Generally a right-to-left shunt index in pulmonary area was calculated from total body and pulmonary area by scintillations count using 9mTc-MAA pulmonary perfusion scintigraphy. In this study, we devised a newly calculation method for right-to-left shunt index in pulmonary area from 9mTc-MAA pulmonary perfusion scintigraphy by first-pass dynamic data. We compared the proposed method with the conventional method in 26 patients (9 men and 17 women; 3-26 years old): 23 patients with congenital biliary atresia (CBA) post operation and the other 3 patients with right-to-left shunt from hepatopulmonary syndrome. As a result, there was a positive correlation of the index values between the proposed method and the conventional method (r = 0.929). Thus, the present method should be clinically useful.