Comparison of helical and conventional computed tomography of the liver

To compare helical and conventional computed tomography (CT) of the liver in terms of enhancement (with different contrast media) and image quality, using optimal technique for each type of acquisition.

Of 218 consecutive patients referred to a tertiary-care hospital for CT of the liver, 166 were randomly assigned to undergo helical (79 patients) or conventional (87) CT. Fifty patients were excluded from the study because they were unable to hold their breath or were unable to cooperate or because they weighted more than 120 kg. Two other patients were excluded at the time of scanning because of a technical problem. Monophasic injections of contrast agent at 3 mL/second were given to patients undergoing helical CT and biphasic injections at 2 and 0.7 mL/second to patients undergoing conventional CT. The contrast media used were iothalamate meglumine, ioversol, iopamidol and iohexol. For each patient, liver enhancement over baseline attenuation was calculated for every slice, and time to peak enhancement was calculated. In addition, visualization of anatomic landmarks and image quality were scored by two independent reviewers.

Minimum, maximum and mean liver enhancement were significantly greater in the group that underwent helical imaging (49, 62 and 55 Hounsfield units [HU] respectively) than in the group that underwent conventional imaging (36, 51 and 44 HU respectively) (Student's t-test, p < 0.0001). Similar differences were obtained when the results were analysed separately for each contrast medium. Image quality was not significantly different between the two acquisition modes.

For computed tomography of the liver, monophasic injection of contrast medium at a high rate and helical acquisition (rather than biphasic injection and conventional acquisition) resulted in significantly better enhancement, without compromising image quality.