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Hybrid two-dimensional navigator correction: a new technique to suppress respiratory-induced physiological noise in multi-shot echo-planar functional MRI

机译：混合二维导航仪校正：一种在多次回波平面功能性MRI中抑制呼吸诱发的生理噪声的新技术

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摘要

A troublesome source of physiological noise in functional magnetic resonance imaging (fMRI) is due to the spatio-temporal modulation of the magnetic field in the brain caused by normal subject respiration. fMRI data acquired using echo-planar imaging is very sensitive to these respiratory-induced frequency offsets, which cause significant geometric distortions in images. Because these effects increase with main magnetic field, they can nullify the gains in statistical power expected by the use of higher magnetic fields. As a study of existing navigator correction techniques for echo-planar fMRI has shown that further improvements can be made in the suppression of respiratory-induced physiological noise, a new hybrid two-dimensional (2D) navigator is proposed. Using a priori knowledge of the slow spatial variations of these induced frequency offsets, 2D field maps are constructed for each shot using spatial frequencies between ±0.5 cm−1 in k-space. For multi-shot fMRI experiments, we estimate that the improvement of hybrid 2D navigator correction over the best performance of one-dimensional navigator echo correction translates into a 15% increase in the volume of activation, 6% and 10% increases in the maximum and average t-statistics, respectively, for regions with high t-statistics, and 71% and 56% increases in the maximum and average t-statistics, respectively, in regions with low t-statistics due to contamination by residual physiological noise.
机译：功能性磁共振成像（fMRI）中生理噪声的麻烦来源是由于正常受试者呼吸导致的大脑中磁场的时空调制。使用回波平面成像获取的fMRI数据对这些呼吸引起的频率偏移非常敏感，这些频率偏移会导致图像中的明显几何失真。由于这些效应随主磁场而增加，因此它们可以抵消使用较高磁场所期望的统计功率增益。随着对现有用于回声平面fMRI的导航仪校正技术的研究表明，在抑制呼吸诱发的生理噪声方面可以做进一步的改进，提出了一种新型的混合二维（2D）导航仪。利用这些诱导频率偏移的缓慢空间变化的先验知识，使用k空间中±0.5 cm -1 之间的空间频率为每个镜头构建2D场图。对于多镜头fMRI实验，我们估计混合2D导航仪校正相对于一维导航仪回声校正的最佳性能的改进意味着激活量增加了15％，最大和最大增加了6％和10％。对于具有较高t统计量的区域，由于残留生理噪声的污染，其最大t统计量和平均t统计量分别分别增加了71％和56％。

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