Diagnostic imaging in COPD

Abstract

Chronic obstructive pulmonary disease (COPD) is a pathological pulmonary condition characterized by expiratory airflow obstruction due to emphysematous destruction of the lung parenchyma and small airways remodeling. Although spirometry is a very useful diagnostic tool for screening large groups of smokers, it cannot readily differentiate the etiologies of COPD and thus has limited utility in characterizing subjects for clinical and investigational purposes. There has been a longstanding interest in thoracic imaging and its role in the in vivo characterization of smoking-related lung disease. Research in this area has spanned readily available modalities such as chest -ray and computed tomography to more advanced imaging techniques such as optical coherence tomography (OCT) and magnetic resonance imaging (MRI). Although the chest x-ray is almost universally available, it lacks sensitivity in detecting both airway disease and mild emphysema and is not generally amenable to objective analysis. Computed tomography has become the standard modality to objectively visualize lung disease. It can provide useful measures of the presence and extent of emphysema, airway disease, and, more recently, pulmonary vascular disease for clinical correlation. It does, however, face limitations in standardization across brands and generations of scanners, and the ionizing radiation associated with image acquisition is of concern to both patients and health care providers. Newer techniques such as OCT and MRI offer exciting in vivo insights into lung structure and function that were previously available only in necropsy specimens and physiology laboratories. Given the more limited availability of these techniques, they will be viewed here as adjuncts to computed tomographic imaging.

Figure 1

Posteroanterior and Lateral CXR of a normal healthy subject (panels A and B) and one with several emphysematous destruction of the lung parenchyma (Panels C and D).

Figure 2

Examples of centrilobular (A), panlobular (B), and paraseptal emphysema (C). Images provided courtesy of the COPDGene^® Study.

Figure 3

Coronal images of a subject with minimal emphysema (top panels) and severe emphysema (bottom panels). For each subject, density histograms are presented for the upper (blue), middle (green), and lower (yellow) regions of lung divided by lung volume. Note the leftward shift in the density histograms of the subject with severe emphysema compared to the more normal smoker.

Figure 4

Examples of axial and coronal CT images obtained at full inflation (panels A and B) and at relaxed exhalation (panels C and D). Note the mosaic attenuation of the bottom 2 expiratory panels suggesting oligemia or gas trapping within the secondary pulmonary lobule.