“…One can extract a given row (elevation) from each radiograph in this sequence and stack them, creating a sinogram in which small features form a distinct sinusoid pattern as the object rotates. We looked for these sinusoid patterns using the Gradient Direction Matching (GDM) [1] algorithm developed under the Image Content Engine (ICE) LDRD-SI [2], a powerful model-based matching tool (Figure 2). This approach was attractive due to the success of GDM in similar problems, the usefulness of sinogram data to human analysts, and the fact that it does not require image reconstruction.…”