Fig. 2.

Anatomical definitions for LC segmentation. The LC was visible as the hyperintense regions on both group-averaged and single MT-on images (A). To segment the LC using an unbiased and reliable semi-automated, threshold-based method, the upper and lower boundaries for searching the structure were defined at the level of the inferior colliculus and the recess of the 4th ventricle, respectively (B). Multiple brainstem areas were also defined for testing the most appropriate regions to be referenced to (C). Left and right LC searching areas were manually drawn on the axial view of the MT group template by overlaying the coregistered MT-on and MT-off images to avoid contaminations from voxels in the ventricle (D). LC=Locus Coeruleus, MT=Magnetisation Transfer.