HYPERCAPNBIC NORMALIZATION OF BOLD FMRI: COMPARISON ACROSS FIELD STRENGTHS & PU

该子项目是利用 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 中心，不一定是研究者的机构。 血氧水平依赖性（BOLD）功能磁共振成像（fMRI）信号对神经刺激的反应受到许多与刺激无关的因素的影响。这些因素是生理因素，如静息静脉脑血容量（CBV（v））和血管大小，以及实验因素，如脉冲序列和静磁场强度（B（0））。因此，很难比较不同受试者、场强和脉冲序列的任务诱发的fMRI信号。这个问题可以通过由整体高碳酸血症诱导的BOLD信号归一化神经活动诱导的BOLD fMRI响应来克服。为了证明BOLD标准化方法的有效性，在人类受试者中进行了1.5、4和7 T的梯度回波BOLD fMRI和4 T的自旋回波BOLD fMRI。对于神经刺激，受试者以2 Hz的频率进行连续的手指运动，而对于全局刺激，受试者呼吸5%的CO（2）气体混合物。在所有条件下，主要包含大静脉的体素和主要包含活动组织的体素（即，毛细血管和小静脉）在高碳酸血症正常化后表现出可区分的行为。这使得功能活动可以更准确地定位和量化的基础上的变化，静脉血氧单独。由运动任务引起的标准化BOLD信号在不同的磁场和脉冲序列中是一致的，并且与脑血流量测量结果相对应。我们的数据表明，高碳酸血症正常化方法可以提高BOLD信号的空间特异性和解释，允许比较受试者，场强和脉冲序列的BOLD信号。为这种方法提供了一个理论框架。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) signal response to neural stimulation is influenced by many factors that are unrelated to the stimulus. These factors are physiological, such as the resting venous cerebral blood volume (CBV(v)) and vessel size, as well as experimental, such as pulse sequence and static magnetic field strength (B(0)). Thus, it is difficult to compare task-induced fMRI signals across subjects, field strengths, and pulse sequences. This problem can be overcome by normalizing the neural activity-induced BOLD fMRI response by a global hypercapnia-induced BOLD signal. To demonstrate the effectiveness of the BOLD normalization approach, gradient-echo BOLD fMRI at 1.5, 4, and 7 T and spin-echo BOLD fMRI at 4 T were performed in human subjects. For neural stimulation, subjects performed sequential finger movements at 2 Hz, while for global stimulation, subjects breathed a 5% CO(2) gas mixture. Under all conditions, voxels containing primarily large veins and those containing primarily active tissue (i.e., capillaries and small veins) showed distinguishable behavior after hypercapnic normalization. This allowed functional activity to be more accurately localized and quantified based on changes in venous blood oxygenation alone. The normalized BOLD signal induced by the motor task was consistent across different magnetic fields and pulse sequences, and corresponded well with cerebral blood flow measurements. Our data suggest that the hypercapnic normalization approach can improve the spatial specificity and interpretation of BOLD signals, allowing comparison of BOLD signals across subjects, field strengths, and pulse sequences. A theoretical framework for this method is provided.