The fourth method produced population-based, average 3-D hippocampal surface maps for both the control and MCI groups, derived from the manual outlines produced across centers. The methodology for constructing a surface map was described and was initially applied to document the variability of the elderly control, MCI, and AD hippocampus in the Talairach atlas
space, arguing for a refinement of this commonly used space in the functional imaging assessment of the elderly and demented population. Hippocampal
contours were traced using a track ball on each relevant slice. The points that made up a traced contour, after smoothing the effects of irregular hand movements, were connected across slices to create regularly ordered 3-D meshes corresponding to the hippocampal surface. To quantify an individual patient's anatomy an average hippocampal 3-D model was resolved by averaging the vectorial displacements, on a point-by-point basis from the parametric mesh, for each patient's hippocampus.
Hippocampal variability, expressed as a 3-D distance in the common coordinate space, was computed by taking the mean of the square roots of a 3-D displacement vector necessary to align each node along a patient's mesh onto the average representation of the population's hippocampus.
space, arguing for a refinement of this commonly used space in the functional imaging assessment of the elderly and demented population. Hippocampal
contours were traced using a track ball on each relevant slice. The points that made up a traced contour, after smoothing the effects of irregular hand movements, were connected across slices to create regularly ordered 3-D meshes corresponding to the hippocampal surface. To quantify an individual patient's anatomy an average hippocampal 3-D model was resolved by averaging the vectorial displacements, on a point-by-point basis from the parametric mesh, for each patient's hippocampus.
Hippocampal variability, expressed as a 3-D distance in the common coordinate space, was computed by taking the mean of the square roots of a 3-D displacement vector necessary to align each node along a patient's mesh onto the average representation of the population's hippocampus.
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