Db. Bach et al., DYNAMIC ABDOMINAL COMPUTED-TOMOGRAPHY - TOP-DOWN COMPARED WITH BOTTOM-UP IMAGING, Canadian Association of Radiologists journal, 44(5), 1993, pp. 354-358
Dynamic contrast-enhanced computed tomography (CT) of the liver is usu
ally performed from the top down, and there is usually less opacificat
ion of the top slices than the more inferior slices. The authors reaso
ned that reversing the direction of scanning would allow more time for
the parenchyma at the top of the liver to become enhanced and would r
esult in better opacification of the parenchyma and the hepatic veins.
To test this hypothesis they assigned 32 patients to either a ''top-d
own'' or a ''bottom-up'' group; each patient then underwent unenhanced
and contrast-enhanced CT. The method of intravenous administration of
contrast agent was identical in the two groups and consisted of rapid
injection of 135 mL of iohexol by a power injector; scanning was init
iated 30 seconds after the injection was started. Attenuation measurem
ents were obtained at specified areas in the liver and in the hepatic
and portal veins. The degree of enhancement was calculated at each sit
e and was compared between groups. The upper portion of the liver show
ed significantly greater enhancement in the bottom-up sequence than in
the top-down sequence (123% and 22% respectively; p < 0.01); the enti
re liver showed excellent enhancement in the bottom-up sequence. In ad
dition, the hepatic veins showed significantly greater conspicuity in
the bottom-up sequence (p < 0.01). The authors conclude that the dynam
ic bottom-up method yields excellent hepatic enhancement and vascular
opacification and is therefore superior to the standard top-down metho
d.