Computed Tomographic Imaging of the Airways in COPD and Asthma

Abstract

Computed tomography (CT) is the modality of choice for imaging the airways. Volumetric data sets with isotropic spatial resolution based on multidetector thin-section CT with overlapping reconstruction should be used. Chronic obstructive pulmonary disease and asthma are the 2 most common disease entities that are defined by airflow obstruction. The morphologic correlates of airway changes are dilation of the lumen, thickening of the wall, visibility of small airways due to mucus or edema, air trapping, hypoxic vasoconstriction, and collapsibility. To assess air trapping, additional expiratory low-dose scans are recommended. In clinical routine, these findings are visually assessed and should be routinely reported. However, the interobserver variability is high, and there is a clear need for objective software-based measurements. The development of such tools is challenging, and they are just becoming available on a broader scale. Novel techniques based on dual-energy CT aim to measure iodine distribution maps to assess pulmonary perfusion as well as the distribution of inhaled xenon gas to assess the distribution and time course of pulmonary ventilation. However, these techniques are still being investigated in clinical studies. This review will provide an overview of CT for the diagnosis of chronic obstructive pulmonary disease and asthma, its role in phenotyping these diseases, and the measurement of disease severity and functional compromise.

Imaging of Cystic Fibrosis Lung Disease and Clinical Interpretation

“…Some authors have suggested using limited slice sampling to restrict radiation exposure [8,16]. Non-contrast-enhanced multidetector CT with full volume coverage and reconstructed overlapping slice thicknesses of preferably 1.5 mm or less has the highest sensitivity for morphological changes and should be given preference over incremental high-resolution CT [17,18]. These datasets not only allow for exact comparison of follow-up exams, multiplanar reformats and maximum intensity projections (MIP) for better identification of airway changes, but also enable dedicated postprocessing with advanced software tools [17,19].…”

“…Non-contrast-enhanced multidetector CT with full volume coverage and reconstructed overlapping slice thicknesses of preferably 1.5 mm or less has the highest sensitivity for morphological changes and should be given preference over incremental high-resolution CT [17,18]. These datasets not only allow for exact comparison of follow-up exams, multiplanar reformats and maximum intensity projections (MIP) for better identification of airway changes, but also enable dedicated postprocessing with advanced software tools [17,19]. Age-adapted low-dose acquisitions with an effective radiation dose of less than 2 mSv even in adults are sufficient for the evaluation of morphological changes including ground glass opacities and mosaic perfusion [20].…”

“…Multiplanar reformats help to identify central to peripheral bronchiectasis. However, even in MDCT, the visualization of small airways is precluded by the system-inherent resolution of 200 -300 µm [17]. If small airways (by convention smaller than 1 mm in diameter) are affected by wall thickening, mucus plugging or bronchiectasis (usually a combination of all three), they may increase in size over the resolution threshold and become visible as centrilobular nodules, often grouped with a tree-in-bud appearance.…”

Simultaneous Assessment of Airway Instability and Respiratory Dynamics with Low-Dose 4D-CT in Chronic Obstructive Pulmonary Disease: A Technical Note

“…Respiratory dynamics in COPD may be severely impaired in advanced disease, which is a result of different patho-mechanisms [1,2,3]. It has long been demonstrated that a chronic, progressive inflammation throughout the tracheobronchial tree may lead to malacia of cartilaginous airways, resulting in a collapse during the respiratory cycle, which often remains undiagnosed when employing pulmonary function testing only [3,4,5]. The diagnosis of tracheobronchomalacia (TBM) is traditionally made by invasive flexible bronchoscopy, and TBM has been reported in up to 44% of patients with chronic bronchitis [4].…”

“…The diagnosis of tracheobronchomalacia (TBM) is traditionally made by invasive flexible bronchoscopy, and TBM has been reported in up to 44% of patients with chronic bronchitis [4]. TBM has to be differentiated from excessive dynamic airway collapse (EDAC), which is characterized mainly by a bowing of the posterior membranous part of the trachea [5]. Importantly, bronchoscopic examination and severity estimation is not standardized and is highly user-dependent.…”