Quantitative computed tomography imaging of airway remodeling in severe asthma.

Asthma is a heterogeneous condition and approximately 5-10% of asthmatic subjects have severe disease associated with structure changes of the airways (airway remodeling) that may develop over time or shortly after onset of disease. Quantitative computed tomography (QCT) imaging of the tracheobronchial tree and lung parenchyma has improved during the last 10 years, and has enabled investigators to study the large airway architecture in detail and assess indirectly the small airway structure. In severe asthmatics, morphologic changes in large airways, quantitatively assessed using 2D-3D airway registration and recent algorithms, are characterized by airway wall thickening, luminal narrowing and bronchial stenoses. Extent of expiratory gas trapping, quantitatively assessed using lung densitometry, may be used to assess indirectly small airway remodeling. Investigators have used these quantitative imaging techniques in order to attempt severity grading of asthma, and to identify clusters of asthmatic patients that differ in morphologic and functional characteristics. Although standardization of image analysis procedures needs to be improved, the identification of remodeling pattern in various phenotypes of severe asthma and the ability to relate airway structures to important clinical outcomes should help target treatment more effectively.

Relationship between the airway wall area and asthma control score in moderate persistent asthma.

OBJECTIVES: To assess the association between airway wall area and clinical asthma control, assessed by the Asthma Control Test (ACT). METHODS: This cross-sectional study evaluated 96 adults for asthma control ["at least well controlled" (ACT ≥ 20; n = 52) or "not well controlled" (ACT < 20; n = 44) and airway dimensions: luminal area (LA), wall area (WA) and WA%], obtained using automated dedicated software measurements from volumetric CT images. Results were analysed for segmental bronchi, subsegmental bronchi in the right upper lobe and basilar segments, both uncorrected and corrected for body surface area (BSA). RESULTS: For all bronchi corrected for BSA, there was no correlation between airway wall area and ACT score. There was a weak but statistically significant correlation between uncorrected WA and ACT score (r = -0.203; P = 0.047); WA values were numerically higher in the "not well-controlled" versus the "at least well-controlled asthma" subgroups. For sub-segmental bronchi, there was a correlation between the ACT score and both WA/BSA (r = -0.204; P = 0.047) and WA (r = -0.249; P = 0.014), and for upper lobe bronchi, between the ACT score and WA (r = -0.207; P = 0.044). CONCLUSION: We demonstrated a correlation between subsegmental bronchial airway measurements and clinical control of asthma; this is probably a reflection of airway remodelling and structural changes in chronic poorly controlled asthma. KEY POINTS: • Volumetric computed tomography offers new insights into bronchial morphology. • The relationship between current asthma control and airway wall abnormalities is assessed. • Some relationships between airway wall area and clinical control were demonstrated. • We observed less shape variation of bronchi in "not well-controlled" asthma patients.

Multidetector row computed tomography to assess changes in airways linked to asthma control.

BACKGROUND: In asthma, multidetector row computed tomography (MDCT) detects abnormalities that are related to disease severity, including increased bronchial wall thickness. However, whether these abnormalities could be related to asthma control has not been investigated yet. OBJECTIVE: Our goal was to determine which changes in airways could be linked to disease control. METHODS: Twelve patients with poor asthma control were included and received a salmeterol/fluticasone propionate combination daily for 12 weeks. Patients underwent clinical, functional, and MDCT examinations before and after the treatment period. MDCT examinations were performed using a low-dose protocol at a controlled lung volume (65% TLC). Bronchial lumen (LA) and wall areas (WA) were evaluated at a segmental and subsegmental level using BronCare software. Lung density was measured at the base of the lung. Baseline and end-of-treatment data were compared using the Wilcoxon signed-rank test. RESULTS: After the 12-week treatment period, asthma control was achieved. Airflow obstruction and air trapping decreased as assessed by the changes in FEV(1) (p < 0.01) and expiratory reserve volume (p < 0.01). Conversely, LA and WA did not vary significantly. However, a median decrease in LA of >10% was observed in half of the patients with a wide intra- and intersubject response heterogeneity. This was concomitant with a decrease in lung density (p < 0.02 in the anteroinferior areas). CONCLUSIONS: MDCT is insensitive for demonstrating any decrease in bronchial wall thickness. This is mainly due to changes in bronchial caliber which may be linked to modifications of the elastic properties of the bronchopulmonary system under treatment.

Variability of bronchial measurements obtained by sequential CT using two computer-based methods.

This study aimed to evaluate the variability of lumen (LA) and wall area (WA) measurements obtained on two successive MDCT acquisitions using energy-driven contour estimation (EDCE) and full width at half maximum (FWHM) approaches. Both methods were applied to a database of segmental and subsegmental bronchi with LA > 4 mm(2) containing 42 bronchial segments of 10 successive slices that best matched on each acquisition. For both methods, the 95% confidence interval between repeated MDCT was between -1.59 and 1.5 mm(2) for LA, and -3.31 and 2.96 mm(2) for WA. The values of the coefficient of measurement variation (CV(10), i.e., percentage ratio of the standard deviation obtained from the 10 successive slices to their mean value) were strongly correlated between repeated MDCT data acquisitions (r > 0.72; p < 0.0001). Compared with FWHM, LA values obtained using EDCE were higher for LA < 15 mm(2), whereas WA values were lower for bronchi with WA < 13 mm(2); no systematic EDCE underestimation or overestimation was observed for thicker-walled bronchi. In conclusion, variability between CT examinations and assessment techniques may impair measurements. Therefore, new parameters such as CV(10) need to be investigated to study bronchial remodeling. Finally, EDCE and FWHM are not interchangeable in longitudinal studies.

CT imaging of chronic obstructive pulmonary disease: role in phenotyping and interventions.

BACKGROUND: Using CT to define phenotypic abnormalities in patients diagnosed as having chronic obstructive pulmonary disease (COPD) may serve to optimize treatment, guide the prognosis and assess response to potential therapeutic interventions. OBJECTIVE/METHOD: Although the different morphologic abnormalities seen on CT scans of COPD patients often overlap, two separate groups of patients can be identified, those with emphysema predominant disease and those with airway predominant disease due to chronic inflammation with resulting in airway remodelling and narrowing. The former category can be subdivided further based on the type of emphysema present and characterized further by anatomic distribution and severity using visual assessment and volumetric quantitative CT techniques. Patients in the airway predominant category can also be characterized by CT as showing bronchial wall thickening, small airway inflammation, mosaic perfusion and air trapping expressing small airway narrowing, and expiratory bronchial collapse due to cartilage deficiency. Recent advances in automated airway segmentation and quantitative analysis have made measurements of airway dimensions feasible. CONCLUSION: In longitudinal studies, standardization of procedures and quality control are needed, particularly if quantitative CT outcomes are used as end point in clinical trials and ultimately in the clinical management of individual patients.

Investigation of airways using MDCT for visual and quantitative assessment in COPD patients.

Multidetector computed tomography (MDCT) acquisition during a single breath hold using thin collimation provides high resolution volumetric data set permitting multiplanar and three dimensional reconstruction of the proximal airways. In chronic obstructive pulmonary disease (COPD) patients, this technique provides an accurate assessment of bronchial wall thickening, tracheobronchial deformation, outpouchings reflecting dilatation of the submucous glands, tracheobronchomalacia, and expiratory air trapping. New software developed to segment adequately the lumen and walls of the airways on MDCT scans allows quantitative assessment of the airway dimensions which has shown to be reliable in clinical practice. This technique can become important in longitudinal studies of the pathogenesis of COPD, and in the assessment of therapeutic interventions.

Pulmonary airways: 3-D reconstruction from multislice CT and clinical investigation.

In the framework of computer-aided diagnosis, this paper proposes a novel functionality for the computerized tomography (CT)-based investigation of the pulmonary airways. It relies on an energy-based three-dimensional (3-D) reconstruction of the bronchial tree from multislice CT acquisitions, up to the sixth- to seventh-order subdivisions. Global and local analysis of the reconstructed airways is possible by means of specific visualization modalities, respectively, the CT bronchography and the virtual bronchoscopy. The originality of the 3-D reconstruction approach consists in combining axial and radial propagation potentials to control the growth of a subset of low-order airways extracted from the CT volume by means of a robust mathematical morphology operator-the selective marking and depth constrained (SMDC) connection cost. The proposed approach proved to be robust with respect to a large spectrum of airway pathologies, including even severe stenosis (bronchial lumen obstruction/collapse). Validated by expert radiologists, examples of airway 3-D reconstructions are presented and discussed for both normal and pathological cases. They highlight the interest in considering CT bronchography and virtual bronchoscopy as complementary tools for clinical diagnosis and follow-up of airway diseases.