Küblböck Martin, Woletz Michael, Höflich Anna, Sladky Ronald, Kranz Georg S, Hoffmann André, Lanzenberger Rupert, Windischberger Christian
MR Center of Excellence, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria.
Department of Psychiatry and Psychotherapy, Medical University of Vienna, Austria.
Neuroimage. 2014 Dec;103:249-257. doi: 10.1016/j.neuroimage.2014.09.038. Epub 2014 Sep 22.
The (fractional) amplitudes of low-frequency fluctuations (f)ALFF are popular measures for the magnitude of low-frequency oscillations in resting-state fMRI (R-fMRI) data. Both measures can be directly derived from the spectral power of R-fMRI time courses. Numerous studies suggest that ALFF and fALFF might be used as biomarkers for a variety of diseases including schizophrenia, major depressive disorder, and obsessive-compulsive disorder. However, the temporal stability of (f)ALFF values, which is of great importance for the application of (f)ALFF both as a biomarker and scaling parameter, has not been studied in detail yet. Here, we quantify the temporal stability, robustness and reproducibility of both ALFF and fALFF maps obtained from R-fMRI data by performing statistical analyses over 55 minute resting-state scans which included a period of NaCl infusion. We also examine the differences of using either raw or standardised (f)ALFF maps. Our analyses show that no significant changes of (f)ALFF values over the 55minute period occur for both raw and standardised (f)ALFF maps. In addition, we demonstrate that raw (f)ALFF maps across subjects are correlated with head motion as quantified via frame-wise displacement, whereas no such correlation is present in standardised (f)ALFF maps. In conclusion, the results of our study show that both ALFF and fALFF qualify as potential biomarkers due to their high temporal stability.
低频波动（f）ALFF的（分数）振幅是静息态功能磁共振成像（R-fMRI）数据中低频振荡幅度的常用测量指标。这两种测量指标都可以直接从R-fMRI时间序列的频谱功率中得出。大量研究表明，ALFF和fALFF可能用作包括精神分裂症、重度抑郁症和强迫症在内的多种疾病的生物标志物。然而，（f）ALFF值的时间稳定性对于将（f）ALFF用作生物标志物和缩放参数都非常重要，但尚未得到详细研究。在此，我们通过对55分钟的静息态扫描（包括一段氯化钠输注期）进行统计分析，量化了从R-fMRI数据获得的ALFF和fALFF图谱的时间稳定性、稳健性和可重复性。我们还研究了使用原始或标准化（f）ALFF图谱的差异。我们的分析表明，原始和标准化（f）ALFF图谱在55分钟内（f）ALFF值均无显著变化。此外，我们证明，通过逐帧位移量化，跨受试者的原始（f）ALFF图谱与头部运动相关，而标准化（f）ALFF图谱中不存在这种相关性。总之，我们的研究结果表明，由于其高时间稳定性，ALFF和fALFF都有资格作为潜在的生物标志物。
