ISMRM 21st Annual Meeting & Exhibition 20-26 April 2013 Salt Lake City, Utah, USA

Probing Brain Physiology & Metabolism with fMRI
Friday 26 April 2013
Room 255 BC  10:30 - 12:30 Moderators: Richard Hoge, Robert Turner

10:30 0844.   
Baseline GABA Concentration More Strongly Predicts Baseline BOLD Signal Synchrony Than CBF in Visual Cortex
Swati Rane1, Emily Mason2, Subechhya Pradhan1, Erin Hussey2, Kevin Waddell1, John C. Gore1,3, Brandon Ally2,4, and Manus J. Donahue1,4
1VUIIS, Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, United States, 2Neurology, Vanderbilt University, Nashville, TN, United States, 3Biomedical Engineering, Vanderbilt University, Nashville, TN, United States, 4Psychiatry, Vanderbilt University, Nashville, TN, United States

This study investigates the relationship between baseline BOLD synchrony and perfusion (CBF) and baseline GABA concentration in the visual cortex. BOLD synchrony at rest was more strongly correlated with baseline GABA levels than with absolute CBF.

10:42 0845.   
Elimination of Non-Steady-State Blood Spins in Vascular-Space-Occupancy (VASO) FMRI
Jun Hua1,2, Craig K. Jones1,2, Qin Qin1,2, and Peter C.M. van Zijl1,2
1Neurosection, Div. of MRI Research, Dept. of Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States, 2F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, United States

We show that contaminations from the non-steady-state inflowing blood spins in Vascular-space-occupancy (VASO) fMRI can be eliminated by combining the previously proposed “magnetization reset” technique with motion-sensitized crushing gradients. The magnetization reset module is a spatially nonselective saturation applied immediately after readout. The crushing gradients can be implemented with bipolar gradients in a 2D sequence such as 2D gradient echo (GRE) echo-planar-imaging (EPI), or a motion-sensitized driven equilibrium (MSDE) spin preparation module immediately before a 3D sequence such as 3D fast GRE. When performing VASO fMRI of visual stimulation, the combined technique successfully suppressed the non-steady-state blood spins.

10:54 0846.   
Vessel-Specific Quantification of Blood Oxygenation with T2-Relaxation-Under-Phase-Contrast (TRU-PC) MRI
Lisa C. Krishnamurthy1,2, Peiying Liu1, Yulin Ge3, and Hanzhang Lu1
1Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, United States, 2Dept. of Bioengineering, UT Arlington, Arlington, TX, United States, 3Dept. of Radiology, New York University Langone Medical Center, New York, NY, United States

Measurement of venous oxygenation (Yv) is a critical step toward quantitative assessment of brain oxygen metabolism, a key index in many brain disorders. The present study aims to develop a non-invasive, rapid, and reproducible method to measure Yv in a vessel-specific manner. The method, T2-Relaxation-Under-Phase-Contrast (TRU-PC) MRI, utilizes complex subtraction of phase-contrast to isolate pure blood signal, applies non-slice-selective T2-preparation to measure T2, and converts T2 to oxygenation using calibration plot. Following feasibility demonstration, several technical aspects were examined, including validation with an established global Yv technique, test-retest reproducibility, and ability to study veins with a caliber of 1-2 mm.

11:06 0847.   
Cerebral Blood Volume Changes in Negative BOLD Regions During Visual Stimulation in Humans at 7T
Laurentius Huber1, Jozien Goense2, Dimo Ivanov3,4, Steffen N. Krieger3, Robert Turner3, and Harald E. Moeller1
1NMR-Unit, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, 2Physiology of Cognitive Processes, Max Planck Institute for Biological Cybernetics, Tübingen, Germany, 3Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, 4Cognitive and Clinical Neuroscience, Maastricht University, Maastricht, Netherlands

Based on recent studies in monkeys (Goense, J, et al., Neuron, in press), the changes in cerebral blood volume (CBV) were investigated in human brain regions that show negative BOLD responses during a visual task. Therefore a CBV-sensitive VASO method was implemented that can account for BOLD and inflow contaminations at 7T. In regions with negative BOLD responses, significant CBV decreases can be seen. This CBV decrease is dominated by voxels that include the cortical surface at the transition region between grey matter and cerebrospinal fluid, while many voxels in deeper layers show a CBV increase.

11:18 0848.   
Significant BOLD Signal Reduction Induced by Perfluorocarbon Emulsion in the Rat Brain -permission withheld
Xiao Wang1, Xiao-Hong Zhu1, Yi Zhang1, and Wei Chen2
1Center for Magnetic Resonance Research,Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota, United States, 2Center for Magnetic Resonance Research,Department of Radiology, University of Minnesota, Minneapolis, Minnesota, United States

Perfluorocarbon (PFC) emulsion is a promising technique to treat diseases with compromised oxygenation such as ischemia, air embolism and trauma. In the present study, the injection of PFC emulsion to the normal rat led to decreases of the oxyhemoglobin saturation (%HbO2) in the vein (up to 36% at 170 minutes after the injection) and the Blood-Oxygen-Level-Dependent (BOLD) signal in the rat brain cortex (up to 7.5% at 160 minutes after the injection). These changes might be due to the stronger adsorption of oxygen to the PFC than that of hemoglobin, thus, the conversion of HbO2 to deoxyhemoglobin (dHb) occurs when the PFC and hemoglobin are competing for the limited oxygen content. In addition, we found that the images of BOLD signal reduction after the PFC emulsion injection show a similar spatial pattern as that of resting-state cerebral blood flow (CBF) maps, which is consistent with the fact that CBF dominates the BOLD signal. Therefore, the PFC emulsion potentially can be used as an fMRI contrast agent to assess the function of the tissue in addition to the treatment of oxygenation compromised diseases.

11:30 0849.   Measurement of Absolute CMRO2 by Simultaneous Hypercapnic and Hyperoxic Calibration of fMRI Signal
Richard G. Wise1, Ashley D. Harris1, Alan J. Stone1, and Kevin Murphy1
1CUBRIC, School of Psychology, Cardiff University, Cardiff, United Kingdom

We present a method for measuring absolute cerebral metabolic oxygen consumption (CMRO2). ASL and BOLD FMRI were combined with intermittent hyperoxia applied at four different levels of hypercapnia, facilitated by end-tidal forcing. A BOLD signal model permitted estimation of venous oxygenation which when combined with CBF gave estimates CMRO2 in regions of interest and voxel-wise. The sensitivity of the hyperoxia induced BOLD signal changes to CBF induced changes in CBV reduced the need to assume vascular parameters in the BOLD signal model, potentially expanding the range of (patho)physiological conditions in which the method could be applied.

11:42 0850.   
Physiologic Underpinnings of Negative Cerebrovascular Reactivity in Brain Ventricles
Binu Panjikattil Thomas1,2, Peiying Liu1, Kevin S. King3, Matthias J.P. van Osch4, and Hanzhang Lu1
1Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, United States, 2Department of Bioengineering, University of Texas Southwestern Medical Center/University of Texas at Arlington, Arlington, Texas, United States, 3Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States, 4Department of Radiology, Leiden University Medical Center, Leiden, ZA, Netherlands

Cerebral vascular reactivity (CVR), measured by combining BOLD MRI and hypercapnia, could be a promising biomarker for small vessel disease. However, the mechanism of BOLD change during CO2 challenge has not been fully understood. In this study we report an intriguing but robust observation of negative CVR (i.e. BOLD signal decreased during CO2 inhalation) in brain ventricles. We further showed this BOLD signal reduction can be attributed to CSF space shrinkage due to ventricular vessel dilation, but not due to T2* reduction. We also show the negative CVR is not present during O2 challenge, known to cause minimal vessel dilation.

11:54 0851.   
The Impact of Dissolved Oxygen in Blood on Hyperoxia-Based BOLD Calibration
Avery J.L. Berman1, Richard D. Hoge2, and G. Bruce Pike1
1McConnell Brain Imaging Centre, Montreal Neurological Institute, McGill University, Montréal, Québec, Canada, 2IUGM/Université de Montréal, Montréal, Québec, Canada

In a recently published theoretical model it was predicted that paramagnetic oxygen dissolved in blood significantly contributes to a magnetic susceptibility difference between arterial blood and the surrounding tissue when its concentration in blood ishigh, such as during hyperoxia-based BOLD calibration. We present here a revised model and have re-examined the effect of dissolved oxygen on the blood-tissue susceptibility difference using our alternative formulation and compared it with published experimental data. We found a negligible change of the arterial blood-tissue susceptibility difference between hyperoxia and normoxia, resulting in signal contrast in veins and capillaries only.

12:06 0852.   Cerebrovascular Reactivity Measured Using Targeted Hypo/Hypercapnia BOLD Imaging at 7T
Alex Bhogal1, Marielle E.P. Philippens2, Joe Fisher3, Jeroen Cornelis Willem Siero1,4, Peter R. Luijten2, and Hans Hoogduin1
1Radiology, UMC Utrecht, Utrecht, Utrecht, Netherlands, 2Radiotherapy, UMC Utrecht, Utrecht, Utrecht, Netherlands, 3Thornhill Research Inc., Toronto, Ontario, Canada, 4Rudolf Magnus Institute, University Medical Center Utrecht, Utrecht, Utrecht, Netherlands

Cerebrovascular Reactivity (CVR) is measured using targeted PaCO2 breathing challenges in combination with BOLD-EPI imaging at 7T. While maintaining normoxia, traditional block stimulus response is compared with a uniformly increasing PaCO2 'ramp'stimulus. Ramp results are modeled using sigmoidal and linear functions to obtain more information with respect to CVR dynamics and increase calibration accuracy for signal changes attributable to vessel reactivity.

12:18 0853.   Analysis of Calibrated BOLD Based Methods for Quantifying the Resting Oxygen Extraction Fraction
Nicholas P. Blockley1, Valerie E M Griffeth2, Peter Jezzard1, and Daniel P. Bulte1
1FMRIB, University of Oxford, Oxford, United Kingdom, 2Center for Functional MRI, University of California San Diego, La Jolla, California, United States

The calibrated BOLD technique is conventionally used to quantify the BOLD response in terms of changes in oxygen metabolism. Recently such methods were extended to produce absolute measurements of the resting oxygen extraction fraction. However, the sensitivity of this new method to intersubject physiological variability, or to a breakdown of the physiological assumptions that underpin the method, has not been explored. In this work we show that this method is relatively insensitive to physiological variability, but reveal a potential systematic error in the current analysis approach.