| fMRI Calibration |
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Tuesday 21 April 2009 |
| Room 323ABC |
10:30-12:30 |
Moderators: |
Catherine E. Chang and Peter Jezzard |
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10:30 |
212. |
Quantification of CMRO2 and
CBF Using Simultaneous NIRS and FMRI |
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Sungho Tak1,
Jong Chul Ye1
1Bio and Brain Engineering, KAIST, Daejeon,
Korea |
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This paper introduces an
accurate technique to estimate the cerebral
metabolic rate of oxygen (CMRO2) and
cerebral blood flow (CBF) using simultaneously
measured near infrared spectroscopy (NIRS) and blood
oxygenation level dependent (BOLD) fMRI signals.
Owing to simultaneous acquisition of both fMRI and
NIRS, separate hypercapnia condition or arterial
spin labeling (ASL) acquisition are not necessary to
quantify CMRO2 and CBF, which greatly
improves the accuracy of the proposed method. The
dynamic coupling ratio of CBF changes to CMRO2
changes has been also investigated. Experimental
results using finger tapping task showed that the
activation pattern of CBF calculated using NIRS-SPM
software is more specific to the primary motor
cortex than fMRI BOLD and NIRS-HbR signal.
Furthermore, the dynamic couple ratio coincides with
the existing results from the literature. |
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10:42 |
213. |
Evaluation of a New
Quantitative BOLD Approach to Map Local Blood Oxygen
Saturation |
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Thomas Christen1,2,
Benjamin Lemasson1,3, Nicolas Pannetier1,2,
Régine Farion1,2, Christoph Segebarth1,2,
Chantal Rémy1,2, Emmanuel L. Barbier1,2
1Inserm, U836, Grenoble, F-38043, France;
2Université Joseph Fourier, Grenoble Institut
des Neurosciences, UMR-S836, Grenoble, France;
3Oncodesign Biotechnology, Dijon, France |
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Recently, an in vivo
MR approach – quantitative BOLD – was introduced to
obtain blood volume fraction (BVf) and local blood
oxygen saturation (lSO2) maps. The mesoscopic effect
on T2* depends on both BVf and lSO2, but these two
contributions are difficult to separate during data
analysis. To improve the accuracy on the
determination of lSO2, we introduce a different
measurement scheme which combines a steady-state BVf
measurement with standard B0 and T2 mapping. The
proposed scheme was evaluated in healthy rats under
an O2 challenge. Value of lSO2 are consistent with
data from the literature. |
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10:54 |
214. |
Does Global Cerebral Oxygen Metabolism Change During
Hypercapnia and Hypocapnia in Awake Humans? |
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Jean J. Chen1,
G. Bruce Pike1
1McConnell Brain Imaging Centre, Montreal
Neurological Institute, Montreal, Quebec, Canada |
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The effect of CO2
on cerebral metabolism is of great interest, since
hypercapnia is routinely used in calibrated
BOLD-based δCMRo2 estimation and assumes
that CMRo2 remains unchanged during
hypercapnia-induced blood flow increase. Certain
anesthetized-animal studies, however, have put this
claim under question, necessitating its verification
in humans and under the conditions customary of
calibrated BOLD. We report, for the first time, on
steady-state global δCMRo2 measurements
in awake humans during graded hypercapnia and
hypocapnia. Our results show that under the mild
levels of end-tidal CO2 changes commonly
used in calibrated BOLD, there is negligible global
δCMRo2. |
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11:06 |
215. |
CO2 Breathing Suppresses
Cerebral Metabolic Rate of Oxygen |
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Feng Xu1,
Uma Yezhuvath1, Matthew R. Brier2,
John Hart, Jr. 3, Michael A. Kraut4,
Clair Moore2, Hanzhang Lu1
1University of Texas Southwestern Medical
Center at Dallas, Dallas, TX, USA; 2University
of Texas at Dallas, Dallas, TX, USA; 3University
of Texas at Dallas, Dallas, TX, USA; 4Johns
Hopkins University, Baltimore, MD, USA |
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CO2 is highly potent in
modulating cerebral blood flow. However the effect
of CO2 on neuronal activity and brain energy
consumption is not yet known. Here we used a novel
technique to measure global cerebral metabolic rate
of oxygen, CMRO2, during normocapnia and hypercapnia,
and showed that 5% CO2 breathing can reduce the
CMRO2 by 13±5% (n=8, p<0.001). We further used
electroencephalography (EEG) to investigate which
component of the neuron’s energy budget has changed,
and found that the delta band in the EEG signal was
enhanced by 18%, suggesting that brain was switched
to a low-arousal state during CO2 breathing. |
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11:18 |
216. |
CBF-CMRO2 Coupling in the Default Mode Network |
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Pan Lin1,
Jorge Jovicich1, Simon Robinson1
1Center for Mind/Brain Sciences, University of
Trento, Trento, Trentino, Italy |
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The Default Mode is a
network of brain regions which show reduced blood
flow (CBF) and BOLD signal in the task state
relative to baseline, independent of the nature of
the task. There has been controversy over the origin
of these signal fluctuations, which overlap to some
extent with regions affected by respiration rate
variation. We show for the first time that the
coupling ratio between cerebral blood flow and
cerebral metabolic rate of oxygen consumption is the
same in task-independent deactivation as in
activation, and thereby consistent with a neuronal
basis for deactivation of the Default Mode. |
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11:30 |
217. |
Changes in Arterial Oxygen
Tension with Evoked Stimulation in the Rat Somato-Sensory
Cortex: Implications for Quantitative FMRI |
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Alberto L. Vazquez1,
Mitsuhiro Fukuda1, Seong-Gi Kim1
1Radiology, University of Pittsburgh,
Pittsburgh, PA, USA |
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In an effort to
investigate the changes in vascular and tissue
oxygenation with evoked brain function, arterial,
tissue and venous oxygen tension (and saturation)
were measured in the rat somato-sensory cortex using
oxygen micro-electrodes. Significant increases in
the oxygen tension and saturation of pre-penetrating
pial arterioles were observed. The largest increases
in oxygen saturation were observed at the sampled
small emerging pial veins. The observed steep oxygen
tension and saturation gradient indicates that the
quantification of the relative changes in CMRO2 from
high-resolution BOLD fMRI data (hundreds of microns)
will be underestimated. |
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11:42 |
218. |
A
Comparison of Physiologic Modulators of FMRI Signals |
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Hanzhang Lu1,
Feng Xu1, Uma S. Yezhuvath1,
Yamei Cheng1, Rani Varghese1
1Advanced Imaging Research Center, University
of Texas Southwestern Medical Center, Dallas, TX,
USA |
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A critical prerequisite
for fMRI to be possibly used for personalized
disease diagnosis is that we have to understand and
account for differences in fMRI signals across
healthy subjects. Recently, much attention has been
focused on the physiologic markers that can explain
the inter-subject variations. Here we conducted
visual-stimulation fMRI in a group of young, healthy
controls and compared four potential modulators in
explaining the variations in fMRI signals: baseline
venous oxygenation, cerebrovascular reactivity,
resting state BOLD signal fluctuation, and baseline
CBF. It was found that these physiologic parameters
in combination can explain up to 69% of the
inter-subject variations. |
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11:54 |
219. |
Comparison and Validation of
FMRI Calibration Techniques |
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Rasmus Matthias Birn1,
Daniel Handwerker1, Peter A. Bandettini1
1Laboratory of Brain and Cognition, National
Institute of Mental Health, Bethesda, MD, USA |
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The amplitude of the
BOLD response across the brain depends strongly on
the variations in the underlying vasculature, making
it difficult to determine subtle differences in
neuronal activity between regions or subjects. In
this study we test various calibration techniques
designed to account for spatial variability in the
vasculature, and compare their ability to pull out
known subtle underlying variations in neuronal
activity. |
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12:06 |
220. |
An Intra-Subject Investigation of the BOLD Contrast
Mechanism in Response to Visual Stimulation and
Breath Hold at 1.5T, 3.0T and 7.0T: Insight Into the
Extravascular Sensitivity, Resolution-Dependence and
Vascular Origins of BOLD Contrast |
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Manus J. Donahue1,
Hans Hoogduin2, Peter CM van Zijl3,4,
Peter Jezzard1, Reinoud Pieter Harmen
Bokkers2, Matthias JP van Osch5,
Jaco J.M. Zwanenburg2, Peter Luyten2,
Jeroen Hendrikse2
1Clinical Neurology, The University of Oxford,
Oxford, UK; 2University Medical Center
Utrecht, Utrecht, Netherlands; 3Radiology
and Radiological Science, The Johns Hopkins
University School of Medicine, Baltimore, MD, USA;
4FM Kirby Research Center for Functional
Brain Imaging, Kennedy Krieger Institute, Baltimore,
MD, USA; 5Leiden University Medical
Center, Leiden, Netherlands |
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B0-dependence of
gradient-echo BOLD-fMRI contrast was investigated in
the same subjects at 1.5T, 3.0T and 7.0T by
performing (1) BOLD-fMRI (visual) in the presence of
flow-dephasing gradients (b=100 s/mm2) at multiple
TEs, (2) BOLD-fMRI (visual) at high (1.5x1.5x1.5mm3)
and low (3.5x3.5x3.5mm3) spatial resolution, and (3)
BOLD-fMRI (breath hold). Extravascular (EV)
contributions to total BOLD ΔR2* were 45±13%, 70±11%
and 92±19% at 1.5T, 3.0T and 7.0T, respectively,
suggesting that BOLD fMRI performed at 7.0T is
almost purely EV. Caution should be exercised when
comparing total BOLD reactivity at different B0 due
to different EV contributions. |
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12:18 |
221. |
Physiological Noise Effects on
the Flip Angle Selection in BOLD FMRI |
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Jerzy Bodurka1,
Peter Bandettini1,2
1Functional MRI Facility, National Institute
of Mental Health, NIH, Bethesda, MD, USA; 2Section
on Functional Imaging Methods, National Institute of
Mental Health, NIH, Bethesda, MD, USA |
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Here we have considered
theoretically and experimentally the physiological
noise effects on the flip angle selection. We will
shown that for given TR, temporal signal to noise
ratio (TSNR=mean voxel time course signal/time
course standard deviation) versus flip angle plots
are significantly affected by the physiological
noise. For situations where available SNR is high
and physiological noise dominates over
system/thermal noise the selection of Ernst angle
does not results in large improvements in TSNR. In
fact it is possible to select much smaller flip
angle and have similar TSNR as for the Ernst angle,
however smaller flip angle have important benefits
of reducing possible inflow effect. |
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