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IMPROVEMENT OF DETECTABILITY OF BRAIN ACTIVATION IN FUNCTIONAL MAGNETIC RESONANCE IMAGING

提高功能磁共振成像中大脑激活的可检测性

基本信息

批准号：
12670848
负责人：
DATE Hiroyuki
金额：
$ 1.86万
依托单位：
HOKKAIDO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-12670848/
关键词：
magnetic resonance brain function medical imaging image processing artifac MRI

项目摘要

The purpose of this study was to improve the detectability of brain activated area in functional magnetic resonance imaging (fMRI). In fMRI, influence of cardiac pulsation is the most difficult factor to be eliminated for enhancing the detectability since it induces intracranial vibration. We found that partial volume of cerebrospinal fluid in the activated voxel vibrates owing to cardiac pulsation and then the detectability of activated area deteriorates. PhysionFix is one of the best software packages to make physiological corrections in fMRI. We clarified that the efficacy of PhysioFix depends on correlation between cardiac pulsation or respiration and the task paradigm frequency. A signal increase in fMRI has been believed to be a result of a decrease of paramagnetic deoxygenated hemoglobin (deoxyHb) content in the neutral activation area. However, experimental studies using optical techniques, such as near infrared spectroscopy (NIRS), that directly measure hemoglobin changes show disagreements with the canonical blood oxygenation level dependent (BOLD) theory. To improve the detectability in fMRI, it was necessary to make clear the reason for the disagreements and to understand the true hemodynamics associated with brain activation. We developed a new theory bridging magnetic resonance (MR) signal and hemoglobin changes. It was found that the deviation from the value expected by the canonical BOLD theory is caused by the fact that the BOLD theory ignores the effect of the capillaries. The new theory enables us to explain the paradoxical phenomena of the oxygenated hemoglobin and deoxyHb contributions to the MR signal and to have a new insight into the precise hemodynamics of activation by analyzing fMRI and NIRS data. We concluded that the capillary hemodynamics of activation focus should be taken into account for further improvements of detectability in fMRI, in addition to counter-measures against the influence of physiological fluctuations.

本研究旨在提高功能性磁共振成像(FMRI)中脑激活区的可探测性。在功能磁共振成像中，心脏搏动的影响是最难消除的因素，因为它会引起颅内振动，从而提高检测能力。我们发现激活的体素中的脑脊液的部分体积由于心脏的跳动而振动，从而使激活区域的可探测性变差。PhysionFix是在功能磁共振成像中进行生理校正的最好的软件包之一。我们阐明了PhysioFix的有效性取决于心跳或呼吸与任务范例频率之间的相关性。功能磁共振成像信号的增加被认为是中性激活区顺磁脱氧血红蛋白(DeoxHb)含量减少的结果。然而，使用光学技术，如近红外光谱(NIRS)，直接测量血红蛋白变化的实验研究表明，与典型的血氧水平依赖(BOLD)理论不一致。为了提高功能磁共振成像的可探测性，有必要弄清楚分歧的原因，并了解与脑激活相关的真实血流动力学。我们开发了一种新的理论，将磁共振(MR)信号与血红蛋白变化联系起来。结果发现，偏离典型BOLD理论的期望值是由于BOLD理论忽略了毛细血管的影响所致。这一新理论使我们能够解释有氧血红蛋白和脱氧Hb对磁共振信号贡献的矛盾现象，并通过分析fMRI和NIRS数据对激活的精确血流动力学有一个新的见解。我们的结论是，除了针对生理波动的影响采取对策外，还应考虑激活灶的毛细血管血流动力学，以进一步提高fMRI的检测能力。