Identification of Chronic Active Multiple Sclerosis Lesions on 3T MRI

Abstract

Background and purpose: MR imaging-pathologic studies have reported that paramagnetic rims on 7T susceptibility-based MR imaging identify, in vivo, the subset of MS lesions with compartmentalized inflammation at the lesion edge and associated remyelination failure. Here, we assessed the reliability of detecting these rims on high-resolution 3T phase images.

Materials and methods: High-resolution T2* and phase MR imaging was collected in 20 patients with MS at 3T (3D segmented EPI, 0.65 mm³) and 7T (2D gradient-echo, 0.2 × 0.2 × 1 mm) MR imaging. In each case, 5 discrete chronic (nonenhancing) MS lesions were selected on T2 FLAIR images for rim evaluation. Five raters experienced in MS imaging contributed to the rim assessment, of whom 3 worked independently on 3T data, and 2, on 7T data. Consensus agreement was reached for both 3T and 7T rim evaluations. Discrepancies between 3T and 7T were discussed, and consensus was reached.

Results: Phase rims were seen in 34 lesions at 7T and in 36 lesions at 3T by consensus. Inter- and intrarater reliability were "substantial/good" both at 3T and 7T analysis (Cohen κ, >0.71). Based on consensus agreement, the reliability of rim visualization at 3T versus 7T was 0.78 (κ) with a pair-wise agreement of 90%. More lesions were judged to be false-positive or false-negative at 3T than at 7T.

Conclusions: Nearly all 7T paramagnetic rims can also be seen at 3T. Imaging at 3T opens the possibility of implementing paramagnetic rims as an outcome measure in multicenter, MR imaging-based clinical trials aimed at treating perilesional persistent inflammation and its potential effects on remyelination.

Fig 1.

A right periventricular lesion in a 55-year-old woman with relapsing-remitting MS. A paramagnetic rim can be easily seen on 3T and 7T phase images (magnified view) as well as on the 7T T2* magnitude image (red arrows). On susceptibility images, medullary veins crossing the lesion are also prominent.

Fig 2.

Representative examples of MS lesions in which a paramagnetic rim (red arrows) can be easily seen on both 7T and 3T phase images. Note the superior image quality at 7T in at least 3 of the 4 examples.

Fig 3.

A left centrum semiovale lesion in a 30-year-old woman with relapsing-remitting MS; the time lapse between 3T and 7T scans was 6 months. In this case, the lesion was judged to have a rim on 3T (red arrows), but not on 7T phase images. The false-positive rim at 3T is related to the configuration of blood vessels at the lesion edge. On the other hand, the central vein of the lesion is prominent in both phase images (white arrows).