FIGURE 3.

Landmarks and semilandmarks superimposed on a digital representation of the pelvis to show the configurations used in this study. Landmarks were placed on the sacrum and surrounding structures of the human hip bones, in eight different ways: (a) First sacral vertebra (S1). (b) Entire sacrum. (c) Pelvic inlet. (d) Sacrum, iliac crest, and pelvic inlet. (e) S1, iliac crest, and pelvic inlet. (f) Sacrum and pelvic inlet. (g) Proximate portion of the iliac crest and arcuate line in combination with the S1. (h) S1 and arcuate line. The size of the pelvic models correlates with the performance of the corresponding landmark configurations to detect segmentation anomalies at the lumbosacral border. Accordingly, a landmark configuration focusing on the first sacral vertebra was most informative, followed by a configuration representing the entire sacrum and a configuration covering the pelvic inlet. For a detailed description of landmarks see Table 2