T1/T2 Ratio Imaging Improves Cortical Lesion Contrast in Multiple Sclerosis on 3T MRI

ABSTRACT Background Cortical demyelinated lesions are prevalent in multiple sclerosis (MS) and associated with disability; their presence on MRI has recently been incorporated into MS diagnostic criteria. Presently, advanced and ultra-high-field MRI — not routinely available in clinical practice — are the most sensitive methods for detection of cortical lesions, and approaches utilizing MRI sequences obtainable in routine clinical practice remain an unmet need. Objective To assess the sensitivity of the ratio of T 1 -weighted and T 2 -weighted (T 1 /T 2 ) signal intensity for focal cortical lesions in comparison to other established, sensitive, advanced and high-field imaging methods. Methods 3-tesla (3T) and 7-tesla (7T) MRI collected from 10 adults with MS participating in a natural history study at the National Institutes of Health were included in the study. T 1 /T 2 images were calculated by dividing 3T T 1 w images by 3T T 2 w fluid-attenuated inversion recovery (FLAIR) images for each participant. Cortical lesions were identified using 7T T 2 *w and T 1 w images and corresponding voxels were assessed on registered 3T images. For each participant, ratios derived from the median signal intensity of nonlesional tissue in the cortical region of the lesion and the median lesional voxel intensity were computed. These values were compared across 3T imaging sequences, including the calculated T 1 /T 2 image, as well as T 1 w, T 2 w, and Inversion Recovery Susceptibility Weighted Imaging with Enhanced T 2 weighting (IR-SWIET) images. Results 614 cortical lesions were identified on 7T images. 3T T 1 /T 2 images demonstrated a larger contrast between median nonlesional cortical signal intensity and median cortical lesion signal intensity (median ratio = 1.29, range 1.19 – 1.38) when compared to T 1 w (1.01, 0.97 – 1.10, p<0.002), T 2 w (1.17, 1.07 – 1.26, p<0.002), and IR-SWIET (1.21, 1.01 – 1.29, p<0.03). Conclusion T 1 /T 2 images are sensitive to cortical lesions. Approaches incorporating T 1 /T 2 could improve the accessibility of cortical lesion detection in research settings and clinical practice.