The thickened frontoparietal in pachycephalosaurid dinosaurs expands dramatically during ontogeny from a flat-headed to a domed state. This expansion results in the formation of zonal tissue characterized largely by differences in vascularity and bony tissue structure that changes through ontogeny. Void space identified in CT scans of the frontoparietal is a suitable proxy for relative vascularity. An increase in relative vascularity occurs with the development of the dome in the pachycephalosaur Stegoceras validum, followed by a significant decrease in late stage ontogeny. We employ a script adapted from an algorithm for human cortical bone imaging to: (1) determine the percent vascularity in any given CT slice; (2) quantify these observed changes in relative vascularity within a complete frontoparietal; and (3) identify ontogenetic changes in vascularity from a cranial growth series of Stegoceras. Morphological landmarks identified in the CT scans facilitate an accurate slice-by-slice comparison of homologous regions of the dome between skulls. This new tool enables: (1) a complete assessment of bone vascularity from CT scans; (2) is applicable to any fossil or modern bone in the vertebrate skeleton; and (3) provides an alternative measure to pixel-by-pixel manual thresholding, a time intensive and subjective process.