Diffusion fMRI and BOLD-fMRI: Towards Better Understanding of White and Grey Matters Function

Field: Neuroscience (Life Sciences)

Event Abstract Back to Event Diffusion fMRI and BOLD-fMRI: Towards Better Understanding of White and Grey Matters Function Saïd Boujraf1* 1 University of Fez, Department of Biophysics and Clinical MRI Methods, Clinical Neuroscience Laboratory, Faculty of Medicine and Pharmacy, Morocco Since early observations of the BOLD effect (1), fMRI has rapidly become a tool of choice for in vivo exploration of the functionality of the brain, with applications ranging from brain pathology and plasticity to repair and functional recovery. BOLD-fMRI is especially useful for investigations of the cortex and of grey matter and is highly sensitive. However its spatial specificity is compromised by the diversity of vasculature present in the brain. Large draining veins, for example, are often distant from sites of neural activity (2). While significant progress has been made in understanding the functional role of grey matter regions, little is known about their relationship with underlying white matter structures. It is possible that these structures play an active role in mediating functional processes in the healthy and pathological brain. Study of white matter structures and the association between these structures and activated grey matter structures could thus add to our understanding of well-documented neural networks subserving functional processes. As an alternative to the BOLD approach, Song et al. (3) have suggested a new contrast mechanism based on functional changes in the Apparent Diffusion Coefficient (ADC). In this early application of their approach, we studied the extent to which variability in the activation of task-related cortical areas depends on the presence of nearby white matter structures. Our study used a range of different diffusion tensor parameters including average diffusion (trace) and fractional anisotropy. Basically, diffusion fMRI is based on measurements of Intravoxel Incoherent Motion (IVIM) (3). IVIM models two major components in the diffusion signal: the first is generated by intravascular blood flow, the second by extravascular diffusion of water. The intravascular component signals high mobility and therefore persists only when using lower diffusion weighting. It can thus be used to map flow and volume changes in microvascular networks. Song (3) showed that the ADC increases with increases blood flow increases, regardless of whether vessel volume fraction increases or remains constant. In general, ADC depicts changes in blood volume and flow at the level of arteries, arterioles, and capillaries, while BOLD reflects changes in oxygenation in capillaries, venules and veins. The combination of the two sources of information can identify capillary activation, leading to enhanced spatial localization of the functional signal. The time course of the ADC-based functional signal precedes the BOLD signal by about 1 second, confirming that ADC contrast is sensitive to changes in blood volume and flow changes in the arterial and capillary network. We have found that high diffusion weighting produce a lag in the time course with respect to lower values. This implies that we can use diffusion weighting to tune sensitivity to vessels of different sizes. The ADC-fMRI method can be further refined by using flow-moment-nulling to compensate for the effect of changes in blood flow. In cases where the main changes are in volume, this improves the sensitive of the functional signal from smaller vessels (4). Diffusion characteristics of peripheral white matter and application of ROI and connectivity analyses revealed the existence of connections worthy of further study. These findings suggested that studies of peripheral white matter morphology can make a useful contribution to our understanding of the brain. Such studies will require further refinements of the ADC method and its relation to functional, behavioral and structural indices. References 1. Ogawa, S., et al. 1993b. Functional brain mapping by blood oxygenation level-dependent contrast magnetic resonance imaging: A comparison of signal characteristics with a biophysical model. Biophys. J. 64 (3), 803-12.2. Lai, S., Hopkins, et al. 1993. Identification of vascular structures as a major source of signal contrast in high resolution 2D and 3D functional activation imaging of the motor cortex at 1.5 T: preliminary results. Magn. Reson. Med. 30, 387-92.3. Song AW., et al. 2007. Single-shot ADC imaging for fMRI. Magn. Reson. Med. 57, 417-22.4. Song AW., Li, T., 2003. Improved spatial localization based on flow-moment-nulled and intra-voxel incoherent motion-weighted fMRI. NMR Biomed. 16, 137-43. Conference: 2nd NEUROMED Workshop, Fez, Morocco, 10 Jun - 12 Jun, 2010. Presentation Type: Oral Presentation Topic: Oral Session 4: Technological developments for neurosciences Citation: Boujraf S (2010). Diffusion fMRI and BOLD-fMRI: Towards Better Understanding of White and Grey Matters Function. Front. Neurosci. Conference Abstract: 2nd NEUROMED Workshop. doi: 10.3389/conf.fnins.2010.12.00043 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 04 Jun 2010; Published Online: 04 Jun 2010. * Correspondence: Saïd Boujraf, University of Fez, Department of Biophysics and Clinical MRI Methods, Clinical Neuroscience Laboratory, Faculty of Medicine and Pharmacy, Fez, Morocco, sboujraf@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Saïd Boujraf Google Saïd Boujraf Google Scholar Saïd Boujraf PubMed Saïd Boujraf Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.