Hippocampal Subfield Susceptibility Alterations in Mild Cognitive Impairment Revealed by 7T MRI

Clinical Snapshot

Key Findings

• P Value: P = 0.003 for visual rating; P = 0.03 for DG susceptibility

• Effect Size: Hedges g = 1.43 for visual rating scale, Hedges g = 0.88 for left dentate gyrus susceptibility

• Primary Outcome: Hippocampal subfield magnetic susceptibility differences between MCI and controls

• Nnt Or Sensitivity: No sensitivity/specificity data provided - only group comparison statistics

• Confidence Interval: 95% CI 0.60-2.35 for visual rating; 95% CI 0.10-1.72 for DG susceptibility

Clinical Application

Limited by 7T MRI availability - restricted to major research centres and select tertiary hospitals Very limited 7T MRI access in Australia. Not covered by Medicare or PBS. Primarily research tool at institutions like Melbourne Brain Centre or Neuroscience Research Australia Individuals with suspected mild cognitive impairment requiring advanced neuroimaging assessment

Abstract

BACKGROUND AND PURPOSE: Hippocampal magnetic susceptibility alterations may serve as early neurodegenerative biomarkers of Alzheimer disease (AD), but subfield-level evidence in mild cognitive impairment (MCI) remains limited. This study uses submillimeter high-resolution quantitative susceptibility mapping (QSM) to investigate hippocampal subfield susceptibility changes in MCI. MATERIALS AND METHODS: Thirteen individuals with MCI and 13 cognitively normal controls (NC) underwent 7T MRI scans including MP2RAGE and multiecho gradient echo imaging (for QSM). The visibility of hippocampal strata radiatum, lacunosum, and moleculare (SRLM) was assessed using a visual rating scale. Hippocampal subfields (Cornu Ammonis 1 [CA1], CA2, CA3, dentate gyrus [DG], and subiculums) were segmented, and magnetic susceptibility values (χ) were extracted for each subfield. The susceptibility difference between the DG and other subfields was also calculated. Associations between subfield susceptibility measures and cognitive performance were then assessed. RESULTS: Qualitative analysis revealed a distinct hyperintense curved pattern in the hippocampus on the 7T QSM image, corresponding to the SRLM. In NC, this pattern was clearly visible exhibiting consistently delineated boundaries, while it appeared blurred or absent in most subjects with MCI. The visual rating results showed that NC had significantly higher scores than subjects with MCI (Hedgesg = 1.43, 95% confidence interval) [95% CI, 0.60-2.35; P = .003], with most NC rating 3-4 and most subjects with MCI rating 1-2. Quantitative analysis of hippocampal subfield susceptibility revealed significantly elevated susceptibility [χ] in the left DG in those with MCI compared with NC (Hedgeg = 0.88, 95% CI, 0.10-1.72; P = .03), leading to reduced susceptibility contrast between the SRLM and adjacent CA1-CA3 or DG. Furthermore, regional differences of susceptibility between key subfields (left CA1 versus DG and subiculum versus DG) were significantly reduced in MCI, reflecting a loss of subfield contrast. These quantitative changes were significantly associated with lower cognitive performance, even when controlling for age. CONCLUSIONS: 7T QSM reveals susceptibility changes in hippocampal substructures in individuals with MCI, providing a potential early biomarker for AD.

References

1. 1.Zheng, G., Yu, F. F., Huang, Y., Mazumder, S., Vargas, S. L., Unschuld, P. G., Kagerer, S. M., Li, X., & Liu, J. (2026). Hippocampal subfield susceptibility alterations in mild cognitive impairment revealed by 7T MRI. AJNR American Journal of Neuroradiology. https://doi.org/10.1016/j.neuroimage.2019.116332