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Figure 3a.  Use of volume rendering versus MIP rendering for pulmonary artery mapping. (a) Volume-rendered image clearly depicts pulmonary arteries in the midplane including central vessels. (b) Corresponding MIP image appears to depict more vessels but is actually displaying the entire vascular map of the data set. This is best appreciated by noting the highly opacified superior vena cava and right innominate vein. One limitation of MIP is the inability to clearly define individual structures when they overlap. Interactive volume rendering does not have this limitation.