Stone position * Extrahepatic main bile duct stone position The diagnosis of extrahepatic main bile duct stone position by MRCP had the sensitivity (Se) of 97.5%, the specificity (Sp) of 93.75%, the accuracy (ACC) of 96.42%, the positive predictive value (PPV) of 98.5%, and the negative predictive value (NPV) of 88.23% (Table 3.13).