CHARACTERIZATION OF URINARY CALCULI - IN-VITRO STUDY OF TWINKLING ARTIFACT REVEALED BY COLOR-FLOW SONOGRAPHY

OBJECTIVE. The ''twinkling artifact'' is a color-flow sonographic arti fact described behind calcifications and presenting as a random color encoding in the region where shadowing would be expected on gray-scale images. Our purpose was to study the relationship between this twinkl ing artifact seen behind urinary stones on color-flow sonography and t he morphology or biochemical composition of these urinary stones. MATE RIALS AND METHODS. Forty-seven urinary stones were studied in vitro wi th color-flow sonography. Transmit frequency, color gain, velocity ran ge, color filters, focal depth, and depth of field were changed during scanning. The twinkling artifact was graded 0 when absent, 1 when pre sent but occupying a portion of acoustic shadowing, and 2 when occupyi ng the entire acoustic shadowing. Stones were studied under a binocula r magnifying glass to characterize the surface, and infrared spectroph otometry was used to determine the chemical composition. RESULTS. Calc uli of calcium oxalate dihydrate and calcium phosphate always produced a grade 1 or grade 2 twinkling artifact. Absence of artifact was note d only for calcium oxalate monohydrate and urate stones. In 100% of gr ade 0 calcium oxalate stones, the monohydrate compound was predominant (>93%). In 100% of grade 2 calcium oxalate stones, the dihydrate comp ound was predominant (>75%). For calcium oxalate stones, the surface p attern was correlated with their composition. Sensitivity and specific ity for absence of artifact, as indicative of calcium oxalate monohydr ate, were 60% and 83%, respectively, for all stones and 56% and 100%, respectively, only for radiopaque stones. CONCLUSION. An in vitro rela tionship exists between the twinkling artifact and the morphology of u rinary stones. Color-flow sonography could play a role in detecting de nse calcium oxalate monohydrate calculi, which in turn may help predic t fragmentability.