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Poster Sessions<br />

1125. Linearity of Neural Responses in the Somatosensory Cortex and Their Relationship to BOLD FMRI.<br />

Fan Wang 1 , Claire Stevenson 1 , Matthew Brookes 1 , Peter Morris 1<br />

1 Physics, Sir Peter Mansfield Magnetic Resonance Centre, Nottingham, Nottinghamshire, United Kingdom<br />

We use the combination of MEG and fMRI to study the neural basis for BOLD non-linearity. Both nonlinear neural responses to stimuli and nonlinear<br />

vascular responses to neural activity may contribute to BOLD non-linearity and the relative contribution of these two effects remains poorly understood. We<br />

extended the study of non-linear neural response to both phase locked evoked response and time related beta oscillations in somatosensory cortex. The N20<br />

peak amplitudes show non-linearities with ISI of 0.25-2s, influenced by beta power at the time of stimulation, suggesting that best oscillation should also be<br />

considered for BOLD convolution.<br />

1126. Simultaneous BOLD and NIRS Signal Correlation During Hypoxia<br />

Matthew Borzage 1,2 , Marvin Nelson 3 , Istvan Seri 1,4 , Stefan Blüml 3,5<br />

1 Neonatal Medicine, Childrens Hospital Los Angeles, Los Angeles, CA, United States; 2 Viterbi School of Engineering, University of<br />

Southern California, Los Angeles, 90007, United States; 3 Department of Radiology, Childrens Hospital Los Angeles, Los Angeles,<br />

CA, United States; 4 Keck School of Medicine, University of Southern California, Los Angeles, CA, United States; 5 Rudi Schulte<br />

Research Institute, Santa Barbara, CA, United States<br />

Studying changes in cerebral hemodynamics is possible via MR, including blood oxygen level dependent (BOLD) imaging. We used near infrared<br />

spectroscopy (NIRS) to sample oxy- and deoxyhemoglobin directly, and utilized a nitrogen challenge to change FiO2 and thus cause measurable changes in<br />

blood oxygenation. We have observed good correlation between the BOLD and NIRS signals, with higher correlation in the gray matter than in the white<br />

matter. In the near future, we will use this paradigm to study the limited autoregulation of cerebral blood flow in preterm neonates.<br />

1127. Cerebral Blood Volume Changes in Arterial and Post-Arterial Compartments and Their Relationship<br />

with Cerebral Blood Flow Alteration During Brief Breath-Holding and Visual Stimulation in Human Brain<br />

Jun Hua 1 , Robert Stevens 1 , Manus J. Donahue 1,2 , Alan J. Huang 1 , James J. Pekar 1 , Peter C.M. van Zijl 1<br />

1 Department of Radiology, The Johns Hopkins University, Baltimore, MD, United States; 2 Department of Clinical Neurology, Oxford<br />

University, Oxford, United Kingdom<br />

Changes in CBF/CBV/arterial-CBV(CBV a )/post-arterial-CBV(CBV pa ) were measured in human brain during breath-hold and visual stimulation. δCBV/CBV<br />

was larger during breath-hold (54.9+/-5.8%) than visual stimulation (28.2+/-5.2%), a difference primarily originating from δCBV pa /CBV pa (54.5+/-4.9% vs.<br />

22.2+/-3.8%); δCBV a /CBV a (53+/-6%) and δCBF/CBF (61+/-7%) were comparable in both tasks. During breath-hold, vasodilation distributed<br />

proportionally among arterial and post-arterial compartments, whereas, during visual stimulation, relative change in CBV a was greater than that in CBV pa .<br />

Our data indicate that the coupling between arterial-CBV and CBF was largely preserved during both tasks (rCBVa=rCBF 0.86+/-0.05 ), while the relationship<br />

between total-CBV and CBF was substantially different between breath-hold (rCBV=rCBF 0.90+/-0.05 ) and visual (rCBV=rCBF 0.52+/-0.04 ) stimulation.<br />

1128. Impact of the Mono-Exponential Signal Decay Approximation on the Numerically Predicted Spatial<br />

BOLD Specificity for Spin Echo Sequences<br />

Daniel Pflugfelder 1 , Kaveh Vahedipour 1 , Kamil Uludag 2 , Nadim Jon Shah 1,3 , Tony Stöcker 1<br />

1 Institute of Neuroscience and Medicine 4, Medical Imaging Physics, Forschungszentrum Jülich GmbH, Jülich, Germany; 2 Max-<br />

Planck Institute for Biological Cybernetics, Tuebingen, Germany; 3 Faculty of Medicine, Department of Neurology, RWTH Aachen<br />

University, Aachen, Germany<br />

To increase the spatial specificity of the BOLD signal, a large ratio R of microvascular to macrovascular BOLD signal is desirable. This can be be achieved<br />

using spin echo sequences. To simplify the calculation the extravascular BOLD signal (EV) is often approximated by a mono-exponential decay (MEA). To<br />

investigate the effect of the MEA we calculated R for multiple B0 and TE without using this approximation. The parameter range for an optimal R was<br />

considerable different to the results obtained using the MEA. This is mainly due to an vessel radius dependent delay of the EV which is not reproduced by<br />

the MEA.<br />

1129. A Realistic Vascular Model for BOLD Signal Up to 16.4 T.<br />

Bernd Michael Müller-Bierl 1 , Verena Pawlak 2 , Jason Kerr 2 , Kamil Ugurbil 3 , Kamil Uludag 1<br />

1 MRC, Max-Planck Institute for Biological Cybernetics, Tübingen, Germany; 2 NWG, Max-Planck Institute for Biological<br />

Cybernetics, Tübingen, Germany; 3 Center for Magnetic Resonance Research, University of Minnesota, Minnesota, Minneapolis,<br />

United States<br />

We present a realistic vascular model based on Monte-Carlo modeling of diffusion and the finite element method to compute the background magnetic field<br />

of partly oxygenated finite venules exposed to up to 16.4 T. Our data show that the realistic vasculature data set is necessary to account for the effects due to<br />

finite-sized vessels. The venule data herein stems from 2 photon microscopy of the rat brain. Results show that the infinite vessel model is prone to error so<br />

that the use of realistic vascular data sets is necessary to get precise results. However, for a better understanding more realistic vascular data sets should be<br />

examined in future work.<br />

1130. Relaxation of Blood at High Field: Another Exchange Regime<br />

Ksenija Grgac 1,2 , Qin Qin 1,3 , Michael McMahon 1,3 , Jason Zhao 1 , Peter C.M. van Zijl 1,3<br />

1 Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD, United States;<br />

2 Department of Chemistry, Johns Hopkins University, Baltimore, MD, United States; 3 F.M. Kirby Research Center for Functional<br />

Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States<br />

To study the intravascular BOLD mechanism, we used a physiologically controlled blood perfusion system at 9.4T under oxygenated conditions for a series<br />

of hematocrits. Previous studies have shown that, at such high fields, the two-site (eryhtrocyte-plasma) fast exchange model can not describe oxygenationbased<br />

relaxation changes properly in that it gives incorrect lifetimes for water in erythrocytes (1-3ms). We show that, for the physiological range of

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