Bodurka J, Ye F, Petridou N, Murphy K, Bandettini P A
Functional MRI Facility, National Institute of Mental Health (NIMH), National Institutes of Health (NIH), 10 Center Drive, Building 10, Room 1D80, Bethesda, MD 20892-1148, USA.
Neuroimage. 2007 Jan 15;34(2):542-9. doi: 10.1016/j.neuroimage.2006.09.039. Epub 2006 Nov 13.
This work addresses the choice of the imaging voxel volume in blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI). Noise of physiological origin that is present in the voxel time course is a prohibitive factor in the detection of small activation-induced BOLD signal changes. If the physiological noise contribution dominates over the temporal fluctuation contribution in the imaging voxel, further increases in the voxel signal-to-noise ratio (SNR) will have diminished corresponding increases in temporal signal-to-noise (TSNR), resulting in reduced corresponding increases in the ability to detect activation induced signal changes. On the other hand, if the thermal and system noise dominate (suggesting a relatively low SNR) further decreases in SNR can prohibit detection of activation-induced signal changes. Here we have proposed and called the "suggested" voxel volume for fMRI the volume where thermal plus system-related and physiological noise variances are equal. Based on this condition we have created maps of fMRI suggested voxel volume from our experimental data at 3T, since this value will spatially vary depending on the contribution of physiologic noise in each voxel. Based on our fast EPI segmentation technique we have found that for gray matter (GM), white matter (WM), and cerebral spinal fluid (CSF) brain compartments the mean suggested cubical voxel volume is: (1.8 mm)3, (2.1 mm)3 and (1.4 mm)3, respectively. Serendipitously, (1.8 mm)3 cubical voxel volume for GM approximately matches the cortical thickness, thus optimizing BOLD contrast by minimizing partial volume averaging. The introduced suggested fMRI voxel volume can be a useful parameter for choice of imaging volume for functional studies.
这项工作探讨了血氧水平依赖（BOLD）功能磁共振成像（fMRI）中成像体素体积的选择。体素时间历程中存在的生理源性噪声是检测小激活诱导的BOLD信号变化的一个阻碍因素。如果生理噪声贡献在成像体素中超过了时间波动贡献，那么体素信噪比（SNR）的进一步增加将导致时间信噪比（TSNR）的相应增加减少，从而导致检测激活诱导信号变化的能力的相应增加减少。另一方面，如果热噪声和系统噪声占主导（表明信噪比相对较低），信噪比的进一步降低会阻碍激活诱导信号变化的检测。在这里，我们提出并将fMRI的“建议”体素体积称为热噪声加系统相关噪声与生理噪声方差相等的体积。基于这一条件，我们根据3T实验数据创建了fMRI建议体素体积图，因为该值会因每个体素中生理噪声的贡献而在空间上有所变化。基于我们的快速EPI分割技术，我们发现对于灰质（GM）、白质（WM）和脑脊液（CSF）脑区，平均建议的立方体素体积分别为：(1.8 mm)³, (2.1 mm)³ 和 (1.
