Room 255 BC

10:30 - 12:30

Moderators:

Richard Hoge, Robert Turner

Swati Rane¹, Emily Mason², Subechhya Pradhan¹, Erin Hussey², Kevin Waddell¹, John C. Gore^1,3, Brandon Ally^2,4, and Manus J. Donahue^1,4
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.

Jun Hua^1,2, Craig K. Jones^1,2, Qin Qin^1,2, and Peter C.M. van Zijl^1,2
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.

Lisa C. Krishnamurthy^1,2, Peiying Liu¹, Yulin Ge³, and Hanzhang Lu^1
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.

Laurentius Huber¹, Jozien Goense², Dimo Ivanov^3,4, Steffen N. Krieger³, Robert Turner³, and Harald E. Moeller^1
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.

Xiao Wang¹, Xiao-Hong Zhu¹, Yi Zhang¹, and Wei Chen^2
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.

Richard G. Wise¹, Ashley D. Harris¹, Alan J. Stone¹, and Kevin Murphy^1
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.

Binu Panjikattil Thomas^1,2, Peiying Liu¹, Kevin S. King³, Matthias J.P. van Osch⁴, and Hanzhang Lu^1
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.

Avery J.L. Berman¹, Richard D. Hoge², and G. Bruce Pike^1
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.

Alex Bhogal¹, Marielle E.P. Philippens², Joe Fisher³, Jeroen Cornelis Willem Siero^1,4, Peter R. Luijten², and Hans Hoogduin^1
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.

Nicholas P. Blockley¹, Valerie E M Griffeth², Peter Jezzard¹, and Daniel P. Bulte^1
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.