Evaluation of four-dimensional computed tomography (4D-CT)-based pulmonary ventilation: The high correlation between 4D-CT ventilation and 81mKr-planar images was found

Purpose To evaluate four-dimensional computed tomography (4D-CT)-derived pulmonary ventilation by comparing with 81m Kr-gas ventilation (V RI ). We also proposed two methods to improve the functional accuracy of 4D-CT ventilation images and evaluated these methods. Methods and materials Eleven lung cancer patients with 4D-CT and V RI were analyzed. Hounsfield unit-based (V HU ) and a Jacobian-based (V Jac ) 4D-CT ventilation images were calculated. They were evaluated by voxel-by-voxel spearman's rank correlation coefficient ( r ) between 4D-CT ventilation and V RI images. After applying an averaging ventilation method and a slope calculating method, correlations were also calculated. Results 4D-CT ventilation showed the high correlation to V RI ( r =0.875 with V HU ). An averaging method brought significantly higher ( p =0.012) correlations to nuclear medicine images with V HU . The improvement was not significant ( p =0.619) with V Jac . Slope calculating method improved the correlation with V HU and slightly worsened the correlation with V Jac . Conclusions The averaging method we proposed might be useful to improve 4D-CT ventilation images. We found good agreement between 4D-CT ventilation and nuclear medicine ventilation, indicating the high physiologic accuracy of 4D-CT ventilation.