Fig 1.

Normal anatomy. In vivo UHF high-resolution gradient recalled-echo T2* sequence acquisition of the pre- and postcentral gyri (A) and its schematic representation (B) in healthy subjects. The postcentral gyrus resembles the classic ex vivo UHF MR imaging appearance of the unimodal sensory cortices: a low signal intensity tier corresponding to heavily myelinated intracortical layer IV (external band of Baillarger) (arrows) and a subcortical hypointensity (arrowheads) corresponding to arcuate U-fibers demarcating the gray-white matter junction.⁵⁶ The cortical ribbon of M1 (bracket) as the functional counterpart of Brodmann area 4³⁵ is thicker than S1⁵⁷because it is agranular³⁶ and contains the giant Betz pyramidal cells. The superficial hyperintense layer in MR imaging (dots) is due to the lightly myelinated superficial layers relative to the more heavily myelinated deep layers.⁵⁸ M1 does not have an intermediate sharp hypointense line as in S1 but shows a more widespread slight hypointensity of the deeper cortical layer corresponding to its astriate myeloarchitecture.^59,60 The deeper layers of M1 are not easily distinguished from the underlying white matter due to the heavily myelinated M1 cortex.^32,58 ALS features. UHF high-resolution gradient recalled-echo T2* sequence acquisition of the pre- and postcentral gyri in a patient with ALS (D) and the corresponding schematic view (E). Beneath a preserved superficial cortical layer (dots), the deep layers in M1 are thinner and more hypointense (bracket) than those in healthy subjects and show an inconstant track appearance. The M1 signal hypointensity in ALS could be due to paramagnetic effects of the iron-containing microglia within the deep motor cortex. The method adopted for quantitative measurement of signal intensity and thickness in a healthy subject (C) and in patients with ALS (F) is reported. Quantitative assessments of the deep layers of M1 are obtained by drawing an oval ROI within them for the signal intensity measurement and a line with an electronic caliper for the thickness quantification.