Strain measurement on four-dimensional dynamic-ventilation CT: quantitative analysis of abnormal respiratory deformation of the lung in COPD

Abstract

PurposeStrain 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 methodsThirty-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.ResultsThe 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.ConclusionAbnormal 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.

<p>Difference in Local Lung Movement During Tidal Breathing Between COPD Patients and Asthma Patients Assessed by Four-dimensional Dynamic-ventilation CT Scan</p>

“…It was reported that normal deformation of the lung would appear at lung areas with large respiratory movements, such as the lung base and the dorsal part of the lung, and abnormal deformation is observed throughout the lung caused by heterogeneous ventilation or partial airtrapping due to emphysema and airway disease of COPD. 9 These observations suggest that abnormal pulmonary deformation by ventilation can be observed in COPD patients who smoked heavily and this differentiates them from asthma patients. Hida et al reported the maximal diaphragmatic motion in severe COPD patients during forced breathing was smaller compared to normal subjects.…”

Strain Analysis in Patients at High-Risk for COPD Using Four-Dimensional Dynamic-Ventilation CT

“…Our study added to the growing body of evidence supporting the utility of strain measurement in quantitative analysis of COPD. 17 …”

“… 16–18 Mathematically speaking, strain on a point of a deformable body is determined from the derivatives of the displacement field that deforms the body. 19–23 Xu et al 17 have firstly introduced strain analysis in COPD to monitor pulmonary motion during ventilation. Although that study demonstrated the potential of strain measurement for evaluating pulmonary mechanics, only the “middle” field of the lung were analyzed with single strain-related parameter (maximum principal strain).…”

“…Although that study demonstrated the potential of strain measurement for evaluating pulmonary mechanics, only the “middle” field of the lung were analyzed with single strain-related parameter (maximum principal strain). 17 Despite the significant correlations were observed between the strain-related parameter and spirometry, evidence that strain measurement can reflect lung function changes was insufficiently presented. Considering the regional heterogeneity of emphysema in COPD, especially in the upper-lower direction, 3–5 substantial improvements in the method of strain analysis, particularly analyze scope covering the whole lung and multi-dimensional parameters setting, are needed.…”

<p>Influence of Emphysema and Air Trapping Heterogeneity on Pulmonary Function in Patients with COPD</p>

“…Our results suggest that AT heterogeneity on full-expiration better reflects pulmonary function than emphysema heterogeneity on full-inspiration, which is rarely reported in the literature. A more heterogeneous distribution of emphysema and/or AT corresponds to relatively more residual normal lung parenchyma, better synchronization of respiratory movements that can be quantitatively assessed by strain measurement using dynamic-ventilation CT, and better pulmonary function 17,18. In the early stage of small airway lesions, expiratory dysfunction manifests exclusively, while with the progression of disease, both inspiratory and expiratory functions show impairment.…”