Smith Stephen, Jenkinson Mark, Beckmann Christian, Miller Karla, Woolrich Mark
Oxford University Centre for Functional MRI of the Brain (FMRIB), UK.
Neuroimage. 2007 Jan 1;34(1):127-36. doi: 10.1016/j.neuroimage.2006.09.019. Epub 2006 Oct 27.
Optimising the efficiency of an experimental design is known to be of great importance. However, existing methods for calculating design rank deficiency and contrast estimability (an important aspect of experimental design) relate to computational precision rather than image noise and are therefore not very meaningful. For example, a contrast between two experimental conditions may be mathematically "estimable" while requiring a huge differential BOLD response for statistical significance to be reached. In this paper we formulate standard efficiency equations in terms of required BOLD effect, and use this to generate measures of rank/estimability which are meaningful. This takes into account the strength and smoothness of the timeseries noise and is applicable to complex contrasts; we show how to re-express several regressors and an associated contrast vector as a single equivalent regressor, so that we can calculate the contrast's effective peak-peak height unambiguously. We also present some example results on typical designs, and characterise noise results from a range of typical FMRI acquisitions, in order to allow experimenters to apply efficiency estimation in advance of acquiring data.
优化实验设计的效率至关重要。然而，现有的计算设计秩亏缺和对比可估计性（实验设计的一个重要方面）的方法与计算精度相关，而非图像噪声，因此意义不大。例如，两个实验条件之间的对比在数学上可能是“可估计的”，但要达到统计显著性却需要巨大的BOLD反应差异。在本文中，我们根据所需的BOLD效应制定了标准效率方程，并用此生成有意义的秩/可估计性度量。这考虑了时间序列噪声的强度和平滑度，适用于复杂对比；我们展示了如何将几个回归量和一个相关的对比向量重新表示为单个等效回归量，以便我们能够明确计算对比的有效峰峰值高度。我们还给出了一些典型设计的示例结果，并对一系列典型功能磁共振成像采集的噪声结果进行了表征，以便实验人员在采集数据之前就能应用效率估计。
