Figure 2

(A) The fetal pig section and (B) the results of spatially-aware sparse clustering with C = 15 clusters. Note that the clusters are regions of homogenous chemical composition and often match up with visually distinguishable anatomical features, while also revealing possible hidden chemical structures in regions that are visually ambiguous. (C) The mean mass spectrum of the cluster corresponding to the liver and part of the brain with the 25 structurally-important ions selected via regularization for s = 0.6 marked in red and (D) the ion image for one such peak at m/z 888.