In this study, a computerized method for detection of pulmonary embolism in spiral CT angiography was developed. The method is based on segmentation of pulmonary vessels to limit the search space for thrombi. Several three-dimensional image features such as local contrast, second derivatives, and distance to the vessel wall were employed for detection of thrombi and for elimination of false positives. Volume rendering was applied for display of detection results. Preliminary results based on several clinical data show the potential of our method.