The Visibility of Urinary Stone in Picture Archive and Communication System : A Phantom Study

Background and Purpose: Stones in the urinary systems of most patients suspected to have renal colic are not visible by radiography. The question remains whether urinary stones are truly absent or whether stones with a particular composition or those too small in size are not radiopaque. Hence we designed a study to determine the radiographic visibility of urinary stones of different sizes and compositions. Methods: Twelve major types of stones (e.g., calcium oxalate, calcium phosphate, uric acid, and magnesium salts) of different sizes (0.2, 0.4, 0.6, 0.8, 1.0, 1.5, and 2 cm in diameter) were studied. The stones were placed in both renal and non-renal porcine tissues. Three board-certified radiologists evaluated radiographic images to ascertain the visibility of the stones of different sizes and compositions. We then calculated the sensitivity, specificity, and receiver operating characteristic curves of imaging for urinary stone detection. Results: Stone visibility increased as the stone size increased (P ＜ 0.001) and may have been affected by the chemical composition of the stone (P ＜ 0.05). Calcium oxalate was the most easily detected, whereas uric acid was the most poorly detected among all stone types studied. Conclusions: Awareness of the radiopacity of chemical components of stones is a useful aid when evaluating plain radiography images and could avoid unnecessary examinations such as intravenous urography and computed tomography, thus providing advantages such as reduced patient exposure to radiation doses and improved cost-effectiveness.