Perfusion fMRI for Cognitive Neuroscience

University Of Pennsylvania, Philadelphia PA

Investigators

Abstract

Because of the close coupling between regional neural activity and changes in regional cerebral blood flow (CBF), imaging methods capable of measuring changes in CBF may be used to visualize changes in regional brain activity. Functional magnetic resonance imaging (fMRI) methods have emerged as the preeminent method for visualizing the neural correlates of cognition. Imaging methods are typically the sole means of directly assessing human brain function and provide an important link between behavior and brain that complements observations made in individuals with brain lesions, providing converging evidence of functional localization and organization. Most fMRI studies have utilized blood oxygenation level dependent (BOLD) contrast, which reflects a complex interaction between changes in blood flow, blood volume, and other biophysical parameters. While BOLD fMRI contrast is relatively easy to obtain, BOLD fMRI is only reliable for measuring relative changes in signal intensity over a few minutes or less, and BOLD fMRI signal changes are difficult to detect in regions of high static susceptibility. An alternative approach to visualizing regional brain activity with fMRI is to measure CBF changes directly using magnetic arterial spin labeling (ASL) as a noninvasive and nominally diffusible flow tracer. ASL perfusion MRI allows absolute CBF to be quantified both at rest and with task activation, and is stable over prolonged periods. Furthermore, the effects of ASL can be sampled using any imaging sequence, allowing perfusion to be measured in regions of high static susceptibility gradients. This approach is particularly suitable for imaging a broad range of cognitive processes that may affect resting brain function, occur gradually, or involve brain regions affected by susceptibility artifacts. With funding from the National Science Foundation to Dr. John A. Detre, this project will continue the development and application of high field ASL perfusion fMRI for specific use in cognitive neuroscience. Previous work from the PI's laboratory has demonstrated the feasibility of using ASL perfusion fMRI to measure brain function at rest or with sensorimotor task activation in the presence of artificially created susceptibility gradients and over prolonged durations. More recently, the benefits of high magnetic field strength for increasing the sensitivity of ASL perfusion fMRI and its applications to more subtle activation during cognitive paradigms have been demonstrated. Technical development during this project will focus on improving sensitivity, spatial resolution, and temporal resolution of ASL perfusion fMRI through the use of high field, optimized 3-dimensional imaging, multicoil arrays, parallel imaging, background suppression, and minimization of physiological noise. Validation of improved ASL perfusion fMRI for cognitive neuroscience will focus on subtle cognitive activation in orbitofrontal cortex (OFC) during risk and reward assessment that is challenging to detect with BOLD fMRI, and will directly compare brain activation obtained using ASL and BOLD fMRI. There are many potential impacts of this research. The work will broaden applications of fMRI by providing an alternative to BOLD imaging. Advances in perfusion imaging will be disseminated to other research sites by the multidisciplinary research team.