Department of Psychiatry and Psychotherapy, Medical University of Vienna, Austria.
Neuroimage. 2013 Nov 15;82:336-43. doi: 10.1016/j.neuroimage.2013.06.010. Epub 2013 Jun 12.
Progressing from 3T to 7 T functional MRI enables marked improvements of human brain imaging in vivo. Although direct comparisons demonstrated advantages concerning blood oxygen level dependent (BOLD) signal response and spatial specificity, these mostly focused on single brain regions with rather simple tasks. Considering that physiological noise also increases with higher field strength, it is not entirely clear whether the advantages of 7T translate equally to the entire brain during tasks which elicit more complex neuronal processing. Therefore, we investigated the difference between 3T and 7 T in response to transcutaneous electrical painful and non-painful stimulation in 22 healthy subjects. For painful stimuli vs. baseline, stronger activations were observed at 7 T in several brain regions including the insula and supplementary motor area, but not the secondary somatosensory cortex (p<0.05 FWE-corrected). Contrasting painful vs. non-painful stimulation limited the differences between the field strengths to the periaqueductal gray (PAG, p<0.001 uncorrected) due to a similar signal increase at 7 T for both the target and specific control condition in most brain regions. This regional specificity obtained for the PAG at higher field strengths was confirmed by an additional spatial normalization strategy optimized for the brainstem. Here, robust BOLD responses were obtained in the dorsal PAG at 7 T (p<0.05 FWE-corrected), whereas at 3T activation was completely missing for the contrast against non-painful stimuli. To summarize, our findings support previously reported benefits obtained at ultra-high field strengths also for complex activation patterns elicited by painful electrical stimulation. However, this advantage depends on the region and even more on the contrast of interest. The greatest gain at 7 T was observed within the small brainstem region of the PAG, where the increased field strength offered marked improvement for the localization of activation foci with high spatial specificity.
从 3T 到 7T 的功能磁共振成像（fMRI）能够显著改善人体大脑的活体成像。虽然直接比较显示了血氧水平依赖（BOLD）信号响应和空间特异性方面的优势，但这些主要集中在具有相对简单任务的单个脑区。考虑到生理噪声也随着场强的增加而增加，目前尚不清楚在引发更复杂神经处理的任务中，7T 的优势是否同样适用于整个大脑。因此，我们在 22 名健康受试者中研究了经皮电刺激痛觉和非痛觉刺激时 3T 和 7T 之间的差异。与基线相比，在几个脑区（包括岛叶和辅助运动区）中观察到 7T 时疼痛刺激的激活更强，但在次级体感皮层中则没有（p<0.05 经 FWE 校正）。与疼痛刺激相比，疼痛刺激与非疼痛刺激的对比将场强之间的差异限制在导水管周围灰质（periaqueductal gray，PAG），这是因为在大多数脑区中，7T 对两个目标和特定对照条件的信号均有相似的增加。在更高场强下，PAG 的这种区域特异性是通过一种针对脑干进行优化的额外空间归一化策略来确认的。在这里，在 7T 时（p<0.05 经 FWE 校正），在 PAG 的背侧获得了强烈的 BOLD 反应，而在 3T 时，与非痛觉刺激的对比则完全没有激活。总之，我们的发现支持了之前在超高场强下获得的复杂激活模式的优势，这些模式由疼痛电刺激引发。然而，这种优势取决于区域，甚至更取决于感兴趣的对比。在 PAG 的小脑干区域，7T 带来的增益最大，增加的场强为具有高空间特异性的激活焦点的定位提供了显著改善。
