Helical CT has profound implications for routine imaging in the chest and abdomen as well for specialized imaging of hollow organs and blood vessels. The ability to image the chest or abdomen in a single breath and to review overlapping images retrospectively has improved our ability to detect and measure the attenuation of small lesions. Because of its speed, multiple helical CT scans can be performed sequentially during a single injection of contrast material, which is advantageous for imaging the same organ during multiple phases of contrast enhancement (such as the liver, pancreas, or kidney), or for extending the coverage for a given organ (such as the aorta and iliac arteries). Certain 3-D rendering techniques have become routine for post-processing axial helical CT image sets (such as maximum and minimum intensity projections for vascular and tracheobronchial imaging, respectively). Other more sophisticated techniques are emerging for imaging the lumina of hollow organs from within and with perspective. The creation and cine display of multiple such images can simulate an endoscopic examination such as bronchoscopy or colonoscopy.