Bianciardi Marta, van Gelderen Peter, Duyn Jeff H
Advanced MRI Section, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland; Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts; Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Building 149, Room 2301, 13th Street, Charlestown, Boston, MA.
Hum Brain Mapp. 2014 May;35(5):2191-205. doi: 10.1002/hbm.22320. Epub 2013 Jul 29.
Although blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) experiments of brain activity generally rely on the magnitude of the signal, they also provide frequency information that can be derived from the phase of the signal. However, because of confounding effects of instrumental and physiological origin, BOLD related frequency information is difficult to extract and therefore rarely used. Here, we explored the use of high field (7 T) and dedicated signal processing methods to extract frequency information and use it to quantify and interpret blood oxygenation and blood volume changes. We found that optimized preprocessing improves detection of task-evoked and spontaneous changes in phase signals and resonance frequency shifts over large areas of the cortex with sensitivity comparable to that of magnitude signals. Moreover, our results suggest the feasibility of mapping BOLD quantitative susceptibility changes in at least part of the activated area and its largest draining veins. Comparison with magnitude data suggests that the observed susceptibility changes originate from neuronal activity through induced blood volume and oxygenation changes in pial and intracortical veins. Further, from frequency shifts and susceptibility values, we estimated that, relative to baseline, the fractional oxygen saturation in large vessels increased by 0.02-0.05 during stimulation, which is consistent to previously published estimates. Together, these findings demonstrate that valuable information can be derived from fMRI imaging of BOLD frequency shifts and quantitative susceptibility changes.
尽管依赖血氧水平的脑功能磁共振成像（BOLD-fMRI）实验通常依赖于信号强度，但它们也提供了可从信号相位中得出的频率信息。然而，由于仪器和生理因素的混杂效应，与BOLD相关的频率信息很难提取，因此很少被使用。在此，我们探索了利用高场强（7T）和专用信号处理方法来提取频率信息，并将其用于量化和解释血氧水平及血容量变化。我们发现，优化的预处理提高了对大脑皮层大面积区域任务诱发和自发的相位信号变化以及共振频率偏移的检测能力，其灵敏度与信号强度相当。此外，我们的结果表明，在至少部分激活区域及其最大引流静脉中绘制BOLD定量磁化率变化图是可行的。与信号强度数据的比较表明，观察到的磁化率变化源自神经元活动，是由软脑膜和皮质内静脉中血容量和氧合的变化所诱导的。此外，根据频率偏移和磁化率值，我们估计，相对于基线，在刺激过程中大血管内的血氧饱和度分数增加了0.02 - 0.05，这与先前发表的估计结果一致。总之，这些发现表明，可从BOLD频率偏移和定量磁化率变化的功能磁共振成像中获得有价值的信息。
