Griffeth Valerie E M, Blockley Nicholas P, Simon Aaron B, Buxton Richard B
Department of Bioengineering and Medical Scientist Training Program, University of California San Diego, La Jolla, California, United States of America.
PLoS One. 2013 Jun 27;8(6):e68122. doi: 10.1371/journal.pone.0068122. Print 2013.
Functional MRI (fMRI) using the blood oxygenation level dependent (BOLD) signal is a common technique in the study of brain function. The BOLD signal is sensitive to the complex interaction of physiological changes including cerebral blood flow (CBF), cerebral blood volume (CBV), and cerebral oxygen metabolism (CMRO2). A primary goal of quantitative fMRI methods is to combine BOLD imaging with other measurements (such as CBF measured with arterial spin labeling) to derive information about CMRO2. This requires an accurate mathematical model to relate the BOLD signal to the physiological and hemodynamic changes; the most commonly used of these is the Davis model. Here, we propose a new nonlinear model that is straightforward and shows heuristic value in clearly relating the BOLD signal to blood flow, blood volume and the blood flow-oxygen metabolism coupling ratio. The model was tested for accuracy against a more detailed model adapted for magnetic fields of 1.5, 3 and 7T. The mathematical form of the heuristic model suggests a new ratio method for comparing combined BOLD and CBF data from two different stimulus responses to determine whether CBF and CMRO2 coupling differs. The method does not require a calibration experiment or knowledge of parameter values as long as the exponential parameter describing the CBF-CBV relationship remains constant between stimuli. The method was found to work well for 1.5 and 3T but is prone to systematic error at 7T. If more specific information regarding changes in CMRO2 is required, then with accuracy similar to that of the Davis model, the heuristic model can be applied to calibrated BOLD data at 1.5T, 3T and 7T. Both models work well over a reasonable range of blood flow and oxygen metabolism changes but are less accurate when applied to a simulated caffeine experiment in which CBF decreases and CMRO2 increases.
利用血氧水平依赖（BOLD）信号的功能磁共振成像（fMRI）是脑功能研究中的常用技术。BOLD信号对包括脑血流量（CBF）、脑血容量（CBV）和脑氧代谢（CMRO2）在内的生理变化的复杂相互作用敏感。定量fMRI方法的一个主要目标是将BOLD成像与其他测量（如用动脉自旋标记测量的CBF）相结合，以获取有关CMRO2的信息。这需要一个准确的数学模型来将BOLD信号与生理和血流动力学变化联系起来；其中最常用的是戴维斯模型。在此，我们提出了一种新的非线性模型，该模型简单明了，在将BOLD信号与血流量、血容量以及血流-氧代谢耦合率清晰联系起来方面具有启发式价值。该模型针对适用于1.5、3和7T磁场的更详细模型进行了准确性测试。启发式模型的数学形式提出了一种新的比率方法，用于比较来自两种不同刺激反应的BOLD和CBF组合数据，以确定CBF和CMRO2耦合是否不同。只要描述CBF-CBV关系的指数参数在不同刺激之间保持恒定，该方法就不需要校准实验或参数值的知识。结果发现该方法在1.5T和3T时效果良好，但在7T时容易出现系统误差。如果需要关于CMRO2变化的更具体信息，那么在与戴维斯模型相似的准确性下，启发式模型可应用于1.5T、3T和7T的校准BOLD数据。这两种模型在血流量和氧代谢合理变化范围内都能很好地工作，但在应用于模拟咖啡因实验（其中CBF降低而CMRO2增加）时准确性较低。
