Twinkling artifact on color doppler ultrasound: Comparison among various composition of stones and various central frequencies of transducers

To evaluate the relationship between the degree of twinkling artifact generated on color Doppler sonography and the biochemical composition of renal stones and different central frequencies of transducers. Three types of renal stones (A=90% calcium oxalate +10% calcium hydrogen phosphate, B=50% calcium oxalate +5% calcium hydrogen phosphate +45% ammonium urate, and C=55% urate 35% calcium oxalate +5% ammonium urater +5% calcium hydrogen phosphate) removed from the subjects and one artificially made plastic-ball (D) were examined in vitro with color Doppler ultrasonography. Four transducers (C4-5, C7-4, L7-4, L10-5 MHz) were used. All stones were placed in a depth of between 3 and 4 cm in an agar plate. Grading of twinkling artifact was done: 0=absent, 1=present but occupying less than half of a stone, 3=occupying the entire stone and 2=between 1 and 3. Color Doppler gain was set to the point just below the threshold for color noise. Each artifact was graded by two independent observers, and if there was interobserver difference, the consensus was reached. The size of stones ranged from 6 to 10 mm (mean=8 mm). Type A stone produced grade 1 artifact on C4-2, grade 2 on C7-4 and grade 3 on L7-4 and L10-5. Type B stone produced grade 1 artifact on all transducers; type C stone produced grade 0 artifact on C4-2, grade 2 on C7-4, and grade 1 on L7-4, and L10-5. The plastic ball produced grade 1 artifact on L10-5, and grade 0 on other transducers. Different grades of twinkling artifact on color Doppler ultrasonography were evoked depending on the biochemical composition of renal stones and different central frequencies of transducers. The major limitation of our study was that the number of the subjects were small.