Advanced MRI technique may identify Alzheimer’s risk years before symptoms

Researchers at Johns Hopkins University report that a specialized MRI technique can measure brain iron levels that are associated with an increased risk of developing mild cognitive impairment (MCI), a frequent precursor to Alzheimer’s disease, years before symptoms appear.

In a study published in the journal Radiology, investigators used quantitative susceptibility mapping (QSM), an MRI method that quantifies tissue magnetic susceptibility, to assess iron concentrations in 158 cognitively unimpaired participants drawn from a prior research cohort. After a median follow-up of about 7½ years, higher iron levels in the entorhinal cortex and putamen were associated with a two- to fourfold greater risk of progressing to MCI and with faster cognitive decline, the authors reported.

"QSM is an advanced MRI technique developed over the last decade to measure tissue magnetic susceptibility with good precision," said Xu Li, associate professor of radiology at Johns Hopkins and the study’s senior author. "QSM can detect small differences in iron levels across different brain regions, providing a reliable and non-invasive way to map and quantify iron in patients, which is not possible with conventional MR approaches."

The study found that the association between elevated iron and cognitive decline was stronger in participants who also had higher levels of amyloid pathology, the abnormal protein deposits long linked to Alzheimer’s disease. The authors said iron can amplify neurotoxicity and neurodegeneration when it interacts with amyloid and tau proteins, another hallmark of Alzheimer’s pathology.

QSM differs from standard imaging tools used in Alzheimer’s research and care, such as PET scans, because it is noninvasive and less costly, the researchers noted. That raises the possibility that QSM could be more readily deployed in clinical settings if larger studies replicate the findings and the technique is standardized, the team said. Funding for the study came from the National Institute of Biomedical Imaging and Bioengineering, the National Institute on Aging and the National Institutes of Health.

The research has limitations. The cohort was relatively small and not broadly representative: participants were primarily White, highly educated and had a strong family history of Alzheimer’s disease. The authors cautioned that additional studies in larger and more diverse populations are needed to determine whether QSM measurements can be generalized across clinical settings and demographic groups.

"The key takeaway of our study is that higher brain iron levels, especially in some critical brain regions related to memory and learning (entorhinal cortex and putamen, as shown in our study), are linked to a two to four times higher risk of developing MCI and faster cognitive decline," Li said. "And such brain iron changes may be measured years before memory loss, when the participants are still cognitively normal."

Li and colleagues also noted that iron is essential for normal brain development and function, and that its role in neurodegeneration is complex. Therapeutic strategies aimed at lowering brain iron, including iron chelation, are under investigation but have not yet demonstrated clear clinical benefit, according to the researchers.

If validated in independent and more heterogeneous cohorts, QSM could serve both as an early biomarker to identify individuals at elevated risk for cognitive impairment and as a tool to guide trials of preventive therapies. The study team said they plan to work on standardizing and accelerating the QSM technique to make it more accessible for clinical research and eventual routine use.