| Contrast Agents & Microvascular Function: Methods |
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Thursday 23 April 2009 |
| Room 316BC |
16:00-18:00 |
Moderators: |
Timothy J. Carroll and Linda Knutsson |
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16:00 |
719. |
Measuring the Concentration of
Contrast Agent in Blood for DSC MRI from the
Extra-Vascular Phase Shift |
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Samuel James Wharton1,
Natalia Petridou1, Ashley E. Lotfipour1,
Penny A. Gowland1, Richard Bowtell1
1Sir Peter Mansfield Magnetic Resonance
Centre, School of Physics and Astronomy, University
of Nottingham, Nottingham, UK |
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Recently, it has been
shown that the susceptibility of a uniform object
with arbitrary geometry can be quantified by
least-squares fitting phase data measured in
gradient echo imaging to a simulated field-shift.
The large phase shifts associated with blood
vessels, amplified in the presence of paramagnetic
contrast agents, provide ample information for such
a fitting process to be applied in-vivo.
Here, we present a robust method for directly
calculating the susceptibility of blood in the human
brain from extra-vascular phase data and describe
its application in Dynamic Susceptibility Contrast
MRI experiments at 7T. |
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16:12 |
720. |
Robust Quantification of
Contrast Agent Concentration with Magnetic Field
Correlation Imaging |
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Vishal Patil1,
Glyn Johnson1, Jens H. Jensen1
1Radiology, NYU School of Medicine, New York,
USA |
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Estimation of gadolinium
concentration, [Gd], is the essential first step in
the measurement of a number of different parameters
by contrast enhanced perfusion MRI. Generally, [Gd]
is estimated assuming a linear relationship between
relaxation rate and concentration. However, it is
known that this assumption is false in tissue.
Magnetic Field Correlation (MFC) depends
quadratically on [Gd] to a very good approximation
and may therefore be a more accurate means of
estimating concentration. The purpose of this study
is to compare the accuracy of [Gd] measurement using
MFC and relaxivity rates in yeast phantoms. |
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16:24 |
721. |
The Effects of Equilibrium
Intercompartmental Water Exchange Kinetics on MRI
Estimation of Tissue Concentration of Contrast
Agents |
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Ramesh Paudyal1,2,
Hassan Bagher-Ebadian1,2, Tavarekere
Nagaraja3, Swayam Panda2,
Joseph D. Fenstermacher3, James R. Ewing1,2
1Physics, Oakland University, Rochester, MI,
USA; 2Neurology, Henry Ford Health
Systems, Detroit, MI, USA; 3Anesthesiology,
Henry Ford Health Systems, Detroit, MI, USA |
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This study address the
effects of equilibrium intercompartmental water
exchange kinetics on the tissue water protons
relaxation rate utilizing the Look-Locker pulse
sequence for the Bloch McConnell equation of a three
site two exchange [3S2X] model, in which
paramagnetic relaxation agents (CA) are restricted
only to certain compartment. The relationship
between the tissue water relaxation rate R1 versus
the tissue concentration of CA is examined by using
both modeling and experimental methods. |
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16:36 |
722. |
Gas-Filled
Microbubbles as Intravascular R2*
Contrast Agent for Liver MRI |
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April M.
Chow1,2, Jerry S. Cheung1,2,
Alfred Yu2, Hua Guo1,2, Ed X.
Wu1,2
1Laboratory of Biomedical Imaging and
Signal Processing, The University of Hong Kong, Hong
Kong SAR, China; 2Department of
Electrical and Electronic Engineering, The
University of Hong Kong, Hong Kong SAR, China |
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Gas-filled microbubbles possess the potential to
become a unique MR contrast agent because of their
magnetic susceptibility effect, high
biocompatibility and unique cavitation and
sonoporation properties. In this study, microbubble
susceptibility induced changes were investigated
using custom-made albumin-coated microbubbles and a
commercially available lipid-based clinical
ultrasound contrast agent SonoVue® in rat livers
in vivo with dynamic susceptibility weighted MRI
at 7T. The results demonstrate the potential of
gas-filled microbubble as an intravascular R2*
contrast agent for liver MRI at high field. |
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16:48 |
723. |
Repeatable
First Pass DSC-MRI Measurements Using Saline as a
Reverse-Effect Contrast Agent |
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Christopher Chad Quarles1, John
Christopher Gore1
1Institute of Imaging Science, Radiology
and Radiological Sciences, Biomedical Engineering,
Vanderbilt University, Nashville, TN, USA |
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Dynamic
susceptibility contrast MRI provides measures of
tissue hemodynamics but is limited to one
measurement per imaging session limiting its use for
pharmacological and functional studies. The goal of
the present study is to assess the potential of
saline for use as a reverse-effect contrast agent
for multiple DSC-MRI measurements. This method
relies on the reduction of the blood signal
intensity using a pre-injection of an iron oxide
contrast agent prior to a bolus injection(s) of
saline. Saline enhanced the signal intensity by 25%
and yielded dynamic time series similar to those
measured with a conventional contrast agent. |
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17:00 |
724. |
Analysis
of Partial Volume Effects on Arterial Input
Functions Using Gradient Echo: A Simulation Study |
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Birgitte
Fuglsang Kjolby1, Irene Klærke Mikkelsen1,
Michael Pedersen2, Leif Oestergaard1,
Valerij G. Kiselev3
1Center for Functionally Integrative
Neuroscience, Aarhus University Hospital, Aarhus,
Denmark; 2MR Research Center, Aarhus
University Hospital, Aarhus, Denmark; 3Department
of Diagnostic Radiology, Medical Physics, University
Hospital Freiburg, Freiburg, Germany |
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Quantitative perfusion
weighted MRI requires an accurately measured
arterial input function (AIF). Due to limited
spatial resolution, AIF voxels cannot be placed
completely within a feeding artery. We present a
two-compartment model of an AIF voxel including
relaxation properties of blood and tissue. The aim
is to analyze the shape of partial volumed AIF
signals and quantify the impact of partial volume
effects on the quantitative perfusion metrics. We
find that the tissue contribution broadens and
introduces fluctuations in the AIF. Furthermore, PVE
bias perfusion metrics in a nonlinear fashion,
compromising quantitative perfusion estimates and
profoundly effecting local AIF selection. |
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17:12 |
725. |
Phase
Contrast MRI Absolute Cerebral Blood Flow
Estimation: A Method to Obtain Absolute Cerebral
Blood Flow Maps from Dynamic Susceptibility Contrast
Imaging |
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David
Bonekamp1, Peter B. Barker2
1Johns Hopkins University, Baltimore, MD,
USA; 2Johns Hopkins University, USA |
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We
propose a method to calibrate dynamic susceptibility
contrast MRI (DSC-MRI) relative cerebral blood flow
(rCBF) maps using a single slice phase contrast MRI
(PC-MRI) technique to obtain absolute cerebral blood
flow (tCBF) maps. This technique requires only a
minimal extension of the clinical protocol by a 50
sec sequence. Initial results demonstrate that the
white matter CBF estimate in the hemisphere
contralateral to the pathology demonstrates
significantly less variability and better agreement
with literature values than uncorrected data. |
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17:24 |
726. |
A New
Constrained Blind Estimation Algorithm for
Determination of the Arterial Input Function Without
Reference Tissues |
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Matthias
Christian Schabel1, Edward V. R. Di Bella1
1Radiology, University of Utah, Salt Lake
City, UT, USA |
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We
describe an efficient constrained method for blind
estimation of the arterial input function that does
not require reference tissues or clustering of
similar tissue curves. This method has been
validated by Monte Carlo simulations and in human
subjects with solid tumors, and demonstrates
excellent consistency with high-quality measured
AIFs as well as reproducibility in longitudinal
studies. |
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17:36 |
727. |
Comparison
of Arterial Blood Volume Obtained from Model-Free
Arterial Spin Labelling (ASL) and Cerebral Blood
Volume Obtained from Contrast Enhanced Dynamic
Susceptibility Weighted Imaging (DSC) in Brain
Tumours |
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Danielle
van Westen1, Linda Knutsson2,
Esben Thade Petersen3,4, Karin Markenroth
Bloch5, Freddy Ståhlberg1,6,
Stig Holtås1
1Department of Diagnostic Radiology, Lund
University, Lund, Sweden; 2Department of
Medical Radiation Physics, Lund University, Lund,
Sweden; 3Neuroradiology, National
Neuroscience Institute, Singapore, Singapore; 4
CFIN, Aarhus University Hospital, Aarhus, Denmark;
5Philips Medical Systems, Lund, Sweden;
6Department of Medical Radiation Physics,
Lund University , Lund, Sweden |
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Cerebral
blood volume (CBV) in brain tumours can be used to
differentiate intracranial tumour types. Measurement
of CBV with dynamic susceptibility weighted imaging
(DSC-MRI) requires injection of a contrast agent. As
an alternative, a recently introduced, model-free
arterial spin labelling technique (ASL) named QUASAR
enables quantification of CBF and arterial blood
volume (aBV). In this study, aBV and CBF calculated
from ASL and CBV and CBF obtained from DSC-MRI were
determined in three types of brain tumours. We
conclude that aBV is a potential tool for
characterisation of intracranial tumours, of special
clinical interest since its measurement is
non-invasive. |
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17:48 |
728. |
Software
Solution for Automated Assessment of DWI/PWI
Mismatch in Acute Stroke Patients: The RAPID
MISMATCH |
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Matus
Straka1, Maarten G. Lansberg2,
Gregory W. Albers2, Roland Bammer1
1Lucas Center, Department of Radiology,
Stanford University, Stanford, CA, USA; 2Stroke
Center, Department of Neurology and Neurological
Sciences, Stanford University, Stanford, CA, USA |
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DWI/PWI
mismatch is method to identify acute stroke patients
that might benefit from reperfusion therapies. We
have implemented a fully automated system aimed on
assessment of mismatch from DWI and Tmax perfusion
maps. The automated approach can deliver the
mismatch maps within 5 minutes after the scan to
scanner and PACS. The statistical evaluation of 74
cases has shown robustness of the system and good
correlanion between manual and automated results. |
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