TRADITIONAL POSTER - ismrm

Poster Sessions
2996. Orientation Dependence of Magnetization Transfer in Human White Matter.
Dirk K. Müller 1 , André Pampel 1 , Harald E. Möller 1
1 Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany
We present an investigation of the dependence of quantitative magnetization transfer (qMT) on fibre orientation. QMT parameters obtained from
experiments using pulsed off-resonance irradiation were correlated to the orientation of the diffusion tensor obtained from DTI data. In particular, we
observed a correlation between the fiber orientation with respect to B 0 and the transverse relaxation rate of the semi-solid pool (T 2b ).
2997. Quantification of the Magnetization Transfer Phenomenon in the Human Head at 7T
Olivier E. Mougin 1 , Penny A. Gowland 1
1 Sir Peter Mansfield Magnetic Resonance Centre, School of Physics & Astronomy,University of Nottingham, Nottingham,
Nottinghamshire, United Kingdom
Magnetization Transfer and related effects such as CEST are important sources of contrast in MRI. Sensitivity and increase spectral resolution make possible
the measurement of MT effects at 7T in vivo. We used pulsed saturation with Turbo Field Echo readout with a range of saturation offset frequencies on the
approach to steady-state, providing data that can be used to measure MT parameters at 7T in a reasonable imaging time at a resolution of 1.25mm isotropic.
2998. A Simple Iterative Reduction Method for Optimization of Quantitative Magnetization Transfer
Imaging
Ives R. Levesque 1 , John G. Sled 2 , G Bruce Pike 1
1 Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada; 2 Mouse Imaging Centre, Hospital For Sick Children,
Toronto, Ontario, Canada
A method is presented for the selection of an optimal acquisition scheme for quantitative magnetization transfer imaging using pulsed off-resonance
saturation. This method is based on the iterative reduction of a discrete sampling of the Z-spectrum. In vivo results demonstrate that optimized sampling
improves parameter map quality and longitudinal reproducibility. The reduction method avoids clustering and repeated points, an attractive feature for the
purpose of MT model validation. The optimal number of MT weightings is also investigated.
2999. Measuring Scan-Rescan Reliability in Quantitative Brain Imaging Reveals Instability in an Apparently
Healthy Imager and Improves Statistical Power in a Clinical Study.
Becky Ilana Haynes 1 , Nick G. Dowell 1 , Paul S. Tofts 1
1 Clinical Imaging Sciences Centre, Brighton and Sussex Medical School, Brighton, United Kingdom
Repeatability of MTR and ADC brain histograms of healthy volunteers in our centre showed disturbingly large differences, even though the scanner was
producing high quality images. Such instrumental variation could mask small between-group differences in a cross-sectional study, and increase the number
of participants needed to see an effect. Repeat scans in phantoms and healthy controls highlighted the variability and showed when the problem had been
fixed. Our current normal standard deviations are at the lower end of the published range. Ongoing QA for quantitative studies should include explicit
measurement of short- and long-term repeatability in controls.
3000. Reconstruction of Bound Pool Fraction Maps from Subsets of Cross-Relaxation Imaging Data at 3.0 T:
Accuracy, Time-Efficiency and Error Analysis
Hunter R. Underhill 1,2 , Chun Yuan 1 , Vasily L. Yarnykh 1
1 Radiology, University of Washington, Seattle, WA, United States; 2 Bioengineering, University of Washington, Seattle, WA, United
States
In this study, we compare strategies for the time-efficient acquisition of the bound pool fraction in the in vivo human brain at 3.0 T. The bound pool fraction
can be accurately estimated using only two off-resonant magnetization transfer data points by applying appropriate, field-strength specific constraints to the
transfer rate constant and transverse relaxation parameters. In so doing, whole-brain, three-dimensional, high-resolution f-maps can be obtained in a
clinically acceptable scan time. Simulations demonstrate that the effects of parameter constraints induce minimal error in determining f in grey matter, white
matter and multiple sclerosis lesions.
3001. Five-Site Modeling of Protons Chemical Exchange Processes for in Vivo CEST-Based Molecular
Imaging
Julien Flament 1 , Benjamin Marty 1 , Céline Giraudeau 1 , Sébastien Mériaux 1 , Julien Valette 1 , Christelle
Médina 2 , Caroline Robic 2 , Marc Port 2 , Franck Lethimonnier 1 , Gilles Bloch 1 , Denis Le Bihan 1 , Fawzi
Boumezbeur 1
1 NeuroSpin, I²BM, Commissariat à l'Energie Atomique, Gif-sur-Yvette, France; 2 Guerbet, Research Division, Roissy-Charles de
Gaulle, France
LipoCEST are a new class of contrast agents for CEST-MRI which provide a tremendous amplification factor but suffer from a quite small chemical shift (2-
28 ppm) compared to paramagnetic complexes. Consequently, their detection in vivo is hampered by endogenous Magnetization Transfer contrast. It is
therefore important to separate specific LipoCEST signal from endogenous background coming from macromolecules. Thus in this study, we propose to
characterize water exchange processes using a five-site model by measuring and fitting the Z-spectrum of each tissular compartment of mouse brain in order
to achieve quantitative CEST imaging with LipoCEST contrast agents.