Each year more than 20,000 Canadians are treated surgically for lower back pain. Image guided surgical (IGS) techniques can reduce the number of complications that arise in about 20-30% of classical surgical procedures. Patients are often scanned for a CT pre-operatively and then, during the surgery, are scanned again using Ultrasound. The registration of the pre-operative CT scans with intra-operative ultrasound scans can help surgeons to perform surgeries with higher precisison. The segmentation of the spine in CT scans is, however, quite challenging. Inhomogenous regions inside and outside the vertebrae require the application of advanced segmentation methods. Signal loss at the boundaries of the vertebrae can further hinder the segmentation process. In this project we are working on developing precise and accurate models of the human vertebral column in collaboration with Dr. Louis Collins. To this end we are applying geometric flow methods combined with shape priors to automatically segment the entire spinal column as well as each vertebrae individually.