Volumetric comparison of hippocampal subfields extracted from 4-minute accelerated vs. 8-minute high-resolution T2-weighted 3T MRI scans

Abstract

The hippocampus has been widely studied using neuroimaging, as it plays an important role in memory and learning. However, hippocampal subfield information is difficult to capture by standard magnetic resonance imaging (MRI) techniques. To facilitate morphometric study of hippocampal subfields, ADNI introduced a high resolution (0.4 mm in plane) T2-weighted turbo spin-echo sequence that requires 8 min. With acceleration, the protocol can be acquired in 4 min. We performed a comparative study of hippocampal subfield volumes using standard and accelerated protocols on a Siemens Prisma 3T MRI in an independent sample of older adults that included 10 cognitively normal controls, 9 individuals with subjective cognitive decline, 10 with mild cognitive impairment, and 6 with a clinical diagnosis of Alzheimer's disease (AD). The Automatic Segmentation of Hippocampal Subfields (ASHS) software was used to segment 9 primary labeled regions including hippocampal subfields and neighboring cortical regions. Intraclass correlation coefficients were computed for reliability tests between 4 and 8 min scans within and across the four groups. Pairwise group analyses were performed, covaried for age, sex and total intracranial volume, to determine whether the patterns of group differences were similar using 4 vs. 8 min scans. The 4 and 8 min protocols, analyzed by ASHS segmentation, yielded similar volumetric estimates for hippocampal subfields as well as comparable patterns of differences between study groups. The accelerated protocol can provide reliable imaging data for investigation of hippocampal subfields in AD-related MRI studies and the decreased scan time may result in less vulnerability to motion.

Keywords: Alzheimer’s disease; Hippocampal subfields; Magnetic resonance imaging; Segmentation; Volumetric analysis.

Fig. 1

Coronal Views: (a–c) Conventional MRI, 4-min high resolution MRI, and 8-min high resolution MRI. (d–f) Left hippocampal area on conventional MRI, 4-min high resolution MRI, and 8-min high resolution MRI. (g–i) Right hippocampal area on conventional MRI, 4-min high resolution MRI, 8-min high resolution MRI.

Fig. 2

Examples of automatic segmentation results from (a) 4-min scans and (b) 8-min scans: Five coronal slices and one sagittal slice are shown.

Fig. 3

Results of Intraclass Correlation Coefficients (ICC) analysis for the following groups: (a) CN participants, (b) SCD participants, (c) MCI participants, and (d) AD participants. Error bar indicates the 95% confidence interval.

Fig. 4

Group comparison for each of primary labels and compound labels. Mean and standard error (as error bar) are shown for each group (HC, SCD, MCI, or AD).

Fig. 5

Effect sizes (Cohen’s d) of the pair-wised comparisons between four diagnosis groups (CN, SCD, MCI, and AD) evaluated for hippocampal subfield volumes. Subfield volumes are adjusted by age, gender and ICV by DX group.