International Journal of COPD (Dec 2018)
Strain measurement on four-dimensional dynamic-ventilation CT: quantitative analysis of abnormal respiratory deformation of the lung in COPD
Abstract
Yanyan Xu,1,2 Tsuneo Yamashiro,1 Hiroshi Moriya,3 Maho Tsubakimoto,1 Yukihiro Nagatani,4 Shin Matsuoka,5 Sadayuki Murayama1 On behalf of ACTIve Study Group 1Department of Radiology, Graduate School of Medical Science, University of the Ryukyus, Nishihara, Okinawa, Japan; 2Department of Radiology, China-Japan Friendship Hospital, Beijing, Republic of China; 3Department of Radiology, Ohara General Hospital, Fukushima-City, Fukushima, Japan; 4Department of Radiology, Shiga University of Medical Science, Otsu, Shiga, Japan; 5Department of Radiology, St Marianna University School of Medicine, Kawasaki, Kanagawa, Japan Purpose: Strain measurement is frequently used to assess myocardial motion in cardiac imaging. This study aimed to apply strain measurement to pulmonary motion observed by four-dimensional dynamic-ventilation computed tomography (CT) and to clarify motion abnormality in COPD. Materials and methods: Thirty-two smokers, including ten with COPD, underwent dynamic-ventilation CT during spontaneous breathing. CT data were continuously reconstructed every 0.5 seconds. In the series of images obtained by dynamic-ventilation CT, five expiratory frames were identified starting from the peak inspiratory frame (first expiratory frame) and ending with the fifth expiratory frame. Strain measurement of the scanned lung was performed using research software that was originally developed for cardiac strain measurement and modified for assessing deformation of the lung. The measured strain values were divided by the change in mean lung density to adjust for the degree of expiration. Spearman’s rank correlation analysis was used to evaluate associations between the adjusted strain measurements and various spirometric values. Results: The adjusted strain measurement was negatively correlated with FEV1/FVC (ρ=-0.52, P<0.01), maximum mid-expiratory flow (ρ=-0.59, P<0.001), and peak expiratory flow (ρ=-0.48, P<0.01), suggesting that abnormal deformation of lung motion is related to various patterns of expiratory airflow limitation. Conclusion: Abnormal deformation of lung motion exists in COPD patients and can be quantitatively assessed by strain measurement using dynamic-ventilation CT. This technique can be expanded to dynamic-ventilation CT in patients with various lung and airway diseases that cause abnormal pulmonary motion. Keywords: COPD, computed tomography, CT, dynamic-ventilation CT, strain measurement, emphysema
