STRUCTURAL AND FUNCTIONAL EVALUATION OF THE HUMAN MIDBRAIN DOPAMINERGIC SYSTEM USING HIGH RESOLUTION MRI AT 7 T By

A number of optimization steps needed to be implemented in order to develop an MR imaging protocol that could accurately capture the anatomy of the midbrain dopaminergic (DA) ventral tegmental area (VTA) and substantia nigra (SN). The current study explored imaging parameters that included MR sequence selection, slice orientation and positioning, spatial voxel resolution, TE (Time to Echo) and CNR (Contrast to Noise Ratio) measurements. Our goal was to achieve superior quality images compared to previous studies, at very high resolution with distinguishable contrast between regions of interest (ROIs) in the midbrain. Twoand threedimensional pulse sequences were explored because of their ability to provide high T2and T2*weighted contrast in the midbrain. Imaging slices were positioned in the axial orientation with an oblique angle tilted towards the occipital cortex. A TE value between 16 22 ms was concluded to be optimal based on the combined T2* values of the SN and the VTA. CNR was applied as a quantitative metric to show signal and noise differences between ROIs in the midbrain.