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

Current advances in pulmonary functional imaging

Recent advances in imaging analysis have enabled evaluation of ventilation and perfusion in specific regions by chest computed tomography (CT) and magnetic resonance imaging (MRI), in addition to modalities including dynamic chest radiography, scintigraphy, positron emission tomography (PET), ultrasound, and electrical impedance tomography (EIT). In this review, an overview of current functional imaging techniques is provided for each modality. Advances in chest CT have allowed for the analysis of local volume changes and small airway disease in addition to emphysema, using the Jacobian determinant and parametric response mapping with inspiratory and expiratory images. Airway analysis can reveal characteristics of airway lesions in chronic obstructive pulmonary disease (COPD) and bronchial asthma, and the contribution of dysanapsis to obstructive diseases. Chest CT is also employed to measure pulmonary blood vessels, interstitial lung abnormalities, and mediastinal and chest wall components including skeletal muscle and bone. Dynamic CT can visualize lung deformation in respective portions. Pulmonary MRI has been developed for the estimation of lung ventilation and perfusion, mainly using hyperpolarized 129Xe. Oxygen-enhanced and proton-based MRI, without a polarizer, has potential clinical applications. Dynamic chest radiography is gaining traction in Japan for ventilation and perfusion analysis. Single photon emission CT can be used to assess ventilation-perfusion (V˙/Q˙) mismatch in pulmonary vascular diseases and COPD. PET/CT V˙/Q˙ imaging has also been demonstrated using "Galligas". Both ultrasound and EIT can detect pulmonary edema caused by acute respiratory distress syndrome. Familiarity with these functional imaging techniques will enable clinicians to utilize these systems in clinical practice.

Association of Respiratory Functional Indices and Smoking with Pleural Movement and Mean Lung Density Assessed Using Four-Dimensional Dynamic-Ventilation Computed Tomography in Smokers and Patients with COPD

Purpose

To correlate the ratio of the non-dependent to dependent aspects of the maximal pleural movement vector (MPMV_ND/D) and gravity-oriented collapse ratio (GCR_ND/D), and the mean lung field density (MLD) obtained using four-dimensional (4D) dynamic-ventilation computed tomography (DVCT) with airflow limitation parameters and the Brinkman index.

Materials and Methods

Forty-seven patients, including 22 patients with COPD, 13 non-COPD smokers, and 12 non-smokers, with no/slight pleural adhesion confirmed using a thoracoscope, underwent 4D-DVCT with 16 cm coverage. Coordinates for the lung field center, as well as ventral and dorsal pleural points, set on the central trans-axial levels in the median and para-median sagittal planes at end-inspiration, were automatically measured (13-17 frame images, 0.35 seconds/frame). MPMV_ND/D and GCR_ND/D were calculated based on MPMV and GCR values for all the included points and the lung field center. MLD was automatically measured in each of the time frames, and the maximal change ratio of MLD (MLD_CR) was calculated. These measured values were compared among COPD patients, non-COPD smokers, and non-smokers, and were correlated with the Brinkman index, FEV₁/FVC, FEV₁ predicted, RV/TLC, and FEF_25-75% using Spearman's rank coefficients.

Results

MPMV_ND/D was highest in non-smokers (0.819±0.464), followed by non-COPD smokers (0.405±0.131) and patients with COPD (-0.219±0.900). GCR_ND/D in non-smokers (1.003±1.384) was higher than that in patients with COPD (-0.164±1.199). MLD_CR in non-COPD smokers (0.105±0.028) was higher than that in patients with COPD (0.078±0.027). MPMV_ND/D showed positive correlations with FEV₁ predicted (r=0.397, p=0.006), FEV₁/FVC (r=0.501, p<0.001), and FEF_25-75% (r=0.368, p=0.012). GCR_ND/D also demonstrated positive correlations with FEV₁ (r=0.397, p=0.006), FEV₁/FVC (r=0.445, p=0.002), and FEF_25-75% (r=0.371, p=0.011). MPMV_ND/D showed a negative correlation with the Brinkman index (r=-0.398, p=0.006).

Conclusion

We demonstrated that reduced MPMV_ND/D and GCR_ND/D were associated with respiratory functional indices, in addition to a negative association of MPMV_ND/D with the Brinkman index, which should be recognized when assessing local pleural adhesion on DVCT, especially for ventral pleural aspects.

Semiautomatic assessment of respiratory dynamics using cine MRI in chronic obstructive pulmonary disease

Purpose

The quantitative assessment of impaired lung motions and their association with the clinical characteristics of COPD patients is challenging. The aim of this study was to measure respiratory kinetics, including asynchronous movements, and to analyze the relationship between lung area and other clinical parameters.

Materials and methods

This study enrolled 10 normal control participants and 21 COPD patients who underwent dynamic MRI and pulmonary function testing (PFT). The imaging program was implemented using MATLAB®. Each lung area was detected semi-automatically on a coronal image (imaging level at the aortic valve) from the inspiratory phase to the expiratory phase. The Dice index of the manual measurements was calculated, with the relationship between lung area ratio and other clinical parameters, including PFTs then evaluated. The asynchronous movements of the diaphragm were also evaluated using a sagittal image.

Results

The Dice index for the lung region using the manual and semi-automatic extraction methods was high (Dice index = 0.97 ± 0.03). A significant correlation was observed between the time corrected lung area ratio and percentage of forced expiratory volume in 1 s (FEV₁%pred) and residual volume percentage (RV%pred) (r = −0.54, p = 0.01, r = 0.50, p = 0.03, respectively). The correlation coefficient between each point of the diaphragm in the group with visible see-saw like movements was significantly lower than that in the group without see-saw like movements (value = −0.36 vs 0.95, p = 0.001).

Conclusion

Semi-automated extraction of lung area from Cine MRI might be useful for detecting impaired respiratory kinetics in patients with COPD.

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

Purpose

To quantitatively identify abnormal lung motion in chronic obstructive pulmonary disease (COPD) using strain analysis, and further clarify the potential differences of deformation in COPD with different severity of airflow limitation.

Materials and Methods

Totally, 53 patients at high-risk for COPD were enrolled in this study. All CT examinations were performed on a 320-row MDCT scanner, and strain measurement based on dynamic-ventilation CT data was performed with a computational fluid dynamics analysis software (Micro Vec V3.6.2). The strain-related parameters derived from the whole expiration phase (PSmax-all, PSmean-all, Speedmax-all ), the first 2s of expiration phase (PSmax2s, PSmean2s, Speedmax2s ) were divided respectively by the changes in lung volume to adjust for the degree of expiration. Spearman rank correlation analysis was used to evaluate associations between the strain-related parameters and various spirometric parameters. Comparisons of the strain-related parameters between COPD and non-COPD patients, between GOLD I (mild airflow restriction) and GOLD II-IV (moderate to severe airflow restriction) were made using the Mann-Whitney U-test. Receiver-operating characteristic (ROC) analysis was performed to evaluate the diagnostic performance of the strain-related parameters for COPD. P <0.05 was considered statistically significant.

Results

Strain-related parameters demonstrated positive correlations with spirometric parameters (ρ=0.275~0.687, P<0.05), suggesting that heterogeneity in lung motion was related to abnormal spirometric results. Strain-related parameters can quantitatively distinguish COPD from non-COPD patients with moderate diagnostic significance with the AUC values ranged from 0.821 to 0.894. Furthermore, parameters of the whole expiration phase (PSmax-all, Speedmax-all) demonstrated significant differences (P=0.005; P=0.04) between COPD patients with mild and moderate to severe airflow limitation.

Conclusion

Strain-related parameters derived from dynamic-ventilation CT data covering the whole lung associated with lung function changes in COPD, reflecting the severity of airflow limitation in some degree, even though its utility in severe COPD patients remains to be investigated.