Phase vs. magnitude information in functional magnetic resonance imaging time series: toward understanding the noise
Phase vs. magnitude information in functional magnetic resonance imaging time series: toward understanding the noise
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DOI：
10.1016/j.mri.2009.02.006
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发表时间：
2009-10-01
影响因子：
2.5
通讯作者：
Bowtell, Richard
中科院分区：
文献类型：
--
作者：
Petridou, Natalia;Schaefer, Andreas;Bowtell, Richard
尽管已经表明，来自大脑的MR信号的相位特别容易由于呼吸而变化，但是相位时间序列中包含的总体生理信息还没有被很好地理解。这里.我们探讨了不同的生理过程的相位时间序列噪声，确定其时空特性，并检查它们的关系BOLD相关和非BOLD相关的生理噪声的幅度时间序列。这是通过调节TE和体素体积来操纵生理噪声对总信号方差的贡献，并使用短TR来充分采样生理信号波动来执行的。在使用RETROICOR去除主要呼吸和心脏频率处的信号波动之前和之后，比较相位和幅度信号。我们发现，作为生理噪声的结果，时间相位噪声随着TE以比I/TSNR预测的更快的速率增加。如先前的研究所建议的，相位生理噪声的主要贡献者是在大尺度（>1 cm）上表现出的呼吸相关效应。值得注意的是，RETROICOR去除了呼吸相关的大规模伪影，这导致时间相位稳定性的显著改善（7-90%）。RETROICOR后幅度时间序列中的生理噪声包括低频BOLD相关波动（
Although it has been shown that the phase of the MR signal from the brain is particularly prone to variation due to respiration, the overall physiological information contained in phase time series is not well understood. Here. we explore the different physiological processes contributing to the phase time series noise, identify their spatiotemporal characteristics and examine their relationship to BOLD-related and non-BOLD-related physiological noise in the magnitude time series. This was performed by manipulating the contribution of physiological noise to the total signal variance by modulating the TE and voxel volume, and using a short TR in order to adequately sample physiological signal fluctuations. The phase and magnitude signals were compared both before and after removal of signal fluctuations at the primary respiratory and cardiac frequencies with RETROICOR. We found that the temporal phase noise increased with TE at a faster rate than predicted by I/TSNR as a result of physiological noise. As suggested by previous studies, the primary contributor to phase physiological noise was respiration-related effects which were manifested at a large scale (>1 cm). Notably, RETROICOR removed respiration-related large-scale artifacts and this resulted in considerable improvements in the temporal phase stability (7-90%). Physiological noise in the magnitude time series after RETROICOR consisted of low-frequency BOLD-related fluctuations (