Electronic poster

Wednesday 13:30-15:30 Computer 126

13:30 5111. Automated Phase-Based Segmentation of the Cerebral Cortex in 7T MR Images of the Elderly

Nhat Trung Doan¹, Maarten J. Versluis², Sanneke van Rooden, Jeroen van der Grond, Andrew Webb², Mark A. van Buchem, Johan H.C. Reiber¹, Julien Milles<sup>1

1</sup>LKEB - Department of Radiology, Leiden University Medical Center, Leiden, Zuid Holland, Netherlands; ²CJ Gorter Center - Department of Radiology, Leiden University Medical Center, Leiden, Zuid Holland, Netherlands

The aim of this work is to implement a phase-based approach for the automated segmentation of the cerebral cortex in T2* data of elderly patients acquired using a 7T MR scanner. These data show essentially no gray/white matter contrast on magnitude images. The method is divided into two stages. The first step makes use of k-means clustering to segment the outer layer of the cortex. The obtained contour is subsequently deformed to match the gray/white matter interface based on the improved contrast in phase images, thereby resulting in a full segmentation of the cerebral cortex.

14:00 5112. Classification of Calcium Salts: Correlation of Magnetic Susceptibility with Susceptibility Weighted Imaging (SWI)

Ali Fatemi¹, E Mark Haacke^2,3, Michael D. Noseworthy<sup>4

1</sup>Medical Physics and Applied Radiation Sciences, McMaster University, Hamilton, Ontario, Canada; ²Radiology, Wayne State University, Detroit, MI, United States; ³The MRI Institute for Biomedical Research, Detroit, MI, United States; ⁴Electrical and Computer Engineering, School of Biomedical Engineering, McMaster University, Hamilton, Ontario, Canada

We propose that by looking at the local magnetic field pattern of corrected phase images, it is possible to quantify local magnetic susceptibility, which is equivalent to classifying different calcium salts. This may lead to not only identification of breast cancer calcification but their biochemical characterization.

14:30 5113. Dipole Matched Filter with SWIFT

Curtis Andrew Corum^1,2, Djaudat Idiyatullin¹, Steen Moeller¹, Ryan Chamberlain¹, Michael Garwood<sup>1,2

1</sup>Center for Magnetic Resonance Research, Dept. of Radiology, Medical School, University of Minnesota, Minneapolis, MN, United States; ²Cancer Center, Medical School, University of Minnesota, Minneapolis, MN, United States

The combination of the SWIFT sequence and a secular dipole matched filter give positive contrast at dipole sites.

15:00 5114. Forward-Field Calculations Improve Contrast of Unwrapped MR Phase Images

Martijn D. Steenwijk¹, Maarten J. Versluis², Mark A. van Buchem, Johan H C Reiber¹, Andrew Webb², Julien Milles<sup>1

1</sup>Division of Image Processing, Leiden University Medical Center, Leiden, Zuid-Holland, Netherlands; ²CJ Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, Zuid-Holland, Netherlands

The aim of this work is to evaluate the gray matter / white matter (GM/WM) contrast improvement obtained by using forward-field calculations when unwrapping MR phase images of the brain. Standard phase unwrapping methods, such as high-pass filtering, prove sub-optimal in eliminating phase wraps with high spatial frequencies. Forward-field calculations can be used to compute geometry-dependent artifact-corrected (GDAC) images in which the residual phase wrapping is reduced significantly. We applied this technique to a high-resolution T2*-weighted sequence at 7T to study its effects on GM/WM contrast. The GDAC technique results in a more favourable trade-off between unwrapping and GM/WM contrast.

Thursday 13:30-15:30 Computer 126

13:30 5115. Segmentation of the Structure of the Mouse Spinal Cord on DTI Images

Michaël Sdika¹, Virginie Callot¹, Mathias Hebert¹, Guillaume Duhamel¹, Patrick J. Cozzone<sup>1

1</sup>CRMBM/CNRS UMR6612, Faculté de médecine, Université de la Méditérranée, Marseille, France, France

In this work, a fully automated method is proposed to segment the sub-structures of the mouse spinal Cord. WM/GM segmentation is used as input of the proposed method and on output, the GM substructures are distributed in Left Ventral and Dorsal GM and Right ventral and dorsal GM whereas substructures of WM were distributed into Left Lateral WM, Right Lateral WM, Ventral WM and Dorsal WM. The method has been evaluated by visual assessment and correlation with manual segmentation on 10 DTI images of mice acquired at 11.75T and show promising results.

14:00 5116. Longitudinal Changes of White Matter Lesions

Snehashis Roy¹, Aaron Carass¹, Navid Shiee¹, Dzung L. Pham², Susan Resnick³, Jerry L. Prince<sup>1,2

1</sup>Electrical and Computer Engg, Johns Hopkins University, Baltimore, MD, United States; ²Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD, United States; ³Laboratory of Personality and Cognition, National Institute on Aging, Baltimore, MD, United States

Progression of white matter lesions are important for early detection and monitoring of diseases like Alzheimer's or Multiple Sclerosis. FLAIR images provide superior contrast for lesions compared to traditional T1 or T2 weighted images. But they are often not acquired for time and cost constraints. We developed an atlas based method to synthesize FLAIR images from T1 and T2 acquisitions. We use this method to quantify the progression of lesions on a pool of 20 subjects. Synthesizing FLAIRs can be seen as a potential way to reduce unnecessary data acquisition.

14:30 5117. Accurate Adipose Tissue Segmentation from Single Gradient Echo Phase Images by Adaptive Local Thresholding

Christian Würslin¹, Frank Eibofner¹, Fabian Springer¹, Fritz Schick<sup>1

1</sup>Department of Diagnostical and Interventional Radiology, Section on Experimental Radiology, University Hospital Tübingen, 72076 Tübingen, Germany

In many applications, a quantification of fat is desired. Most (semi-)automatic procedures use T1-weighted spin echo images to accomplish this. These approaches are time-consuming and a precise quantification is usually complicated by a high amount of partial volume effects. We propose a quantification procedure based on one single phase image, acquired with a gradient echo technique and opposed-phase condition. This maximizes the contrast in between fat- and water- dominated tissues and is less time-consuming. The phase divergence, arising from inhomogeneities, is compensated for using an automated algorithm, enabling a precise fat quantification by thresholding. Phantom measurements show a high precision.

15:00 5118. Improving Robustness of Cartilage Segmentation Using IDEAL Water and Fat Images

Raghu Kokku<sup>1

1</sup>MR SW & Apps , GTO-I, Wipro GE Healthcare, Bangalore, Karnataka, India

Accurate and reliable quantification of cartilage volume in MRI is required for diagnosis of many degenerative and inflammatory diseases such as osteoarthritis or rheumatoid arthritis. A Novel approach to segment the anatomical structures and cartilage using IDEAL knee MRI data is proposed. Variation in the characteristics of similar structures in IDEAL water and fat images is used to generate the guidance map for automated segmentation. Segmented structures are analyzed qualitatively and quantitatively with manually segmented datasets from GE 1.5T scanner. Reported DSC with the experimental datasets (>85%) indicates that the proposed solution improved the robustness of segmentation.

Contrast Mechanisms

Hall B Monday 14:00-16:00 Computer 127

14:00 5119. The Effect of NMR-Invisible Susceptibility Inclusions on Phase Maps.

Samuel James Wharton¹, Richard Bowtell<sup>1

1</sup>Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, Nottingham, United Kingdom

Phase images generated at high field show exquisite anatomical contrast resulting from small changes of the NMR frequency linked to variation of the local magnetic susceptibility across tissues. When a significant contribution to the average susceptibility comes from NMR-invisible inclusions, the average NMR frequency offset is not however simply proportional to the average susceptibility. Here, we derive a simple expression based on the use of the conventional sphere of Lorentz, which allows the average NMR frequency offset to be calculated for compartments containing inclusions of varying shape and concentration. The expression is tested by comparison with the results of simulations.

14:30 5120. MRI Signal Response Mapping (SIRMA) to Dephaser to Quantify Susceptibility Gradient

florence franconi¹, Jean-Jacques Le Jeune², Pascal Richomme¹, Laurent Lemaire<sup>2

1</sup>PIAM, Université d'Angers, Angers, France, Metropolitan; ²UMR-S646, INSERM, Angers, France

SIgnal Response MApping to dephaser (SIRMA) method is proposed to quantify susceptibility gradient. In gradient echo acquisitions, the SIRMA method measures the echo shifts in k-space of susceptibility affected spins from a series of dephased images collected with additional incremental slice refocusing gradient offset or incremental reconstruction window off-centering. SIRMA applicability and performances have been demonstrated in vitro through quantization of susceptibility gradient induced in a cylinder model and in vivo through the quantitative detection of SPIO distribution volume. With respect to its quantitative nature, its computational simplicity, this method deserves further attention for application in molecular or cellular imaging.

15:00 5121. Simultaneous δR1 and δR2* Quantification in 5s to Monitor Blood and Tissue Oxygenation with Dynamic (C)O₂ Enhanced MRI

Stefanie Remmele¹, Tobias Voigt², Jochen Keupp¹, Christian Stehning¹, Julien Sénégas<sup>1

1</sup>Philips Research Europe, Hamburg, Germany; ²University of Karlsruhe, Karlsruhe, Germany

This work presents an approach to simultaneous and dynamic dR1, dR2* estimation that combines the beneficial features of currently used techniques for dynamic R1 quantification in DCE-MRI and for dynamic R2*-quantification in D(C)O2E-MRI. The technique aims at increasing the specificity of R2* BOLD imaging during respiratory challenges. Its accuracy and sensitivity is evaluated in phantom and breathold experiments.

15:30 5122. Susceptibility Weighted Imaging and Susceptibility Mapping (SWIM): A New Means to Visualize Veins and Quantify Susceptibility

Ewart Mark Haacke^1,2, Jin Tang³, Yu-Chung Norman Cheng¹, Jaladhar Neelavalli<sup>2,4

1</sup>Academic Radiology, Wayne State University, Detroit, MI, United States; ²The MRI Institute for Biomedical Research, Detroit, MI, United States; ³McMaster University, Hamilton, Ontario, Canada; ⁴Nuffield Department of Surgery, University of Oxford, Oxford, United Kingdom

A new means of visualizing veins which is independent of orientation of vessels (or the head) relative to the main magnetic field is presented. This new venous imaging method is based on direct mapping of the susceptibility using the inverse Green’s function approach.

Tuesday 13:30-15:30 Computer 127

13:30 5123. Feasibility of Brain Lesion Characterization at 1.5T – Whole-Brain Susceptibility Mapping Using A Homogeneous Lesion Constraint

Ferdinand Schweser¹, Andreas Deistung², Berengar Wendel Lehr², Jürgen Rainer Reichenbach<sup>2

1</sup>Medical Physics Group, Department of Diagnostic and Interventional Radiology , Jena University Hospital, Jena, Germany; ²Medical Physics Group, Department of Diagnostic and Interventional Radiology, Jena University Hospital, Jena, Germany

A method is presented for high-quality whole-brain susceptibility mapping based on standard clinical single-shot low-field SWI-data. Feasibility of in-vivo lesion characterization is demonstrated for clinical patient data.

14:00 5124. Towards an In-Vivo and Post-Mortem Characterization of Chronic Multiple Sclerosis Lesions Using Susceptibility Related Mechanisms of Contrast at Ultra-High Field MRI with R2* and Phase Images

Bing Yao¹, Francesca Bagnato², Eiji Matsuura², Hellmut Merkle¹, Peter van Gelderen¹, Henry McFarland², Jeff H. Duyn<sup>1

1</sup>AMRI, NINDS, National Institutes of Health, Bethesda, MD, United States; ²Neuroimmunology Branch, NINDS, National Institutes of Health

High field magnetic susceptibility-weighted MRI provides information on healthy and diseased human brain. Although the sources that contribute to the R2* and frequency shifts associated with susceptibility contrast are not fully understood, previous studies suggest that iron and myelin content may contribute. In this study, we used in-vivo and post-mortem brain tissues of multiple sclerosis (MS) as a model of disease to investigate the contribution of tissue iron and myelin content to the image contrast. We found that the iron and myelin may affect phase and R2* differently.

14:30 5125. Non-Lorentzian Sphere Behavior of Magnetic Susceptibility Induced MR Signal Frequency Shift in White Matter: Validation Study

Xiang He¹, Jie Luo², Dmitriy A. Yablonskiy<sup>1

1</sup>Mallinckrodt Institute of Radiology, Washington University in St Louis, School of Medicine, St. Louis, MO, United States; ²Department of Chemistry, Washington University in St Louis, St Louis, MO, United States

Previously proposed generalized Lorentzian approach that allows evaluation of magnetic susceptibility induced MR signal frequency shift in brain tissue is validated here using ex vivo fresh rat optic nerve positioned in the buffer solution. The frequency shift within and around the optic nerve is measured using double-echo gradient echo MRI at two orientations of optic nerve – parallel and perpendicular to the external magnetic field. Our results demonstrate that generalized Lorentzian approach, which takes into account cellular anisotropic microstructure of axons, provides satisfactory explanation of experimental data while Lorentzian sphere approximation fails to describe experimental measurements.

15:00 5126. Very Fast T2* Imaging by Using Improved Echo-Shifted Gradient-Recalled-Echo (IESGRE)

Jian Zhang^1,2, Chunlei Liu³, Michael Moseley<sup>2

1</sup>Department of Electrical Engineering, Stanford University, Stanford, CA, United States; ²Department of Radiology, Stanford University, Stanford, CA, United States; ³Brain Imaging and Analysis Center, Duke University Medical Center, Durham, NC, United States

Echo-Shifted Gradient-Recalled-Echo (ESGRE) can be used to acquire GRE images at TE>TR. This property makes it an appealing approach for fast T2* imaging. However, the original method didn’t work well with multiple-echo shift due to the ghosting artifacts. We demonstrate an improved ESGRE method here, in which extra crusher gradients are introduced to help establish a single steady-state among all phase encodes. By using this approach, high quality T2* images can be acquired with an arbitrary echo shift index. Very fast 2D/3D T2* imaging can be achieved with iESGRE.

Wednesday 13:30-15:30 Computer 127

13:30 5127. T2 Contrast Due to Signal Decay During Radial Readout in UTE (Ultrashort TE) Sequences

Jing-Tzyh Alan Chiang¹, Michael Carl², Jiang Du¹, Mark Bydder¹, Nick Szeverenyi¹, Robert F. Mattrey¹, Graeme Bydder<sup>1

1</sup>Radiology, University of California, San Diego, CA, United States; ²GE Healthcare

When imaging short T2 objects using ultrashort TE (UTE) pulse sequences, significant T2 decay can occur during radial readout for T2s comparable or less than the readout duration (typically ~1 ms), leading to signal amplitude loss in the image. Here, we study the relationship between T2 and the amount of signal amplitude loss – i.e. T2 contrast due to signal decay during radial readout in UTE. Significant T2 contrast is present, especially for T2s in the 0.1 to 1 millisecond range. We also observe important dependencies of this T2 contrast on object size as well as gradient parameters.

14:00 5128. 3D Radial UTE MRI for Serial Assessment of Fibrosis Development and Silicone Implant Distortion in Rat.

Lindsey Alexandra Crowe¹, Giorgio Petramaggiori², Sonia Nielles-Vallespin³, Peter Speier³, Enrico Vigato⁴, Hicham Majd⁴, Jean-Paul Vallée<sup>1

1</sup>Department of Radiology, Geneva University Hospital, University of Geneva, Faculty of Medicine, Geneva, Switzerland; ²Department of Surgery, Geneva University Hospital, Geneva, Switzerland; ³Siemens AG Medical Solutions, Erlangen, Germany; ⁴Department of Surgery, University of Geneva, Faculty of Medicine, Geneva, Switzerland

Fibrotic reaction around implantable medical devices is an increasingly important problem, limiting function and causing pain. Up to 10-15% of silicone breast implants develop capsular contraction, necessitating replacement. A 3D radial MRI technique with ultrashort TE is proposed as an early, pre-clinical quantification method and to serially assess the formation of capsular tissue. With the reduction of chemical shift effect and motion artifacts, and high isotropic resolution, distortion, rupture and tissue build-up around the implants can be segmented and quantified. Results may lead to standardized methods for early detection of excessive capsular formation, decreasing complication rates in patients.

14:30 5129. Design of Iron Sensitivity Phantom Suitable for Quantitative MRI and Atomic Spectrometry

Catherine Anusha Mallik¹, David Bellis², David J. Lythgoe¹, Rebeca Santamaria-Fernandez², Gareth J. Barker<sup>1

1</sup>Centre for Neuroimaging Sciences, Institute of Psychiatry, London, United Kingdom; ²Laboratory of Government Chemists, Teddington, Middlesex, United Kingdom

There is a growing body of MRI research on the effects of abnormal levels of iron in the brain. Validation of quantitative MRI with a phantom of known iron concentrations, is necessary for comparing different MRI measures. To allow cross-validation with Atomic spectrometry (AS) three different AS and MRI compatible phantoms were manufactured using various substrates and concentrations of iron. Phantoms were imaged at 3T with three different iron-sensitive MRI techniques. Imaging results show that a thrombin-fibrinogen gel doped with ferritin is a suitable phantom for both MRI and AS.

15:00 5130. Liposome-Loaded Microspheres as a Magnetic Susceptibility Agent for PH Sensing

Kannie W. Y. Chan^1,2, April M. Chow^1,2, Ed X. Wu<sup>1,2

1</sup>Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Pokfulam, Hong Kong SAR, China; ²Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam, Hong Kong SAR, China

MR susceptibility contrast agents have been used for imaging of vasculature and tumors, such as microbubbles and iron oxides. We have developed a susceptibility agent for pH sensing, especially for acidic tumor environment, increasing sensitivity around physiological pH using liposome-loaded microspheres. Our in vitro data showed that both R2 and R2* decreased at low pH, and the percentage change in R2* is larger when compared to controls at pH 6.8-7.2. Liposome-loaded microspheres showed a substantial increase in pH-dependence of R2*, which favoured by localization of liposomes on microspheres, and is first demonstrated to an improve pH sensitivity at 7T.

Thursday 13:30-15:30 Computer 127

13:30 5131. Experimental Investigation of the Relationship Between Phase Contrast and Orientation of White-Matter Fiber Orientation

Ferdinand Schweser¹, Berengar Wendel Lehr¹, Andreas Deistung¹, Jürgen Rainer Reichenbach¹, Daniel Güllmar<sup>1

1</sup>Medical Physics Group, Department of Diagnostic and Interventional Radiology, Jena University Hospital, Jena, Germany

Based on a recently published theoretical framework, we investigate experimentally, the relationship between phase images and white matter fiber orientation with respect to the orientation of the magnetic field of the MR scanner system. A volunteer was scanned in four different positions with respect to the external magnetic field. Phase information was plotted against the different fiber orientation settings and we found that the obtained correlation reflects at least in parts the proposed theoretical dependency.

14:00 5132. Phase Derived Frequency Shift Mapping and DTI of White Matter Regions at 3T

Gisela E. Hagberg¹, Andrea Cherubini¹, Umberto Sabatini¹, Carlo Caltagirone<sup>1

1</sup>Santa Lucia Scientific Foundation, Rome, Italy

Frequency shift, R2* and DTI-derived parameters (FA,MD) were evaluated in automatically parcellated white matter. The type of phase pre-processing affected the range and spatial contiguity of FS. The rank order of the 48 structures was significantly different between the evaluated parameters. The anterior and posterior limbs of the internal capsule had similar FA and MD, while the FS decreased and the R2* increased. In the commissural fibers, FS and MD values decreased from anterior to posterior while FA increased and T2* was greatest in the callosal body. The combined informational content thus depended both on fiber orientation and myelin density.

14:30 5133. Maximal Contrasts Using MR Complex Data: With an Application to Visualise Cortical Structure

Zhaolin Chen¹, Leigh A. Johnston², Gary F. Egan<sup>3

1</sup>Florey Neuroscience Institutes, Carlton, VIC, Australia; ²Electrical and Electronic Engineering, University of Melbourne; ³Centre for Neuroscience, University of Melbourne

Recent developments in MR phase imaging enable analyses of MR signals in the complex domain. However, in clinical diagnoses and anatomical studies, it is necessary to objectively map complex MR signals to a one-dimensional signal for visualisation. The Susceptibility Weighted Imaging (SWI) method uses the phase image to calculate a phase mask that is multiplied with the magnitude image to enhance the contrast caused by tissue susceptibility. SWI has demonstrated great advantage in contrast enhancement for various applications. In this work, we introduce a new method called Maximum Contrast Image (MCI) to further improve the image contrast from complex MR signals. Enhanced image contrasts obtained with the new method have been demonstrated using a 3T dataset of a cortical brain section. Furthermore, in contrast to the nonlinear operation in SWI, the MCI method uses a linear operation, which permits meaningful quantification of the MCI signals.

15:00 5134. Phase-Imaging Study in Restless Legs Syndrome

David Neil Manners¹, Giovanni Rizzo^1,2, Claudia Testa¹, Caterina Tonon¹, Roberto Vetrugno², Sara Marconi², Giuseppe Plazzi², Fabio Pizza², Federica Provini², Emil Malucelli¹, Bruno Barbiroli¹, Pasquale Montagna², Raffaele Lodi<sup>1

1</sup>Spectroscopy Unit, Department of Internal Medicine, Aging and Nephrology, Università di Bologna, Bologna, BO, Italy; ²Neurological Sciences, University of Bologna, Bologna, BO, Italy

Objectives. To apply phase imaging to the evaluation of brain iron content in patients with Restless Legs Syndrome. Methods. 11 RLS patients and 11 controls were studied using gradient echo imaging, and localised and whole brain ROIs selected on derived phase maps, sensitive to paramagnetic tissue. Results. In the whole brain analysis, RLS patients showed 10th and 90th percentile phase values significantly different from controls. The 10th percentile for RLS patients correlated with disease duration. Conclusions. Whole brain phase analysis is a suitable technique to study brain iron content and disclose reduced cerebral iron in RLS patients.