Quantitative CT is increasingly used to quantify the features of COPD, specifically emphysema, air trapping, and airway abnormality. For quantification of emphysema, the density mask technique is most widely used, with threshold on the order of-950 HU, but percentile cutoff may be less sensitive to volume changes. Sources of variation include depth of inspiration, scanner make and model, technical parameters, and cigarette smoking. On expiratory CT, air trapping may be quantified by evaluating the % of lung volume less than a given threshold (e.g. -856 HU), by comparing lung volumes and attenuation on expiration and inspiration, or more recently by co-registering inspiratory and expiratory CT scans. These indices all correlate well with the severity of physiologic airway obstruction. By constructing a three-dimensional model of the airway from volumetric CT, it is possible to measure dimensions (external and internal diameters, and airway wall thickness) of segmental and subsegmental airways orthogonal to their long axes. Measurement of airway parameters correlates with severity of airflow obstruction and with history of COPD exacerbation.

Quantitative computed tomography in chronic obstructive pulmonary disease.

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.

/pdf/quantitative-computed-tomography-in-copd-possibilities-and-2dyewf5r8p.pdf

Quantitative computed tomography in COPD: possibilities and limitations.

Background: The advent of endoscopic lung volume reduction (ELVR), especially relying on valve technology to achieve atelectasis, has aroused new interest in the assessment of collateral ventilation, which has been implicated in ELVR failures. We are reporting on the use of a catheter-based device that measures airway pressures and flows, and calculates airway resistance in vivo. Objectives: To assess the safety of this catheter-based system and the feasibility of obtaining measurements predictive of atelectasis after ELVR. Methods: Patients undergoing ELVR were prospectively included in this double-blind cohort study. Each lobe targeted for ELVR was blocked with a catheter system (Chartis® System; Pulmonx, Inc., Redwood, Calif., USA); pressures and flows were assessed continuously. The primary endpoints were to evaluate the safety and feasibility; the secondary endpoint was to assess whether there was a relationship between the measurements and the incidence of atelectasis following ELVR. Results: From June 2008 to November 2008, 25 patients were included in the study. All procedures could be performed without any complications. Due to pneumothorax in 1 case and inability to assess the catheter-based measurements in 4 cases, the final analysis included 20 patients. Atelectasis occurred in 8 out of 20 cases following implantation. In 18 patients (90%), the resistance measurements correlated with the postimplantation atelectasis visualized on a chest X-ray; in 2 patients (10%), a mismatch was detected. Conclusions: Resistance measurements were safely and successfully achieved. In 90% of the analyzable cases, the resistance measurements correlated with the occurrence of atelectasis after ELVR. The clinical impact of these findings will need to be evaluated in subsequent trials.

/pdf/predicting-atelectasis-by-assessment-of-collateral-2511shrg92.pdf

Predicting atelectasis by assessment of collateral ventilation prior to endobronchial lung volume reduction: a feasibility study.

OBJECTIVE. The purpose of this study was to determine whether measurements of lung attenuation at inspiration and expiration obtained from 3D lung reconstructions reflect the severity of chronic obstructive pulmonary disease.SUBJECTS AND METHODS. Seventy-six patients with chronic obstructive pulmonary disease underwent MDCT with 3D postprocessing at full inspiration and full expiration. Inspiratory and expiratory mean lung density, percentage of lung volume with attenuation values less than -910 HU and -950 HU at inspiration and expiration, expiratory to inspiratory mean lung density ratio, and fifth and 15th percentiles of the lung attenuation distribution curve at inspiration and expiration were measured.RESULTS. When forced expiratory volume in the first second of expiration (FEV1) was 50% or greater than predicted value, mean lung density and lower attenuation volume measured from inspiratory MDCT scans correlated better with FEV1 and ratio of FEV1 to forced vital capacity (FVC) than did those from ex...

https://www.ajronline.org/doi/pdfplus/10.2214/AJR.07.3953

Quantitative CT in chronic obstructive pulmonary disease: inspiratory and expiratory assessment.

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

Characterisation and quantification of emphysema are necessary for planning of local treatment and monitoring. Sensitive, easy to measure, and stable parameters have to be established and their relation to the well-known pulmonary function testing (PFT) has to be investigated. A retrospective analysis of 221 nonenhanced thin-section MDCT with a corresponding PFT was carried out, with a subgroup analysis in 102 COPD stage III+IV, 44 COPD stage 0, and 33 investigations into interstitial lung disease (ILD). The in-house YACTA software was used for automatic quantification of lung and emphysema volume [l], emphysema index, mean lung density (MLD [HU]) and 15th percentile [HU]. CT-derived lung volume is significantly smaller in ILD (3.8) and larger in COPD (7.2) than in controls (5.9, p < 0.0001). Emphysema volume and index are significantly higher in COPD than in controls (3.2 vs. 0.5, p < 0.0001, 45% vs. 8%, p < 0.0001). MLD and 15th percentile are significantly smaller in COPD (−877/−985, p < 0.0001) and significantly higher in ILD (−777, p < 0.0006/−914, p < 0.0001) than in controls (−829/−935). A relevant amount of COPD patients apparently do not suffer from emphysema, while controls who do not fulfil PFT criteria for COPD also demonstrate CT features of emphysema. Automatic quantification of thin-section CT delivers convincing parameters and ranges that are able to differentiate among emphysema, control and ILD. An emphysema index of lower 20%, MLD higher than −850, and 15th percentile lower than −950 might be regarded as normal (thin-section, nonenhanced, B40, YACTA). These ranges might be helpful in the judgement of individual measures.

Fully automatic quantitative assessment of emphysema in computed tomography: comparison with pulmonary function testing and normal values.

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Fully automatic quantitative assessment of emphysema in computed tomography: comparison with pulmonary function testing and normal values.