The relationship between lung function impairment and quantitative computed tomography in chronic obstructive pulmonary disease

Quantitative Analysis for Lung Disease on Thin-Section CT

Thin-section computed tomography (CT) is widely employed not only for assessing morphology but also for evaluating respiratory function. Three-dimensional images obtained from thin-section CT provide precise measurements of lung, airway, and vessel volumes. These volumetric indices are correlated with traditional pulmonary function tests (PFT). CT also generates lung histograms. The volume ratio of areas with low and high attenuation correlates with PFT results. These quantitative image analyses have been utilized to investigate the early stages and disease progression of diffuse lung diseases, leading to the development of novel concepts such as pre-chronic obstructive pulmonary disease (pre-COPD) and interstitial lung abnormalities. Quantitative analysis proved particularly valuable during the COVID-19 pandemic when clinical evaluations were limited. In this review, we introduce CT analysis methods and explore their clinical applications in the context of various lung diseases. We also highlight technological advances, including images with matrices of 1024 × 1024 and slice thicknesses of 0.25 mm, which enhance the accuracy of these analyses.

Computed Tomography Lung Density Analysis: An Imaging Biomarker Predicting Physical Inactivity in Chronic Obstructive Pulmonary Disease: A Pilot Study

Physical inactivity correlates with poor prognosis in chronic obstructive pulmonary disease (COPD) and is suggested to be related to lung hyperinflation. We examined the association between physical activity and the expiratory to inspiratory (E/I) ratio of mean lung density (MLD), the imaging biomarker of resting lung hyperinflation. COPD patients (n = 41) and healthy controls (n = 12) underwent assessment of pulmonary function and physical activity with an accelerometer, as well as computed tomography at full inspiration and expiration. E/I_MLD was calculated by measuring inspiratory and expiratory MLD. Exercise (EX) was defined as metabolic equivalents × duration (hours). COPD patients had higher E/I_MLD (0.975 vs. 0.964) than healthy subjects. When dividing COPD patients into sedentary (EX < 1.5) and non-sedentary (EX ≥ 1.5) groups, E/I_MLD in the sedentary group was statistically higher than that in the non-sedentary group (0.983 vs. 0.972). E/I_MLD > 0.980 was a good predictor of sedentary behavior in COPD (sensitivity, 0.815; specificity, 0.714). Multivariate analysis showed that E/I_MLD was associated with sedentary behavior (odds ratio, 0.39; p = 0.04), independent of age, symptomology, airflow obstruction, and pulmonary diffusion. In conclusion, higher E/I_MLD scores are associated with sedentary behavior and can be a useful imaging biomarker for the early detection of physical inactivity in COPD.

Impulse Oscillometry as a Diagnostic Test for Pulmonary Emphysema in a Clinical Setting

Body plethysmography (BP) is the standard pulmonary function test (PFT) in pulmonary emphysema diagnosis, but not all patients can cooperate to this procedure. An alternative PFT, impulse oscillometry (IOS), has not been investigated in emphysema diagnosis. We investigated the diagnostic accuracy of IOS in the diagnosis of emphysema. Eighty-eight patients from the pulmonary outpatient clinic at Lillebaelt Hospital, Vejle, Denmark, were included in this cross-sectional study. A BP and an IOS were performed in all patients. Computed tomography scan verified presence of emphysema in 20 patients. The diagnostic accuracy of BP and IOS for emphysema was evaluated with two multivariable logistic regression models: Model 1 (BP variables) and Model 2 (IOS variables). Model 1 had a cross-validated area under the ROC curve (CV-AUC) = 0.892 (95% CI: 0.654-0.943), a positive predictive value (PPV) = 59.3%, and a negative predictive value (NPV) = 95.0%. Model 2 had a CV-AUC = 0.839 (95% CI: 0.688-0.931), a PPV = 55.2%, and an NPV = 93.7%. We found no statistically significant difference between the AUC of the two models. IOS is quick and easy to perform, and it can be used as a reliable rule-out method for emphysema.

Quantitative CT parameters correlate with lung function in chronic obstructive pulmonary disease: A systematic review and meta-analysis

Objective

This study aimed to analyze the correlation between quantitative computed tomography (CT) parameters and airflow obstruction in patients with COPD.

Methods

PubMed, Embase, Cochrane and Web of Knowledge were searched by two investigators from inception to July 2022, using a combination of pertinent items to discover articles that investigated the relationship between CT measurements and lung function parameters in patients with COPD. Five reviewers independently extracted data, and evaluated it for quality and bias. The correlation coefficient was calculated, and heterogeneity was explored. The following CT measurements were extracted: percentage of lung attenuation area <-950 Hounsfield Units (HU), mean lung density, percentage of airway wall area, air trapping index, and airway wall thickness. Two airflow obstruction parameters were extracted: forced expiratory volume in the first second as a percentage of prediction (FEV₁%pred) and FEV₁ divided by forced expiratory volume lung capacity.

Results

A total of 141 studies (25,214 participants) were identified, which 64 (6,341 participants) were suitable for our meta-analysis. Results from our analysis demonstrated that there was a significant correlation between quantitative CT parameters and lung function. The absolute pooled correlation coefficients ranged from 0.26 (95% CI, 0.18 to 0.33) to 0.70 (95% CI, 0.65 to 0.75) for inspiratory CT and 0.56 (95% CI, 0.51 to 0.60) to 0.74 (95% CI, 0.68 to 0.80) for expiratory CT.

Conclusions

Results from this analysis demonstrated that quantitative CT parameters are significantly correlated with lung function in patients with COPD. With recent advances in chest CT, we can evaluate morphological features in the lungs that cannot be obtained by other clinical indices, such as pulmonary function tests. Therefore, CT can provide a quantitative method to advance the development and testing of new interventions and therapies for patients with COPD.

Quantitative inspiratory-expiratory chest CT findings in COVID-19 survivors at the 6-month follow-up

We evaluated pulmonary sequelae in COVID-19 survivors by quantitative inspiratory-expiratory chest CT (QCT) and explored abnormal pulmonary diffusion risk factors at the 6-month follow-up. This retrospective study enrolled 205 COVID-19 survivors with baseline CT data and QCT scans at 6-month follow-up. Patients without follow-up pulmonary function tests were excluded. All subjects were divided into group 1 (carbon monoxide diffusion capacity [DL_CO] < 80% predicted, n = 88) and group 2 (DL_CO ≥ 80% predicted, n = 117). Clinical characteristics and lung radiological changes were recorded. Semiquantitative total CT score (0-25) was calculated by adding five lobes scores (0-5) according to the range of lesion involvement (0: no involvement; 1: < 5%; 2: 5-25%; 3: 26-50%; 4: 51-75%; 5: > 75%). Data was analyzed by two-sample t-test, Spearman test, etc. 29% survivors showed air trapping by follow-up QCT. Semiquantitative CT score and QCT parameter of air trapping in group 1 were significantly greater than group 2 (p < 0.001). Decreased DL_CO was negatively correlated with the follow-up CT score for ground-glass opacity (r = - 0.246, p = 0.003), reticulation (r = - 0.206, p = 0.002), air trapping (r = - 0.220, p = 0.002) and relative lung volume changes (r = - 0.265, p = 0.001). COVID-19 survivors with lung diffusion deficits at 6-month follow-up tended to develop air trapping, possibly due to small-airway impairment.

Cluster analysis of emphysema for predicting pulmonary complications after thoracoscopic lobectomy

 

OBJECTIVES

Despite significant advances in surgical techniques, including thoracoscopic approaches and perioperative care, the morbidity rate remains high after lung resection. This study focused on a low attenuation cluster analysis, which represented the size distribution of pulmonary emphysema and assessed its utility for predicting postoperative pulmonary complications after thoracoscopic lobectomy.

METHODS

From April 2013 to September 2018, lung cancer patients who received spirometry and computed tomography (CT) before surgery and underwent thoracoscopic lobectomy were included. The cumulative size distribution of the low attenuation area (LAA, defined as ≤-950 Hounsfield unit on CT) clusters followed a power-law characterized by an exponent D-value, a measure of the complexity of the alveolar structure. D-value and LAA% (LAA/total lung volume) were calculated using preoperative 3-dimensional CT software. The relationship between pulmonary complications and patient characteristics, including D-value and LAA%, was investigated.

RESULTS

Among 471 patients, there were 61 respiratory complication cases (12.9%). Receiver operation characteristic curve analysis revealed that the best predictive cut-off value of D-value and LAA% for pulmonary complications was 2.27 and 16.5, respectively, with an area under the curve of 0.72 and 0.58, respectively. D-value was significantly correlated with % forced expiratory volume in 1 s. Per univariate analysis, gender, smoking history, forced expiratory volume in 1 s/forced vital capacity, LAA% and D-value were risk factors for predicting postoperative pulmonary complications. In the multivariate analysis, D-value remained a significant predictive factor.

CONCLUSION

Preoperative assessment of emphysema cluster analysis may represent the vulnerability of the operated lung and could be the novel predictor for pulmonary complications after thoracoscopic lobectomy.

Computed tomography based measurements to evaluate lung density and lung growth after congenital diaphragmatic hernia

Emphysema-like-change of lung is one aspect of lung morbidity in children after congenital diaphragmatic hernia (CDH). This study aims to evaluate if the extent of reduced lung density can be quantified through pediatric chest CT examinations, if side differences are present and if emphysema-like tissue is more prominent after CDH than in controls. Thirty-seven chest CT scans of CDH patients (mean age 4.5 ± 4.0 years) were analyzed semi-automatically and compared to an age-matched control group. Emphysema-like-change was defined as areas of lung density lower than - 950 HU in percentage (low attenuating volume, LAV). A p-value lower than 0.05 was regarded as statistically significant. Hypoattenuating lung tissue was more frequently present in the ipsilateral lung than the contralateral side (LAV 12.6% vs. 5.7%; p < 0.0001). While neither ipsilateral nor contralateral lung volume differed between CDH and control (p > 0.05), LAV in ipsilateral (p = 0.0002), but not in contralateral lung (p = 0.54), was higher in CDH than control. It is feasible to quantify emphysema-like-change in pediatric patients after CDH. In the ipsilateral lung, low-density areas are much more frequently present both in comparison to contralateral and to controls. Especially the ratio of LAV ipsilateral/contralateral seems promising as a quantitative parameter in the follow-up after CDH.

Visual and Quantitative Assessments of Regional Xenon-Ventilation Using Dual-Energy CT in Asthma-Chronic Obstructive Pulmonary Disease Overlap Syndrome: A Comparison with Chronic Obstructive Pulmonary Disease

Objective

To assess the regional ventilation in patients with asthma-chronic obstructive pulmonary disease (COPD) overlap syndrome (ACOS) using xenon-ventilation dual-energy CT (DECT), and to compare it to that in patients with COPD.

Materials and Methods

Twenty-one patients with ACOS and 46 patients with COPD underwent xenon-ventilation DECT. The ventilation abnormalities were visually determined to be 1) peripheral wedge/diffuse defect, 2) diffuse heterogeneous defect, 3) lobar/segmental/subsegmental defect, and 4) no defect on xenon-ventilation maps. Emphysema index (EI), airway wall thickness (Pi10), and mean ventilation values in the whole lung, peripheral lung, and central lung areas were quantified and compared between the two groups using the Student's t test.

Results

Most patients with ACOS showed the peripheral wedge/diffuse defect (n = 14, 66.7%), whereas patients with COPD commonly showed the diffuse heterogeneous defect and lobar/segmental/subsegmental defect (n = 21, 45.7% and n = 20, 43.5%, respectively). The prevalence of ventilation defect patterns showed significant intergroup differences (p < 0.001). The quantified ventilation values in the peripheral lung areas were significantly lower in patients with ACOS than in patients with COPD (p = 0.045). The quantified Pi10 was significantly higher in patients with ACOS than in patients with COPD (p = 0.041); however, EI was not significantly different between the two groups.

Conclusion

The ventilation abnormalities on the visual and quantitative assessments of xenon-ventilation DECT differed between patients with ACOS and patients with COPD. Xenon-ventilation DECT may demonstrate the different physiologic changes of pulmonary ventilation in patients with ACOS and COPD.

Prevalence of and risk factors for pulmonary complications after curative resection in otherwise healthy elderly patients with early stage lung cancer

BACKGROUND AND OBJECTIVE

The prevalence of lung cancer has been increasing in healthy elderly patients with preserved pulmonary function and without underlying lung diseases. We aimed to determine the prevalence of and risk factors for postoperative pulmonary complications (PPCs) in healthy elderly patients with non-small cell lung cancer (NSCLC) to select optimal candidates for surgical resection in this subpopulation.

METHODS

We included 488 patients older than 70 years with normal spirometry results who underwent curative resection for NSCLC (stage IA-IIB) between 2012 and 2016.

RESULTS

The median (interquartile range) age of our cohort was 73 (71-76) years. Fifty-two patients (10.7%) had PPCs. Severe PPCs like acute respiratory distress syndrome, pneumonia, and respiratory failure had prevalences of 3.7, 3.7, and 1.4%, respectively. Compared to patients without PPCs, those with PPCs were more likely to be male and current smokers; have a lower body mass index (BMI), higher American Society of Anesthesiologists (ASA) classification, more interstitial lung abnormalities (ILAs), and higher emphysema index on computed tomography (CT); and have undergone pneumonectomy or bilobectomy (all p < 0.05). On multivariate analysis, ASA classification ≥3, lower BMI, ILA, and extent of resection were independently associated with PPC risk. The short-term all-cause mortality was significantly higher in patients with PPCs.

CONCLUSIONS

Curative resection for NSCLC in healthy elderly patients appeared feasible with 10% PPCs. ASA classification ≥3, lower BMI, presence of ILA on CT, and larger extent of resection are predictors of PPC development, which guide treatment decision-making in these patients.

Emphysema quantification on computed tomography and its value in predicting radiation pneumonitis in lung cancer treated by stereotactic body radiotherapy

A large portion of patients with early-stage non-small-cell lung cancer (NSCLC) who are receiving stereotactic body radiation therapy (SBRT) are medically inoperable due to compromised pulmonary function, and among these patients pulmonary emphysema (PE) is common. However, the relationship between PE and radiation-induced lung injuries remains unclear. In this study, we aimed to describe the full spectrum of computed tomography (CT) features after SBRT for NSCLC, and to explore their relationship with variables, including PE and dosimetric factors. In all, 71 patients were enrolled. PE was quantified as the percentage of low attenuation area [attenuation values of <-860 Hounsfield units (HU)] within the radiation field (%LAA-860). Spearman's correlation and logistic regression were used to explore factors related to radiological features and radiation pneumonitis (RP). At the 1-year follow-up, acute radiological changes included: (i) diffuse consolidation, 11.3%; (ii) patchy consolidation and ground-glass opacities, 42.3%; and (iii) patchy ground-glass opacity, 14.1%. Late morphological changes occurred in 61.9% of patients (50.7% with a modified conventional pattern, 5.6% with a mass-like pattern and 5.6% with a scar-like pattern). Lower %LAA-860 was the only factor that was significantly associated with consolidation changes at 6 months after SBRT [odds ratio (OR), 0.008; P = 0.009], and it was also a significant predictor for Grade ≥ 2 RP (OR, 0.003; P = 0.04). Our study showed that patients with PE can benefit from SBRT on the condition that good control of dose-volume constraints is achieved.

Functional respiratory imaging (FRI) for optimizing therapy development and patient care

Functional imaging techniques offer the possibility of improved visualization of anatomical structures such as; airways, lobe volumes and blood vessels. Computer-based flow simulations with a three-dimensional element add functionality to the images. By providing valuable detailed information about airway geometry, internal airflow distribution and inhalation profile, functional respiratory imaging can be of use routinely in the clinic. Three dimensional visualization allows for highly detailed follow-up in terms of disease progression or in assessing effects of interventions. Here, we explore the usefulness of functional respiratory imaging in different respiratory diseases. In patients with asthma and COPD, functional respiratory imaging has been used for phenotyping these patients, to predict the responder and non-responder phenotype and to evaluate different innovative therapeutic interventions.

Relationship of spirometric, body plethysmographic, and diffusing capacity parameters to emphysema scores derived from CT scans

Phenotyping of chronic obstructive pulmonary disease (COPD) with computed tomography (CT) is used to distinguish between emphysema- and airway-dominated type. The phenotype is reflected in correlations with lung function measures. Among these, the relative value of body plethysmography has not been quantified. We addressed this question using CT scans retrospectively collected from clinical routine in a large COPD cohort. Three hundred and thirty five patients with baseline data of the German COPD cohort COPD and Systemic Consequences-Comorbidities Network were included. CT scans were primarily evaluated using a qualitative binary emphysema score. The binary score was positive for emphysema in 52.5% of patients, and there were significant differences between the positive/negative groups regarding forced expiratory volume in 1 second (FEV₁), FEV₁/forced vital capacity (FVC), intrathoracic gas volume (ITGV), residual volume (RV), specific airway resistance (sRaw), transfer coefficient (KCO), transfer factor for carbon monoxide (TLCO), age, pack-years, and body mass index (BMI). Stepwise discriminant analyses revealed the combination of FEV₁/FVC, RV, sRaw, and KCO to be significantly related to the binary emphysema score. The additional positive predictive value of body plethysmography, however, was only slightly higher than that of the conventional combination of spirometry and diffusing capacity, which if taken alone also achieved high predictive values, in contrast to body plethysmography. The additional information on the presence of CT-diagnosed emphysema as conferred by body plethysmography appeared to be minor compared to the well-known combination of spirometry and CO diffusing capacity.

Transfer coefficients better reflect emphysematous changes than carbon monoxide diffusing capacity in obstructive lung diseases

The overlap between asthma and chronic obstructive pulmonary disease (COPD) has attracted the interest of pulmonary physicians; thus, measurement of carbon monoxide diffusion capacity (DLco) and/or transfer coefficients (Kco, DLco/V_A) may become valuable in clinical settings. How these parameters behave in chronic obstructive lung diseases is poorly understood. We predicted that Kco might more accurately reflect emphysematous changes in the lungs than DLco. We examined DLco and Kco in nonsmokers and smokers with asthma and investigated their relationships with forced expiratory volume in 1 s (%FEV₁) by group. We then selected nonsmokers (As-NS) and smokers with asthma (As-Sm) in both groups and those with COPD while controlling for the degree of airflow limitation across groups. Emphysema volumes [%lung attenuation volume (%LAV)] and percentage of cross-sectional area of small pulmonary vessels <5 mm² (%CSA_<5) were measured by computed tomography. In As-NS, %Kco was significantly higher when FEV₁% was reduced, but such a correlation was not seen in As-Sm. %Kco successfully differentiated among the three groups when airflow limitation levels were matched. However, %DLc, was significantly reduced only in patients with COPD. Both %LAV and %CSA_<5 were better correlated with %Kco than with %DLco. There was discordance between %DL_CO and %Kco in As-Sm, which was not seen in As-NS. Overall, %Kco better reflects emphysematous changes in obstructive lung diseases than %DLco. NEW & NOTEWORTHY Despite differing behaviors of %Kco and %DLco in several diseases, the characteristics of these parameters have not been fully examined in smokers with asthma. Here, we demonstrated that %Kco is a more sensitive parameter of pathophysiology, better reflecting emphysematous changes in chronic obstructive lung diseases overall, compared with %DLco. Thus, more precise interpretations of %DLco and %Kco may provide clues for understanding the pathophysiology of obstructive lung diseases.

Relationship of CT-quantified emphysema, small airways disease and bronchial wall dimensions with physiological, inflammatory and infective measures in COPD

BACKGROUND

COPD is a complex, heterogeneous disease characterised by progressive development of airflow limitation. Spirometry provides little information about key aspects of pathology and is poorly related to clinical outcome, so other tools are required to investigate the disease. We sought to explore the relationships between quantitative CT analysis with functional, inflammatory and infective assessments of disease to identify the utility of imaging to stratify disease to better predict outcomes and disease response.

METHODS

Patients from the AERIS study with moderate-very severe COPD underwent HRCT, with image analysis determining the quantity of emphysema (%LAA_<- 950), small airways disease (E/I MLD) and bronchial wall thickening (Pi10). At enrolment subjects underwent lung function testing, six-minute walk testing (6MWT), blood sampling for inflammatory markers and sputum sampling for white cell differential and microbiological culture and PCR.

RESULTS

122 subjects were included in this analysis. Emphysema and small airways disease had independent associations with airflow obstruction (β = - 0.34, p < 0.001 and β = - 0.56, p < 0.001). %LAA_<- 950 had independent associations with gas transfer (β = - 0.37, p < 0.001) and E/I MLD with RV/TLC (β = 0.30, p =0.003). The distance walked during the 6MWT was not associated with CT parameters, but exertional desaturation was independently associated with emphysema (β = 0.73, p < 0.001). Pi10 did not show any independent associations with lung function or functional parameters. No CT parameters had any associations with sputum inflammatory cells. Greater emphysema was associated with lower levels of systemic inflammation (CRP β = - 0.34, p < 0.001 and fibrinogen β = - 0.28, p =0.003). There was no significant difference in any of the CT parameters between subjects where potentially pathogenic bacteria were detected in sputum and those where it was not.

CONCLUSIONS

This study provides further validation for the use of quantitative CT measures of emphysema and small airways disease in COPD as they showed strong associations with pulmonary physiology and functional status. In contrast to this quantitative CT measures showed few convincing associations with biological measures of disease, suggesting it is not an effective tool at measuring disease activity.

Heterogeneity in pulmonary emphysema: Analysis of CT attenuation using Gaussian mixture model

PURPOSE

To utilize Gaussian mixture model (GMM) for the quantification of chronic obstructive pulmonary disease (COPD) and to evaluate the combined use of multiple types of quantification.

MATERIALS AND METHODS

Eighty-seven patients (67 men, 20 women; age, 67.4 ± 11.0 years) who had undergone computed tomography (CT) and pulmonary function test (PFT) were included. The heterogeneity of CT attenuation in emphysema (HC) was obtained by analyzing a distribution of CT attenuation with GMM. The percentages of low-attenuation volume in the lungs (LAV), wall area of bronchi (WA), and the cross-sectional area of small pulmonary vessels (CSA) were also calculated. The relationships between COPD quantifications and the PFT results were evaluated by Pearson's correlation coefficients and through linear models, with the best models selected using Akaike information criterion (AIC).

RESULTS

The correlation coefficients with FEV1 were as follows: LAV, -0.505; HC, -0.277; CSA, 0.384; WA, -0.196. The correlation coefficients with FEV1/FVC were: LAV, -0.640; HC, -0.136; CSA, 0.288; WA, -0.131. For predicting FEV1, the smallest AIC values were obtained in the model with LAV, HC, CSA, and WA. For predicting FEV1/FVC, the smallest AIC values were obtained in the model with LAV and HC. In both models, the coefficient of HC was statistically significant (P-values = 0.000880 and 0.0441 for FEV1 and FEV1/FVC, respectively).

CONCLUSION

GMM was applied to COPD quantification. The results of this study show that COPD severity was associated with HC. In addition, it is shown that the combined use of multiple types of quantification made the evaluation of COPD severity more reliable.

Significance of Low-Attenuation Cluster Analysis on Quantitative CT in the Evaluation of Chronic Obstructive Pulmonary Disease

Objective

To assess clinical feasibility of low-attenuation cluster analysis in evaluation of chronic obstructive pulmonary disease (COPD).

Materials and Methods

Subjects were 199 current and former cigarette smokers that underwent CT for quantification of COPD and had physiological measurements. Quantitative CT (QCT) measurements included low-attenuation area percent (LAA%) (voxels ≤ -950 Hounsfield unit [HU]), and two-dimensional (2D) and three-dimensional D values of cluster analysis at three different thresholds of CT value (-856, -910, and -950 HU). Correlation coefficients between QCT measurements and physiological indices were calculated. Multivariable analyses for percentage of predicted forced expiratory volume at one second (%FEV1) was performed including sex, age, body mass index, LAA%, and D value had the highest correlation coefficient with %FEV1 as independent variables. These analyses were conducted in subjects including those with mild COPD (global initiative of chronic obstructive lung disease stage = 0-II).

Results

LAA% had a higher correlation coefficient (-0.549, p < 0.001) with %FEV1 than D values in subjects while 2D D_-910HU (-0.350, p < 0.001) revealed slightly higher correlation coefficient than LAA% (-0.343, p < 0.001) in subjects with mild COPD. Multivariable analyses revealed that LAA% and 2D D value_-910HU were significant independent predictors of %FEV1 in subjects and that only 2D D value_-910HU revealed a marginal p value (0.05) among independent variables in subjects with mild COPD.

Conclusion

Low-attenuation cluster analysis provides incremental information regarding physiologic severity of COPD, independent of LAA%, especially with mild COPD.

Quantitative computed tomography measurements to evaluate airway disease in chronic obstructive pulmonary disease: Relationship to physiological measurements, clinical index and visual assessment of airway disease

PURPOSE

To correlate currently available quantitative CT measurements for airway disease with physiological indices and the body-mass index, airflow obstruction, dyspnea, and exercise capacity (BODE) index in patients with chronic obstructive pulmonary disease (COPD).

MATERIALS AND METHODS

This study was approved by our institutional review board (IRB number 2778). Written informed consent was obtained from all subjects. The subjects included 188 current and former cigarette smokers from the COPDGene cohort who underwent inspiratory and expiratory CT and also had physiological measurements for the evaluation of airflow limitation, including FEF25-75%, airway resistance (Raw), and specific airway conductance (sGaw). The BODE index was used as the index of clinical symptoms. Quantitative CT measures included % low attenuation areas [% voxels≤950 Hounsfield unit (HU) on inspiratory CT, %LAA_-950ins], percent gas trapping (% voxels≤-856HU on expiratory CT, %LAA _-856exp), relative inspiratory to expiratory volume change of voxels with attenuation values from -856 to -950HU [Relative Volume Change (RVC)_{-856 to -950}], expiratory to inspiratory ratio of mean lung density (E/I-ratio _MLD), Pi10, and airway wall thickness (WT), luminal diameter (LD) and airway wall area percent (WA%) in the segmental, subsegmental and subsubsegmental bronchi on inspiratory CT. Correlation coefficients were calculated between the QCT measurements and physiological measurements in all subjects and in the subjects with mild emphysema (%LAA_-950ins <10%). Univariate and multiple variable analysis for the BODE index were also performed. Adjustments were made for age, gender, smoking pack years, FEF25-75%, Raw, and sGaw.

RESULTS

Quantitative CT measurements had significant correlations with physiological indices. Among them, E/I-ratio _MLD had the strongest correlations with FEF25-75% (r=-0.648, <0.001) and sGaw (r=-0.624, <0.001) while in the subjects with mild emphysema subsegmental WA% and segmental WA% had the strongest correlation with FEF25-75% (r=-0.669, <0.001) and sGaw (r=-0.638, <0.001), respectively. The multiple variable analyses showed that RVC_{-856 to -950} was an independent predictor of the BODE index showing the highest R² (0.468) as an independent variable among the QCT measurements.

CONCLUSION

Quantitative CT measurements of gas trapping such as E/I-ratio _MLD, correlate better with physiological indices for airway disease than those of airway such as WA% or LD. In mild emphysema, however, quantitative CT measurements of airway correlate better with the physiological indices. RVC_{-856 to -950} is a predictor of the BODE index.

Application of the homology method for quantification of low-attenuation lung region inpatients with and without COPD

Background

Homology is a mathematical concept that can be used to quantify degree of contact. Recently, image processing with the homology method has been proposed. In this study, we used the homology method and computed tomography images to quantify emphysema.

Methods

This study included 112 patients who had undergone computed tomography and pulmonary function test. Low-attenuation lung regions were evaluated by the homology method, and homology-based emphysema quantification (b₀, b₁, nb₀, nb₁, and R) was performed. For comparison, the percentage of low-attenuation lung area (LAA%) was also obtained. Relationships between emphysema quantification and pulmonary function test results were evaluated by Pearson’s correlation coefficients. In addition to the correlation, the patients were divided into the following three groups based on guidelines of the Global initiative for chronic Obstructive Lung Disease: Group A, nonsmokers; Group B, smokers without COPD, mild COPD, and moderate COPD; Group C, severe COPD and very severe COPD. The homology-based emphysema quantification and LAA% were compared among these groups.

Results

For forced expiratory volume in 1 second/forced vital capacity, the correlation coefficients were as follows: LAA%, −0.603; b₀, −0.460; b₁, −0.500; nb₀, −0.449; nb₁, −0.524; and R, −0.574. For forced expiratory volume in 1 second, the coefficients were as follows: LAA%, −0.461; b₀, −0.173; b₁, −0.314; nb₀, −0.191; nb₁, −0.329; and R, −0.409. Between Groups A and B, difference in nb₀ was significant (P-value = 0.00858), and those in the other types of quantification were not significant.

Conclusion

Feasibility of the homology-based emphysema quantification was validated. The homology-based emphysema quantification was useful for the assessment of emphysema severity.

Present and future utility of computed tomography scanning in the assessment and management of COPD

Computed tomography (CT) is the modality of choice for imaging the thorax and lung structure. In chronic obstructive pulmonary disease (COPD), it used to recognise the key morphological features of emphysema, bronchial wall thickening and gas trapping. Despite this, its place in the investigation and management of COPD is yet to be determined, and it is not routinely recommended. However, lung CT already has important clinical applications where it can be used to diagnose concomitant pathology and determine which patients with severe emphysema are appropriate for lung volume reduction procedures. Furthermore, novel quantitative analysis techniques permit objective measurements of pulmonary and extrapulmonary manifestations of the disease. These techniques can give important insights into COPD, and help explore the heterogeneity and underlying mechanisms of the condition. In time, it is hoped that these techniques can be used in clinical trials to help develop disease-specific therapy and, ultimately, as a clinical tool in identifying patients who would benefit most from new and existing treatments. This review discusses the current clinical applications for CT imaging in COPD and quantification techniques, and its potential future role in stratifying disease for optimal outcome.

Asthma COPD Overlap Syndrome on CT Densitometry: A Distinct Phenotype from COPD

Patients with asthma COPD overlap syndrome (ACOS) are an important but poorly characterized group. This study sought to explore the distinct characteristics of ACOS on CT densitometry. The study population was randomly selected from communities via questionnaires. All participants underwent low-dose volumetric chest CT both before and after bronchodilator administration. Each CT scan was performed at full-inspiration and full-expiration for CT densitometry. Emphysema index (EI), air trapping (AT), mean lung density (MLD) and total lung volume (TLV) were measured and compared between the ACOS and COPD groups. The distributions of both EI and AT were compared between patients with ACOS and COPD. The variations between the pre- and post-BD measurements observed in patients with ACOS were compared with those in patients with COPD. A total of 71 patients completed the study, including 32 patients with COPD and 39 patients with ACOS. The patients with ACOS exhibited lower EI and more upper-zone-predominant EI distributions, compared with the patients with COPD. No significant differences were exhibited in AT and its distribution. Following bronchodilator administration, the variations in AT and expiratory MLD were greater in patients with ACOS than in patients with COPD. No differences were observed in the variations of EI and inspiratory MLD. Our results indicate that patients with ACOS have lower extent of emphysema and different emphysema distribution, as well as greater post-BD variations in air trapping, compared with patients with COPD. These findings suggest that CT densitometry characterizes ACOS as a distinct phenotype from COPD.

Optimal threshold of subtraction method for quantification of air-trapping on coregistered CT in COPD patients

OBJECTIVES

To investigate the optimal threshold of subtraction method for quantification of air trapping on co-registered CT in COPD patients in correlation with pulmonary function parameters.

METHODS

From June 2005 to October 2010, 174 patients were included in our study. Inspiration and expiration CT were performed followed by non-rigid registration using in-house software. The subtraction value per voxel between inspiration and registered expiration CT was obtained, and volume fraction of air trapping (air trapping index, ATI), using variable thresholds was calculated. ATI, expiration/inspiration ratio of mean lung density (E/I MLD) and the percentage of lung voxels below -856 HU on expiration CT (Exp-856) were correlated with FEF25-75% and RV/TLC.

RESULTS

The highest correlation coefficient with FEF25-75% was -0.656, using the threshold of 80 HU. As for RV/TLC, the highest correlation coefficient was 0.664, using the threshold of 30 HU. When plotting the relationship between subtraction thresholds and FEF25-75% and RV/TLC, the threshold of 60 HU was most suitable (r = -0.649 and 0.651). Those correlation coefficients were comparable to the results with E/I MLD (r = -0.670 and 0.657) and Exp-856 (r = -0.604 and 0.565).

CONCLUSIONS

The optimal threshold for quantification of air trapping was 60 HU and showed comparable correlations with pulmonary function parameters.

KEY POINTS

• The optimal CT threshold of subtraction method for air trapping was 60 HU. • ATI with 60 HU threshold was comparable to E/I MLD and Exp -856 . • Emphysema may substantially contribute to air trapping with statistical significance (P < 0.001).

How Common Is Airflow Limitation in Patients With Emphysema on CT Scan of the Chest?

BACKGROUND

COPD has traditionally been defined by the presence of irreversible airflow limitation on spirometry using either the GOLD (Global Initiative for Chronic Obstructive Lung Disease) or American Thoracic Society/European Respiratory Society criteria (lower limit of normal [LLN]). We have observed that some patients with clinical COPD and emphysema on chest CT scan have no obstruction on spirometry. The purpose of this study was to assess the prevalence of obstruction by GOLD and LLN criteria in patients with emphysema on CT scan and determine which radiographic criteria were associated with a clinical diagnosis of COPD.

METHODS

We retrospectively analyzed the clinical records and spirometry of all patients who had radiographically defined emphysema on chest CT scans completed at the University of Vermont in 2011. We compared spirometric criteria and CT scan factors with the presence of clinical COPD based on chart review.

RESULTS

We identified 274 patients with CT scan-defined emphysema. GOLD criteria detected obstruction in 228 patients (83%), and LLN detected obstruction in 206 patients (75%). However, GOLD failed to correctly identify 19 patients (6.9%) and LLN failed to identify 38 patients (13.9%) (average 10.4%) who had radiographic emphysema and a clinical diagnosis of COPD. Obese patients had a lower prevalence of obstruction whether classified by LLN or GOLD. Among patients with spirometric obstruction, there were greater degrees of emphysema and more severely increased airway wall thickness. Factors that were independently associated with clinical COPD were lower FVC % predicted, lower FEV1/FVC ratio, and increasing airway wall thickness.

CONCLUSIONS

Spirometry missed 10.4% of patients with clinical COPD who have significant emphysema on chest CT scan.

Pulmonary function parameters in high-resolution computed tomography phenotypes of chronic obstructive pulmonary disease

BACKGROUND

Heterogeneity of clinical presentation of chronic obstructive pulmonary disease (COPD) attributes to different pathological basis. High-resolution computed tomography (HRCT) phenotypes of COPD may reflex the pathological basis of COPD indirectly by evaluating the small airway inflammation and emphysema. How the pulmonary function related with different HRCT phenotypes has not been well known. The aim was to explore the features of pulmonary function parameters in the 3 phenotypes.

METHODS

Sixty-three stable COPD patients were allocated in 3 groups based on HRCT findings: phenotype A (absence of emphysema, with minimal evidence of emphysema with or without bronchial wall thickening [BWT]), phenotype E (emphysema without BWT) and phenotype M (emphysema with BWT). The pulmonary function testing was also analyzed.

RESULTS

The values of forced expiratory volume in 1 second (FEV1)/forced vital capacity (FVC%), FEV1% and maximum expiratory flows (MEF)50% were the highest in phenotype A (P < 0.05), so was residual volume (RV)/total lung capacity (TLC%) in phenotype E (P < 0.05). Those with MEF50/MEF25 ratio >4.0 were more prevalence in phenotype A than in E and M (odds ratio = 2.214; P < 0.05). The occurrences of RV/TLC% >40% were higher in phenotype E than in A and M (odds ratio = 3.906; P < 0.05). Receiver operating characteristic analysis showed that the cutoff value of MEF50/MEF25 ratio for identifying phenotype A was 2.5, with sensitivity 66.7% and specificity 92.9%. The cutoff value of RV/TLC% for identifying phenotype E was 57.4%, with sensitivity 75.0% and specificity 79.1%.

CONCLUSIONS

The different features of pulmonary function parameters were found in various HRCT phenotypes; MEF50/MEF25 ratio could imply phenotype A, whereas RV/TLC% may be the indicator of phenotype E.

Quantitative assessment of pulmonary perfusion using dynamic contrast-enhanced CT in patients with chronic obstructive pulmonary disease: correlations with pulmonary function test and CT volumetric parameters

BACKGROUND

Pulmonary function test (PFT) is commonly used to help diagnose chronic obstructive pulmonary disease (COPD) and other lung diseases. However, it cannot be used to evaluate regional function and morphological abnormalities.

PURPOSE

To quantitatively evaluate pulmonary perfusion imaging using dynamic contrast-enhanced (DCE) computed tomography (CT) and observe its correlations with PFT and CT volumetric parameters in COPD patients.

MATERIAL AND METHODS

PFT and CT pulmonary perfusion examination were performed in 63 COPD patients. Perfusion defects were quantitated by calculating the CT value ratio (RHU) between perfusion defects (HUdefect) and normal lung (HUnormal). Volumetric CT data were used to calculate emphysema index (EI), total lung volume (TLV), and total emphysema volume (TEV). Emphysematous parenchyma was defined as the threshold of lung area lower than -950 HU. Correlations between RHU and TLV, TEV, EI, and PFT were assessed using Spearman correlation analysis.

RESULTS

The positive rate of perfusion defects on CT perfusion images was higher than that of emphysema on CT mask images (χ(2) = 17.027, P < 0.001). The Spearman correlation test showed that RHU was positively correlated with FEV1 (R = 0.59, P < 0.001), FEV1% Predicted (R = 0.61, P < 0.001), FVC (R = 0.47, P = 0.002), and FEV1/FVC (R = 0.65, P < 0.001), and negatively correlated with EI (R = -0.67, P < 0.001).

CONCLUSION

CT perfusion imaging is more sensitive in detecting emphysema that is inconspicuous on CT images. RHU is correlated with PFT and CT volumetric parameters, suggesting that it is more sensitive in detecting early COPD changes and may prove to be a potential predictor of focal lung function.

The COPD assessment test correlates well with the computed tomography measurements in COPD patients in China

Background

The chronic obstructive pulmonary disease (COPD) assessment test (CAT) is a validated simple instrument to assess health status, and it correlates well with the severity of airway obstruction in COPD patients. However, little is known about the relationships between CAT scores and quantitative computed tomography (CT) measurements of emphysema and airway wall thickness in COPD patients in the People’s Republic of China.

Methods

One hundred and twelve participants including 63 COPD patients and 49 normal control subjects were recruited. All participants were examined with high-resolution CT to get the measurements of emphysema (percentage of pixels below −950 HU [%LAA–950]) and airway wall thickness (wall area percentage and the ratio of airway wall thickness to total diameter). Meanwhile, they completed the CAT and modified Medical Research Council questionnaire independently.

Results

Significantly higher CAT scores and CT measurements were found in COPD patients compared with normal control subjects (P<0.05), and there was a tendency of higher CAT scores and CT measurements with increasing disease severity measured by GOLD staging system. Positive correlations were found between CAT scores and CT measurements (P<0.01). Using multiple linear stepwise regression, CAT score =−46.38+0.778× (wall area percentage) +0.203× (%LAA–950) (P<0.001). Meanwhile, CAT scores and CT measurements in COPD patients all positively correlated with the modified Medical Research Council grades and negatively correlated with FEV₁% (P<0.01).

Conclusion

CAT scores correlate well with the quantitative CT measurements in COPD patients, which may provide an imaging evidence that the structural changes of the lungs in this disease are associated with the health status measured by CAT.

Paired inspiratory/expiratory volumetric CT and deformable image registration for quantitative and qualitative evaluation of airflow limitation in smokers with or without copd

RATIONALE AND OBJECTIVES

To evaluate paired inspiratory/expiratory computed tomography (CT; iCT/eCT) and deformable image registration for quantitative and qualitative assessment of airflow limitation in smokers.

MATERIALS AND METHODS

Paired iCT/eCT images acquired from 35 smokers (30 men and 5 women) were coregistered and subtraction images (air trapping CT images [aCT]) generated. To evaluate emphysema quantitatively, the percentage of low-attenuation volume (LAV%) on iCT was calculated at -950 HU, as were mean and kurtosis on aCT for quantitative assessment of air trapping. Parametric response maps of emphysema (PRMe) and of functional small airways disease (PRMs) were also obtained. For qualitative evaluation of emphysema, low-attenuation areas on iCT were scored by consensus of two radiologists using Goddard classification. To assess air trapping qualitatively, the degree of air trapping on aCT was scored. For each quantitative and qualitative index, the Spearman rank correlation coefficient for forced expiratory flow in 1 second was calculated, and differences in correlation coefficients were statistically tested.

RESULTS

The correlation coefficients for the indices were as follows: mean on aCT, 0.800; kurtosis on aCT, -0.726; LAV%, -0.472; PRMe, -0.570; PRMs, -0.565; addition of PRMe and PRMs, -0.653; emphysema score, -0.502; air trapping score, -0.793. The indices showing significant differences were as follows: mean on aCT and addition of PRMe and PRMs (P = 1.43 × 10(-8)); air trapping score and emphysema score (P = .0169).

CONCLUSIONS

Air trapping images yielded more accurate quantitative and qualitative evaluation of airflow limitation than did LAV%, PRMe, PRMs, and Goddard classification.

Airflow limitation in chronic obstructive pulmonary disease: ratio and difference of percentage of low-attenuation lung regions in paired inspiratory/expiratory computed tomography

RATIONALE AND OBJECTIVES

The purpose of this study was to analyze the relationship between airflow limitation and two types of computed tomography (CT) measurements: expiratory/inspiratory (E/I) ratio and E/I difference of percentage of low-attenuation lung regions (LAA%).

MATERIALS AND METHODS

Thirty patients who underwent inspiratory and expiratory CT scans were included in this study. The CT data were used to calculate the LAA% E/I ratio and E/I difference. Other types of CT measurements were also obtained, including the E/I ratio and E/I difference of lung volume, mean lung density, standard deviation, skewness, and kurtosis. LAA% was calculated at 20 thresholds (-990 to -800 HU). Pearson's correlation between the measurements and forced expiratory flow in 1 second was used to determine the efficacy of LAA% E/I ratio and E/I difference. P values of <5.88 × 10⁻⁵ were considered statistically significant with Bonferroni correction.

RESULTS

The LAA% E/I ratio and E/I difference significantly correlated with forced expiratory flow in 1 second. The best correlation coefficient for the LAA% E/I ratio was -0.699 (P = 1.75 × 10⁻⁵) and for the LAA% E/I difference was -0.723 (P = 6.53 × 10⁻⁶). The best correlation coefficient for the LAA% E/I difference was stronger than that for the other types of CT measurements.

CONCLUSIONS

The LAA% E/I ratio and E/I difference significantly correlated with airflow limitation in chronic obstructive pulmonary disease.

Pulmonary function and CT biomarkers as risk factors for cardiovascular events in male lung cancer screening participants: the NELSON study

OBJECTIVE

The objective of this study was to investigate the association of spirometry and pulmonary CT biomarkers with cardiovascular events.

METHODS

In this lung cancer screening trial 3,080 male participants without a prior cardiovascular event were analysed. Fatal and non-fatal cardiovascular events were included. Spirometry included forced expiratory volume measured in units of one-second percent predicted (FEV1%predicted) and FEV1 divided by forced vital capacity (FVC; FEV1/FVC). CT examinations were quantified for coronary artery calcium volume, pulmonary emphysema (perc15) and bronchial wall thickness (pi10). Data were analysed via a Cox proportional hazard analysis, net reclassification improvement (NRI) and C-indices.

RESULTS

184 participants experienced a cardiovascular event during a median follow-up of 2.9 years. Age, pack-years and smoking status adjusted hazard ratios were 0.992 (95% confidence interval (CI) 0.985-0.999) for FEV1%predicted, 1.000 (95%CI 0.986-1.015) for FEV1/FVC, 1.014 (95%CI 1.005-1.023) for perc15 per 10 HU, and 1.269 (95%CI 1.024-1.573) for pi10 per 1 mm. The incremental C-index (<0.015) and NRI (<2.8%) were minimal. Coronary artery calcium volume had a hazard ratio of 1.046 (95%CI 1.034-1.058) per 100 mm(3), an increase in C-index of 0.076 and an NRI of 16.9% (P < 0.0001).

CONCLUSIONS

Pulmonary CT biomarkers and spirometry measurements were significantly associated with cardiovascular events, but did not contain clinically relevant independent prognostic information for cardiovascular events.

KEY POINTS

• Pulmonary CT biomarkers and spirometry are associated with cardiovascular events • These pulmonary measurements do not contain clinically relevant independent prognostic information • Only coronary calcium score improved cardiovascular risk prediction above age and smoking.

Mass and fat infiltration of intercostal muscles measured by CT histogram analysis and their correlations with COPD severity

RATIONALE AND OBJECTIVES

Chronic obstructive pulmonary disease (COPD) is characterized by progressive respiratory function impairment and respiratory muscle dysfunction. We hypothesized that the mass and fat infiltration of respiratory muscles correlates with COPD severity and emphysema extent.

MATERIALS AND METHODS

Ninety-eight male patients with COPD underwent chest computed tomography (CT) and spirometry. The mass and fat infiltrations of intercostal and latissimus muscles were quantified as the cross-sectional area (CSA) and attenuation of these muscles using CT histogram analysis. Intercostal index and latissimus index were defined as intercostal CSAs and latissimus CSAs divided by body mass index. The emphysema extent was measured as the ratio of the emphysematous lung volume to the total lung volume using a density-mask technique. Pearson correlation analyses were performed to evaluate the relationships between these parameters. Multiple regression analysis was performed using forced expiratory volume in 1 second (FEV1) as the dependent parameter and the clinical and CT data as the independent parameters.

RESULTS

FEV1 was significantly correlated with intercostal index (r = 0.57), latissimus index (r = 0.34), intercostal attenuation (r = 0.62), and latissimus attenuation (r = 0.38). Emphysema extent was significantly correlated with intercostal index (r = -0.36) and intercostal attenuation (r = -0.50). Multiple regression analysis showed that FEV1 was predicted by intercostal attenuation (B = 0.40), intercostal CSA (B = 0.23), emphysema extent (B = -0.23), and age (B = -0.21, R(2) = 0.64, P < .001).

CONCLUSIONS

A decrease in intercostal mass and an increase in intercostal fat are associated with worsening of COPD severity.

Direct assessment of lung function in COPD using CT densitometric measures

To investigate whether lung function in patients with chronic obstructive pulmonary disease (COPD) can be directly predicted using CT densitometric measures and assess the underlying prediction errors as compared with the traditional spirometry-based measures. A total of 600 CT examinations were collected from a COPD study. In addition to the entire lung volume, the extent of emphysema depicted in each CT examination was quantified using density mask analysis (densitometry). The partial least square regression was used for constructing the prediction model, where a repeated random split-sample validation was employed. For each split, we randomly selected 400 CT exams for training (regression) purpose and the remaining 200 exams for assessing performance in prediction of lung function (e.g., FEV1 and FEV1/FVC) and disease severity. The absolute and percentage errors as well as their standard deviations were computed. The averaged percentage errors in prediction of FEV1, FEV1/FVC%, TLC, RV/TLC% and DLco% predicted were 33%, 17%, 9%, 18% and 23%, respectively. When classifying the exams in terms of disease severity grades using the CT measures, 37% of the subjects were correctly classified with no error and 83% of the exams were either correctly classified or classified into immediate neighboring categories. The linear weighted kappa and quadratic weighted kappa were 0.54 (moderate agreement) and 0.72 (substantial agreement), respectively. Despite the existence of certain prediction errors in quantitative assessment of lung function, the CT densitometric measures could be used to relatively reliably classify disease severity grade of COPD patients in terms of GOLD.

Relationship between CT air trapping criteria and lung function in small airway impairment quantification

BACKGROUND

Small airways are regarded as the elective anatomic site of obstruction in most chronic airway diseases. Expiratory computed tomography (CT) is increasingly used to assess obstruction at this level but there is no consensus regarding the best quantification method. We aimed to evaluate software-assisted CT quantification of air trapping for assessing small airway obstruction and determine which CT criteria better predict small airway obstruction on single breath nitrogen test (SBNT).

METHODS

Eighty-nine healthy volunteers age from 60 to 90 years old, underwent spirometrically-gated inspiratory (I) and expiratory (E) CT and pulmonary function tests (PFTs) using SBNT, performed on the same day. Air trapping was estimated using dedicated software measuring on inspiratory and expiratory CT low attenuation area (LAA) lung proportion and mean lung density (MLD). CT indexes were compared to SBNT results using the Spearman correlation coefficient and hierarchical dendrogram analysis. In addition, receiver operating characteristic (ROC) curve analysis was performed to determine the optimal CT air-trapping criterion.

RESULTS

43 of 89 subjects (48,3%) had dN2 value above the threshold defining small airway obstruction (i.e. 2.5% N2/l). Expiratory to inspiratory MLD ratio (r = 0.40) and LAA for the range -850 -1024 HU (r = 0.29) and for the range -850 -910 HU (r = 0.37) were positively correlated with SBNT results. E/I MLD was the most suitable criterion for its expression. Expiratory to inspiratory MLD ratio (E/I MLD) showed the highest AUC value (0.733) for small airway obstruction assessment.

CONCLUSION

Among all CT criteria, all correlating with small airway obstruction on SBNT, E/I MLD was the most suitable criterion for its expression in asymptomatic subjects with mild small airway obstruction

TRIAL REGISTRATION

Registered at Clinicaltrials.gov, identifier: NCT01230879.

PHYSIOLOGIC AND QUANTITATIVE COMPUTED TOMOGRAPHY DIFFERENCES BETWEEN CENTRILOBULAR AND PANLOBULAR EMPHYSEMA IN COPD

BACKGROUND

The purpose was to define the differences between centrilobular (CLE) and panlobular emphysema (PLE) phenotypes in cigarette smokers with COPD by a combined qualitative-quantitative computed tomography (CT) analysis.

METHODS

Chest CT scans of 116 cigarette smokers were visually scored by 22 chest radiologists and 29 pulmonologists in a single setting for the predominant emphysema phenotype (e.g. CLE or PLE) and automatically quantified for emphysema{% low attenuation area (LAA) ≤ -950 HU - %LAA_insp-950, gas trapping extent and bronchial metrics{wall area % for segmental (%WAsegm) and subsegmental (%WAsubsegm) bronchi}. These quantitative CT indexes were compared and related to FEV₁, FEV₁/FVC, and smoking history as stratified for emphysema phenotype.

RESULTS

Although more frequent than CLE in GOLD stages 3 and 4 (p = 0.01), PLE was also scored in 38.2% of combined GOLD stages 1 and 2. PLE was positively associated with %LAA_insp-950 (OR = 1.18, 95% CI: 1.12 to 1.27, β coefficient = 0.17, p = <0.0001) and negatively associated with pack-years of smoking (OR = 0.97, 95% CI: 0.95 to 0.99, β coefficient = -0.02, p = 0.03). Both %WAsegm and %WAsubsegm were more strongly associated with FEV₁% (R² = 0.6 for both measures, p< 0.001) in CLE as compared to PLE (R²= 0.15, p = 0.02; R² = 0.26, p< 0.001).

CONCLUSIONS

PLE likely represents a more advanced phase of emphysema, which may also occur in earlier COPD stages and show different interplay with airway disease as compared to CLE.

Association between physical activity and major depressive disorder among current or former smokers with pulmonary disease

OBJECTIVE

To examine the association between physical activity and major depressive disorder (MDD) in a nationally representative sample of current or former smokers with pulmonary impairments.

METHODS

The analyzed sample from the National Health and Nutrition Examination Survey (NHANES) 2007-2010 included 536 adults who indicated that they were current or former smokers, had at least mild pulmonary impairment (FEV1/FVC<0.70), and provided depression and physical activity data.

RESULTS

After controlling for asthma status, pulmonary impairment, age, poverty-to-income ratio (PIR), education, gender, marital status, body mass index (BMI), cotinine, comorbidity index, race-ethnicity, and smoking status, those who met physical activity guidelines had a 59% (odds ratio (OR)=0.41; 95% confidence interval (CI): 0.18-0.94) lower odds of having MDD. Using multivariate linear regression with depression symptoms as the outcome variable, and after adjustments, physical activity was inversely associated with depression symptoms in a dose-response manner; lowest tertile was the referent group, middle tertile coefficient: -1.06 (95% CI: -1.98 to -0.14), and highest tertile coefficient: -1.10 (95% CI: -1.84 to -0.34).

CONCLUSIONS

Physical activity inversely associates with MDD in adults with pulmonary impairments, and does so in a dose-response manner. This suggests that individuals with pulmonary impairments should be encouraged to engage in enjoyable, safe forms of physical activity in a progressive manner.

Pulmonary emphysema in cystic fibrosis detected by densitometry on chest multidetector computed tomography

Background

Histopathological studies on lung specimens from patients with cystic fibrosis (CF) and recent results from a mouse model indicate that emphysema may contribute to CF lung disease. However, little is known about the relevance of emphysema in patients with CF. In the present study, we used computationally generated density masks based on multidetector computed tomography (MDCT) of the chest for non-invasive characterization and quantification of emphysema in CF.

Methods

Volumetric MDCT scans were acquired in parallel to pulmonary function testing in 41 patients with CF (median age 20.1 years; range 7-66 years) and 21 non-CF controls (median age 30.4 years; range 4-68 years), and subjected to dedicated software. The lung was segmented, low attenuation volumes below a threshold of -950 Hounsfield units were assigned to emphysema volume (EV), and the emphysema index was computed (EI). Results were correlated with forced expiratory volume in 1 s percent predicted (FEV1%), residual volume (RV), and RV/total lung capacity (RV/TLC).

Results

We show that EV was increased in CF (457±530 ml) compared to non-CF controls (78±90 ml) (P<0.01). EI was also increased in CF (7.7±7.5%) compared to the control group (1.2±1.4%) (P<0.05). EI correlated inversely with FEV1% (r_s=-0.66), and directly with RV (r_s=0.69) and RV/TLC (r_s=0.47) in patients with CF (P<0.007), but not in non-CF controls. Emphysema in CF was detected from early adolescence (~13 years) and increased with age (r_s=0.67, P<0.001).

Conclusions

Our results indicate that early onset emphysema detected by densitometry on chest MDCT is a characteristic pathology that contributes to airflow limitation and may serve as a novel endpoint for monitoring lung disease in CF.

Diagnosis of chronic obstructive pulmonary disease in lung cancer screening Computed Tomography scans: independent contribution of emphysema, air trapping and bronchial wall thickening

Background

Beyond lung cancer, screening CT contains additional information on other smoking related diseases (e.g. chronic obstructive pulmonary disease, COPD). Since pulmonary function testing is not regularly incorporated in lung cancer screening, imaging biomarkers for COPD are likely to provide important surrogate measures for disease evaluation. Therefore, this study aims to determine the independent diagnostic value of CT emphysema, CT air trapping and CT bronchial wall thickness for COPD in low-dose screening CT scans.

Methods

Prebronchodilator spirometry and volumetric inspiratory and expiratory chest CT were obtained on the same day in 1140 male lung cancer screening participants. Emphysema, air trapping and bronchial wall thickness were automatically quantified in the CT scans. Logistic regression analysis was performed to derivate a model to diagnose COPD. The model was internally validated using bootstrapping techniques.

Results

Each of the three CT biomarkers independently contributed diagnostic value for COPD, additional to age, body mass index, smoking history and smoking status. The diagnostic model that included all three CT biomarkers had a sensitivity and specificity of 73.2% and 88.%, respectively. The positive and negative predictive value were 80.2% and 84.2%, respectively. Of all participants, 82.8% was assigned the correct status. The C-statistic was 0.87, and the Net Reclassification Index compared to a model without any CT biomarkers was 44.4%. However, the added value of the expiratory CT data was limited, with an increase in Net Reclassification Index of 4.5% compared to a model with only inspiratory CT data.

Conclusion

Quantitatively assessed CT emphysema, air trapping and bronchial wall thickness each contain independent diagnostic information for COPD, and these imaging biomarkers might prove useful in the absence of lung function testing and may influence lung cancer screening strategy. Inspiratory CT biomarkers alone may be sufficient to identify patients with COPD in lung cancer screening setting.

Paired inspiratory-expiratory chest CT scans to assess for small airways disease in COPD

Background

Gas trapping quantified on chest CT scans has been proposed as a surrogate for small airway disease in COPD. We sought to determine if measurements using paired inspiratory and expiratory CT scans may be better able to separate gas trapping due to emphysema from gas trapping due to small airway disease.

Methods

Smokers with and without COPD from the COPDGene Study underwent inspiratory and expiratory chest CT scans. Emphysema was quantified by the percent of lung with attenuation < −950HU on inspiratory CT. Four gas trapping measures were defined: (1) Exp₋₈₅₆, the percent of lung < −856HU on expiratory imaging; (2) E/I MLA, the ratio of expiratory to inspiratory mean lung attenuation; (3) RVC_856-950, the difference between expiratory and inspiratory lung volumes with attenuation between −856 and −950 HU; and (4) Residuals from the regression of Exp₋₈₅₆ on percent emphysema.

Results

In 8517 subjects with complete data, Exp₋₈₅₆ was highly correlated with emphysema. The measures based on paired inspiratory and expiratory CT scans were less strongly correlated with emphysema. Exp₋₈₅₆, E/I MLA and RVC_856-950 were predictive of spirometry, exercise capacity and quality of life in all subjects and in subjects without emphysema. In subjects with severe emphysema, E/I MLA and RVC_856-950 showed the highest correlations with clinical variables.

Conclusions

Quantitative measures based on paired inspiratory and expiratory chest CT scans can be used as markers of small airway disease in smokers with and without COPD, but this will require that future studies acquire both inspiratory and expiratory CT scans.

Optimal threshold in CT quantification of emphysema

OBJECTIVES

To determine the optimal threshold by quantitatively assessing the extent of emphysema at the level of the entire lung and at the level of individual lobes using a large, diverse dataset of computed tomography (CT) examinations.

METHODS

This study comprises 573 chest CT examinations acquired from subjects with different levels of airway obstruction (222 none, 83 mild, 141 moderate, 63 severe and 64 very severe). The extent of emphysema was quantified using the percentage of the low attenuation area (LAA%) divided by the total lung or lobe volume(s). The correlations between the extent of emphysema, and pulmonary functions and the five-category classification were assessed using Pearson and Spearman's correlation coefficients, respectively. When quantifying emphysema using a density mask, a wide range of thresholds from -850 to -1,000 HU were used.

RESULTS

The highest correlations of LAA% with the five-category classification and PFT measures ranged from -925 to -965 HU for each individual lobe and the entire lung. However, the differences between the highest correlations and those obtained at -950 HU are relatively small.

CONCLUSION

Although there are variations in the optimal cut-off thresholds for individual lobes, the single threshold of -950 HU is still an acceptable threshold for density-based emphysema quantification.

The effect of iterative reconstruction on computed tomography assessment of emphysema, air trapping and airway dimensions

OBJECTIVES

To determine the influence of iterative reconstruction (IR) on quantitative computed tomography (CT) measurements of emphysema, air trapping, and airway wall and lumen dimensions, compared to filtered back-projection (FBP).

METHODS

Inspiratory and expiratory chest CTs of 75 patients (37 male, 38 female; mean age 64.0 ± 5.7 years) were reconstructed using FBP and IR. CT emphysema, CT air trapping and airway dimensions of a segmental bronchus were quantified using several commonly used quantification methods. The two algorithms were compared using the concordance correlation coefficient (p (c)) and Wilcoxon signed rank test.

RESULTS

Only the E/I-ratio(MLD) as a measure of CT air trapping and airway dimensions showed no significant differences between the algorithms, whereas all CT emphysema and the other CT air trapping measures were significantly different at IR when compared to FBP (P < 0.001).

CONCLUSION

The evaluated IR algorithm significantly influences quantitative CT measures in the assessment of emphysema and air trapping. However, the E/I-ratio(MLD) as a measure of CT air trapping, as well as the airway measurements, is unaffected by this reconstruction method. Quantitative CT of the lungs should be performed with careful attention to the CT protocol, especially when iterative reconstruction is introduced.

KEY POINTS

• New techniques in CT allow numerous quantitative measurements of lung function. • Iterative reconstruction influences quantitative CT measurements of emphysema and air trapping. • Expiratory-to-inspiratory ratio of mean lung density and airway measurements are unaffected by iterative reconstruction. • Quantitative lung-CT should be performed with careful attention to the CT protocol.

Quantitative computed tomography in COPD: possibilities and limitations

Chronic obstructive pulmonary disease (COPD) is a heterogeneous disease that is characterized by chronic airflow limitation. Unraveling of this heterogeneity is challenging but important, because it might enable more accurate diagnosis and treatment. Because spirometry cannot distinguish between the different contributing pathways of airflow limitation, and visual scoring is time-consuming and prone to observer variability, other techniques are sought to start this phenotyping process. Quantitative computed tomography (CT) is a promising technique, because current CT technology is able to quantify emphysema, air trapping, and large airway wall dimensions. This review focuses on CT quantification techniques of COPD disease components and their current status and role in phenotyping COPD.