Quantitative Magnetic Susceptibility of the Developing Mouse Brain

Abstract

<p>Cerebral development involves a complex cascade of events which are difficult </p><p>to visualize in vivo. In this study we combine information from Diffusion Tensor </p><p>Imaging (DTI) and Quantitative Susceptibility Mapping (QSM) on developing mouse </p><p>brains at five stages, for three central white matter (WM) regions. QSM can be calculated </p><p>using frequency shift Gradient Echo MR images acquired at high field. Extracted mean </p><p>values from small white matter regions of QSM brain maps depend on the orientation of </p><p>the neuronal fibers of each voxel to the main magnetic field B0. Using fiber tracking </p><p>information from DTI a correlation of the myelin content of regions of interest (ROI) to </p><p>the orientation of those fibers to B0 can be made. Plots of the myelin anisotropy, as it </p><p>increases with age, were generated with this method, suggesting that the neuronal axon </p><p>is paramagnetic while the myelin surrounding the axon is diamagnetic. In addition the </p><p>fractional anisotropy (FA) and the mean Apparent Diffusion Coefficient (ADC) of the </p><p>same ROI were plotted against age. Histological exams were also performed to evaluate</p><p>myelin and iron content. It is confirmed that the main source of magnetic susceptibility in WM </p><p>is the myelin content. The interpretation of all this brain data will provide valuable </p><p>information on the architecture of the brain during development and a more accurate</p><p>diagnosis in the case of a myelin degenerative disease.</p>