Jeffrey N Stout¹, Elfar Adalsteinsson^1,2, Bruce R Rosen³, and Divya S Bolar^3,4
1Harvard-MIT Health Sciences and Technology, Institute of Medical Engineering and Science, Cambridge, Massachusetts, United States, ²Department of Electrical Engineering and Computer Science, MIT, MA, United States, ³Martinos Center for Biomedical Imaging, MGH/Harvard Medical School, MA, United States, ⁴Department of Radiology, Massachusetts General Hospital, Boston, MA, United States

Using a turbo spin echo version of QUIXOTIC we measure changes in oxygen extraction fraction (OEF) in the visual cortex at baseline and during visual stimulation in a fraction of the time required by the original QUIXOTIC technique. The measured baseline and relative change in oxygen extraction fraction (OEF) compares favorably to literature values and suggests that with further validation tQUIXOTIC MRI may be useful to monitor regional OEF in the clinic.

Vikram Jakkamsetti¹, Levi Good¹, Dorothy Kelly¹, Sergey Cheshkov², Karthik Rajasekaran¹, Dean Sherry², Juan Pascual¹, Craig Malloy², and Ivan Dimitrov^2,3
1Neurology and Neurotherapeutics, UT Southwestern Medical Center, Dallas, TX, United States, ²Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, United States, ³Philips Medical Systems, Cleveland, Ohio, United States

13C NMR spectra measure the rate of energy production in vivo for human brains, but require prolonged 90–120 min infusions in the magnet which is difficult for patients with brain disorders. We infused 13C-enriched glucose to steady-state outside the magnet followed by an hour of 13C NMR spectroscopy at 7T without 1H decoupling. We report stable (for at least 60 min) and distinctly identified signals for spin-coupled doublet D45 and natural abundance singlet in glutamate C5, a prominent 13C- bicarbonate signal and essentially undetectable alanine and lactate.

Youngkyoo Jung^1,2, Naeim Bahrami², and Megan E Johnston^2
1Radiology, Wake Forest School of Medicine, Winston-Salem, North Carolina, United States, ²Biomedical Engineering, Wake Forest School of Medicine, Winston-Salem, North Carolina, United States

Oxygen extraction fraction (OEF) is an important indicator of the oxygen metabolism in the brain. Currently there are two approaches to measure or map OEF in the brain using MRI; one approach uses the T2 of venous blood, while the other uses the magnetic susceptibility difference between tissue and blood. We introduce a novel OEF estimation method using the joint information of T2 and the magnetic susceptibility difference of blood signal, and present voxel-wise CMRO2 mapping in conjunction with CBF measured with an arterial spin labeling method. A breath-hold paradigm was performed to test the feasibility of the algorithm.

Xiao-Hong Zhu¹, Hannes M Wiesner¹, Byeong-Yeul Lee¹, Ming Lu¹, Kamil Ugurbil¹, and Wei Chen^1
1CMRR, Department of Radiology, University of Minnesota Medical School, Minneapolis, MN, United States

The ability to noninvasively imaging the cerebral metabolic rate of oxygen (CMRO₂) is essential for studying oxygen metabolism and its roles in human brain function and dysfunction. We have recently established an in vivo ¹⁷O-MR based approach incorporated with a simple breathing test and a sophisticated quantification model capable of quantitative and simultaneous imaging of three important physiology parameters of CMRO₂, cerebral blood flow (CBF) and oxygen extraction factor (OEF) in the human brain via a brief ¹⁷O-labeled oxygen gas inhalation. In the present study, we apply this approach to study these parameters and their correlations in the resting brains of healthy human volunteers and the inter- and/or intra-subject variations at 7 Tesla. We found that the resting state CMRO₂, CBF and OEF values were in good agreement with the literature; they also varied in different subjects, brain tissues and regions. A strong dependence of CMRO₂ on gray matter fraction, a positive correlation between CMRO₂ and CBF, and a negative correlation between CBF and OEF were consistently observed in all subjects studied. The overall findings indicate that the ¹⁷O-MR based approach provides a robust and quantitative neuroimaging tool for noninvasive assessment of CMRO₂, CBF and OEF in healthy and diseased human brains.

Petr Bednarik^1,2, Ivan Tkac¹, Federico Giove^3,4, Dinesh Deelchand¹, Lynn Eberly¹, Felipe Barreto^1,5, and Silvia Mangia^1
1University of Minnesota, Minneapolis, MN, United States, ²Central European Institute of Technology, Masaryk University, Brno, Czech Republic,³MARBILab c/o Fondazione Santa Lucia, "Enrico Fermi" Centre, Rome, Italy, ⁴", Department of Physics - G1 Group, University of Rome "La Sapienza", Rome, Italy, ⁵Physics Department, University of Sao Paulo, Sao Paulo, Brazil

Different functional metabolisms might be expected in selectively activated blob and interblob neuronal populations due to different cytochrome-oxidase contents. Here we acquired fMRI and fMRS data during chromatic and achromatic visual stimuli, which selectively activate blob and interblob neurons, respectively. Neurochemical and fMRI-BOLD responses were measured from 12 subjects, each scanned twice. We observed robust BOLD-fMRI signals as well as functional changes in concentration of Glu, Lac, Asp and Glc for both stimuli. No significant differences in neurochemical and BOLD responses between chromatic and achromatic stimuli were found, consistent with equal aerobic responses in blob and interblob neuronal populations.

Xiaopeng Song¹, Shaowen Qian², Kai Liu², Zhenyu Zhou³, Gang Sun², and Yijun Liu^1
1Department of Biomedical Engineering, Peking University, Beijing, Beijing, China, ²Department of Medical Imaging, Jinan Military General Hospital, Shandong, China, ³GE Health Care, Beijing, China

We found that subject with slower resting-state BOLD oscillation frequency in DMN reacted faster in psychomotor vigilance test under both normothermic and hyperthermic conditions. CBF mainly contributes to BOLD oscillations of 0.01-0.04Hz under both conditions. The coupling of CBF and BOLD oscillations in 0-0.01Hz and 0.04-0.1Hz were significantly decreased with hyperthermia. Our study linked resting-state brain rhythms to task performance, and for the first time revealed the frequency-specific coupling between blood supply and BOLD oscillation topology during rest and its modulation in response to hyperthermia, which may shed light on the physiological basis of resting-state BOLD activities.

Ying Cheng^1,2, Qin Qin^1,3, Peter C. M. van Zijl^1,3, James J. Pekar^1,3, and Jun Hua^1,3
1F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, United States, ²Dept. of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland, United States, ³Neurosection, Div. of MRI Research, Dept. of Radiology and Radiological Science, Johns Hopkins University, Baltimore, Maryland, United States

Quantitative approaches have been developed to estimate CMRO2 dynamics from BOLD, CBF, and CBV responses. The ability to measure BOLD, CBF, and CBV signals in one single scan would be useful to improve acquisition efficiency and reduce temporal variations. We extended the recently proposed 3D “VASO-FAIR” approach, which combines the VASO and FAIR-ASL techniques to simultaneously detect CBV and CBF responses, with a T2-preparation module to induce T2-weighted BOLD contrast, allowing concurrent measurement of BOLD, CBV, and CBF responses. For visual stimulation, the proposed method could achieve similar activation patterns, image quality, tSNR, and CNR as the separate individual scans.

Jeroen C.W. Siero¹, Carlos C. Faraco², Alex Bhogal¹, Megan K. Strother², Peiying Liu³, Hanzhang Lu³, Jeroen Hendrikse¹, and Manus J. Donahue^2
1Radiology, University Medical Center Utrecht, Utrecht, Utrecht, Netherlands, ²Radiology and Radiological Sciences, Nashville, Vanderbilt University School of Medicine, Tennessee, United States, ³Radiology Advanced Imaging Research Center, UTSouthwestern Medical Center, Texas, United States

Here we evaluate the assumption that two common hypercapnic stimuli (5%CO2; and carbogen) are iso-metabolic using MRI-based measures of changes in venous blood oxygenation. Wholebrain CBF (pCASL), and Yv (TRUST-MRI) changes were measured for hypercapnic-normoxia, normocapnia-hyperoxia, and hypercapnic-hyperoxia stimuli allowing calculation of OEF and CMRO2. After correcting for the plasma-dissolved arterial and venous O2, no significant differences in OEF were found between 5%CO2 and carbogen. Significant CMRO2 decreases from room air were observed only for the hypercapnic-normoxic condition. We believe these findings will be of importance for interpreting calibrated fMRI and BOLD CVR measurements using hypercapnic or carbogen stimuli.

Felipe Rodrigues Barreto¹, Silvia Mangia², and Carlos Ernesto Garrido Salmon^3
1Department of Physics, University of Sao Paulo, RIbeirao Preto, SP, Brazil, ²Department of Radiology, CMRR, University of Minnesota, MN, United States,³Department of Physics, University of Sao Paulo, Ribeirao Preto, SP, Brazil

In the present study we used multimodal fMRI to quantify in the human visual cortex the effects of mild hypoxic hypoxia on stimulus induced variations of cerebral blood flow (CBF), cerebral blood volume (CBV), BOLD signal, as well as oxygen consumption (CMRO2) and oxygen extraction fraction (OEF) during visual stimulation. Hypoxia produced substantial reductions in the active volumes detected in BOLD, CBF and CBV images, which might indicate smaller cortex recruitment. The brain regions commonly activated during hypoxia and normoxia had reduced BOLD amplitudes and smaller OEF reductions, but no changes in the amplitude of vascular and CMRO2 responses.

Hongxia Lei^1,2, Frederic Preitner³, Bernard Thorens³, and Rolf Gruetter^4,5
1AIT, Center for Biomedical Imaging (CIBM), Ecole Polytechnique Fédérale de Lausanne, Lausanne, Vaud, Switzerland, ²University of Geneva, Geneva, Geneva, Switzerland, ³Center for Integrative Genomics (CIG), University of Lausanne, Lausanne, Vaud, Switzerland, ⁴Laboratory for Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Vaud, Switzerland, ⁵Department of Radiology, University of Lausanne, Lausanne, Vaud, Switzerland

Glucose transporter isoform 2 (glut2) has been shown to not only meditating glucose sensing mechanism in pancreatic tissue but also preferentially being highly located in brain regions and nuclei which regulate the neuroendocrine and autonomic nervous system. we hypothesized that glut2 positive brain cells might be involved in glucose sensing mechanism in brain and thus deleting glut2 would affect brain metabolism under euglycemia and mediate vascular responses upon hypoglycemia. This study applied a non-invasive perfusion MRI technique, continuous arterial spin labeling (CASL), to measure cerebral blood flow (CBF) under euglycemia and upon hypoglycemia in glut2 positive brain cells nulled mice compared to their countertypes. Unlike the elevated CBF increases in the wild type mice, the dimished repsponses were observed. We conclude that brain cells expressing glut2 are implicated in regulating the CBF response to hypoglycemia.