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Quantitative Susceptibility Mapping of the Hippocampal Fimbria in Alzheimer's Disease
Chun Ki Franklin Au1, Jill Abrigo1, Chunlei Liu2,3
1Department of Imaging and Interventional Radiology, The Chinese University of Hong Kong, Prince of Wales Hospital, Hong Kong, China.
Background:
The fimbria is a small white matter bundle that connects the hippocampus to the rest of the brain. Damage to the hippocampal gray matter is established in Alzheimer's disease (AD), but the hippocampal fimbrial status in the pathogenesis of AD is unclear. AD-related demyelination and iron deposition alter the diamagnetic and paramagnetic composition of tissues, which can be measured by quantitative susceptibility mapping (QSM).
Hypothesis:
AD is associated with microstructural changes in the fimbria that might be detected by QSM.
Study Type:
Retrospective cross-sectional study.
Subjects:
In all, 53 adults comprised of controls (n = 30), subjects with early stage AD (n = 13), and late stage AD (n = 10) who were classified according to their amyloid and tau status and presence of hippocampal atrophy.
Field Strength / Sequence:
3T; 3D fast-field echo sequence for QSM analysis and 3D T1 -weighted MP-RAGE sequence for anatomical analysis.
Assessment:
Segmentation of the left hippocampal fimbria subfield was performed on T1 -weighted images and was applied to the coregistered QSM map for extraction of the mean, median, minimum, and maximum values of QSM.
Statistical Tests:
Group comparison of QSM values using analysis of variance (ANOVA) with post-hoc Tukey's test, accuracy of binary differentiation using receiver operating characteristic (ROC), and individual classification using discriminant analysis.
Results:
QSMmean and QSMmedian values were significantly different among the three groups (P < 0.05) and showed a shifting from negative in the control group to positive in the AD group. The control and early AD subjects, who have normal hippocampal volumes, were differentiated by the QSMmean value (area under the curve [AUC] 0.744, P < 0.05) and the QSMmedian value (AUC 0.782, P < 0.05). Up to 76% of subjects (inclusive of 26 controls and six with early AD) were correctly classified using a model incorporating clinical and radiologic data.
Data Conclusion:
The fimbria showed higher magnetic susceptibility in AD compared with controls.
Level Of Evidence:
2 TECHNICAL EFFICACY STAGE: 3.
Insights
Quantitative susceptibility mapping (QSM) reveals altered magnetic properties in the fimbria of Alzheimer's disease (AD) patients. This imaging technique can differentiate between healthy individuals and those with early-stage AD, aiding in diagnosis.
Area of Science:
- Neuroimaging
- Biomarkers
- Neurodegenerative Diseases
Background:
- Alzheimer's disease (AD) is characterized by hippocampal gray matter damage, but the role of the fimbria, a white matter tract, remains unclear.
- AD-associated demyelination and iron deposition alter tissue magnetic properties, measurable by quantitative susceptibility mapping (QSM).
Purpose of the Study:
- To investigate microstructural changes in the fimbria using QSM in individuals with and without Alzheimer's disease.
- To determine if QSM can detect AD-related alterations in the fimbria and differentiate between disease stages.
Main Methods:
- A retrospective cross-sectional study involving 53 adults (30 controls, 13 early AD, 10 late AD).
- Quantitative susceptibility mapping (QSM) was performed using a 3T scanner with a 3D fast-field echo sequence.
- Fimbrial segmentation and QSM value extraction (mean, median, min, max) were conducted on T1-weighted images.
Main Results:
- Significant differences in mean and median QSM values were observed across control, early AD, and late AD groups (P < 0.05).
- Fimbrial QSM values shifted from negative in controls to positive in AD patients.
- QSM mean and median values accurately differentiated control and early AD subjects (AUC 0.744 and 0.782, respectively).
Conclusions:
- The fimbria exhibits higher magnetic susceptibility in individuals with Alzheimer's disease compared to controls.
- QSM is a promising imaging biomarker for detecting fimbrial changes in AD and may aid in early diagnosis.
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