MALDI MSI analysis of intracranial GBM12 PDX model: a) H&E stained serial tissue section demonstrating highly cellular tumor region, b) segmentation map of MALDI MSI data produced via bisecting k-means clustering (k = 8), whereby different clusters are labelled with different colors, and two separate clusters are indicated within the tumor region indicating spectral differences between these regions, c-e) MALDI MSI ion images of three different long chain acylcarnitines: c) myristoylcarnitine: m/z 410.2666, detected as [M+K]+ , d) palmitoylcarnitine: m/z 400.3422, detected as [M+H]+ , and e) stearoylcarnitine: m/z 428.3734, detected as [M+H]+ .