High kVp vs. low kVp for T-tube and operative cholangiography

Based on several considerations, high kVp and high contrast agent concentration should produce better-quality operative and T-tube cholangiograms than the currently recommended low kVp and low contrast agent concentration. To test this theory, two kinds of studies were performed. In a laboratory phantom, the influence of kVp and contrast agent concentration on detectability of different size phantom stones was evaluated. High kVp and high contrast agent concentration (110 kVp, 38% iodine) were also compared with low kVp and low contrast agent concentration (75 kVp, 15% iodine) in 62 patients undergoing operative or T-tube cholangiography. Almost all phantom stones were well shown with all kVps and iodine concentrations. As the kVp was raised there was a mild decrease in stone detectability but this decrease was partially corrected by raising the iodine concentration. Overall stone detectability with high kVp and high contrast agent concentration technique was better than or similar to the currently recommended low kVp and low contrast agent concentration technique. Evaluation of the direct cholangiograms by five radiologists revealed that the high kVp, high contrast agent concentration studies were superior or similar to the low kVp and low contrast agent concentration radiographs in 70% of the cases. Based on these results high kVp (100-110) and a high contrast agent concentration (38%) are recommended for direct cholangiography.