Abstract: Objective: To define several boundary lines with diagnostic significance for lung cancer staging,demonstrated with CT and MR imaging and according to ATS/AJCC regional lymph nodal classification.Methods: In 5 cadavers,intrathoracic lymph nodes were observed and classified using ATS and AJCC systems.Stations 4,5,6 and 10 were identified with 2 assisted lines and 2 imaging based anatomic landmarks by comparing CT and MR images with 4 series of cross sectional specimens.Results: In the segment from the superior border of aortic arch to the main pulmonary artery trunk,a coronal line through the sectional center of the ascending aorta divided Stations 5 and 6.The line between the centers of ascending and descending aorta separated Station 5 from Station 4 L(ATS,AJCC),or 10L(ATS) on axial images.The left pulmonary artery separated Station 5 from 10L(ATS),or 4L(AJCC) and the arch of azygos vein separated Station 4R from 10R(ATS),or superior and inferior subset of 4R(AJCC).Conclusions: The boundary lines between the stations designed in our study facilitate the application of ATS and AJCC classification system,which is helpful to lung cancer staging with CT and MR imaging.