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Manus Joseph Donahue¹, ², Jun Hua¹, ², Richard Anthony Edden, ¹³, Seth A. Smith¹, ², Peter van Zijl¹, ²

¹The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA; ²The Kennedy Krieger Institute, Baltimore, Maryland, USA; ³Cardiff University, Cardiff, UK

During increased brain activity, magnetic susceptibility changes in parenchyma, which will lead to increases in parenchymal T2 and a more narrow saturation line shape. We show that when a direct saturation pulse is applied at the correct frequency offset, short duration and low power, the MR signal increases (1.3±0.2%) during elevated brain activity, which we attribute to a narrowing in the saturation line shape of parenchyma consequential to neuronal activation. The results provide the basis for a new, short-TE spin echo approach for performing fMRI based on direct water saturation.

Shin-ichi Urayama¹, Kenji Aso¹, Toshihiko Aso², Satoru Kohno¹, Nobukatsu Sawamoto¹, Hidenao Fukuyama¹, Denis Le Bihan²

¹Kyoto Univ., Kyoto, Japan; ²CEA, France

To investigate vascular contribution to DfMRI (Diffusion weighted fMRI) signal, responses to visual stimulation and hypercapnia challenge were monitored and analyzed on an individual subject basis. Although the % signal changes of DfMRI and BOLD responses were not significantly different with the visual stimulation, the response is much larger with BOLD than DfMRI during CO2 inhalation. This results show that at least half of the DfMRI signal is not explained by vascular sources.

Erin Mazerolle¹, Xiaowei Song¹, Kimberly Brewer¹, Steven Beyea², Ryan D'Arcy¹

¹National Research Council, Halifax , Canada; ²National Research Council, Halifax, Canada

Functional MRI activity is believed to be restricted to gray matter. White matter (WM) activation is controversial. Due to the relative reduction of blood flow/volume and the drop in reliance on synaptic transmission, it is often thought to be an artifact. Despite this, an increasing number of studies are reporting WM activation. The current study evaluated this notion using an established neurological model for interhemispheric transfer of visual/motor information across the corpus callosum. The results revealed activation in callosal regions consistent with visual/motor transfer. The findings highlight the importance of investigating the potential for fMRI in WM.

Ivana Drobnjak¹, Gaby Pell, Mark Jenkinson

¹University of Oxford, Oxford, UK

Direct neuronal current imaging is a method that could potentially provide direct access to neuronal activity with an excellent spatial (mm) and temporal resolution (ms). However, so far it has not been convincingly demonstrated that MRI has adequate sensitivity to detect neuronal currents in vivo. In order to pin down the most influential factors in the signal formation, with the goal of eventually optimizing them for the MR detectable signal change, Pell et al. used a simple conducting wire model with various scanning and field parameters to investigate signal magnitude changes. The experimental results indicate not only significant changes in signal magnitude but also in spatial pattern. Specifically, the current can create a very localized Gibbs ringing in the image. We show both experimentally and analytically that the timing of the current within the pulse sequence completely determines the width and the magnitude of the ringing. Since currently we are on the limit of neuronal-current MR sensitivity, this is a significant finding as it can help us both tune the parameters of the acquisition to achieve maximal sensitivity as well as understand the effects of arbitrary neuronal currents on the MR signals.

Hanzhang Lu¹

¹University of Texas Southwestern Medical Center, Dallas, USA

VASO is a technique targeting for CBV based fMRI. However, recent evidences have suggested that the mechanism of VASO signal may contain contributions from flow-related effects due to non-steady-state blood spins. We aim to eliminate non-steady-state spins and “reset” the magnetization by adding a non-slice-selective 90º saturation RF pulse immediately after the image acquisition (post-sat). Experiments and numerical simulations showed that the post-sat pulse can eliminate virtually all fresh spins and bring the VASO signal back to a level consistent with predominantly CBV-contrast for a TR range of 1-1.6s. At intermediate TR range, the post-sat also reduced the flow contributions.

Lin Tang¹, Malcolm J. Avison¹, John C. Gore¹

¹Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA

We used transcranial near-infrared spectroscopy (NIRS) and fMRI at 3T to investigate both positive and negative BOLD effects. Using NIRS we recorded concentration changes in both oxy- and deoxy- as well as total hemoglobin levels by measuring changes of absorption at two different wavelengths in brain in response to both transient activations and deactivations. Similar experiments were also performed using fMRI. In addition to previous observed different nonlinearity of BOLD responses to activation and deactivation, we also compared BOLD and NIRS measurements during various stimulation paradigms and tried to explain the mechanism of the observed BOLD.

Xiao-Hong Zhu¹, Yi Zhang¹, Wei Chen¹

¹Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA

In vivo ³¹P MRS combined with magnetization saturation transfer (MT) method has been recently demonstrated to be capable of noninvasively measuring the Cerebral Metabolic Rate of the CK enzyme reaction (CMR_CK) and ATPase enzyme reaction (CMR_ATP) simultaneously in living brains. We have also demonstrated that both CMR_CK and CMR_ATP are tightly coupled with varied brain activity in the resting brain. In this study, we have applied the in vivo ³¹P MT approach to address the question whether CMR_CK or CMR_ATP changes in the cat visual cortex during visual stimulation. Our results show: i) both CMR_CK and CMR_ATP increased significantly in the activated visual cortex with relative less extent for CMR_CK; ii) the feasibility for obtaining 3D functional metabolic CK rate maps in the cat brain; and iii) a similar percentage changes of the elevated CMR_ATP and CMRO₂. These findings indicate a tight coupling between the oxygen utilization and oxidative phosphorylation during stimulation and the essential roles of oxidative phosphorylation in brain bioenergetics associated with brain function and activation.

Silvina G. Horovitz¹, Masaki Fukunaga¹, Dante Picchioni², Walter S. Carr³, Jacco A. de Zwart¹, Thomas J. Balkin², Allen Braun⁴, Jeff H. Duyn¹

¹NINDS , NIH, Bethesda, Maryland, USA; ²Walter Reed Army Institute of Research, Silver Spring, Maryland, USA; ³Naval Medical Research Center, Silver Spring, Maryland, USA; ⁴NIDCD, NIH, Bethesda, Maryland, USA

EEG slow oscillations have been suggested to facilitate the beneficial effects of sleep on learning. Here, we  investigated the metabolic imprint of these oscillations by performing concurrent EEG and BOLD fMRI during sleep in normal volunteers. The results confirm earlier observations from electrophysiology that associate thalamic and sensory areas with the phenomenon of EEG slow oscillations.

Claire Stevenson¹, Matthew Brookes¹, Peter Morris¹

¹The University of Nottingham, Nottingham, UK

A combination of fMRI and MEG may provide insight into the neuronal basis of the BOLD effect. Here, we investigate the correlation and linearity of evoked and induced MEG signals and the BOLD response elicited by visual stimuli of varying contrasts. This experiment allows spatial separation of the evoked, beta and gamma MEG responses and provides a method of determining the extent to which each of the individual responses contribute to the BOLD response. The excellent co-localisation of the MEG and BOLD data suggests that the two are intimately linked.

Rishma Vidyasagar¹, Andrej Stancak², Laura M. Parkes¹

¹MARIARC , University of Liverpool, Liverpool, UK; ²School of Psychology, University of Liverpool, UK

This study investigates the phenomenon of repetition suppression in the visual cortex using behavioural, fMRI and MEG data. 9 subjects were tested with the same paradigm using all three modalities and data were analysed according to specific visual areas. Significant suppression of BOLD and MEG responses were observed in V2/V3 areas when paired stimuli with the same characteristics were presented at an interstimulus interval (ISI) of 200 msec, compared to paired stimuli of different characteristics at the same ISI. This study uses the data in an attempt to explain the reasoning behind repetition suppression using previously proposed models.