Magnetic resonance imaging of oscillating electrical currents
Magnetic resonance imaging of oscillating electrical currents
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DOI：
10.1073/pnas.1003146107
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发表时间：
2010-05-11
影响因子：
11.1
通讯作者：
Pines, Alexander
中科院分区：
文献类型：
--
作者：
Halpern-Manners, Nicholas W.;Bajaj, Vikram S.;Pines, Alexander
功能磁共振成像已成为研究人员和临床医生的重要工具，他们试图了解伴随感觉和认知过程的神经元激活模式。然而，功能磁共振成像图像的解释依赖于神经元放电和血液动力学反应之间的关系的假设，这些假设没有严格的理论或实验证据。此外，血氧水平依赖性的影响，这相关的MRI可观察到的神经元放电，在一段时间内，这是2个数量级以上的潜在过程，被认为是导致it.here，我们而不是演示实验，直接成像振荡电流的MRI。该方法依赖于施加的射频场和样品中的振荡磁场之间的共振相互作用，因此，允许定量，频率选择性测量电流密度，而无需空间或时间取消。我们将这种方法应用于电流环体模，映射其磁场，并实现检测神经元电流所需的阈值附近的检测灵敏度。由于对比机制是在光谱控制下，我们能够证明斜坡和相位调制的自旋锁辐射如何提高实验的灵敏度和鲁棒性。我们进一步展示了这些方法与远程检测的结合，在这种技术中，MRI实验的编码和检测通过样本流或翻译分离。我们说明，远程检测的MRI允许测量电流在小体积的流动的水具有高灵敏度和空间分辨率。
Functional MRI has become an important tool of researchers and clinicians who seek to understand patterns of neuronal activation that accompany sensory and cognitive processes. However, the interpretation of fMRI images rests on assumptions about the relationship between neuronal firing and hemodynamic response that are not firmly grounded in rigorous theory or experimental evidence. Further, the blood-oxygen-level-dependent effect, which correlates an MRI observable to neuronal firing, evolves over a period that is 2 orders of magnitude longer than the underlying processes that are thought to cause it. Here, we instead demonstrate experiments to directly image oscillating currents by MRI. The approach rests on a resonant interaction between an applied rf field and an oscillating magnetic field in the sample and, as such, permits quantitative, frequency-selective measurements of current density without spatial or temporal cancellation. We apply this method in a current loop phantom, mapping its magnetic field and achieving a detection sensitivity near the threshold required for the detection of neuronal currents. Because the contrast mechanism is under spectroscopic control, we are able to demonstrate how ramped and phase-modulated spin-lock radiation can enhance the sensitivity and robustness of the experiment. We further demonstrate the combination of these methods with remote detection, a technique in which the encoding and detection of an MRI experiment are separated by sample flow or translation. We illustrate that remotely detected MRI permits the measurement of currents in small volumes of flowing water with high sensitivity and spatial resolution.