Observation of Frequency Shifts Induced by Chemical Exchange in Brain Tissue
Karin Shmueli¹, Steve Dodd², T-Q Li³, Jeff H. Duyn^1
1Advanced MRI Section, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States; ²Functional and Molecular Metabolism Section, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States; ³Department of Medical Physics, Karolinska Huddinge, Stockholm, Sweden

Water-macromolecular exchange has been proposed to explain brain gray and white matter frequency (phase) contrast. We extended previous observations of exchange-induced frequency shifts (f_exch) in protein solutions by performing chemical shift imaging experiments using reference chemicals (TSP and dioxane) to observe positive f_exch in fixed human and fresh pig brain tissue. Substantial negative GM-WM δf_exch was observed which was similar for all tissues and references but opposite to in-vivo GM-WM frequency contrast, implying that tissue magnetic susceptibility may have a greater contribution. Exchange should therefore be included in frequency contrast models but is insufficient to explain in-vivo GM-WM phase contrast.

Classical Interpretation of T1rho and T2rho Relaxation
Michael Carl¹, Mark Bydder², Eric Han¹, Graeme Bydder^2
1GE Healthcare, Waukesha, WI, United States; ²University of California, San Diego, San Diego, CA, United States

We present a simulation model based solely on classical equations to study spin-lattice relaxation in the rotating frame. Without the confound of a quantum mechanical treatment, this model allows for an intuitive understanding of spin locking such as T1rho dispersion, oscillations caused by residual dipolar interactions (RDI), and T2rho.

Quantitative T1rho Imaging Using Phase Cycling for B0 and B1 Field Inhomogeneity Compensation
Weitian Chen¹, Atsushi Takahashi¹, Eric T. Han^1
1MR Applied Science Lab, GE Healthcare, Menlo Park, CA, United States

T1rho imaging is promising in clinical applications such as early detection of osteoarthritis. T1rho imaging, however, is sensitive to B0 and B1 RF field inhomogeneities. In this work, we report on a phase cycling method to eliminate B1 RF inhomogeneity effects in T1rho imaging. The presences of B0 field inhomogeneity can compromise B1 RF inhomogeneity compensation approaches. We present a method which combines the phase cycling approach with a composite RF pulse scheme proposed by Dixon et al for simultaneous compensation of B0 and B1 RF field inhomogeneity in T1rho imaging. The proposed T1rho RF preparation methods can be combined with an SNR-efficient 3D T1rho imaging method MAPSS without compromising scan time.

Quantitative Magnetization Transfer Imaging of Human Brain at 3T Using Selective Inversion Recovery
Richard D. Dortch^1,2, Ke Li^1,2, Ashish A. Tamhane³, E B. Welch^2,4, Dan F. Gochberg^1,2, John C. Gore^1,2, Seth A. Smith^1,2
1Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, United States; ²Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States; ³Department of Biomedical Engineering, Illinois Institute of Technology, Chicago, IL, United States; ⁴MR Clinical Science, Philips Healthcare, Cleveland, OH, United States

Quantitative magnetization transfer (qMT) yields quantitative information about interactions between immobile macromolecular protons and free water protons. Because of its relatively short scan times, the pulsed, off-resonance saturation qMT approach is most commonly employed on clinical systems; however, it suffers from complicated data analysis and sensitivity to macromolecular proton lineshape assumptions. The selective inversion recovery (SIR) approach does not suffer from these shortcomings, but has not been widely implemented on clinical systems. In this study, the SIR approach was implemented on a clinical 3T system. The resultant qMT parameters in healthy brain were in good agreement with previously published values.

Magnetization Transfer Mapping of Myelinated Fiber Tracts in Living Mice at 9.4 T
Susann Boretius¹, Peter Dechent², Jens Frahm¹, Gunther Helms^2
1Biomedizinische NMR Forschungs GmbH, Max-Planck-Institut für Biophysikalische Chemie, Göttingen, Germany; ²MR-Research in Neurology and Psychiatry, University Medical Center, Göttingen, Germany

MRI of mouse models is an integral part of translational research on white matter diseases and myelin disorders. Thus, the delineation of myelinated fiber tracts in mice becomes of growing interest. Here we used in healthy adult mice a novel FLASH-based parameter for magnetization transfer that was recently established for human applications. In comparison to maps of MT ratio and T1, this parameter provides an improved gray-white matter contrast that allows for the visualization of small neuronal fiber bundles such as the mammilothalamic tract and fasciculus retroflexus.

Molecular Mechanisms of Magnetization Transfer
Scott David Swanson^1
1Department of Radiology, University of Michigan, Ann Arbor, MI, United States

We present a look at the molecular mechanisms of MT in agarose and gelatin samples.  MT is found to be driven by whole water exchange in agarose and proton exchange in gelatin.

CEST-Dixon MRI for Sensitive and Accurate Measurement of Amide Proton Transfer in Humans at 3T
Jochen Keupp¹, Holger Eggers^1
1Philips Research Europe, Hamburg, Germany

CEST-MRI based measurement of endogenous proteins using the amide proton transfer (APT) signal could find important clinical applications in oncology (tumor metabolism) and in neurology (ischemic acidosis). As APT-MRI is very sensitive to B₀ inhomogeneity, we propose to apply multi gradient-echo sequences and derive a B₀ map by the Dixon technique, as opposed to previously described methods like full CEST-spectra interpolation or separate water resonance mapping.  Furthermore, technical limits for pulse lengths on clinical scanners are addressed and a saturation of 1 second is achieved (human head).  Feasibility of APT-MRI within 6 minutes (SENSE R=3) is demonstrated in volunteers at 3T.

Detection of Myo-Inositol In-Vivo Using MR Chemical Exchange Saturation Transfer Imaging (MICEST)
Mohammad Haris¹, Kejia Cai¹, Anup Singh¹, Feliks Kogan¹, Walter Witschey¹, Hari Hariharan¹, Ravinder Reddy^1
1CMROI, Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States

In the current study, we demonstrated the mapping of Myo-inositol (MI) in human brain at 7T by exploiting chemical exchange saturation transfer (CEST) of labile hydroxyl proton (-OH) on the MI. The Z-spectrum of MI showed an asymmetry around~0.625ppm downfield to the bulk water resonance. The CEST imaging on healthy human brain clearly shows the distribution of MICEST contrast in gray and white matter regions and negligible contrast from cerebrospinal fluid.

Differentiation Between Glioma and Radiation Necrosis Using Molecular Imaging of Endogenous Proteins and Peptides
Jinyuan Zhou¹, Erik Tryggestad², Zhibo Wen¹, Bachchu Lal³, Tingting Zhou¹, Rachely Grossman⁴, Kun Yan¹, Silun Wang¹, De-Xue Fu⁵, Eric Ford², John Laterra³, Peter C.M. van Zijl^1
1Department of Radiology, Johns Hopkins University, Baltimore, MD, United States; ²Department of Radiation Oncology, Johns Hopkins University, Baltimore, MD, United States; ³Department of Neurology, Kennedy Krieger Institute, Baltimore, MD, United States; ⁴Department of Neurosurgery, Johns Hopkins University, Baltimore, MD, United States; ⁵Department of Oncology, Johns Hopkins University, Baltimore, MD, United States

We show that it is possible to differentiate between glioma and radiation necrosis using the amide proton signals of endogenous cellular proteins and peptides as imaging biomarker. Using a radiation necrosis model (dose, 40 Gy; area, 10x10 mm2) and a SF188/V+ human glioma model in rats, tumors and radiation necrosis had similar conventional MRI features. However, gliomas were consistently hyperintense on amide proton transfer (APT) images, while radiation necrosis (observed about six months post-radiation) was hypointense to isointense. APT MRI as an imaging biomarker for tumor presence provides unique visual information for assessing active tumor versus treatment-related injury, such as radiation necrosis.

Fast T1 Mapping Using Modified Double-Inversion Recovery Pre-Pulse
Marcelo E. Andia¹, Rene M. Botnar^1
1Division of Imaging Sciences, Kings College London, London, United Kingdom

In this work we present a new technique for fast T1 estimation where the intensity of each pixel is linearly related to its T1 value. The technique is based on a modified Double Inversion Recovery pre-pulse and only requires the acquisition of a single 2D or 3D dataset. The technique was validated in a T1 phantom and in a pre-clinical study of renal perfusion using a gadolinium based contrast agent. Potential applications include fast T1 quantification in myocardial perfusion, infarct or fibrosis imaging.