Optimal EPI parameters for reduction of susceptibility-induced BOLD sensitivity losses: A whole-brain analysis at 3 T and 1.5 T
Optimal EPI parameters for reduction of susceptibility-induced BOLD sensitivity losses: A whole-brain analysis at 3 T and 1.5 T
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DOI：
10.1016/j.neuroimage.2006.07.029
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发表时间：
2006-11-01
期刊：
影响因子：
5.7
通讯作者：
Deichmann, Ralf
中科院分区：
文献类型：
--
作者：
Weiskopf, Nikolaus;Hutton, Chloe;Deichmann, Ralf
大多数功能磁共振成像（fMRI）研究使用快速梯度回波回波平面成像（GE EPI）记录血氧水平依赖（BOLD）信号。然而，GE EPI可能遭受由静磁场中的不均匀性引起的大量信号丢失。这些场不均匀性发生在空气/组织界面附近，因为它们是由磁化率的变化产生的。因此，功能磁共振成像研究往往是有限的降低BOLD敏感性（BS）在大脑下部区域。最近，已经开发了一种方法，该方法允许通过专门调整切片倾斜、相位编码（PE）的方向和z匀场矩来优化丢失区域中的BS。然而，仅报告了眶额皮质（OFC）和下颞叶的最佳成像参数。本研究确定了最佳的切片倾斜，PE方向，并在3 T和1.5 T，否则使用标准的功能磁共振成像采集参数的z-匀场矩。结果报告所有的大脑区域，产生一个最佳参数的全脑图谱。在这两种场强下，最佳参数在OFC的许多体素中将BS增加60%以上，在其他脱落区域中至少增加30%。BS增益在3 T时更普遍，表明在更高的磁场下，漏失补偿的益处增加。即使是一个大的大脑区域的平均BS，例如，包括内侧OFC，可以增加超过15%。最佳参数的地图允许评估的可行性和改善功能磁共振成像的大脑区域受易感性引起的BS损失。(c)2006年爱思唯尔公司All rights reserved.
Most functional magnetic resonance imaging (fMRI) studies record the blood oxygen level-dependent (BOLD) signal using fast gradient-echo echo-planar imaging (GE EPI). However, GE EPI can suffer from substantial signal dropout caused by inhomogeneities in the static magnetic field. These field inhomogeneities occur near air/tissue interfaces, because they are generated by variations in magnetic susceptibilities. Thus, fMRI studies are often limited by a reduced BOLD sensitivity (BS) in inferior brain regions. Recently, a method has been developed which allows for optimizing the BS in dropout regions by specifically adjusting the slice tilt, the direction of the phase-encoding (PE), and the z-shim moment. However, optimal imaging parameters were only reported for the orbitofrontal cortex (OFC) and inferior temporal lobes. The present study determines the optimal slice tilt, PE direction, and z-shim moment at 3 T and 1.5 T, otherwise using standard fMRI acquisition parameters. Results are reported for all brain regions, yielding a whole-brain atlas of optimal parameters. At both field strengths, optimal parameters increase the BS by more than 60% in many voxels in the OFC and by at least 30% in the other dropout regions. BS gains are shown to be more widespread at 3 T, suggesting an increased benefit from the dropout compensation at higher fields. Even the mean BS of a large brain region, e.g., encompassing the medial OFC, can be increased by more than 15%. The maps of optimal parameters allow for assessing the feasibility and improving fMRI of brain regions affected by susceptibility-induced BS losses. (c) 2006 Elsevier Inc. All rights reserved.