Douglas Mental Health University Institute, McGill University, Montreal, Canada.
Douglas Mental Health University Institute, McGill University, Montreal, Canada; Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
Neuroimage. 2017 Apr 1;149:233-243. doi: 10.1016/j.neuroimage.2017.01.025. Epub 2017 Feb 1.
Computational anatomy studies typically use T1-weighted magnetic resonance imaging contrast to look at local differences in cortical thickness or grey matter volume across time or subjects. This type of analysis is a powerful and non-invasive tool to probe anatomical changes associated with neurodevelopment, aging, disease or experience-induced plasticity. However, these comparisons could suffer from biases arising from vascular and metabolic subject- or time-dependent differences. Differences in blood flow and volume could be caused by vasodilation or differences in vascular density, and result in a larger signal contribution of the blood compartment within grey matter voxels. Metabolic changes could lead to differences in dissolved oxygen in brain tissue, leading to T1 shortening. Here, we analyze T1 maps and T1-weighted images acquired during different breathing conditions (ambient air, hypercapnia (increased CO) and hyperoxia (increased O)) to evaluate the effect size that can be expected from changes in blood flow, volume and dissolved O concentration in computational anatomy studies. Results show that increased blood volume from vasodilation during hypercapnia is associated with an overestimation of cortical thickness (1.85%) and grey matter volume (3.32%), and that both changes in O concentration and blood volume lead to changes in the T1 value of tissue. These results should be taken into consideration when interpreting existing morphometry studies and in future study design. Furthermore, this study highlights the overlap in structural and physiological MRI, which are conventionally interpreted as two independent modalities.
计算解剖学研究通常使用 T1 加权磁共振成像对比来观察皮质厚度或灰质体积在时间或受试者之间的局部差异。这种类型的分析是一种强大的、非侵入性的工具，可以探测与神经发育、衰老、疾病或经验诱导的可塑性相关的解剖变化。然而，这些比较可能会受到与血管和代谢有关的、与受试者或时间相关的差异的影响。血流和体积的差异可能是由血管扩张或血管密度的差异引起的，从而导致灰质体素中血液部分的信号贡献更大。代谢变化可能导致脑组织中溶解氧的差异，从而导致 T1 缩短。在这里，我们分析了在不同呼吸条件（环境空气、高碳酸血症（增加 CO）和高氧血症（增加 O））下获得的 T1 图谱和 T1 加权图像，以评估血流、体积和溶解 O 浓度变化在计算解剖学研究中可以预期的效应大小。结果表明，高碳酸血症期间血管扩张引起的血液体积增加与皮质厚度（1.85%）和灰质体积（3.32%）的高估有关，而 O 浓度和血液体积的变化都会导致组织 T1 值的变化。在解释现有的形态计量学研究和未来的研究设计时，应考虑到这些结果。此外，本研究强调了结构和生理 MRI 的重叠，这两种 MRI 通常被解释为两种独立的模式。
