Diagnosis of emphysema and air-trapping in high resolution computed tomography

Conventional computed tomography has several limitations, connected with long scanning time, and using 1cm thick collimation. Improvement in quality of images of lung parenchyma led to the development of high resolution computed tomography (HRCT). It optimizes the morphological images of the lung parenchyma at the level of the lung lobule, becoming the modality of choice in evaluating the lung interstitium. The aim of the study was assessment of the usefulness of HRCT in diagnosis of emphysema, determining its character and presence of air-trapping. The emphysema and air-trapping are interstitial changes, causing inhomogeneous lung density on HRCT sections. Emphysema is usually a permanent destruction of lung parenchyma, while in the case of air-trapping the pathology may be potentially reversible. HRCT is considered to be the most accurate diagnostic modality in emphysema. The focal areas of low attenuation are clearly seen among the areas of normal lung parenchyma of higher density, provided sufficiently low window level is established (-600 to -800 H.U.). The HRCT sections statistically significantly increased the frequency of diagnosis of emphysema on inspiratory sections, and air-trapping on expiratory scans. In revealing of air-trapping HRCT is diagnostic modality of choice. The expiratory sections reveal presence of air-trapping invisible on expiratory scans. The HRCT section enables differentiation of different kinds of emphysema that were invisible on plain radiograms, sensitivity of which in revealing small emphysematous changes is very poor. HRCT makes it possible to quantify emphysematous changes, the degree of parenchymal destruction, secondary functional disorders. It is more sensitive and specific in determining the type and extension of emphysema.