| Water Exchange & Binding |
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Monday 20 April 2009 |
| Room 313BC |
16:30-18:30 |
Moderators: |
R. Mark Henkelman and Bruce Pike |
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16:30 |
180. |
Young Investigator Award
Finalist:
MRI Contrast from Relaxation Along a
Fictitious Field (RAFF) |
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Timo Liimatainen1,
Dennis Sorce1, Michael Garwood1,
Shalom Michaeli1
1Center for Magnetic Resonance Research, Dept.
of Radiology, University of Minnesota, Minneapolis,
MN, USA |
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A method is described to
create MRI contrast using rapid amplitude and
frequency modulated RF irradiation in a
sub-adiabatic condition, referred to relaxation
along a fictitious field (RAFF). Bloch simulation of
RAFF shows that magnetization follows a fictitious
field when magnetization is oriented initially along
the fictitious field. Theoretical calculations show
sensitivity of RAFF to slow molecular motions with
similar sensitivity as the continuous wave
spin-locking experiment. The data obtained from
human brain shows images with significant
contribution of steady state which can be accounted
for in the analysis. |
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16:50 |
181. |
Balanced SSFP Profile Asymmetries Detect Small
Frequency Shifts in White Matter |
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Karla L. Miller1,
Peter Jezzard1
1FMRIB Centre, Oxford University, Oxford,
Oxon, UK |
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We study a novel
contrast mechanism based on the frequency dependence
of the balanced SSFP signal. The balanced SSFP
profile is theoretically symmetric with respect to
frequency if only T1, T2 and
diffusion effects are considered. However, the
convolution model for the SSFP signal predicts that
the profile becomes asymmetric for asymmetric
lineshapes. Asymmetries are observed in white
matter. The model is fit to data using a simple
lineshape parameterization, and data is shown to be
consistent with lineshape effects at small frequency
offsets. SSFP asymmetries may be a sensitive marker
of tissue microstructure, as reflected by small
frequency shifts. |
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17:02 |
182. |
Characterizing White Matter
Pathology with Quantitative Magnetization Transfer
Imaging: Insight from a Four-Pool Model |
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Ives R. Levesque1,
G. Bruce Pike1
1Montreal Neurological Institute, McGill
University, Montreal, Quebec, Canada |
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Magnetization transfer
is usually modeled using two proton pools. A model
with four compartments is required to capture all of
the commonly observed relaxation and
cross-relaxation properties of human white matter;
however, it is impractical for in vivo
imaging. Simulations of magnetization transfer
experiments were performed using variations on a
basic four-model model of white matter, to
investigate how these changes are reflected in the
two-pool model of MT. We show that compartmental
water exchange is negligible on an MT time-scale,
and that estimation of the semi-solid-to-liquid pool
ratio is robust, despite the presence of two liquid
and semi-solid pools. |
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17:14 |
183. |
A New, Polynomial-Based (PARA)CEST
Analysis Method with B0 Correction and Increased
Sensitivity |
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Lan Lu1, Tejas Shah2, Mark
A. Griswold1,2, Chris A. Flask1,2
1Radiology, Case Western Reserve University,
Cleveland, OH, USA; 2Biomedical
Engineering, Case Western Reserve University,
Cleveland, OH, USA |
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Chemical Exchange
Saturation Transfer (CEST) MRI is rapidly becoming a
popular tool for many in vivo imaging
applications. However, the analysis of CEST imaging
data has been limited for many studies which have
utilized simple 2-point subtraction techniques to
quantify the CEST effect which is susceptible to
significant errors from both B0 and B1 variation. We
have developed a new polynomial fitting technique to
quantify the chemical exchange from CEST spectra.
This new polynomial fitting technique allows for
accurate B0 correction and is inherently less
sensitive to experimental factors, such as B1
variation, that can broaden the CEST peaks. |
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17:26 |
184. |
1H-CEST and 19F
MRI of Temperature-Responsive Liposomal Contrast
Agents for Image Guided Drug Delivery |
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Jochen Keupp1,
Sander Langereis2, Inge de Roos2,
Dirk Burdinski2, Jeroen Pikkemaat2,
Holger Gruell2,3
1Philips Research Europe, Hamburg, Germany;
2Philips Research Europe, Eindhoven,
Netherlands; 3Eindhoven University of
Technology, Eindhoven, Netherlands |
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Localized delivery of
anti-cancer drugs by external stimulation of
nanocarriers (temperature, pH) promises a larger
therapeutic window with reduced side effects of the
treatment. The present imaging study is based on a
new type of temperature-responsive liposomes, which
are dually labeled for 1H-CEST and
19F MR imaging and release an encapsulated
payload near the melting temperature (Tm)
of their lipid membrane (38 C). In their lumen, a
chemical shift agent for 1H-lipoCEST
imaging and NH4PF6 for 19F
detection is contained. Inside the liposome, the
19F spectral lines are strongly broadened
and not detectable. Upon reaching Tm, the
lipoCEST contrast vanishes, due to the release of
the chemical shift agent and, simultaneously, the
19F MR signal becomes visible. Hence, the
19F signal could be used to quantify the
amount of released drug payload, while the CEST
signal could measure the local nanocarrier
concentration before the release. The study
demonstrates the potential of the new liposomal
nanocarriers for MRI-guided drug delivery in cancer
therapy. |
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17:38 |
185. |
ZAPI Analysis of Z-Spectral
Components in Acute Cerebral Ischemia |
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Johanna Närväinen1,
Kimmo T. Jokivarsi2, Penny Louise Hubbard3,
Olli H. Grohn4, Risto A. Kauppinen5,
Gareth A. Morris6
1Biomedical Imaging Unit, University of Kuopio,
Kuopio, Finland; 2Dept. of Neurobiology,
University of Kuopio, Kuopio, Finland; 3School
of Medicine, University of Manchester, Manchester,
UK; 4Dept. of Neurobiology, University of
Kuopio, Kuopio, Finland; 5Dept. of
Radiology, Dartmouth College, Hanover, NH, USA;
6School of Chemistry, University of
Manchester, Manchester, UK |
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T2-selective
Z-spectroscopy (ZAPI) was applied to acute cerebral
ischemia. It was shown that the magnetization
transfer (MT) component can be measured directly at
and near water resonance using sinusoidally
modulated low-power RF saturation. This information
was used to improve the separation of MT from other
components in a Z-spectrum. In this study, a small
decrease in MT asymmetry in stroke was observed. In
the ischemic striatum the amide signals at 3.5 ppm
showed decreased amide-water exchange, while
aliphatic signals at -3.5 ppm remained unchanged. |
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17:50 |
186. |
PCEST: Positive Contrast Using
Chemical Exchange Saturation Transfer |
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Elena Vinogradov1,
Todd C. Soesbe2, James A. Balschi3,
Dean A. Sherry2,4, Robert E. Lenkinski1
1Department of Radiology, Beth Israel
Deaconess Medical Center, Harvard Medical School,
Boston, MA, USA; 2Advanced Imaging
Research Center, University of Texas Southwestern
Medical Center, Dallas, TX, USA; 3NMR
Laboratory for Physiological Chemistry, Brigham and
Women’s Hospital, Harvard Medical School, Boston,
MA, USA; 4Department of Chemistry,
University of Texas at Dallas, Dallas, TX, USA |
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Chemical Exchange
Saturation Contrast utilizes selective presaturation
of a small pool of exchanging protons and is
manifested in the decrease of the free water signal.
Thus, CEST contrast is negative and requires the
detection of small signal changes on top of a strong
background signal. Here we introduce a Positive CEST
(PCEST) scheme that results in the increased signal
intensity in the presence of the agent and RF.
Similar to the original CEST, the contrast can be
switched “ON” and “OFF”. The sequence leads to
better utilization of the dynamic range and results
in the substantial background suppression. |
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18:02 |
187. |
Z-Spectrum Asymmetry :
From 3T to 7T |
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Olivier E. Mougin1, Ron Coxon1,
Penny A. Gowland1
1Sir Peter Mansfield Magnetic Resonance
Centre, School of Physics and Astronomy, University
of Nottingham, Nottingham, Nottinghamshire, UK |
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Magnetization Transfer
and related effects such as CEST are important
sources of contrast in MRI. Studying MT in vivo
at 7T is challenging due to the increase in
longitudinal relaxation time and SAR limits. We used
pulsed saturation with EPI readout a range of offset
frequencies and on the approach to steady-state,
providing data that can be used to measure MT
parameters at 7T in a reasonable imaging time and to
compare the z-spectrum at 7 and 3T. We have found
considerably increased sensitivity to CEST at 7T. |
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18:14 |
188. |
GlycoCEST Using FISPCEST |
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Tejas Jatin Shah1,2,
Lan Lu2, Paul R. Ernsberger3,
Christopher Allan Flask1,2
1Biomedical Engineering, Case Western Reserve
University, Cleveland, OH, USA; 2Department
of Radiology, University Hospitals of Cleveland,
Cleveland, OH, USA; 3Department of
Nutrition, Case Western Reserve University,
Cleveland, OH, USA |
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In vivo and
non-invasive measures of hepatic and muscular
glycogen are needed to effectively study diabetes
and metabolism in humans and animals. More recently,
glycogen’s inherent CEST effect has been proposed as
an alternative to C13-MRS1. While this initial
“GlycoCEST” work is promising, the in vivo
utility of the GlycoCEST technique is limited
because of the long acquisition times (1-3 hours)
for quantitative CEST-MRI acquisitions. In this
study, we have developed and optimized a rapid
GlycoCEST acquisition using our recently developed
FISP-CEST technique to obtain quantitative glycogen
CEST spectra in phantoms and ex vivo livers in 15-45
minutes. |
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