Value of color Doppler twinkling artifact and CT in distinguishing uric acid stones from cystine stones: an experimental study

Abstract

Objective To quantitatively analyze the value of color Doppler twinkling artifact and CT in distinguishing urinary stone composition of uric acid from that of cystine, and to assess the ability of color Doppler twinkling artifact and CT to diagnose urinary stone composition of uric acid. Methods Artificial stones made of uric acid and cystine were inserted in porcine kidneys respectively. Color Doppler ultrasound and CT scanning were performed in vitro and twinkling artifact videos were recorded. The CT attenuation value, the width and length of twinkling artifact (TAW, TAL) were measured. The color pixels representing twinkling artifact intensity (TAI) were calculated. The differences between artificial cystine and artificial uric acid stones in TAW, TAL, TAI and CT attenuation value were compared. The receiver operating characteristic (ROC) curve was used to assess the ability of TAW, TAL, TAI and CT attenuation value to diagnose urinary stone composition of uric acid. Results The TAW [(4.16±1.54)mm vs (4.97±1.93)mm], TAL[(3.75±1.05)mm vs (5.12±2.51)mm] and TAI [(3 005.50±812.33) vs (5 433.86±2 505.81)] of artificial cystine stones were less than those of artificial uric acid stones while the CT attenuation value of artificial cystine stones [(573.75±110.10)HU vs (364.09±67.28)HU] were greater (P<0.05). The ROC curve was displayed to diagnose urinary stone composition of uric acid, and the area under curve of CT attenuation value was bigger than that of TAI (0.936 vs 0.817, Z=2.308, P=0.021). Combination of color Doppler twinkling artifact and CT value would dramatically increase the diagnostic accuracy to 98%. Conclusions Both color Doppler ultrasound and CT were reliable examinations for distinguishing urinary stone composition of cystine from that of uric acid. Combination of color Doppler ultrasound and CT would be good references to diagnose urinary stone composition of uric acid. Key words: Ultrasonography, Doppler, color; Calculi; Twinkling artifact; Tomography, X-ray computer