Neurophysiology Imaging Facility Core: Functional and Structural MRI

National Institute Of Mental Health

Investigators

Linked publications & trials

Abstract

Magnetic resonance imaging (MRI) technology continues to push forward, with the images gleaned from the human brain growing ever more impressive. Because blood flow is locally coupled to neural activity, it is possible to localize track the distribution of activity throughout human brain during cognitive tasks, something that was unthinkable one generation ago. The advances that have shaped MRI technology and impacted human medicine have come from basic science laboratories and preclinical research programs. The Neurophysiology Imaging Facility (NIF) is an NIH-wide core that makes structural and functional MRI imaging available and straightforward to a broad range of NIH basic science laboratories. A primary goal 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. 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 will also train scientists to gain autonomy in conducting their own experiments, including operation of the scanners. The NIF facility focuses particularly on functional MRI (fMRI), which allows researchers to visualize activity patterns within the brain of an awake subject. This approach to neuroscience often involves mapping the responses for one type of sensory stimulus relative to that for another. 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. Because most neuroscience researchers 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. In addition to two MRI scanners, the NIF facility also houses CT and PET/CT scanners, allowing 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. Six staff members including Dr. Leopold, 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. Many users of the NIF core focus only on structural scanning, for which the staff takes over most of the procedure 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. For functional scanning, scientists in individual laboratories carry out the testing, initially under guidance from the NIF staff. The fMRI studies go beyond mapping functional specialization in the brain. 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. 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 addition, we completed studies 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.