Neurophysiology Imaging Facility Core: Functional and Structural MRI

在过去的几十年里，磁共振成像的扩展极大地改变了科学家、临床医生和公众看待人脑的方式。从本质上讲，核磁共振成像是基于组成各种不同脑组织的水质子的核自旋特性。通过这些质子的共振特性，以及周围组织的不同影响，可以探测这些自旋特性，并最终组装成直接反映解剖结构的图像。此外，血液含量和含氧量会影响这些图像，使人能够在每个时刻局部估计神经活动。后一种技术，功能磁共振成像(FMRI)是目前最有效和最强大的研究人脑活动的方法。它的使用为研究人类认知过程的生理学基础提供了一个抓手，尽管以前还达不到。重要的是，它使我们能够研究精神疾病中大脑的功能和功能障碍，希望加深我们对其原因的理解。 这个名为神经生理学成像设施(NIF)的核心设施结合了电生理学和功能磁共振研究，以及神经药理学和消融研究。这种组合方法的目的是提供对灵长类大脑的解剖学和生理学的描述，比目前在人类中使用非侵入性成像方法所能达到的更详细和全面。在许多情况下，不同类型的实验是同时进行的。例如，在最近的一项研究中，我们在清醒的动物身上同时进行了电生理和fMRI记录。在另一项研究中，神经药物操作与靶向消融和功能磁共振成像相结合，以表现出动物的行为。为了实现这些实验，NIF设施创建并分发为个别灵长类成像实验量身定做的设备。作为一个集中的核心设施，NIF为三个赞助机构(NIMH、NINDS和NEI)的各种研究人员提供服务和产品。在强磁场中测试动物需要开发一系列与MRI兼容的设备，包括动物椅子、约束设备、奖励发放设备、眼睛位置跟踪摄像头和手动反应键。因此，该设施为用户提供了猴子功能磁共振成像的这些和其他关键组件，允许他们以最小的开发开始他们的研究。 NIF设施中的扫描程序需要每天三个3小时的时间，其中一些专门用于高分辨率解剖扫描，使研究人员能够确定电极的位置，执行手术计划，并评估药理药物的传播。大多数扫描都是为清醒和行为正常的动物进行的功能成像。功能性核磁共振成像和侵入性技术在清醒、行为正常的猴子身上的常规组合使NIH内壁研究计划成为执行非人类灵长类研究的独特场所。使用NIF核心设施的NIH研究人员正在研究一系列与基本神经功能、动机、决策、情绪和抑郁相关的主题。 最近，该设施的工作还针对扩散加权成像(DWI)的开发和优化，该成像基于白质束中水分子的不对称扩散。这种方法的一个版本，扩散张量成像，或DTI，目前在人类神经成像社区非常流行，因为它允许估计大脑区域之间的结构连接。在NIF设施中，我们目前正在使用恒河猴和绒猴的固定大脑标本来探索弥散加权成像的极限。大脑在体外连续扫描长达四天，实现了前所未有的空间分辨率和角度分辨率。我们目前正在进行一项研究，以了解这些因素对纤维束成像或纤维路径的估计所起的作用。这项研究可能会对一系列人体和临床研究产生重要影响，对这些研究来说，患者舒适度和空间分辨率之间的权衡很重要。它还可以阐明DTI方法的总体精度。

The expansion of magnetic resonance imaging in the past decades had greatly changed the way scientists, clinicians, and the public view the human brain. At its essence, MRI is based on the nuclear spin properties of water protons that compose various different brain tissues. Through the resonance properties of these protons, and the differential influence of the surrounding tissues, these spin properties can be probed and, ultimately, assembled into images that directly reflect the anatomical structure. Moreover, the blood content and oxygenation can influence these images, allowing one to locally estimate neural activity at each moment in time. The latter technique, functional magnetic resonance imaging (fMRI) is presently the most efficient and powerful way to study activity in the human brain. Its use has provided a grip on studying the physiological basis of human cognitive processes previously though out of reach. Importantly, it allows us to study the function and dysfunction of the brain in psychiatric diseases, with the hope of deepening our understanding of their causes. The core facility called the Neurophysiology Imaging Facility (NIF) combines electrophyisology and fMRI studies, along with neuropharmacological and ablation studies. The aim of this combined approach is to provide a description of the anatomy and physiology of the primate brain that is more detailed and comprehensive than can currently be achieved with noninvasive imaging approaches in the human. In many cases, rather different types of experiments are carried out simultaneously. For example, in a recent study, we carried out electrophysiological and fMRI recordings simultaneously in awake animals. In another, neuropharmacological manipulation was combined with targeted ablations and fMRI in behaving animals. In order to achieve these experiments, the NIF facility creates and distributes custom-made equipment tailored for individual primate imaging experiments. As a centralized core facility, the NIF offers services and products to a wide range of investigators in each of the three sponsoring institutes (NIMH, NINDS, and NEI). Testing animals inside a strong magnetic field has required the development of a wide array of MRI-compatible equipment, including animal chairs, restraint devices, reward delivery apparatus, eye position tracking cameras, and manual response keys. The facility thus provides users with these and other critical components of monkey fMRI, allowing them to initiate their studies with minimal development on their part. The scanning routine in the NIF facility entails three 3-hour slots per day, some of which are devoted to high-resolution anatomical scanning, which allows investigators to determine the position of their electrodes, perform surgical planning, and evaluate the spread of pharmacological agents. The majority of the scans are reserved for functional imaging in awake and behaving animals. The routine combination of fMRI and invasive techniques in awake, behaving monkeys makes the NIH Intramural Research Program a unique site to perform nonhuman primate research. NIH investigators that use the NIF core facility are studying a wide range of topics related to basic neurological function, motivation, decision-making, emotion, and depression. Recently, work in the facility has also been directed toward the development and optimization of diffusion weighted imaging (DWI), which is based on the asymmetric diffusion of water molecules in white matter tracts. One version of this method, diffusion tensor imaging, or DTI, is currently very popular in the human neuroimaging community, since it allows for an estimation of structural connections between brain areas. In the NIF facility, we are presently exploring the limits of DWI using fixed brain specimens of both rhesus and marmoset monkeys. The brains are scanned ex-vivo for up to four days continuously, allowing for unprecedented spatial resolution and angular resolution. We are presently conducting a study to understand the role that these factors have on tractography, or the estimation of fiber pathways. This study could have important implications for a range of human and clinical studies for which the trade of between patient comfort and spatial resolution is important. It can also shed light on the overall accuracy of the DTI method.