Fig 1. T2-weighted images coregistered to the T1 maps illustrating the definition of pixel classes in 1 female patient with primary progressive MS (aged 59.5 years; disease duration, 8.3 years; cerebral lesion volume, 14.9 mL; EDSS score, 4.0; MSFC score, 0.54). For greater clarity, the 2 pixel classes, lesion core and lesion rim, are displayed as a single class (Lesions) in this figure. The perilesional NAWM pixel classes (Layer 1 through Layer 4) are defined as consecutive layers of a single pixel width around these lesion masks. Distant NAWM consists of NAWM pixels that are at least 4 mm away from the lesion masks in all directions. Details of the definition of the pixel classes are provided in the text. Note that the coregistration of the lesion masks to the T1 maps was chosen to overestimate the lesions, to be conservative toward NAWM. Note also that because of less-reliable segmentation in deep gray matter and periventricular regions, these regions were excluded from the NAWM pixel classes. As a result, there are several lesions in this region without perilesional NAWM pixel layers around them (visible mainly in the images in the second row).