Early DAT is distinguished from aging by high-dimensional mapping of the hippocampus

Objective: To determine the feasibility of using high-dimensional brain map ping (HDBM) to assess the structure of the hippocampus in older human subje cts, and to compare measurements of hippocampal volume and shape in subject s with early dementia of the Alzheimer type (DAT) and in healthy elderly an d younger control subjects, Background: HDBM represents the typical structu res of the brain via the construction of templates and addresses their vari ability by probabilistic transformations applied to the templates. Local ap plication of the transformations throughout the brain (i.e., high dimension ality) makes HDBM especially valuable for defining subtle deformities in br ain structures such as the hippocampus, Methods: MR scans were obtained in 18 subjects with very mild DAT, 18 healthy elderly subjects, and 15 healthy younger subjects. HDBM was used to obtain estimates of left and right hipp ocampal volume and eigenvectors that represented the principal dimensions o f hippocampal shape differences among the subject groups. Results: Hippocam pal volume loss and shape deformities observed in subjects with DAT disting uished them from both elderly and younger control subjects. The pattern of hippocampal deformities in subjects with DAT was largely symmetric and sugg ested damage to the CA1 hippocampal subfield. Hippocampal shape changes wer e also observed in healthy elderly subjects, which distinguished them from healthy younger subjects. These shape changes occurred in a pattern distinc t from the pattern seen in DAT and were not associated with substantial vol ume loss. Conclusions: Assessments of hippocampal volume and shape derived from HDBM may be useful in distinguishing early DAT from healthy aging.