fMRI Quantitative Physiology & Metabolism
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Wednesday 9 May 2012
Room 201  16:00 - 18:00 Moderators: Richard B. Buxton, Clarisse I. Mark

16:00 0468.   
Validating the Physiological Assumptions Made in Hyperoxia Calibrated BOLD
Paula L. Croal1, Emma L. Hall1, Ian D. Driver1, Penny A. Gowland1, and Susan T. Francis1
1Sir Peter Mansfield MR Centre, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom

Hyperoxia calibrated BOLD relies on the assumption that hyperoxia has no significant effects on neuronal activity or associated CBF and aCBV. The effect of isocapnic hyperoxia on resting state activity was assessed by use of PC-MRA, LLEPI FAIR ASL and MEG. A small non-significant decrease was observed in CBF and aCBV suggestive that previously observed reductions were dominated by hypocapnia. A small focal reduction in neural oscillatory power was observed in the visual cortex, however it is contrast to the much larger global reduction observed with hypercapnia and so is unlikely to have a significant effect of neuronal activity.

16:12 0469.   
Voxel-wise Estimation of M and CMRO2 at 7T
Emma Louise Hall1, Ian D. Driver1, Susan E. Pritchard1, Penny A. Gowland1, and Susan T. Francis1
1Sir Peter Mansfield MR Centre, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom

The Davis model is widely used to estimate the change in CMRO2 in response to a stimulus. This requires the measurement of CBF and BOLD in response to a stimulus and hypercapnia. Increased sensitivity at 7T allows voxelwise assessment of CBF and BOLD, and multiphase ASL allows transit time independent estimation of CBF. Here we estimate M and CMRO2 for a motor task on a voxel-by-voxel basis compared to standard ROI analysis, for a CBF and BOLD ROI. A BOLD based ROI leads to overestimation of M and reduction in CMRO2 compared to voxelwise analysis, and a CBF based ROI.

16:24 0470.   Physiological Magnetic Resonance Imaging (PMRI)
Daniel Bulte1, Michael Kelly1, Michael Germuska1, Jingyi Xie1, Michael Chappell1, Thomas Okell1, Molly Bright2, and Peter Jezzard1
1FMRIB Centre, University of Oxford, Oxford, Oxfordshire, United Kingdom, 2CUBRIC, Cardiff University, Cardiff, Wales, United Kingdom

FMRI is typically unable to match the physiological information obtainable from positron emission tomography. The MRI technique introduced here attempts to address some of these limitations in a bid to provide physiological data comparable with PET measurements. We present an 18-minute MRI protocol that produces multi-slice, whole-brain coverage and yields quantitative images of resting cerebral blood flow, cerebral blood volume, oxygen extraction fraction, CMRO2, arterial arrival time and cerebrovascular reactivity of the human brain in the absence of any specific functional task. The technique uses a combined hyperoxia and hypercapnia paradigm with a modified arterial spin labelling sequence.

16:36 0471.   
A turn-key solution for the quantification of brain oxygen metabolism
Peiying Liu1, Feng Xu1, and Hanzhang Lu1
1Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, United States

Cerebral metabolic rate of oxygen (CMRO2) is an important index of tissue viability and brain function. Previous MRI measurements of CMRO2 are not yet widely available for clinical applications due to various technical and feasibility reasons. The present study proposed a turn-key solution for quantitative assessment of global CMRO2. While the lack of spatial resolution is the main limitation of the proposed method, it is non-invasive (no exogenous agent), fast (<5 min in scan time), and reliable (Coefficient of variation<3%) and can be performed on a standard clinical scanner. These features afford this technique great potentials for immediate clinical applications.

16:48 0472.   
Simultaneous OEF and Haematocrit assessment using T2 Prepared Blood Relaxation Imaging with Inversion Recovery
Esben Thade Petersen1,2, Jill De Vis1, Thomas Alderliesten3, Karina J Kersbergen3, Manon Benders3, Jeroen Hendrikse1, and C. A. T. van den Berg2
1Department of Radiology, UMC, Utrecht, Netherlands, 2Department of Radiotherapy, UMC, Utrecht, Netherlands, 3Neonatology, Wilhemina Children's Hospital, Utrecht, Netherlands

In this work we present a robust method which simultaneously measures T1 and T2 of the venous blood using a “T2-Prepared Tissue Relaxation Inversion Recovery” (T2-TRIR) sequence from where both oxygen extraction fraction (OEF) and haematocrit (Htc) are estimated. Four volunteers and 5 neonates were scanned using T2-TRIR. The initial results pinpoints the heterogeneity of T1 (Htc) and T2 (OEF) in neonates as compared to adults which necessitates mapping of bloods T1 to correct cerebral blood flow quantification using ASL or for calibrating OEF in these patients. Similar heterogeneity can be expected in cancer patients undergoing chemo and radio therapy.

17:00 0473.   Measurement of Parenchymal Extravascular R2* using Multi-echo VASO MRI at 7T
Ying Cheng1,2, Peter C. M. van Zijl2,3, and Jun Hua2,3
1Dept. of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, United States, 2F. M. Kirby Research Center for Functional Brain Imaging, KKI, Baltimore, MD, United States, 3Neurosection, Div. of MRI Research, Dept. of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, United States

Extravascular R2* is an important parameter for quantitative BOLD studies and has been previously determined at 1.5T and 3T. At 7T, only changes in R2* (ΔR2*) upon neuronal stimulation have been reported. In this study, we employed multi-echo vascular-space-occupancy (VASO) MRI to measure absolute parenchymal extravascular R2* values in human brain at 7T. Average extravascular R2* values in human visual cortex at 7T were 43.78±2.82 s-1 at baseline and 42.71±3.32 s-1 during visual stimulation (n=4). The extravascular BOLD contributions at 7T were estimated with the ratio of extravascular to total R2* changes during stimulation to be 90±11%.

17:12 0474.   Direct Non-invasive MRI Measurement of the Absolute CBV-CBF Relationship during Visual Stimulation in Normal Humans
Pelin Aksit Ciris1, Maolin Qiu1, and Robert Todd Constable1
1Yale University, New Haven, CT, United States

BOLD signal reflects changes in CBV, CBF, blood oxygenation and metabolism, the quantification and physiological interpretation of which typically assumes that CBV=0.88CBF0.38 based on PET monkey measurements by Grubb et al. In this study, the absolute CBV-CBF relationship was measured directly in MRI non-invasively on 12 volunteers during visual stimulation. Measurements were within physiologically expected ranges, consistent with prior PET and contrast enhanced results in cortical GM. Non-invasive characterization of the CBV-CBF relationship in humans under various metabolic or functional challenges can advance understanding of fMRI signal mechanisms, with further potential clinical utility in vascular state or treatment monitoring.

17:24 0475.   
Comparable spatio-temporal characteristics but differences in metabolism-CBF coupling in intrinsic connectivity networks identified from simultaneous BOLD and CBF
Stephen D Mayhew1, Karen J Mullinger2, Andrew P Bagshaw1, Richard Bowtell2, and Susan T Francis2
1Birmingham University Imaging Centre, School of Psychology, University of Birmingham, Birmingham, West Mids, United Kingdom, 2SPMMRC, School of Physics and Astronomy, University of Nottingham, Nottingham, United Kingdom

Highly correlated, spontaneous fluctuations in fMRI signals define functionally relevant intrinsic connectivity networks (ICNs). BOLD and ASL data were simultaneously acquired during median nerve stimulation. Group ICA was performed on both BOLD and ASL data sets, and the components reflecting the default-mode network (DMN) and dorsal attention network (DAN) identified. Both ICNs showed a high degree of spatio-temporal correlation between BOLD and CBF data at the group and individual level. However, the coupling between metabolism and CBF was substantially higher in the DMN than the DAN, possibly reflecting a difference in the BOLD signal mechanisms in the ICNs.

17:36 0476.   High temporal resolution quantification of global CMRO2 during apneic challenge
Zach Rodgers1, Varsha Jain1, Michael Langham2, and Felix W Wehrli2
1Bioengineering, University of Pennsylvania, Philadelphia, PA, United States, 2Radiology, University of Pennsylvania, Philadelphia, PA, United States

CMRO2 was quantified during an apnea paradigm using an interleaved, multi-slice GRE pulse sequence. A temporal resolution of five seconds was achieved through a combination of projection velocity quantification and keyhole phase difference mapping to derive venous oxygen saturation (SvO2). CMRO2 was observed to remain constant during apnea due to a concomitant increase in flow and SvO2, but drop immediately post-apnea due to a delay in the equilibration of SvO2 relative to flow. The technique described can be applied to study cerebral metabolism and neurovascular coupling during dynamic physiologic challenges.

17:48 0477.   Propofol Increases GABA Concentration and Decreases Regional CBF in the Thalamus – an In-vivo 1H MRS/MRI Study in Normal Human Volunteers
Maolin Qiu1, Ramachandran Ramani2, Magret Rose2, and R. Todd Constable1
1Diagnostic Radiology, Yale University, New Haven, CT, United States, 2Anesthesiology, Yale University, New Haven, CT, United States

GABA is the main inhibitory neurotransmitter in the brain. In-vitro studies have shown it plays an important role in anesthesia introduced by Propofol. The anesthesia state could be achieved by the potentiation of the GABAA receptor, facilitation of the GABA release, and regulation of the ambient GABA level. Most reports investigating the actions of general anesthetics on their targets are based on in vitro data. Using both MRI and MRS, we have measured the resting-state regional CBF for the whole brain and the GABA and glutamate/glutamine concentrations in the thalamus in healthy volunteers. Our results show the thalamus is a region strongly influenced by Propofol anesthesia. GABA plays a major role in achieving anesthesia. This study supports the hypothesis that the thalamus is the key structure in the brain whose function is altered upon administration of the anesthetic agent Propofol.