In vivo quantification of hippocampal subfields using 4.7 T fast spin echo imaging.

Several neuropsychiatric disorders involving hippocampal structural changes have been studied extensively using volumetric magnetic resonance imaging (MRI). These studies have mostly measured total hippocampal volume while the present study aimed to delineate and measure hippocampal subfields within the whole hippocampus and subdivisions along its longitudinal axis. Images were acquired at 4.7 T in 11 healthy subjects (5 males and 6 females, aged 23-56 years), using a fast spin echo (FSE) sequence with 0.52 x 0.68 x 1.0 mm(3) native resolution, collecting 90 contiguous coronal slices. Subiculum, cornu ammonis (CA1-3), and dentate gyrus were traced manually within the hippocampal head, body, and tail. We reported volumes for the subfields and demonstrated differences in the distribution within the hippocampus and its parts. The biggest part of the dentate gyrus was located in the hippocampal body, following the hippocampal head and tail. In contrast, the hippocampal head had the largest part of CA1-3, following the hippocampal body and tail. The hippocampal tail had the smallest portion of the subiculum compared to hippocampal head and tail. Subfield volumes were consistent between hemispheres and showed distributions within the longitudinal subdivisions that were consistent with histological data. Direct measurements of subfield distribution along the longitudinal axis of the hippocampus may be more sensitive to detecting disease effects than total volume measures and the differential distribution of subfield volumes may aid in the interpretation of measurements obtained at lower field strength and spatial resolution.