Figure 3.

Schematic overview of the semi-automatic analysis procedure used to extract individual locus coeruleus (LC) intensity values across the rostrocaudal extent. (a) Native space neuromelanin-sensitive brainstem scans of three randomly selected subjects (axial slices are shown). Hyperintensities corresponding to the LC are indicated by red arrows. (b) Neuromelanin-sensitive scans were aligned and pooled across subjects in order to increase signal-to-noise ratio and facilitate LC delineation using a template-based approach. On a group level, LC location (red) was semi-automatically determined based on an intensity threshold relative to a pontine reference area (blue; see inlays). (c) Areas surviving the thresholding are grouped into a volume of interest (search space: upper plot; 3D representation) and used to restrict automatized extraction of individual peak intensities and their location. Observed peak LC locations were converted to a LC probability map (lower plot). (d) In standard space, the LC probability map was successfully validated using published maps by Keren and colleagues (2009)⁴¹ and Betts and colleagues (2017)⁶¹. Circle radius indicates map size (i.e., number of voxels). We freely share the resulting LC probability map here: https://www.mpib-berlin.mpg.de/LC-Map