Evaluation of material decomposition for pulmonary function test in spectral computed tomography: A Monte Carlo simulation study

Due to various factors, the number of chronic obstructive pulmonary disease (COPD) patients continues to grow. In addition, the mortality from COPD is increasing because of the difficult in the early detection of COPD. Both of radiologic and respiratory examinations should be performed for detecting COPD. But, since the conventional respiratory test uses spirometer, there is the air leakage between mouth and measurement machine, which reduces the accuracy and reproducibility of measurement. Also, it is difficult to apply respiratory examinations to all ages because the long respiration is needed. In this study, we confirmed the feasibility of material decomposition for pulmonary function test by combining dual-energy X-ray imaging based on a photon-counting detector. Non-radioactive Xe was used for determining pulmonary region. The RMSEs and contrast of each material in decomposition images were analyzed to quantitatively evaluate an accuracy of material decomposition images, and the volume including each material was calculated from material decomposition images. Results showed the high accuracy of material decomposition and volume measurements. The average RMSE values of PMMA, lung, and non-radioactive Xe were 0.07, 0.28, and 0.08%. The percentage errors of volume measurements for pure PMMA, lung, non-radioactive Xe, and total lung were 2.72, 8.46, 4.06, and 3.72%, respectively. Therefore, the diagnosis of COPD can be simplified through the material decomposition imaging using non-radiologic Xe, and the pulmonary function can be evaluated by decomposing the actual gas exchange volume form the total lung volume.