Advanced imaging in COPD: insights into pulmonary pathophysiology

Abstract

Chronic obstructive pulmonary disease (COPD) involves a complex interaction of structural and functional abnormalities. The two have long been studied in isolation. However, advanced imaging techniques allow us to simultaneously assess pathological processes and their physiological consequences. This review gives a comprehensive account of the various advanced imaging modalities used to study COPD, including computed tomography (CT), magnetic resonance imaging (MRI), and the nuclear medicine techniques positron emission tomography (PET) and single-photon emission computed tomography (SPECT). Some more recent developments in imaging technology, including micro-CT, synchrotron imaging, optical coherence tomography (OCT) and electrical impedance tomography (EIT), are also described. The authors identify the pathophysiological insights gained from these techniques, and speculate on the future role of advanced imaging in both clinical and research settings.

Keywords: Chronic obstructive pulmonary disease (COPD); medical imaging; pulmonary ventilation; respiratory function tests; respiratory physiology.

Figure 1

High-resolution CT scan of a 69-year-old man with allergic bronchopulmonary aspergillosis. Three axial reconstructions of (A) 6 mm, (B) 2.0 mm and (C) 0.625 mm thickness. Note the increasing spatial resolution with decreasing slice thickness. (Helical acquisition with the following settings to maximize spatial resolution: 120 kVp, 548 mAs, tube rotation time 0.5 s, collimator width 0.625 mm, pitch 1.375, voxel dimensions 0.76 mm × 0.76 mm × 0.625 mm).

Figure 2

Micro-computed tomography (micro-CT) of a 2 cm pig lung cube. Lungs were inflation-fixed in formalin steam prior to scanning. (A) Cross-sectional high-resolution CT image and (B) corresponding micro-CT image of the same region of interest. Exquisite detail is seen with micro-CT. Scale bars =1 cm.

Figure 3

Technegas ventilation SPECT/CT fusion images of a 68-year-old man with moderately severe COPD. (A) Axial dimension, with well-ventilated areas (bright yellow), less ventilated areas (red) and non-ventilated areas (black). Green indicates emphysema determined by a CT density mask, with pixel density less than –910 HU. Note that poorly ventilated areas tend to correspond to areas of emphysema. Some non-ventilated areas are not associated with emphysema, suggesting airway obstruction without macroscopic parenchymal destruction in these areas; (B) coronal reconstruction of ventilation map.