Neurophysiology Imaging Facility Core: Functional and Structural MRI

National Institute Of Mental Health

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Abstract

A primary goal of the NIF facility is to lower conceptual and practical barriers involved in the scanning itself so that researchers can pursue combinatorial methods for furthering their own research agendas. These research agendas are sometimes related to the nature of fMRI though most often about studying circuitry in the brain related to elements of cognition. The NIF staff works with users to determine their needs and set upon optimal scanning protocols and methods. For investigators wanting to have scanning central to their research projects, the staff trains scientists to gain autonomy in conducting their own experiments, including operation of the scanners. The main devices within the Neurophysiology Imaging Facility (NIF) are a small-bore and a large-bore magnetic resonance imaging (MRI) scanner. These are used broadly for anatomical imaging for many NIH investigators, as well for functional MRI for a more limited number of laboratories. In fMRI, the coupling of blood flow with neural activity makes it possible to noninvasively map activity patterns across the brain. This technology has been extremely impactful for both neuroscience and medicine. However, the underlying biological linkage between the brain’s electrical activity and the local regulation of blood flow is complex and an area of intense investigation, including in the NIF facility. In addition to two MRI scanners, the NIF facility also operates a computed tomography (CT) and positron emission tomography (PET) scanner, which allow for a spectrum of different scanning possibilities for researchers across NIH, ranging from routine anatomical scans to intricate, multimodal fMRI projects. These scanners play an increasingly important role for biomedical and disease research at the NIH, with interested parties now looking forward to the future to determine what the next addition to the core facility might be. The NIF core staff is composed of six members, each from a different scientific background and with different skills, aim to provide the most efficient functional scanning services possible for a broad range of investigators. The core has now been in operation for more than 20 years. Since the founding of the NIF core facility, functional MRI (fMRI) has been its primary focus. This method allows researchers to visualize activity patterns within the brain of an awake subject. This approach has been widely adopted among neuroscientists, who seek to map the responses for a sensory stimulus relative or cognitive process. Because most neuroscience researchers conducting fMRI experimens are not experts in the physics or engineering aspects of MRI, they rely heavily on experts in these domains to develop and maintain the best scanning environment possible. Thus, MRI is an inherently interdisciplinary enterprise, and experiments are typically done in the context of a dedicated core imaging facility. For many specialized studies, the challenges of MRI are compounded by technical issues, such as the production of specialized radiofrequency (RF) coils and the need to learn nonstandard procedures. Scanning is sometimes combined with other procedures such as pharmacological manipulation or simultaneous electrophysiological recording, often further complicating the imaging procedure. Overcoming these obstacles is of enormous value, since fMRI uniquely allows one to map activity over the entire brain and combine this method with other manipulations. Functional scanning procedures more often rely on scientists in individual laboratories carrying out the testing and MRI scanning. This is initially done under guidance and supervision from the NIF staff. The fMRI studies include mapping the functional specialization in the brain, but can also involve more complicated experimental designs. For example, experiments within the facility typically combine fMRI with other procedures, such as microelectrode recordings or pharmacological inactivation. The fMRI experiments produce large data files that must be processed to evaluate the functional activity patterns across the brain. The facility provides storage of these data, guidance in the initial processing steps, and server machines for full data analysis. Further, there are many analytic steps between the acquisition of raw MR signals and the scientific interpretation of the measured neural signals. This is particularly true for functional MRI (fMRI), where activity maps are generated based upon the evaluation of time varying intensity values throughout the brain from a series of MR volumes. At the NIH we are fortunate to have other core facilities, such as the Scientific Statistical Computing Core, who help users contend with the rich but complex fMRI data. In addition to fMRI, NIF facility aids NIH laboratories through the facilitation of anatomical and structural scanning. For such procedures, the NIF staff generally takes over the scanning and the scientist provides information about the target sites and basic scanning requirements. This approach is widely used to identify electrophysiological target sites and the position of indwelling microelectrodes, and to evaluate the experimental precision of a brain manipulation such as an injection. One particularly valuable use of structural imaging is the direct comparison of electrical recording sites with foci of fMRI responses in the context of a cognitive task. There are a range of contrast options, including diffusion weighted scans that can identify features in the white matter, or provide the basis for tractography. We have also recently purchased a computerized tomography (CT) machine to reside in the facility, and to serve as part of a pipeline to further improve surgical accuracy for a wide range of users. Beyond its service role, the NIF staff spends a fraction of its time carrying out technical scientific research projects related to MRI and brain imaging. In the past several years, we have focused on completing studies related to diffusion tractography. We have been working in a highly collaborative effort with other groups inside and outside the NIH. We are continuing to study (1) the neuroanatomical basis of diffusion imaging, and (2) comparative fiber pathways across species. In the latter research line, we recently published a new study demonstrating a prominent white matter fasciculus, the vertical occipital fasciculus, is present in all anthropoid and prosimian primates, but not on other mammals. In addition, we are continuing collaborative work on the role of the basal forebrain in resting state spontaneous fMRI signals, as well as collaborative work involved in atlases, templates, and data sharing. At present, research in the facility is focused on the design and testing of implanted radiofrequency coils, with the hope that this method can become routine for users seeking to obtain higher signal-to-noise images. Other research lines in the facility involve the development of scanning with newly available contrast agents.