Reliability of paramagnetic rim lesion detection at 1.5T MRI in multiple sclerosis patients

Background: Paramagnetic rim lesions (PRL) are valuable for diagnosing and prognosing multiple sclerosis (MS) and detectable at 7T and 3T MRI. For translation into clinical practice, it is essential assessing their visibility on 1.5T clinical scanners. Objective: To evaluate the reliability of detecting PRL using commercially available susceptibility-weighted imaging (SWI) at 1.5 versus 3T MRI. Methods: SWI images were obtained in 20 people with MS at 1.5T and 3T MRI, with an average scan interval of 1.1 years. Only stable, non-enhancing lesions visible on both scans were analyzed. PRL at 3T were identified by two expert raters using NAIMS PRL criteria and used as a reference. Four raters, blinded to 3T results, assessed PRL at 1.5T. Discrepancies were resolved by consensus. Results: PRL were identified in 16 of 20 patients. At 3T, 95 PRL were identified by consensus (mean 5 PRL per patient, range 0–30). Blinded to 3T scans, 82% of PRL were visible at 1.5T (78 of 95 PRL). Interrater reliability was “almost perfect” for both 1.5 and 3T scans. Raters accurately classified all patients as having ⩾1PRL or not at 1.5T. Conclusion: The majority of PRL are detectable at 1.5T without significantly reducing the specificity of PRL identification or increasing the detection of pseudo-PRL. This may facilitate their clinical use in MS diagnosis and prognosis.