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Updated: Mar 12, 2026
Magnetic Resonance Imaging of Multiple Sclerosis at 7.0 Tesla
Published on: February 19, 2021
Slow expansion of multiple sclerosis iron rim lesions: pathology and 7 T magnetic resonance imaging
Assunta Dal-Bianco1, Günther Grabner2,3, Claudia Kronnerwetter3
1Department of Neurology, Medical University of Vienna, Vienna, Austria.
Abstract:
In multiple sclerosis (MS), iron accumulates inside activated microglia/macrophages at edges of some chronic demyelinated lesions, forming rims. In susceptibility-based magnetic resonance imaging at 7 T, iron-laden microglia/macrophages induce a rim of decreased signal at lesion edges and have been associated with slowly expanding lesions. We aimed to determine (1) what lesion types and stages are associated with iron accumulation at their edges, (2) what cells at the lesion edges accumulate iron and what is their activation status, (3) how reliably can iron accumulation at the lesion edge be detected by 7 T magnetic resonance imaging (MRI), and (4) if lesions with rims enlarge over time in vivo, when compared to lesions without rims. Double-hemispheric brain sections of 28 MS cases were stained for iron, myelin, and microglia/macrophages. Prior to histology, 4 of these 28 cases were imaged at 7 T using post-mortem susceptibility-weighted imaging. In vivo, seven MS patients underwent annual neurological examinations and 7 T MRI for 3.5 years, using a fluid attenuated inversion recovery/susceptibility-weighted imaging fusion sequence. Pathologically, we found iron rims around slowly expanding and some inactive lesions but hardly around remyelinated shadow plaques. Iron in rims was mainly present in microglia/macrophages with a pro-inflammatory activation status, but only very rarely in astrocytes. Histological validation of post-mortem susceptibility-weighted imaging revealed a quantitative threshold of iron-laden microglia when a rim was visible. Slowly expanding lesions significantly exceeded this threshold, when compared with inactive lesions (p = 0.003). We show for the first time that rim lesions significantly expanded in vivo after 3.5 years, compared to lesions without rims (p = 0.003). Thus, slow expansion of MS lesions with rims, which reflects chronic lesion activity, may, in the future, become an MRI marker for disease activity in MS.
Insights
Iron accumulation in microglia/macrophages at multiple sclerosis (MS) lesion edges forms visible rims on 7 Tesla MRI. These rim lesions, indicating chronic activity, significantly expand over time compared to non-rim lesions.
Area of Science:
- Neuroimmunology
- Neuroimaging
- Neuropathology
Background:
- Iron accumulates in activated microglia/macrophages at chronic demyelinated lesion edges in multiple sclerosis (MS), forming signal-reducing rims on susceptibility-based 7 Tesla MRI.
- These iron rims are associated with slowly expanding lesions, suggesting ongoing disease activity.
Purpose of the Study:
- To investigate lesion types and stages associated with iron rims.
- To identify the cells accumulating iron and their activation status.
- To assess the reliability of 7 Tesla MRI in detecting iron rims.
- To determine if MS lesions with rims enlarge over time in vivo.
Main Methods:
- Histological analysis of iron, myelin, and microglia/macrophages in 28 MS brain sections.
- Post-mortem 7 Tesla susceptibility-weighted imaging of 4 MS cases prior to histology.
- Longitudinal in vivo 7 Tesla MRI and neurological examinations of 7 MS patients over 3.5 years.
- Correlation of MRI findings with pathological iron rim presence and lesion expansion.
Main Results:
- Iron rims were found around slowly expanding and some inactive lesions, but not remyelinated plaques.
- Iron was primarily in pro-inflammatory microglia/macrophages, rarely in astrocytes.
- Histology validated 7 Tesla MRI detection of iron rims, with slowly expanding lesions exceeding the iron-laden microglia threshold.
- Rim lesions showed significant in vivo expansion over 3.5 years compared to non-rim lesions.
Conclusions:
- Iron rims in MS lesions are associated with chronic inflammatory activity and are detectable by 7 Tesla MRI.
- Lesions with iron rims exhibit significant in vivo expansion, serving as a potential MRI marker for MS disease activity.
