Observation of Time Dependent Magnetic Field Correlation in the Human Brain

Introduction: The Magnetic Field Correlation (MFC) is a quantitative MRI metric that characterizes magnetic field inhomogeneities (MFI) generated in the brain by iron-rich tissue structures. The MFC gives information beyond that provided by more commonly used parameters for brain iron quantification, such as R2 and R2* [1-5]. Prior work indicates that the MFC increases rapidly during adolescence, consistent with known age-related brain iron changes [6] and that Alzheimer’s patients have elevated MFC values in the basal ganglia compared with age-matched controls [7]. The MFC may be decomposed into macroscopic (macroMFC) and microscopic (microMFC) components that reflect, respectively, MFI which vary on length scales large and small compared to the voxel dimensions [8, 9]. In previous phantom studies, we have shown that the microMFC decreases monotonically with time, as is the theoretically expected behavior in the presence of microscopic MFI [4]. The present work demonstrates the time-dependence of microMFC in vivo by estimating MFC at three different times for selected regions of interest within the brain of 21 normal human subjects.