So far, this book has focused on the detector configuration in which a single row of a detector is irradiated by the x-ray beam. Although helical (spiral) CT has significantly improved volume coverage, many clinical applications demand an even greater volume coverage and thinner slices. A good example is CT angiography. For this application, a rapid volume acquisition is needed during the plateau phase of contrast enhancement. For thoraco-abdominal aorta studies, the volume includes the whole chest and abdomen, which can reach between 45 and 60 cm along the patient (z) axis. A more demanding case is the runoff study of the abdominal aorta and the legs, which covers the area from the celiac artery to the calves, with a typical z coverage between 90 and 120 cm.