Our algorithm contains two major steps: the intervertebral disk localization step, and the vertebra detection and segmentation step. In the first step, we apply a model-based searching method to approximately locate all the intervertebral disk clues between adjacent vertebrae of the whole spine and the best slice selection. A new approach using an intensity profile on a polynomial function for fitting all these disk clues on the best slice is then used to refine the disk search process. Vertebra centers are detected, and initial boundaries are extracted in the second step. The initial test of the algorithm on the five sets of 7 sagittal slices locates all 23 intervertebral disk centers for the best slice of all five sets. For the evaluation of the boundary extraction of 22 vertebrae, our algorithm successfully locates 100%, 96.6%, 93.2%, 95.5%, 87.5% vertebra corners in image set No.1, 2, 3, 4, and 5, respectively.