Weiwei Chen¹, Tian Liu², Shuai Wang³, Wenzhen Zhu¹, and Yi Wang^4,5
1Radiology, Tongji Hospital, Tongji Medical College, Huazhong University of Science&Technology, Wuhan, Hubei, China,²MedImageMetric LLC, New York, NY, United States, ³University of Electronic Science and Technology of China, Chengdu, Sichuan, China, ⁴Radiology, Weill Cornell Medical College, New York, NY, United States, ⁵Biomedical Engineering, Cornell University, Ithaca, NY, United States

38 consecutive patients with suspected pathological intracranial calcifications were imaged with both gradient echo (GRE) MRI and CT. Both GRE phase and quantitative susceptibility mapping (QSM) reconstructed from GRE data were analyzed for detecting calcifications using CT as the reference standard. Our data demonstrated that GRE phase images have poor accuracy, while QSM has a fair good accuracy.

Ferdinand Schweser¹, Andreas Deistung¹, Karsten Sommer¹, and Jürgen Rainer Reichenbach^1
1Medical Physics Group, Dept. of Diagnostic and Interventional Radiology I, Jena University Hospital, Jena, Germany

Magnetic susceptibility is an intrinsic physical tissue property which recently became accessible in vivo by a novel imaging technique called quantitative susceptibility mapping (QSM). The intermixing of contributions of iron and myelin, however, complicates interpretation of susceptibility changes in particular in neurodegenerative diseases where inflammatory myelin-loss and focal iron accumulation may occur simultaneously. We present a novel technique for substantially increasing the specificity of QSM by utilizing additional R2* information. The technique yields two novel contrasts, one is independent of orientation effects, the other is independent of the tissue iron concentration.

Ioannis Argyridis¹, Wei Li¹, and Chunlei Liu^1,2
1Brain Imaging and Analysis Center, Duke University, Durham, NC, United States, ²Department of Radiology, School of Medicine, Duke University, Durham, NC, United States

Myelination of nerve axons is essential for brain function and occurs during early post natal days. We extract data from quantitative susceptibility mapping (QSM) and diffusion-weighted imaging of three central regions in newborn healthy mouse brains at four different stages. Values of fractional anisotropy, apparent diffusion coefficient and magnetic susceptibility are analyzed to track myelin change in vivo. Also a new tool, susceptiblity anisotropy provides insight to the magnetic properties of unmyelinated fibers. Such information has become available recently with the improvement of QSM and can be crucial in the better monitoring, understanding and treatment of neurological demylineation diseases.

Issel Anne L. Lim^1,2, Xu Li^2,3, Craig K. Jones^2,3, Jonathan A. D. Farrell^2,3, Deepti S. Vikram^2,3, Carlos A. Renjifo⁴, and Peter C. M. van Zijl^2,3
1Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States, ²F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, United States, ³Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States, ⁴Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, United States

Quantitative susceptibility imaging (QSM) can characterize the local magnetic environment of the brain, which is affected by chemical content of the tissues. Currently, QSM techniques utilize gradient echo imaging (GRE) to measure spatial differences in signal phase, identify local field (frequency) differences, and calculate susceptibility. We compare susceptibility maps generated from GRE to the WAter Saturation Shift Referencing (WASSR) method, which determines the resonance frequency per voxel through measurement of direct water saturation as a function of RF pulse offset frequency. Results from five normal male volunteers at 3T correlate with iron concentration in the brain.

Jongho Lee¹, Karin Shmueli², B-T Kang³, Bing Yao², Masaki Fukunaga⁴, Peter van Gelderen², Sara Palumbo⁵, Francesca Bosetti⁵, Afonso Silva³, and Jeff Duyn^2
1University of Pennsylvania, Philadelphia, PA, United States, ²AMRI, LFMI, NINDS, NIH, ³LFMI, NINDS, NIH, ⁴Osaka University, ⁵NIA, NIH

In this study, the contribution of myelin to both T2* and frequency contrasts is investigated using a mouse model of cuprizone-induced demyelination. The demyelinated brains showed significantly increased T2* in white matter and a substantial reduction in gray-white matter frequency contrast, suggesting that myelin is a primary source for these contrasts.

Michael J Allison¹, and Jeffrey A Fessler^1
1Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, United States

Existing regularized field map estimators are highly robust, but require the minimization of a non-convex cost function. The current fastest minimization method, an optimization transfer approach with separable quadratic surrogates, requires thousands of iterations to converge. We propose a novel optimization transfer method which uses Huber's algorithm for quadratic surrogates to solve the non-convex problem. By framing the problem in this way, we are able to exploit the sparse banded structure of typical finite differencing matrices. We evaluated our algorithm on a brain image dataset finding that it converged in one hundredth of the time.

Xu Li^1,2, Deepti S Vikram^1,2, Issel Anne L Lim^1,3, Craig K Jones^1,2, Jonathan A.D. Farrell^1,2, and Peter C.M. van Zijl^1,2
1F.M. Kirby research center for functional brain imaging, Kennedy Krieger Institute, Baltimore, MD, United States, ²Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, United States, ³Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, United States

A method is proposed to map the magnetic susceptibility anisotropy (MSA) and mean magnetic susceptibility (MMS) of brain tissue. This is accomplished by combining GRE phase data collected at a small number of head orientations with fiber direction information obtained from DTI. Simulations were performed to test the reconstruction performance. The reconstructed MMS map in vivo shows good contrast between gray and white matter, while the MSA map reveals most of the major central white matter fiber bundles.

Jie Luo¹, Xiang He², and Dmitriy A Yablonskiy^3,4
1Chemistry, Washington University in St.Louis, St. Louis, MO, United States, ²University of Pittsburg, ³Radiology, Washington University in St.Louis,⁴Physics, Washington University in St.Louis, United States

Phase images obtained by gradient echo MRI provide enhanced contrast of the brain anatomy. Possible origins of the phase/frequency contrast such as the magnetic susceptibility and the water-macromolecule exchange effects have been discussed. To describe the influence of tissue magnetic susceptibility on MR signal frequency shift, a proper relationship between these two values should be established. In this study, we have demonstrated that the Generalized Lorentzian Approach provides satisfactory explanation of the angular dependence of the phase contrast in longitudinal structures such as axons in white matter while usually assumed Lorentzian Sphere Approximation fails.

Andreas Deistung¹, Andreas Schäfer², Ferdinand Schweser¹, Karsten Sommer¹, Robert Turner², and Jürgen Rainer Reichenbach^1
1Medical Physics Group, Department of Diagnostic and Interventional Radiology I, Jena University Hospital, Jena, Germany, ²Max-Planck-Institute for Human Cognitive and Brain Sciences, Leipzig, Germany

This study compares quantitative susceptibility maps with conventional gradient-echo (GRE) imaging approaches (magnitude, phase, R2*) with respect to anatomic tissue contrast. The contrast-to-noise ratio analysis suggests that deep gray matter structures are delineated best on susceptibility images. Susceptibility images provide an excellent and local contrast between white matter and cortical grey matter that is superior to the other GRE contrasts. Susceptibility maps also reveal (sub-)structures of the midbrain, thalamus, and basal ganglia that are not observed on corresponding magnitude, phase, and R2* images.

Chunlei Liu^1,2, and Aiming Lu^3
1Brain Imaging and Analysis Center, Duke University, Durham, NC, United States, ²Department of Radiology, Duke University, Durham, NC, United States, ³Center for MR Research, University of Illinois Medical Center, Chicago, IL, United States

This study found that sodium MRI exhibits nearly an order of magnitude larger susceptibility compared to proton. In sodium MRI, the typical gray and white matter susceptibility contrast is absent. While white matter appears largely paramagnetic, some regions may appear diamagnetic due to intravoxel phase wraps caused by the unusually large susceptibility. Our data further indicate a potentially large susceptibility gradient between extra- and intracellular space as sodium resides primarily in the extracellular space. Measuring susceptibility based on sodium MRI may provide additional insights into sub-cellular susceptibility distribution and the complex mechanisms involved in tissue susceptibility contrast.