Increased cortical grey matter lesion detection in multiple sclerosis with 7 Tesla MRI : a postmortem verification study 2 . 3 7 T postmortem MRI and histopathology study

The relevance of cortical grey matter pathology in multiple sclerosis has become increasingly recognised over the past decade. Unfortunately, a large part of cortical lesions remain undetected on MRI using standard field strength. In vivo studies have shown improved detection by using higher magnetic field strengths up to 7 T. So far, a systematic histopathological verification of ultrahigh-field MRI pulse sequences has been lacking. The aim of this study was to determine the sensitivity of 7T versus 3T MRI pulse sequences for the detection of cortical multiple sclerosis lesions by directly comparing them to histopathology. We obtained hemispheric coronally cut brain sections of 19 multiple sclerosis patients and 4 controls after rapid autopsy, formalin-fixed and scanned them on 3T and 7T MRI systems. Pulse sequences included T1 weighted, T2 weighted, fluid attenuated inversion recovery (FLAIR), double inversion recovery (DIR) and T2*. Cortical lesions (type I-IV) were scored on all sequences separately by an experienced rater blinded to histopathology and clinical data. Staining was performed with antibodies against proteolipid protein and scored by a second reader blinded to MRI and clinical data. Subsequently, MRI images were matched to histopathology and sensitivity of pulse sequences was calculated. Additionally, a second unblinded (retrospective) scoring of MR images was performed. Regardless of pulse sequence, 7T MRI detected more cortical lesions than 3 T. 7T FLAIR detected 225% more cortical lesions than 3T FLAIR (Z=2.22, p<0.05) and 7T T2* detected 200% more cortical lesions than 3T T2* (Z=2.05, p<0.05). Sensitivity of 7T MRI was influenced by cortical lesion type: 100% for type I (T2), 11% for type II (FLAIR/ T2), 32% for type III (T2*), and 68% for type IV (T2). We conclude that ultrahigh-field 7T MRI more than doubles detection of cortical multiple sclerosis lesions, compared to 3T MRI. Unfortunately (subpial) cortical pathology remains more extensive than what 7T MRI can reveal. 89 7T postmortem MRI and histopathology study