select (butterfly) gradients to avoid such bias. The butterfly gradients also disrupt experiment design, typically by skewing gradient-vectors towards the slice direction. We propose a simple compensation to the diffusion gradient vector specified to the scanner that counterbalances the butterfly gradients to preserve the intended experiment design.
Results: High-field data fixed from a monkey brain experiments demonstrate the need for both the compensation during acquisition and correct modelling during post-processing for both diffusion tensor imaging and ActiveAx axon-diameter index mapping. Simulations support the results and indicate a similar need in in-vivo human applications.
Conclusion: Correct modelling and compensation are important for practical applications of STEAM diffusion MRI.