Comparing stone attenuation in low-and conventional-dose noncontrast computed tomography

BACKGROUND AND PURPOSE: Noncontrast computed tomography (NCCT) has high sensitivity, specificity, and is able to predict stone composition using Hounsfield units (HU) but is associated with high radiation exposure. In an attempt to reduce radiation exposure, low-dose stone protocols have been developed that provide excellent detection of stones. It is not known, however, whether these protocols are equally effective in determining HU stone density. The purpose of this study is to compare stone HU attenuation between low- and conventional-dose NCCT.

MATERIALS AND METHODS: In this prospective randomized, single blinded study, 7-mm calcium oxalate stones were placed randomly into nine intact urinary systems and scanned in three different cadaveric vehicles. Holding other parameters constant, NCCT was performed at varying mAs levels ranging from 5 to 140. Identical magnified images at each mAs setting were reviewed in a blinded fashion to determine HU attenuation. Statistical analyses were performed using a Kruskal-Wallis test and the Levene test, with P<0.05 considered significant.

RESULTS: In 19 different stone configurations with 133 stones, median attenuation levels were 614, 674, 681, 669, 670, 674, and 667 HU at 5, 7.5, 15, 30, 50, 70, and 140 mAs, respectively. The differences in median attenuation levels were not significantly different (P=0.998). An increasing trend of attenuation variability was noticed as the radiation dose decreased; however, this was not significant (P=1.0).

CONCLUSION: Low-dose NCCT results in similar HU attenuation compared with conventional-dose NCCT. Although there is a slight increase in variability, low-dose NCCT provides similar information to assist in determining stone composition as conventional-dose NCCT.