SIGNAL AND NOICE CHARACTERISTICS OF HAHN SE AND GE BOLD FMRI AT 7T IN HUMANS

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 在非常高的磁场下，GE BOLD fMRI预计将包含非特定贡献，并且表现出与HSE fMRI数据不同的行为。同样，可以想象，这两种方法对时间序列中的时间不稳定性有不同的贡献，而时间序列最终决定了对比度噪声比(CNR)。我们研究了GE和HSE功能磁共振成像数据中的信号和信号涨落特征，分别优化了7T下的每个对比度。在HSE功能MRI中，激活诱导的分数信号变化(Deltas/S)迅速下降，由于生理过程(SigmaPhys)和热噪声(SigmaTherm)引起的图像到图像波动的标准差(SigmaPhys)与热噪声(SigmaTherm)的比率随着体素体积的增加保持不变。相比之下，GE BOLD的Deltas/S和激活的体素体积几乎与体素大小无关，而sigma(Phys)/sigmaTherm随体素大小的增加而增加。与血管区域相比，组织区域的BOLD信号变化比率(GE/HSE)更接近于1。这些观察得出的结论是，在GE数据中，激活诱导的Deltas/S的空间范围要宽得多，与GE fMRI数据相比，在HSE中引起时间波动的生理过程在毫米距离上失去了一致性。虽然还需要进一步的研究来完全确定它的特征，但HSE数据中的sigmaPhys明显不同于GE数据中的sigmaPhys。结论是，与GE成像相比，HSE成像产生的非特异性信号量显著减少，并且将是人类高分辨率应用的首选方法(而不是GE)。

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. At very high magnetic fields, GE BOLD fMRI is expected to contain nonspecific contributions and behave differently than HSE fMRI data. Similarly, the two approaches can conceivably suffer from different contributions to temporal instabilities in a times series that ultimately determine the contrast-to-noise ratio (CNR). We investigate the signal and signal fluctuation characteristics in GE and HSE fMRI data with the imaging parameters separately optimized for each contrast at 7 T. In HSE fMRI, activation-induced fractional signal change (DeltaS/S) decreased rapidly, and the ratio of standard deviations of image-to-image fluctuations due to physiological processes (sigmaPhys) to thermal noise (sigmaTherm) remained constant with increasing voxel volume. In contrast, DeltaS/S as well as volume of activated voxels was virtually independent of voxel size for GE BOLD, and sigma(Phys)/sigmaTherm increased with increasing voxel size. The ratio of BOLD signal changes (GE/HSE) was much closer to 1 in tissue areas compared to vessel areas. These observations led to the conclusions that the spatial extent of the activation-induced DeltaS/S was much broader in the GE data, and that the physiological processes that give rise to the temporal fluctuations lost coherence over millimeter distances in HSE compared to GE fMRI data. While further studies are needed to characterize it fully, sigmaPhys in HSE data was clearly different than in GE data. It was concluded that HSE imaging yields a significantly reduced amount of nonspecific signals compared to GE imaging, and, would be the method of choice (over GE) for high-resolution applications in humans.