Pfeuffer Josef, Shmuel Amir, Keliris Georgios A, Steudel Thomas, Merkle Hellmut, Logothetis Nikos K
Max-Planck Institute for Biological Cybernetics, Department Physiology of Cognitive Processes, 72076 Tübingen, Germany.
Magn Reson Imaging. 2007 Jul;25(6):869-82. doi: 10.1016/j.mri.2007.03.002. Epub 2007 Apr 23.
Functional MR imaging of the alert, behaving monkey is being used more and more often to detect activation patterns and guide electrophysiological research investigating the neural basis of behavior. Several labs have reported fMRI data from the awake monkey, but none of them has studied and systematically corrected the effects of monkeys' motion on fMRI time series. In this study, a significant refinement of acquisition and correction strategies is reported that can be used to minimize magnetic susceptibility artifacts induced by respiration and by jaw and body movement. Real-time acquisition of sensor signals (e.g., signals induced by jaw and body movement) and MR navigator data were combined to optimize fMRI signal-correction strategies. Within trials, the artifact-induced off-resonance changes were small and mainly reflected the effects of respiration; between trials, movements caused major changes of global frequency and shim (>20 Hz/cm). Several methods were used to assess the stability of the fMRI series: k-space analysis ('dynamic intensity and off-resonance changes in k-space', dubbed DICK and DORK) and image analysis using a Laplace operator and a center-of-mass metric. The variability between trials made it essential to correct for inter-trial variations. On the other hand, images were sufficiently stable with our approach to perform fMRI evaluations on single trials before averaging of trials. Different motion correction strategies were compared: DORK, McFLIRT (rigid body model with three translations and three rotations) and 2D image alignment based on a center-of-mass detection (in-plane translation). The latter yielded the best results and proved to be fast and robust for intra- and inter-trial alignment. Finally, fMRI in the behaving monkey was tested for spatial and temporal reproducibility on a trial-to-trial basis. Highly activated voxels also displayed good reproducibility between trials. On average, the BOLD amplitude response to a short 3-s visual stimulus was close to 2%.
功能磁共振成像正在越来越多地用于清醒、行为状态下的猴子，以检测激活模式并指导研究行为神经基础的电生理研究。几个实验室已经报告了清醒猴子的功能磁共振成像数据，但没有一个研究并系统地校正猴子运动对功能磁共振成像时间序列的影响。在本研究中，报告了采集和校正策略的重大改进，可用于最小化由呼吸以及颌部和身体运动引起的磁化率伪影。将传感器信号（例如，由颌部和身体运动引起的信号）的实时采集与磁共振导航数据相结合，以优化功能磁共振成像信号校正策略。在试验过程中，伪影引起的失谐变化很小，主要反映呼吸的影响；在试验之间，运动会导致全局频率和匀场的重大变化（>20 Hz/cm）。使用了几种方法来评估功能磁共振成像序列的稳定性：k空间分析（“k空间中的动态强度和失谐变化”，称为DICK和DORK）以及使用拉普拉斯算子和质心度量的图像分析。试验之间的变异性使得校正试验间变化至关重要。另一方面，我们的方法使图像足够稳定，以便在试验平均之前对单个试验进行功能磁共振成像评估。比较了不同的运动校正策略：DORK、McFLIRT（具有三个平移和三个旋转的刚体模型）以及基于质心检测的二维图像配准（平面内平移）。后者产生了最佳结果，并被证明对于试验内和试验间配准快速且稳健。最后，在逐次试验的基础上测试了行为猴子中功能磁共振成像的空间和时间可重复性。高度激活的体素在试验之间也显示出良好的可重复性。平均而言，对短3秒视觉刺激的血氧水平依赖（BOLD）幅度响应接近2%。
