Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, UK; Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, DE, Germany.
Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, UK.
Neuroimage. 2018 Jun;173:113-126. doi: 10.1016/j.neuroimage.2018.02.020. Epub 2018 Feb 14.
As energy metabolism in the brain is largely oxidative, the measurement of cerebral metabolic rate of oxygen consumption (CMRO) is a desirable biomarker for quantifying brain activity and tissue viability. Currently, PET techniques based on oxygen isotopes are the gold standard for obtaining whole brain CMRO maps. Among MRI techniques that have been developed as an alternative are dual calibrated fMRI (dcFMRI) methods, which exploit simultaneous measurements of BOLD and ASL signals during a hypercapnic-hyperoxic experiment to modulate brain blood flow and oxygenation. In this study we quantified the repeatability of a dcFMRI approach developed in our lab, evaluating its limits and informing its application in studies aimed at characterising the metabolic state of human brain tissue over time. Our analysis focussed on the estimates of oxygen extraction fraction (OEF), cerebral blood flow (CBF), CBF-related cerebrovascular reactivity (CVR) and CMRO based on a forward model that describes analytically the acquired dual echo GRE signal. Indices of within- and between-session repeatability are calculated from two different datasets both at a bulk grey matter and at a voxel-wise resolution and finally compared with similar indices obtained from previous MRI and PET measurements. Within- and between-session values of intra-subject coefficient of variation (CV) calculated from bulk grey matter estimates 6.7 ± 6.6% (mean ± std.) and 10.5 ± 9.7% for OEF, 6.9 ± 6% and 5.5 ± 4.7% for CBF, 12 ± 9.7% and 12.3 ± 10% for CMRO. Coefficient of variation (CV) and intraclass correlation coefficient (ICC) maps showed the spatial distribution of the repeatability metrics, informing on the feasibility limits of the method. In conclusion, results show an overall consistency of the estimated physiological parameters with literature reports and a satisfactory level of repeatability considering the higher spatial sensitivity compared to other MRI methods, with varied performance depending on the specific parameter under analysis, on the spatial resolution considered and on the study design.
由于大脑中的能量代谢主要是氧化的，因此测量大脑氧消耗的代谢率（CMRO）是量化大脑活动和组织活力的理想生物标志物。目前，基于氧同位素的 PET 技术是获得全脑 CMRO 图的金标准。作为替代方法，已经开发出了 MRI 技术，包括双校准 fMRI（dcFMRI）方法，该方法利用在高碳酸血症-高氧实验期间同时测量 BOLD 和 ASL 信号来调节脑血流和氧合。在这项研究中，我们量化了我们实验室开发的 dcFMRI 方法的可重复性，评估了其局限性，并为其在旨在随时间表征人脑组织代谢状态的研究中的应用提供了信息。我们的分析重点是基于描述所采集的双回波 GRE 信号的分析模型的氧提取分数（OEF）、脑血流（CBF）、与 CBF 相关的脑血管反应性（CVR）和 CMRO 的估计值。从两个不同的数据集计算了两次会话之间的重复性指标，分别在整体灰质和体素水平上进行了比较，并最终与以前的 MRI 和 PET 测量获得的类似指标进行了比较。从整体灰质估计值中计算出的个体内变异系数（CV）的两次会话内和两次会话间值分别为 OEF 的 6.7±6.6%（平均值±标准差）和 10.5±9.7%，CBF 的 6.9±6%和 5.5±4.7%，CMRO 的 12±9.7%和 12.3±10%。CV 和组内相关系数（ICC）图显示了重复性指标的空间分布，为该方法的可行性极限提供了信息。总之，结果表明，与文献报告相比，所估计的生理参数具有总体一致性，并且与其他 MRI 方法相比具有更高的空间灵敏度，考虑到重复性水平令人满意，其性能取决于具体的分析参数、考虑的空间分辨率和研究设计。
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