Spiral CT during arterial portography.
Spiral computed tomography (CT) performed during arterial portography offers several advantages compared with portographic studies based on conventional CT technique. Because all hepatic images are derived from a volume data set acquired during a single 24-32-second breath hold timed to coincide with the phase of peak hepatic enhancement, motion artifacts and section misregistration are eliminated and high liver-to-lesion attenuation value differences are present on all sections. These factors, in conjunction with the ability to retrospectively acquire thin, overlapping axial sections, result in improved lesion detection. The ability to produce high vein-to-liver attenuation value differences and two-dimensional multiplanar reconstructions simplifies the identification of hepatic segments and therefore lesion localization. A limitation of all CT portographic methods is the frequent occurrence of nontumorous perfusion defects that, in most cases, demonstrate characteristic locations and appearances. Performing delayed CT following portography is one method by which such pseudolesions may be characterized and differentiated from focal pathologic entities.