School of Psychology and Clinical Language Sciences, University of Reading, Harry Pitt Building, Earley Gate, Reading, RG6 7BE, UK.
Centre for Integrative Neuroscience and Neurodynamics, University of Reading, Earley Gate, Reading, RG6 7BE, UK.
Brain Struct Funct. 2020 Apr;225(3):1153-1158. doi: 10.1007/s00429-020-02053-2. Epub 2020 Mar 5.
Simultaneous multi-slice (SMS) imaging is a popular technique for increasing acquisition speed in echo-planar imaging (EPI) fMRI. However, SMS data are prone to motion sensitivity and slice leakage artefacts, which spread signal between simultaneously acquired slices. Relevant to motion sensitivity, artefacts from moving anatomic structures propagate along the phase-encoding (PE) direction. This is particularly relevant for eye movement. As signal from the eye is acquired along with signal from simultaneously excited slices during SMS, there is potential for signal to spread in-plane and between spatially remote slices. After identifying an artefact temporally coinciding with signal fluctuations in the eye and spatially distributed in correspondence with multiband slice acceleration and parallel imaging factors, we conducted a series of small experiments to investigate eye movement artefacts in SMS data and the contribution of PE direction to the invasiveness of these artefacts. Five healthy adult volunteers were scanned during a blinking task using a standard SMS-EPI protocol with posterior-to-anterior (P ≫ A), anterior-to-posterior (A ≫ P) or right-to-left (R ≫ L) PE direction. The intensity of signal fluctuations (artefact severity) was measured at expected artefact positions and control positions. We demonstrated a direct relationship between eye movements and artefact severity across expected artefact regions. Within-brain artefacts were apparent in P ≫ A- and A ≫ P-acquired data but not in R ≫ L data due to the shift in artefact positions. Further research into eye motion artefacts in SMS data is warranted but researchers should exercise caution with SMS protocols. We recommend rigorous piloting of SMS protocols and switching to R ≫ L/L ≫ R PE where feasible.
同时多层（SMS）成像技术是在功能磁共振成像（fMRI）中提高采集速度的一种常用技术。然而，SMS 数据容易受到运动敏感性和切片渗漏伪影的影响，这些伪影会在同时采集的切片之间传播信号。与运动敏感性相关，运动的解剖结构的伪影沿相位编码（PE）方向传播。这对于眼球运动尤为重要。由于眼球的信号与 SMS 期间同时激发的切片的信号一起被采集，因此信号有在平面内扩散并在空间上远离切片之间传播的潜力。在确定与眼球信号波动时间上一致的伪影，并在与多带切片加速和并行成像因子对应的空间上分布之后，我们进行了一系列小实验，以研究 SMS 数据中的眼球运动伪影以及 PE 方向对这些伪影的侵入性的贡献。使用标准的 SMS-EPI 协议，五名健康的成年志愿者在眨眼任务中进行了扫描，PE 方向为后向前（P > A）、前向后（A > P）或右向左（R > L）。在预期伪影位置和对照位置测量信号波动的强度（伪影严重程度）。我们证明了眼球运动与预期伪影区域内的伪影严重程度之间存在直接关系。在 P > A 和 A > P 采集的数据中可以看到脑内伪影，但在 R > L 数据中则没有，这是由于伪影位置的变化。有必要对 SMS 数据中的眼球运动伪影进行进一步研究，但研究人员应谨慎使用 SMS 协议。我们建议严格试用 SMS 协议，并在可行的情况下切换到 R > L/L > R PE。
