Selection of voxel size and slice orientation for fMRI in the presence of susceptibility field gradients: application to imaging of the amygdala
Selection of voxel size and slice orientation for fMRI in the presence of susceptibility field gradients: application to imaging of the amygdala
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DOI：
10.1016/s1053-8119(03)00091-0
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发表时间：
2003-07-01
期刊：
影响因子：
5.7
通讯作者：
Panych, LP
中科院分区：
文献类型：
--
作者：
Chen, NK;Dickey, CC;Panych, LP
体素几何形状对血氧水平依赖性（BOLD）信号可检测性的影响进行了评估，并在本报告中开发了一种选择适当体素几何形状的定量方法。介绍了该技术在提高人类杏仁核BOLD灵敏度方面的应用。实验测量了1.5 T和3t时的电场不均匀性，并观察到人类杏仁核的优势磁化场梯度大致沿上下方向分布。基于场映射的研究，最佳的切片方向选择是一个倾斜的伪冠状面，其频率编码方向平行于从每个受试者测得的场梯度。实验中，通过比较不同切片方向的时间序列回波平面成像信号的归一化标准差，证实了这一点。在缺乏功能性刺激的情况下。需要通过精心设计的功能性磁共振成像研究进一步确认。虽然BOLD的灵敏度通常可以通过与激活体积相称的体素大小来提高，但我们的定量分析表明，最佳体素大小也取决于磁化场梯度，并且通常小于激活体积。通过混合模拟证实了预测的现象，其中功能激活被数学地添加到实验获得的休息期回波平面成像数据中。(C) 2003 Elsevier Science（美国）版权所有。
The impact of voxel geometry on the blood oxygenation level-dependent (BOLD) signal detectability in the presence of field inhomogeneity is assessed and a quantitative approach to selecting appropriate voxel geometry is developed in this report. Application of the developed technique to BOLD sensitivity improvement of the human amygdala is presented. Field inhomogeneity was measured experimentally at 1.5 T and 3 T and the dominant susceptibility field gradient in the human amygdala was observed approximately along the superior-inferior direction. Based on the field mapping studies, an optimal selection for the slice orientation would be an oblique pseudo-coronal plane with its frequency-encoding direction parallel to the field gradient measured from each subject. Experimentally this was confirmed by comparing the normalized standard deviation of time-series echo-planar imaging signals acquired with different slice orientations. in the absence of a functional stimulus. A further confirmation with a carefully designed functional magnetic resonance imaging study is needed. Although the BOLD sensitivity may generally be improved by a voxel size commensurable with the activation volume, our quantitative analysis shows that the optimal voxel size also depends on the susceptibility field gradient and is usually smaller than the activation volume. The predicted phenomenon is confirmed with a hybrid simulation, in which the functional activation was mathematically added to the experimentally acquired rest-period echo-planar imaging data. (C) 2003 Elsevier Science (USA). All rights reserved.