Max Planck Institute for Biological Cybernetics, High Field Magnetic Resonance Center, Tübingen, Germany; Graduate School of Neural and Behavioural Sciences, International Max Planck Research School, Universität Tübingen, Tübingen, Germany.
Magn Reson Med. 2014 Jan;71(1):209-18. doi: 10.1002/mrm.24656. Epub 2013 Feb 27.
The increased signal-to-noise ratio and blood oxygen level dependent signal at ultra-high field can only help to boost the resolution in functional MRI studies if the spatial specificity of the activation signal is improved. At a field strength of 9.4 T, both gradient-echo and spin-echo based echo-planar imaging were implemented and applied to investigate the specificity of human functional MRI. A finger tapping paradigm was used to acquire functional MRI data with scan parameters similar to standard neuroscientific applications.
Spatial resolution, echo, and readout times were varied to determine their influence on the distribution of the blood oxygen level dependent signal. High-resolution co-localized images were used to classify the signal according to its origin in veins or tissue.
High-quality activation maps were obtained with both sequences. Signal contributions from tissue were found to be smaller or slightly larger than from veins. Gradient-echo echo-planar imaging yielded lower ratios of micro-/macro-vascular signals of around 0.6 than spin-echo based functional MRI, where this ratio varied between 0.75 and 1.02, with higher values for larger echo and shorter readout time.
This study demonstrates the feasibility of human functional MRI at 9.4 T with high spatial specificity. Although venous contributions could not be entirely suppressed, venous effects in spin-echo echo-planar imaging are significantly reduced compared with gradient-echo echo-planar imaging.
在超高场强下，信号与噪声比和血氧水平依赖信号的提高，只有在激活信号的空间特异性得到改善的情况下，才能有助于提高功能磁共振成像研究的分辨率。在 9.4T 的场强下，我们实施了基于梯度回波和自旋回波的回波平面成像，并将其应用于人类功能磁共振的特异性研究。采用手指敲击范式，以类似于标准神经科学应用的扫描参数获取功能磁共振成像数据。
我们改变了空间分辨率、回波和读出时间，以确定它们对血氧水平依赖信号分布的影响。我们使用高分辨率的共定位图像，根据信号的起源是静脉还是组织，对信号进行分类。
两种序列都获得了高质量的激活图。与静脉相比，组织的信号贡献更小或略大。梯度回波的回波平面成像产生的微血管/大血管信号比约为 0.6，而自旋回波的功能磁共振成像的比值在 0.75 到 1.02 之间变化，较大的回波和较短的读出时间产生较高的比值。
本研究证明了在 9.4T 下具有高空间特异性的人类功能磁共振成像的可行性。虽然不能完全抑制静脉贡献，但与梯度回波的回波平面成像相比，自旋回波的回波平面成像中的静脉效应显著降低。
