Nebel Katharina, Stude Philipp, Wiese Holger, Müller Bernhard, de Greiff Armin, Forsting Michael, Diener Hans-Christoph, Keidel Matthias
Department of Neurology, University of Duisburg-Essen, 45122 Essen, Germany.
Hum Brain Mapp. 2005 Feb;24(2):130-43. doi: 10.1002/hbm.20075.
Continuous image acquisition as used in most functional magnetic resonance imaging (fMRI) designs may conflict with specific experimental settings due to attendant, noisy gradient switching. In sparse fMRI, single images are recorded with a delay that allows the registration of the predicted peak of an evoked hemodynamic response (HDR). The aim of this study was to assess validity and sensitivity of single-trial sparse imaging within the visual domain. Thirteen subjects were scanned twice. Either continuous or sparse image acquisition was applied while participants viewed single trains of flashlights. Sparse fMRI results were compared to continuous event-related fMRI results on single- and multisubject level regarding spatial extent, overlap, and intensity of activation. In continuously recorded data, the variability of the HDR peak latency was examined because this measure determined the timing of sparse image acquisition. In sparse fMRI, the sensitivity was analyzed considering different numbers of averaged trials. Sparse imaging detected the core activity revealed using continuous fMRI. The intensity of signal changes detected by continuous or sparse fMRI was comparable. The HDR peak latency was stable across sessions, but intersubject and regional variability might have affected the power of sparse fMRI. In sparse imaging, adding trials resulted in extension of activation and improvement in statistical power. The comparison with established continuous fMRI confirms the validity of sparse imaging. Conventional event-related data acquisition and analysis provided more comprehensive results. However, only sparse fMRI offers the opportunity to apply stimuli and record further biosignals free of scanner-related artifacts during intervals without image acquisition.
大多数功能磁共振成像（fMRI）设计中使用的连续图像采集可能会因伴随的噪声梯度切换而与特定实验设置产生冲突。在稀疏fMRI中，单幅图像以一定延迟进行记录，该延迟允许记录诱发的血液动力学反应（HDR）的预测峰值。本研究的目的是评估视觉领域内单次试验稀疏成像的有效性和敏感性。13名受试者接受了两次扫描。在参与者观看单束手电筒光时，采用连续或稀疏图像采集。将稀疏fMRI结果与连续事件相关fMRI结果在单受试者和多受试者水平上的激活空间范围、重叠情况和强度进行比较。在连续记录的数据中，检查了HDR峰值潜伏期的变异性，因为该测量决定了稀疏图像采集的时间。在稀疏fMRI中，考虑不同数量的平均试验来分析敏感性。稀疏成像检测到了使用连续fMRI揭示的核心活动。连续或稀疏fMRI检测到的信号变化强度具有可比性。HDR峰值潜伏期在各次扫描中稳定，但受试者间和区域变异性可能影响了稀疏fMRI的效能。在稀疏成像中，增加试验次数导致激活范围扩大和统计效能提高。与既定的连续fMRI比较证实了稀疏成像的有效性。传统的事件相关数据采集和分析提供了更全面的结果。然而，只有稀疏fMRI提供了在无图像采集的间隔期间施加刺激并记录无扫描仪相关伪影的进一步生物信号的机会。
