Figure 5.

Comparison of the segmentation obtained with the multimodal procedure using MPRAGE and FLAIR images, relative to a segmentation obtained with the MPRAGE images alone (difference of averaged tissue probability maps). In blue, values that decrease in the multimodal procedure; in red, values that increase. From top to bottom the segmentation output values for gray matter (GM), white matter (WM) and cerebrospinal fluid (CSF) were overlayed on the mean normalized MPRAGE image (coordinates in mm, MNI space). The yellow dotted circles highlight areas affected by susceptibility artifacts (visible at z –28 and in the sagittal images). The orange arrows and letter “v” point to areas where the multimodal segmentation gave different results due to detection of vessels (visible at z –28, –18 and in the sagittal image). The blue arrows at z –18 and –8 show decreases in the GM values in areas affected by the dura problem (present also in slices above). One can also see a shift in intensity from the GM to the WM compartment in the putamen, especially in its posterior portion (magenta arrows at z 2). Decreases of estimated GM volume amounted to an average 67 ± 21 ml in the combined relative to the simple segmentation. In the combined segmentation, WM and CSF volumes were on average 12 ± 8 and 25 ± 35 ml larger, respectively.