Department of Physics, Dalhousie University, Halifax, NS B3H 4R2, Canada(1); Biomedical Translational Imaging Centre (BIOTIC), IWK Health Centre, Halifax, NS B3K 6R8, Canada(2).
J Neurosci Methods. 2013 Oct 15;219(2):312-23. doi: 10.1016/j.jneumeth.2013.08.005. Epub 2013 Aug 17.
Many studies have investigated test-retest reliability of active voxel classification for fMRI, which is increasingly important for emerging clinical applications. The implicit impact of voxel-wise thresholding on this type of reliability has previously been under-appreciated. This has had two detrimental effects: (1) reliability studies use different fixed thresholds, making comparison of results is challenging; (2) typical studies do not assess reliability at the individual level, which could provide information for selecting activation thresholds. To show the limitations of traditional fixed-threshold approaches, we investigated the threshold dependence of fMRI reliability measures, with the goal of developing an automated threshold selection routine. For this purpose, we demonstrated threshold dependence of both novel (ROC-reliability or ROC-r) and established (Rombouts overlap or RR) reliability measures. Both methods rely minimally on statistical assumptions, and provide a data-driven summary of the threshold-reliability relationship. We applied these methods to data from eight subjects performing a simple finger tapping task across repeated fMRI sessions. We showed that the reliability measures varied dramatically with threshold. This variation depended strongly on the individual tested. Finally, we demonstrated novel procedures using ROC-r and overlap analysis to optimize thresholds on a case-by-case basis. Ultimately, a method to determine robust individual-level activation maps represents a critical advance for fMRI as a diagnostic tool.
许多研究都调查了功能磁共振成像（fMRI）中活跃体素分类的重测信度，这对于新兴的临床应用越来越重要。以前，体素水平阈值对这种可靠性的隐含影响被低估了。这有两个不利影响：（1）可靠性研究使用不同的固定阈值，使得结果的比较具有挑战性；（2）典型的研究没有在个体水平上评估可靠性，这可以为选择激活阈值提供信息。为了展示传统固定阈值方法的局限性，我们研究了 fMRI 可靠性测量的阈值依赖性，目的是开发一种自动阈值选择例程。为此，我们展示了新的（ROC-可靠性或 ROC-r）和已建立的（Rombouts 重叠或 RR）可靠性测量的阈值依赖性。这两种方法都很少依赖于统计假设，并提供了阈值可靠性关系的数据分析总结。我们将这些方法应用于八名受试者在重复 fMRI 会话中执行简单的手指敲击任务的数据。我们表明，可靠性测量值随阈值变化剧烈。这种变化强烈依赖于所测试的个体。最后，我们使用 ROC-r 和重叠分析演示了优化逐个案例的阈值的新程序。最终，确定稳健个体水平激活图的方法代表了 fMRI 作为诊断工具的关键进展。
