TRADITIONAL POSTER - ismrm

Poster Sessions
1125. Linearity of Neural Responses in the Somatosensory Cortex and Their Relationship to BOLD FMRI.
Fan Wang 1 , Claire Stevenson 1 , Matthew Brookes 1 , Peter Morris 1
1 Physics, Sir Peter Mansfield Magnetic Resonance Centre, Nottingham, Nottinghamshire, United Kingdom
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
vascular responses to neural activity may contribute to BOLD non-linearity and the relative contribution of these two effects remains poorly understood. We
extended the study of non-linear neural response to both phase locked evoked response and time related beta oscillations in somatosensory cortex. The N20
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
considered for BOLD convolution.
1126. Simultaneous BOLD and NIRS Signal Correlation During Hypoxia
Matthew Borzage 1,2 , Marvin Nelson 3 , Istvan Seri 1,4 , Stefan Blüml 3,5
1 Neonatal Medicine, Childrens Hospital Los Angeles, Los Angeles, CA, United States; 2 Viterbi School of Engineering, University of
Southern California, Los Angeles, 90007, United States; 3 Department of Radiology, Childrens Hospital Los Angeles, Los Angeles,
CA, United States; 4 Keck School of Medicine, University of Southern California, Los Angeles, CA, United States; 5 Rudi Schulte
Research Institute, Santa Barbara, CA, United States
Studying changes in cerebral hemodynamics is possible via MR, including blood oxygen level dependent (BOLD) imaging. We used near infrared
spectroscopy (NIRS) to sample oxy- and deoxyhemoglobin directly, and utilized a nitrogen challenge to change FiO2 and thus cause measurable changes in
blood oxygenation. We have observed good correlation between the BOLD and NIRS signals, with higher correlation in the gray matter than in the white
matter. In the near future, we will use this paradigm to study the limited autoregulation of cerebral blood flow in preterm neonates.
1127. Cerebral Blood Volume Changes in Arterial and Post-Arterial Compartments and Their Relationship
with Cerebral Blood Flow Alteration During Brief Breath-Holding and Visual Stimulation in Human Brain
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
1 Department of Radiology, The Johns Hopkins University, Baltimore, MD, United States; 2 Department of Clinical Neurology, Oxford
University, Oxford, United Kingdom
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
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.
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
proportionally among arterial and post-arterial compartments, whereas, during visual stimulation, relative change in CBV a was greater than that in CBV pa .
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
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.
1128. Impact of the Mono-Exponential Signal Decay Approximation on the Numerically Predicted Spatial
BOLD Specificity for Spin Echo Sequences
Daniel Pflugfelder 1 , Kaveh Vahedipour 1 , Kamil Uludag 2 , Nadim Jon Shah 1,3 , Tony Stöcker 1
1 Institute of Neuroscience and Medicine 4, Medical Imaging Physics, Forschungszentrum Jülich GmbH, Jülich, Germany; 2 Max-
Planck Institute for Biological Cybernetics, Tuebingen, Germany; 3 Faculty of Medicine, Department of Neurology, RWTH Aachen
University, Aachen, Germany
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
using spin echo sequences. To simplify the calculation the extravascular BOLD signal (EV) is often approximated by a mono-exponential decay (MEA). To
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
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
the MEA.
1129. A Realistic Vascular Model for BOLD Signal Up to 16.4 T.
Bernd Michael Müller-Bierl 1 , Verena Pawlak 2 , Jason Kerr 2 , Kamil Ugurbil 3 , Kamil Uludag 1
1 MRC, Max-Planck Institute for Biological Cybernetics, Tübingen, Germany; 2 NWG, Max-Planck Institute for Biological
Cybernetics, Tübingen, Germany; 3 Center for Magnetic Resonance Research, University of Minnesota, Minnesota, Minneapolis,
United States
We present a realistic vascular model based on Monte-Carlo modeling of diffusion and the finite element method to compute the background magnetic field
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
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
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
examined in future work.
1130. Relaxation of Blood at High Field: Another Exchange Regime
Ksenija Grgac 1,2 , Qin Qin 1,3 , Michael McMahon 1,3 , Jason Zhao 1 , Peter C.M. van Zijl 1,3
1 Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD, United States;
2 Department of Chemistry, Johns Hopkins University, Baltimore, MD, United States; 3 F.M. Kirby Research Center for Functional
Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States
To study the intravascular BOLD mechanism, we used a physiologically controlled blood perfusion system at 9.4T under oxygenated conditions for a series
of hematocrits. Previous studies have shown that, at such high fields, the two-site (eryhtrocyte-plasma) fast exchange model can not describe oxygenationbased
relaxation changes properly in that it gives incorrect lifetimes for water in erythrocytes (1-3ms). We show that, for the physiological range of