Objective To analyze the accuracy of ultrasound（US）and acoustic shadow width on measuring the sizeof kidney stone

and to explore the feasibility of measuring kidney stone size by posterior acoustic shadow width.Methods TheUS images and non-enhanced CT images of 51 kidney stones in 49 patients were analyzed retrospectively.Based on CT sizemeasurements

the stones were divided into ≤5.0 mm group（n=15）

5.1～10.0 mm group（n=20）and >10.0 mm group（n=16）.The difference between US stone size and CT stone size was compared.Excluding 14 stones without a shadow

the remaining37 stones were divided into ≤5.0 mm group（n=6）

5.1～10.0 mm group（n=15）and >10.0 mm group（n=16）based on CT sizemeasurements. The difference and absolute difference between US stone size

shadow size and CT stone size were compared.Results A total of 51 stones

the average CT stone size was（8.3±4.6）mm

and the average US stone size was（10.1± 4.3）mm.US stone size overestimated CT stone size with a mean bias of（1.8±2.0）mm

and difference was statistically significant（P<0.05）.The difference between US size and CT size was statistically significant for stones ≤5.0 mm and 5.1～10.0 mm（P=0.001

0.000）.After excluding 14 stones without obvious shadow

the shadow size was closer to the CT size than the US sizefor stones ≤5.0 mm and 5.1～10.0 mm

and there were statistically significant differences in the absolute difference between USstone size

shadow size and the CT stone size（P=0.028

0.015）.However

the US size was closer to the CT size than the shadowsize for stones >10.0 mm

and there was no significant difference in the absolute difference between US stone size

shadow sizeand the CT stone size（P=0.191）.Conclusion Directly measuring the hyperechoic width of the stone by US can overestimate thesize

for stones ≤10.0 mm

measurement of posterior acoustic shadow width of stone is valuable and feasible for improving theaccuracy of ultrasonic measurement of stone size.