The dose efficiency index (DEI) is a dose independent measure that quantifies the low-contrast performance of CT scanners. The purpose of this paper is to compare the results of DEI analysis with those of ROC analysis. A custom-made phantom consisting of diluted contrast targets of various sizes and densities was scanned at 80 & 120 kV on a multislice CT scanner (Hispeed Advantage RP, GE). Eight radiographers reviewed the images and identified discernable targets. The likelihood of detection was measured as a function of the target size and scan conditions. The results of the DEI & ROC analyses showed that the low-contrast resolution was higher at 80kV than at 120kV. The p-value obtained by the paired-t test was 0.000 for both analyses, indicating that the difference was significant. Under the conditions used in this study, the DEI analysis was found to be an effective alternative to ROC analysis for characterizing the low-contrast performance of CT scanners. The evaluation time was about 1/6 compared with ROC analysis. It is much simpler to calculate than ROC and is useful in comparing scanners from different manufacturers or as part of ongoing quality assurance.