Keywords:
Performed at one institution, Experimental, Retrospective, Image registration, Computer Applications-General, CT, Lung
Authors:
S. Maehira1, T. Hiroki1, Y. Fujita2, K. Usui2, E. Kunieda1; 1Kanagawa/JP, 2Tokyo/JP
DOI:
10.26044/ecr2020/C-07928
Results
Anatomic characteristics
Average lung volume was 2279㎤ for free-breathing (FB) CT, 3677㎤ for abdominal breathing (AB) CT, and 3709㎤ for thoracic breathing (TB)CT. Although lung volume increased significantly during AB and TB compared with FB, no significant differences were observed in lung volume between AB and TB.
Fig. 4 shows the lung expansion rate from FB to AB and TB. The intrathoracic AP expansion rate of TB was significantly larger than AB, and CC distance of AB was significantly larger than TB.
Quantitative evaluation of lung motion using DIR
The DVF map generated from DIR shows the vector direction and color-coded magnitude, with the presence of vector arrows dependent upon the display magnification. The complex orientation of the DVFs demonstrates the need to separate them into independent axes and analyze them quantitatively. Histograms of the vector displacement by separating DVFs into different axes show dominant components of deformation. Fig. 5 and Fig. 6 show the DVF maps and histograms of a patient showing typical trends. Fig. 5 shows that the vector magnitude is larger in the lower lobe than in the upper lobe. The difference in deformation due to the breathing maneuvers is well expressed in the direction of the vector on the sagittal planes in Fig. 5. In AB, most vectors tended to show the inferior direction. By contrast, the vectors near the chest wall tended to show the anterior direction in TB. Fig. 6 shows the DVF histograms for each axis. The DVF histograms divided in each axis quantitatively shows lung deformation in each breathing maneuvers. AB lung deformation yielded median values in the inferior direction compared to TB lung deformation. TB lung deformation yielded median values in the anterior direction compared to AB lung deformation.
The boxplots plotted in Fig. 7, Fig. 8 and Fig. 9. summarize the lung deformation and motion between AB and TB for all patients. The box region described the median and interquartile ranges (25%-75%), whereas the whiskers defined 5% and 95% to describe the spread of data. In both abdominal and thoracic breathing, the displacement range of right-left deformation was approximately smaller than anterior-posterior and superior-inferior deformation. Therefore, the lung deformation was dominant in the anterior-posterior and superior-inferior directions. In Fig. 9, the medians and interquartile ranges of AB show inferior direction compared to TB. Consequently, the AB yielded lung deformation and motion predominantly in the inferior direction. In Fig. 8, the medians and interquartile ranges of TB show anterior direction compared to AB. Consequently, the TB yielded lung deformation and motion predominantly in the anterior direction.
Limitation
The limitation of this study is that the accuracy of DIR was not considered. Since the accuracy of DIR differs depending on the algorithm and parameters used for deformation, the amount of motion and deformation may also vary depending on the method of DIR5).