Fig. 4.

Examples of Type 1, 2, 3 and 4 cortical lesions showing their appearance in WHAT images. Type 3 lesions are particularly difficult to detect because of partial voluming artifacts at the boundary of the CSF and because cortical layers can produce local contrast variations that can be mistaken for lesions. The Type 3 lesion indicated was identified by its having intermediate hyperintensity between normal-appearing cortex and CSF as well as existing within the first three to four cortical layers. The other hyperintensities in the zoomed-in section do not exhibit proper location, nor is the contrast at the boundaries as crisp — thereby suggesting that those are more likely local contrast variations than actual lesions.