Novel Contrast Mechanisms
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Wednesday 9 May 2012
Room 210-211  10:00 - 12:00 Moderators: E. Mark Haacke, Jinyuan Zhou

10:00 0378.   Observation of Longitudinal Nuclear Magnetization Dynamics with NMR Field Probes permission withheld
Simon Gross1, Christoph Barmet1, Benjamin Emmanuel Dietrich1, and Klaas Paul Prüssmann1
1Department of Information Technology and Electrical Engineering, Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland

An NMR field probe based method for direct observation of longitudinal nuclear magnetization is presented. While conceptually simple, the technique is capable of measuring sample induced nanotesla field changes with a high temporal resolution. Geometrical considerations render the method robust against background field fluctuations and clock instabilities. As an example, the measurements of spin-lattice relaxation curves of six different liquid samples are shown. This technique is a valuable tool for fast and reliable material characterization for MR engineering and biomedical purposes.

10:12 0379.   
Molecular underpinnings of magnetic susceptibility anisotropy in the brain white matter
Wei Li1, Bing Wu1, Alexandru V. Avram1, and Chunlei Liu1,2
1Brain Imaging & Analysis Center, Duke University, Durham, North Carolina, United States, 2Radiology, Duke University, Durham, North Carolina, United States

Frequency shift and susceptibility from gradient-echo MRI shows excellent gray and white matter contrast, both of which depend on white matter fiber orientation. In this work, we explored the molecular underpinnings of orientation dependence of susceptibility in brain white matter. A biophysical model is developed to link the molecular susceptibility anisotropy of myelin components to the MRI-determined bulk anisotropy. This model provides a consistent interpretation of the orientation dependence of macroscopic magnetic susceptibility and the microscopic origin of anisotropic susceptibility. The results suggested that the cylindrically aligned lipid molecules in myelin are the main source of bulk susceptibility anisotropy.

10:24 0380.   
Non-linear Phase Evolution: The Dominant Source of the Average Frequency Difference between Grey Matter and White Matter in Gradient Echo MRI?
Samuel James Wharton1, and Richard Bowtell1
1Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, United Kingdom

There is an ongoing debate about the source of the small difference in the frequency of signals from cortical grey matter (GM) and adjacent white matter (WM) that is manifested in phase images of the human brain. Recently, it was shown that the evolution of the phase with TE in WM is non-linear. Here, we assess the contribution of this non-linear phase evolution to the average GM/WM frequency difference at 7 T. The results show that non-linear phase effects may be the dominant source of the GM/WM frequency difference seen in phase images acquired using long echo times (> 17ms).

10:36 0381.   
Mapping brown adipose tissue through intermolecular double-quantum magnetic resonance imaging at 7 Tesla
Jianfeng Bao1, Xiaohong Cui1, Zhenyao Zheng1, Congbo Cai1, and Zhong Chen1
1Department of Electronic Science, Fujian Key Laboratory of Plasma and Magnetic Resonance, Xiamen University, Xiamen, Fujian, China

Brown adipose tissue (BAT) has been found to be potential to combat against obesity and related diseases in adults, and has become a focus in biological and medical fields again. However, it is difficult to image BAT directly in vivo, especially when BAT mixes with other tissues. Here, we proposed a new method combining intermolecular double-quantum coherence with Dixon technique to map BAT only. The simulation and experimental results show that BAT can be imaged successfully at cellular scale. This new method may be significant in exploring the dynamic process of BAT in combating obesity.

10:48 0382.   
Characterization of Acoustically Induced Rotary Saturation (AIRS) Effect for Active Contrast Modulation in Molecular Imaging
Bo Zhu1,2, Thomas Witzel1, Shan Jiang3, Daniel G Anderson3, Robert S Langer3, Bruce R Rosen1,2, and Lawrence L Wald1
1Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States,2Harvard-MIT Health Sciences and Technololgy, Massachusetts Institute of Technology, Cambridge, MA, United States, 3Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, United States

Detailed characterization of a contrast mechanism for imaging iron oxide contrast agents is presented, whereby the rotary saturation effect produces tunable signal changes as oscillating magnetic fields generated from vibrating iron oxide nanoparticles resonantly alter the signal in the spin-lock sequence. These signal changes only occur near the vibrating iron oxide agents, selectively localizing their presence. We characterize the the signal changes as a function of vibrational displacement of the contrast agent, duration of spin-lock time, and spin-lock frequency. The measured dependencies indicate desirable regimes of operation for any system using rotary saturation to detect vibrating agents.

11:00 0383.   Changes in MR contrast after fixation: insight from M0, R2*, phase and element imaging by LA-ICP-MS
Ana-Maria Oros-Peusquens1, Andreas Matusch1, Johannes Lindemeyer1, Johanna Sabine Becker2, and N. Jon Shah1
1INM-4, Research Centre Juelich, Juelich, Germany, 2Central Division of Analytical Chemistry, Research Centre Juelich, Juelich, Germany

The origin of T2* and phase contrast in the rat brain and their changes following formalin fixation were investigated by comparison of MR-based maps with element analysis. Element images were obtained from two cryocut half-brain slices (one half native tissue, one half fixed, obtained from the same animal) using Laser Ablation Inductively Coupled Mass Spectrometry. No changes in the Fe, C, P and Cu distributions was observed following fixation. In contrast, the levels of Na, Mg, Cl, K, Mn, Zn change substantially. Qualitatively, a good correspondence between Fe and T2*/phase contrast is observed both in native and fixed tissue.

11:12 0384.   1H Perfusion MRI with the Replacement Effect of D2O
Fu-Nien Wang1, Chin-Tien Lu1, Shin-Lei Peng1, and Tzu-Chen Yeh2
1Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan, 2Department of Medical Research and Education, Taipei Veterans General Hospital, Taipei, Taiwan

D2O was first proposed as a novel contrast agent for 1H MRI. Previously, D2O was used for perfusion imaging by receiving the deuterium signal. In this study, we alternatively measured the 1H signal reduction due to the replacement effect of deuterium. Because the signal sensitivity of 1H is about 100 times larger than deuterium, the SNR could be substantially increased by using this imaging strategy. Phantom and small animal experiments were conducted to proof the concept. Due to the non-toxicity and non-radioactivity, the D2O could be a potential contrast agent for clinical usage without the need of hardware upgrade.

11:24 0385.   Potential of MREIT Conductivity Imaging to Evaluate Brain Abscess: In Vivo Canine Model
Hyung Joong Kim1, Woo Chul Jeong1, Young Tae Kim1, Chae Young Lim2, Hee Myung Park2, and Eung Je Woo1
1Biomedical Engineering, Kyung Hee University, Yongin, Gyeonggi, Korea, Republic of, 2Veterinary Internal Medicine, Konkuk University, Seoul, Korea, Republic of

MREIT can provide conductivity information of suspicious tissue using a current-injection MRI technique. To support its clinical significance, we should demonstrate that the conductivity image provides meaningful diagnostic information that is not available from other imaging modalities. To investigate any change of electrical conductivity due to brain abscess, canine brains having a regional abscess model were scanned along with separate scans of canine brains having no disease model. Conductivity images shown in this study indicated that time-course variations of conductivity contrast between normal and abscess regions are distinguishable in a different way compared with conventional MR image techniques.

11:36 0386.   Electric Properties Tomography (EPT) of the Liver in a Single Breathhold Using SSFP
Christian Stehning1, Tobias Voigt2, Philipp Karkowski1, and Ulrich Katscher1
1Philips Research Europe, Hamburg, Germany, 2Philips Research, Aachen, Germany

MR-based Electric Properties Tomography (EPT) provides a noninvasive means to assess electric tissue properties, provides a framework for an accurate determination of local SAR, and a diagnostic parameter in oncology. We have employed a fast balanced SSFP sequence, which allows for abdominal imaging in a single breathhold. Phantom experiments and first in vivo conductivity scans in the liver of healthy adults are shown.

11:48 0387.   Local Maxwell Tomography Using Transmit-Receive Coil Arrays for Contact-Free Mapping of Tissue Electrical Properties and Determination of Absolute RF Phase
Daniel K. Sodickson1,2, Leeor Alon1,2, Cem Murat Deniz1,2, Ryan Brown1, Bei Zhang1, Graham C. Wiggins1, Gene Y. Cho1,2, Noam Ben Eliezer1, Dmitry S. Novikov1, Riccardo Lattanzi1,2, Qi Duan3, Lester A. Sodickson4, and Yudong Zhu1,2
1Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, 2Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States, 3National Institutes of Health, Bethesda, MD, United States, 4Cambridge Research Associates, Newton, MA, United States

We introduce a new general approach to mapping the electrical properties of tissue or materials. Unlike prior MR-based techniques, Local Maxwell Tomography (LMT) is free of assumptions regarding RF phase and coil/field/magnetization structure. LMT solves simultaneously for key functions of the absolute RF phase distribution along with unknown permittivity and conductivity, using complementary information from the transmit and receive sensitivity distributions of multiple coils to resolve ambiguities. LMT, from which EPT may be derived as a special case, can operate at arbitrary field strength, with a wide range of coil designs, and free of errors associated with rapid field variation.