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，空气/组织界面周围存在大脑中磁场的局部变化。磁场中的这些局部变化的行为类似于施加成像梯度，并且可以影响功能MRI（fMRI）采集中的采集质量和信号的功能加权。该建议的主要假设是，在大脑中的空气/组织界面附近的区域中的fMRI的灵敏度将具有很强的依赖性：采集轨迹，采集定时，磁场匀场，受试者定位和磁场强度。这些协议选择和解剖学变化可能是单独和共同的重要，导致整个大脑对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fMRI灵敏度的影响，文献产生的结果是不完整的，有时是误导性的。该提案将检查磁场诱导的fMRI灵敏度的变化，作为以下因素的函数：1）采集序列和时间，2）受试者定位，3）磁场强度。将在多个指定方向上测量志愿者参与者的三维磁场图，以检查fMRI研究中受试者头部音高变化的影响。将沿着分析个体间解剖变异性的影响，检查由于位置引起的fMRI灵敏度变化。此外，将通过使用产生类似于功能性大脑激活的信号的稳健屏气任务来验证fMRI灵敏度的变化。将检查从磁化率梯度估计的fMRI灵敏度变化，以查看它们是否解释屏气数据的显著差异。将识别受试者之间在预测的fMRI灵敏度方面具有高变异性的大脑区域。此外，将开发并广泛分发功能磁共振成像敏感性评估工具，使神经成像研究人员和临床医生能够根据采集轨迹和受试者的场图评估不同大脑区域的功能数据质量。该工具将能够评价与磁场梯度相关的方案选择。此外，该工具将为未来设计用于研究具有高磁化率的大脑区域的成像协议提供动力。 公共卫生相关性：由于大脑附近的空气空间引起的磁场变化可能对大脑某些区域的功能性磁共振成像的灵敏度产生显著影响。虽然这些信息在解释功能成像结果时至关重要，但在目前的神经影像学研究中，这种影响被忽略了。我们提出了一个框架，用于评估这些空间周围的磁场梯度的影响，并确定协议设置如何影响其对功能成像研究的影响。

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.