Buoyancy of gallstones in varying concentrations of contrast media.

Gallstones from 100 patients were tested for buoyancy in four concentrations of contrast materials commonly used in the biliary tree. In 7 1/2% iodine, fully 68% of the patients' stones floated; in 15% iodine, 82% floated; in 30% iodine, 93% floated; and in 38% iodine, 95% floated. This can lead to confusion with bubbles of air, either when stones are mechanically or hydraulically dislodged or when simple buoyancy of high concentrations of iodine floats stones from their usual location held by accretions and inflammatory reaction in the distal common duct. When floating stones are a problem, as often occurs during percutaneous stone removal, substitution of the most dilute contrast material visible and the use of very low kilovoltage should help in one-fourth of cases.