Imaging cortical multiple sclerosis lesions with ultra-high field MRI

Background Cortical lesions are abundant in multiple sclerosis (MS), yet difficult to visualize in vivo . Ultra-high field (UHF) MRI at 7T and above provides technological advances suited to optimize the detection of cortical lesions in MS. Purpose To provide a narrative and quantitative systematic review of the literature on UHF MRI of cortical lesions in MS. Methods A systematic search of all literature on UHF MRI of cortical lesions in MS published before September 2020. Quantitative outcome measures included cortical lesion numbers reported using 3T and 7T MRI and between 7T MRI sequences, along with sensitivity of UHF MRI towards cortical lesions verified by histopathology. Results 7T MRI detected on average 52±26% (mean ± 95% confidence interval) more cortical lesions than the best performing image contrast at 3T, with the largest increase in type II-IV intracortical lesion detection. Across all studies, the mean cortical lesion number was 17±6/patient. In progressive MS cohorts, approximately four times more cortical lesions were reported than in CIS/early RRMS, and RRMS. Superiority of one MRI sequence over another could not be established from available data. Post-mortem lesion detection with UHF MRI agreed only modestly with pathological examinations. Mean pro- and retrospective sensitivity was 33±6% and 71±10%, respectively, with the highest sensitivity towards type I and type IV lesions. Conclusion UHF MRI improves cortical lesion detection in MS considerably compared to 3T MRI, particularly for type II-IV lesions. Despite modest sensitivity, 7T MRI is still capable of visualizing all aspects of cortical lesion pathology and could potentially aid clinicians in diagnosing and monitoring MS, and progressive MS in particular. However, standardization of acquisition and segmentation protocols is needed.