Filtered-phase imaging versus susceptibility-weighted imaging for paramagnetic rim lesion detection in multiple sclerosis: A head-to-head comparison

BACKGROUND: Paramagnetic rim lesions (PRLs) detected on susceptibility-sensitive magnetic resonance imaging (MRI) represent chronic active lesions and correlate with disease progression in multiple sclerosis (MS). However, optimal detection methods remain unclear. OBJECTIVE: To compare PRL detection using filtered-phase imaging versus susceptibility-weighted imaging (SWI) and assess inter-rater reliability among clinical neuroimmunologists. METHODS: We retrospectively analyzed 3T MRI from 44 relapsing-remitting MS patients. Four neurologists with neuroimmunology training received 30-minute training sessions and evaluated PRLs on both filtered-phase and SWI sequences. Consensus adjudication resolved discordant ratings and served as the reference standard for calculating diagnostic accuracy. RESULTS: PRLs were identified in 21/44 patients (48%). Relative to consensus as the reference standard, SWI demonstrated higher sensitivity than filtered-phase imaging (66.0% vs. 60.4%), while filtered phase showed superior positive predictive value (0.903 vs. 0.714). Both sequences achieved very high specificity (>97%). Inter-rater reliability was good for SWI (Intraclass Correlation Coefficient [ICC] = 0.85) and moderate for filtered phase (ICC = 0.71) for per-subject PRL counts. Vascular complexity was the most common cause of false-positive identification (65% of cases). CONCLUSIONS: Both techniques reliably detect PRLs with substantial inter-rater agreement. Filtered-phase imaging offers superior positive predictive value, while SWI provides better sensitivity and inter-rater reliability. Further development of a standardized training program for assessment of PRL and studies directly comparing susceptibility-sensitive sequences on different vendor platforms are warranted.