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Poster Sessions<br />

2996. Orientation Dependence of Magnetization Transfer in Human White Matter.<br />

Dirk K. Müller 1 , André Pampel 1 , Harald E. Möller 1<br />

1 Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany<br />

We present an investigation of the dependence of quantitative magnetization transfer (qMT) on fibre orientation. QMT parameters obtained from<br />

experiments using pulsed off-resonance irradiation were correlated to the orientation of the diffusion tensor obtained from DTI data. In particular, we<br />

observed a correlation between the fiber orientation with respect to B 0 and the transverse relaxation rate of the semi-solid pool (T 2b ).<br />

2997. Quantification of the Magnetization Transfer Phenomenon in the Human Head at 7T<br />

Olivier E. Mougin 1 , Penny A. Gowland 1<br />

1 Sir Peter Mansfield Magnetic Resonance Centre, School of Physics & Astronomy,University of Nottingham, Nottingham,<br />

Nottinghamshire, United Kingdom<br />

Magnetization Transfer and related effects such as CEST are important sources of contrast in MRI. Sensitivity and increase spectral resolution make possible<br />

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<br />

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.<br />

2998. A Simple Iterative Reduction Method for Optimization of Quantitative Magnetization Transfer<br />

Imaging<br />

Ives R. Levesque 1 , John G. Sled 2 , G Bruce Pike 1<br />

1 Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada; 2 Mouse Imaging Centre, Hospital For Sick Children,<br />

Toronto, Ontario, Canada<br />

A method is presented for the selection of an optimal acquisition scheme for quantitative magnetization transfer imaging using pulsed off-resonance<br />

saturation. This method is based on the iterative reduction of a discrete sampling of the Z-spectrum. In vivo results demonstrate that optimized sampling<br />

improves parameter map quality and longitudinal reproducibility. The reduction method avoids clustering and repeated points, an attractive feature for the<br />

purpose of MT model validation. The optimal number of MT weightings is also investigated.<br />

2999. Measuring Scan-Rescan Reliability in Quantitative Brain Imaging Reveals Instability in an Apparently<br />

Healthy Imager and Improves Statistical Power in a Clinical Study.<br />

Becky Ilana Haynes 1 , Nick G. Dowell 1 , Paul S. Tofts 1<br />

1 Clinical Imaging Sciences Centre, Brighton and Sussex Medical School, Brighton, United Kingdom<br />

Repeatability of MTR and ADC brain histograms of healthy volunteers in our centre showed disturbingly large differences, even though the scanner was<br />

producing high quality images. Such instrumental variation could mask small between-group differences in a cross-sectional study, and increase the number<br />

of participants needed to see an effect. Repeat scans in phantoms and healthy controls highlighted the variability and showed when the problem had been<br />

fixed. Our current normal standard deviations are at the lower end of the published range. Ongoing QA for quantitative studies should include explicit<br />

measurement of short- and long-term repeatability in controls.<br />

3000. Reconstruction of Bound Pool Fraction Maps from Subsets of Cross-Relaxation Imaging Data at 3.0 T:<br />

Accuracy, Time-Efficiency and Error Analysis<br />

Hunter R. Underhill 1,2 , Chun Yuan 1 , Vasily L. Yarnykh 1<br />

1 Radiology, University of Washington, Seattle, WA, United States; 2 Bioengineering, University of Washington, Seattle, WA, United<br />

States<br />

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<br />

can be accurately estimated using only two off-resonant magnetization transfer data points by applying appropriate, field-strength specific constraints to the<br />

transfer rate constant and transverse relaxation parameters. In so doing, whole-brain, three-dimensional, high-resolution f-maps can be obtained in a<br />

clinically acceptable scan time. Simulations demonstrate that the effects of parameter constraints induce minimal error in determining f in grey matter, white<br />

matter and multiple sclerosis lesions.<br />

3001. Five-Site Modeling of Protons Chemical Exchange Processes for in Vivo CEST-Based Molecular<br />

Imaging<br />

Julien Flament 1 , Benjamin Marty 1 , Céline Giraudeau 1 , Sébastien Mériaux 1 , Julien Valette 1 , Christelle<br />

Médina 2 , Caroline Robic 2 , Marc Port 2 , Franck Lethimonnier 1 , Gilles Bloch 1 , Denis Le Bihan 1 , Fawzi<br />

Boumezbeur 1<br />

1 NeuroSpin, I²BM, Commissariat à l'Energie Atomique, Gif-sur-Yvette, France; 2 Guerbet, Research Division, Roissy-Charles de<br />

Gaulle, France<br />

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-<br />

28 ppm) compared to paramagnetic complexes. Consequently, their detection in vivo is hampered by endogenous Magnetization Transfer contrast. It is<br />

therefore important to separate specific LipoCEST signal from endogenous background coming from macromolecules. Thus in this study, we propose to<br />

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<br />

to achieve quantitative CEST imaging with LipoCEST contrast agents.

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