Issel Anne L. Lim1, 2, Ann S. Choe3, 4, Xu Li2, 5, Craig K. Jones2, 5, Peter C. M. van Zijl2, 5
1Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, United States; 2F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States; 3International Center for Spinal Cord Injury, Hugo Moser Research Institute at Kennedy Krieger Inc, Baltimore, MD, United States; 4Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, United States; 5Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, United States
A primary component of quantitative susceptibility mapping (QSM) is determining the resonance frequency per voxel. In the spinal cord, obtaining frequency maps from phase images via traditional gradient echo imaging (GRE) is complicated due to low SNR and many phase wraps at tissue interfaces of large susceptibility differences. By measuring resonance frequency maps with the WAter Saturation Shift Referencing (WASSR) method and fitting the resulting signal as a function of offset frequency to a Lorentzian lineshape, voxel frequencies can be determined without the need for phase unwrapping. WASSR allowed good quality frequency maps to be obtained in the spinal cord.
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