Amygdalar nuclei and hippocampal subfields on MRI: Test‐retest reliability of automated segmentation in old and young healthy volunteers

Background The amygdala and the hippocampus are two limbic structures that play a critical role in cognition and behaviour but their small size hampers their manual segmentation in multicenter datasets. Here, we assessed the reliability of the automated segmentation of amygdalar nuclei and hippocampal subfields across sites and vendors. We applied a new high‐resolution atlas in two independent cohorts of older and younger healthy adults. Method Sixty‐four older (PharmaCog study; age range: 50‐78 years) and 67 younger subjects (CoRR consortium; age range: 18‐43 years) underwent repeated 3D‐T1 MRI at two different time points between 1 and 90 days. Amygdala and hippocampus segmentation was performed using FreeSurfer v6.0. Reliability of functional parcellations was assessed using volume reproducibility error (ε) and spatial overlapping coefficient (DICE) between test and retest session. Nuclei/subfields were considered as single structures and grouped into relevant subregions (for the amygdala, basolateral and the centromedial complexes; for the hippocampus, head, body, and tail subdivisions). Result Differences in MRI site/vendor had a significant impact (p.43, p