Magnetic resonance scanning and image segmentation procedure at 3 T for volumetry of human hippocampal subfields

BACKGROUND: Recent evidence suggests that dementia affects hippocampal substructures differentially and thus identifying anatomical details of this structure is potentially clinically important. Visualising details of human hippocampal substructures in vivo is challenging by imaging due to the small size of the medial temporal lobe structure.

METHODS: MRI data were acquired with a 3 T MR scanner using a 2D multi-echo spin echo pulse sequence at such a spatial resolution to reveal hippocampal subfield boundaries. These images were used to develop a manual segmentation procedure for the hippocampal subfields based on image contrast within the structures and/or geometric constraints by anatomical landmarks.

RESULTS: The T2-images were used to devise a segmentation protocol for Cornu Ammonis (CA) CA1, CA2, CA3, dentate gyrus, subiculum and lumped Stratum Lacunosum + Stratum Moleculare + Stratum Radiatum. The segmentation protocol was applied to MRI data from healthy young and aged controls as well as a small cohort of mild cognitive impairment (MCI) subjects. The reported subfield volumes showed high levels of inter-rater reliability arguing for potential as a tool in documenting subfield volumetry in clinical research.

CONCLUSIONS: A comprehensive and robust MRI protocol which allows the labelling of six separate hippocampal subfields from images acquired with a 3 T clinical scanner is presented to promote hippocampal subfield volumetry of clinical cohorts.