The effect of helical CT and the recently developed multidetector helical CT on abdominal and pelvic imaging has been substantial. The advantage of helical CT over conventional CT is the speed at which imaging can be acquired. The organs in the upper abdomen, including the liver, spleen, and pancreas, can be imaged within a single breath-hold, and therefore, respiratory misregistration and motion artifacts can be minimized. The speed at which images are acquired also allows multiphasic imaging of the liver, spleen, and pancreas after intravenous contrast administration, and this imaging technique often improves lesion detection and characterization and provides information about vascular anatomy and the extent of tumor involvement of adjacent vessels for planning treatment (Foley et al, 2000; Ji et al, 2001).
An important advantage of helical CT is the ability to reconstruct the image data acquired on the initial scan at intervals as small as 1 mm. Such reconstruction can improve lesion conspicuity by placing the lesion directly within the image plane rather than volume-averaging it between 2 contiguous reconstructed images. Smaller lesions can therefore be detected with helical CT. In addition, the reconstructed images can be stacked to form a volume of image data so that they can be displayed in multiple planes or in a 3-dimensional format. This image processing technique forms the basis for CT colonography, CT angiography, and CT cholangiography.
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