Paramagnetic Rim Lesions in Multiple Sclerosis: Comparison of Visualization at 1.5-T and 3-T MRI

UMMS Affiliation

Department of Neurology; Department of Radiology

Publication Date


Document Type



Nervous System Diseases | Neurology | Radiology


Background: Multiple sclerosis (MS) is characterized by both acute and chronic intrathecal inflammation. A subset of MS lesions show paramagnetic rims on susceptibility-weighted MRI sequences, reflecting iron accumulation in microglia. These paramagnetic rim lesions (PRLs) have been proposed as a marker of compartmentalized smoldering disease. PRLs have been demonstrated at 7 T and, more recently, at 3 T. As susceptibility effects are weaker at lower field strength, it remains unclear if PRLs are visible at 1.5 T. Objective: To compare the visualization of PRLs using susceptibility-weighted imaging at 1.5-T and 3-T MRI in patients with MS.

Methods: This retrospective study included 9 patients (5 women, 4 men; mean age, 46.8 years) with MS who underwent both 1.5-T and 3-T MRI using a comparable susceptibility-weighted sequence from the same manufacturer (GE SWAN). Lesions measuring >3 mm were annotated. Two reviewers independently assessed images at each field strength in separate sessions, classifying the annotated lesions based on susceptibility-weighted images as isointense, diffusely paramagnetic, or PRL. Discrepancies were discussed at consensus sessions including a third reviewer. Agreement was assessed using kappa coefficients.

Results: Of 140 annotated lesions, based on the 3-T consensus readings, 115 (82%) were isointense, 16 (11%) were diffusely paramagnetic, and 9 (6%) were PRLs; based on the 1.5-T consensus readings, 115 (82%) were isointense, 14 (10%) were diffusely paramagnetic, and 11 (8%) were PRLs. Mean lesion diameter was 11.9 mm for PRLs, versus 6.4 mm for diffusely paramagnetic lesions (p=.006) and 7.8 mm for isointense lesions (p=.003). Interrater agreement for lesion classification as PRL was substantial at 1.5 T (kappa=0.65) and 3 T (kappa=0.70). Agreement for PRL was also substantial between the consensus readings at the two field strengths (kappa=0.79).

Conclusion: We show comparable identification of PRLs at 1.5-T and 3-T MRI, with substantial interrater agreement at both field strengths and substantial consensus agreement between the field strengths. Clinical Impact: PRL may be an emerging marker of chronic neuroinflammation in MS. Their visibility at 1.5 T supports the translational potential of PRL identification to more widespread clinical settings, where 1.5-T scanners are prevalent.


1.5T, 3T, T2*, chronic active lesion, filtered phase, iron rim lesion, multiple sclerosis, paramagnetic rim lesion, susceptibility imaging

DOI of Published Version



Hemond CC, Reich DS, Dundamadappa SK. Paramagnetic Rim Lesions in Multiple Sclerosis: Comparison of Visualization at 1.5-T and 3-T MRI. AJR Am J Roentgenol. 2021 Dec 1. doi: 10.2214/AJR.21.26777. Epub ahead of print. PMID: 34851712. Link to article on publisher's site

Journal/Book/Conference Title

AJR. American journal of roentgenology

Related Resources

Link to Article in PubMed

PubMed ID