Andersson J L
Subfemtomole Biorecognition project, Uppsala University PET-Centre, S-75185 Uppsala, Sweden.
Neuroimage. 1997 Nov;6(4):237-44. doi: 10.1006/nimg.1997.0302.
A method is suggested to ensure independence between the estimated global flow and changes in local flow in PET activation studies. Global flow is estimated as the average of all intracerebral voxels, except those that exhibit a consistent change in flow as a consequence of the experimental design. This is achieved by performing an initial analysis, using all intracerebral voxels for estimation of global flow, in which an F-map depicting task related changes is produced. A second analysis is performed, now excluding all voxels with a P < 0.05 in the F-map when evaluating global flow, thereby ensuring independence from areas changing in a task-dependent manner. The feasibility of the method is demonstrated on phantom data, showing that the distribution is skewed in nonactivated areas when including the activated areas in the calculation of global flow. By excluding these areas the distribution is translated toward zero and becomes consistent with the null-hypothesis. Furthermore, the usefulness of the suggested scheme is demonstrated on human data. Scans performed while subjects watched a movie featuring snakes were contrasted to scans performed while watching white noise, producing highly significant activations of the visual system. When using the traditional way of estimating global flow, deactivations were observed in very large portions of the frontal, parietal, and temporal lobes. When using the method suggested in the present paper these disappeared, which would be more consistent with the expected effects of stimulation. The method was used in conjunction with both ratio and ANCOVA adjustment with very similar results.
本文提出了一种方法，以确保在PET激活研究中估计的全局血流与局部血流变化之间相互独立。全局血流被估计为所有脑内体素的平均值，但不包括那些因实验设计而呈现血流一致变化的体素。这是通过进行初步分析来实现的，即使用所有脑内体素估计全局血流，并生成一个描绘任务相关变化的F图。然后进行第二次分析，在评估全局血流时排除F图中P<0.05的所有体素，从而确保与以任务依赖方式变化的区域相互独立。该方法在体模数据上证明了其可行性，结果表明，在计算全局血流时若包含激活区域，非激活区域的分布会出现偏斜。通过排除这些区域，分布向零平移并与零假设一致。此外，该方案在人体数据上也证明了其有效性。让受试者观看有蛇的电影时进行的扫描与观看白噪声时进行的扫描进行对比，结果显示视觉系统有高度显著的激活。当使用传统方法估计全局血流时，在额叶、顶叶和颞叶的很大一部分区域观察到了失活。当使用本文提出的方法时，这些失活现象消失了，这与预期的刺激效果更一致。该方法与比率调整和协方差分析调整结合使用，结果非常相似。
