A comparison of two injection protocols using helical and dynamic acquisitions in CT examinations of the pancreas

The patterns of pancreatic enhancement and their relation to various injection parameters remain largely unknown. The purpose of this study was twofold: to compare pancreatic enhancement obtained after high and low rates of i.v. injection of contrast medium and to compare image quality between helical and dynamic sequential CT examinations of the pancreas using optimized scanning parameters.

One hundred patients were randomly allocated to undergo either a helical CT (HC) acquisition after contrast injection at 6 ml/sec or a dynamic sequential CT (DS) acquisition after contrast injection at 2 ml/sec. Both ionic and nonionic contrast material were used in each group. Pancreatic attenuation values were measured on each section in each patient and averaged for each group. Image quality and visualization of anatomic landmarks were scored by two independent reviewers who were blinded to the acquisition technique.

Mean pancreatic enhancement was higher in the HC (61 +/- 17 H) than in the DS group (54 +/- 17 H) (p < .05). Peak pancreatic enhancement was similar in the HC (74 +/- 19 H) and DS (74 +/- 17 H) groups. In the HC group, the optimal pancreatic enhancement index was 47% versus 35% for the DS group. The time to peak enhancement was 39 sec in the HC group and 71 sec in the DS group. The optimal scanning interval was 13 sec in the HC group versus 21 sec in the DS group. Image quality was not significantly different between the protocols, but misregistration and motion artifacts were fewer on HC examinations.

Overall pancreatic enhancement was higher in the HC group, but the faster rate of injection did not increase the peak pancreatic enhancement and decreased the optimal scanning interval (the interval of time during which pancreatic enhancement was greater than 60 H). Image quality was similar with both protocols.