Division Neuropsychology, Institute of Psychology, University of Zurich, Switzerland.
Brain Topogr. 2012 Apr;25(2):182-93. doi: 10.1007/s10548-011-0206-x. Epub 2011 Oct 21.
Sparse and clustered-sparse temporal sampling fMRI protocols have been devised to reduce the influence of auditory scanner noise in the context of auditory fMRI studies. Here, we report an improvement of the previously established clustered-sparse acquisition scheme. The standard procedure currently used by many researchers in the field is a scanning protocol that includes relatively long silent pauses between image acquisitions (and therefore, a relatively long repetition time or cluster-onset asynchrony); it is during these pauses that stimuli are presented. This approach makes it unlikely that stimulus-induced BOLD response is obscured by scanner-noise-induced BOLD response. It also allows the BOLD response to drop near baseline; thus, avoiding saturation of BOLD signal and theoretically increasing effect size. A possible drawback of this approach is the limited number of stimulus presentations and image acquisitions that are possible in a given period of time, which could result in an inaccurate estimation of effect size (higher standard error). Since this line of reasoning has not yet been empirically tested, we decided to vary the cluster-onset asynchrony (7.5, 10, 12.5, and 15 s) in the context of a clustered-sparse protocol. In this study sixteen healthy participants listened to spoken sentences. We performed whole-brain fMRI group statistics and region of interest analysis with anatomically defined regions of interest (auditory core and association areas). We discovered that the protocol, which included a short cluster-onset asynchrony (7.5 s), yielded more advantageous results than the other protocols, which involved longer cluster-onset asynchrony. The short cluster-onset asynchrony protocol exhibited a larger number of activated voxels and larger mean effect sizes with lower standard errors. Our findings suggest that, contrary to prior experience, a short cluster-onset asynchrony is advantageous because more stimuli can be delivered within any given period of time. Alternatively, a given number of stimuli can be presented in less time, and this broadens the spectrum of possible fMRI applications.
稀疏和聚类稀疏时间采样 fMRI 方案已被设计用于减少听觉 fMRI 研究中听觉扫描仪噪声的影响。在这里，我们报告了先前建立的聚类稀疏采集方案的改进。目前，该领域的许多研究人员都在使用一种扫描协议，该协议在图像采集之间包括相对较长的静默暂停（因此，相对较长的重复时间或聚类起始异步）；正是在这些暂停期间呈现刺激。这种方法不太可能使刺激诱导的 BOLD 反应被扫描仪噪声诱导的 BOLD 反应所掩盖。它还允许 BOLD 反应降至基线附近；因此，避免了 BOLD 信号的饱和，并在理论上增加了效应量。这种方法的一个可能缺点是在给定时间段内可能呈现和采集的刺激数量有限，这可能导致效应量的估计不准确（更高的标准误差）。由于这种推理尚未经过实证检验，我们决定在聚类稀疏协议的背景下改变聚类起始异步（7.5、10、12.5 和 15 秒）。在这项研究中，十六名健康参与者听取了口语句子。我们使用全脑 fMRI 组统计和解剖定义的感兴趣区域（听觉核心和关联区域）进行了区域分析。我们发现，与其他涉及较长聚类起始异步的协议相比，包括较短聚类起始异步（7.5 秒）的协议产生了更有利的结果。短聚类起始异步协议显示出更多的激活体素和更大的平均效应量，具有更低的标准误差。我们的研究结果表明，与先前的经验相反，较短的聚类起始异步是有利的，因为在任何给定的时间段内可以提供更多的刺激。或者，可以在更短的时间内呈现给定数量的刺激，从而拓宽了可能的 fMRI 应用范围。
