Controlling sensitivity bias in functional MRI studies due to field inhomogeneity

描述（由申请人提供）：在磁共振成像（MRI）研究期间，大脑中磁场的局部变化存在于空气/组织界面周围。磁场的这些局部变化与应用成像梯度的行为相似，并且可以影响采集的质量和功能MRI （fMRI）采集中信号的功能加权。本研究的主要假设是fMRI在大脑中靠近空气/组织界面区域的灵敏度将强烈依赖于：获取轨迹、获取时间、磁场垫、受试者定位和磁场强度。这些方案的选择和解剖学上的改变可以单独或共同产生重大影响，从而导致对整个大脑功能信号的广泛敏感性。由于研究人员目前忽略了磁场分布对回波时间和功能磁共振成像灵敏度的影响，因此文献所创造的结果是不完整的，有时甚至是误导性的。本提案将研究磁场诱导的fMRI灵敏度的变化，作为以下函数：1)采集顺序和时间，2)受试者定位，以及3)磁场强度。在fMRI研究中，将测量志愿者在多个指定方向上的三维磁场图，以检查受试者头部音高变化的影响。fMRI敏感性的变化，由于位置将检查与分析个体之间的解剖变异的影响。此外，fMRI敏感性的变化将通过使用一个强大的屏气任务来验证，该任务产生类似于功能性大脑激活的信号。从敏感性梯度估计的fMRI敏感性变化将被检查，看看它们是否解释了屏气数据的显著差异。大脑的区域将被识别，在预测的fMRI敏感性在受试者之间具有高度可变性。此外，fMRI敏感性评估工具将被开发和广泛分发，这将允许神经成像研究人员和临床医生评估不同大脑区域的功能数据的质量，给定它们的获取轨迹和受试者的场图。该工具将能够评估协议选择，因为它们与磁场梯度有关。此外，该工具将为未来设计用于研究大脑高磁化率区域的成像方案提供动力。

DESCRIPTION (provided by applicant): During a magnetic resonance imaging (MRI) study, local variations of the magnetic field in the brain exist around air/tissue interfaces. These local variations in the magnetic field behave similarly to apply imaging gradients and can affect both the quality of the acquisition and the functional weighting of the signal in a functional MRI (fMRI) acquisition. The main hypothesis of this proposal is that the sensitivity of fMRI in regions near air/tissue interfaces in the brain will have a strong dependence on: acquisition trajectory, acquisition timing, magnetic field shim, subject positioning, and magnetic field strength. These protocol choices and anatomical changes can be significant both individually and together, resulting in a wide range of sensitivity to functional signals throughout the brain. Because investigators are currently ignoring the effect of magnetic field distribution on echo time and fMRI sensitivity, the literature is creating results that are incomplete and, at times, misleading. This proposal will examine changes in magnetic field induced fMRI sensitivity as a function of: 1) acquisition sequence and timing, 2) subject positioning, and 3) magnetic field strength. Three-dimensional magnetic field maps will be measured on volunteer participants in multiple, specified orientations to examine the impact of variations in the pitch of a subjects head in an fMRI study. fMRI sensitivity changes due to position will be examined along with an analysis of the impact of anatomical variability among individuals. Additionally, changes in fMRI sensitivity will be validated by using a robust breath hold task that produces a signal similar to functional brain activations. The estimated fMRI sensitivity changes from susceptibility gradients will be examined to see if they explain significant variance in the breath hold data. Regions of the brain will be identified that have high variability in predicted fMRI sensitivity between subjects. Additionally, an fMRI sensitivity assessment tool will be developed and widely distributed that will allow neuroimaging researchers and clinicians to assess the quality of the functional data in various brain regions given their acquisition trajectory and a field map of a subject. This tool will enable the evaluation of protocol choices as they relate to magnetic field gradients. Further, the tool will provide motivation for future imaging protocols designed to study regions of the brain with high magnetic susceptibility. PUBLIC HEALTH RELEVANCE: Magnetic field variations due to air spaces next to the brain can have a dramatic effect on the sensitivity of functional magnetic resonance imaging in certain regions of the brain. Although this information is critical in interpreting functional imaging results, the effect is ignored in current neuroimaging studies. We propose a framework for evaluating the effect of magnetic field gradients around these airspaces and determine how protocol settings can influence their impact on functional imaging studies.