New frontiers in CT imaging of airway disease

Abstract

Combining helical volumetric CT acquisition and thin-slice thickness during breath hold provides an accurate assessment of both focal and diffuse airway diseases. With multiple detector rows, compared with single-slice helical CT, multislice CT can cover a greater volume, during a simple breath hold, and with better longitudinal and in-plane spatial resolution and improved temporal resolution. The result in data set allows the generation of superior multiplanar and 3D images of the airways, including those obtained from techniques developed specifically for airway imaging, such as virtual bronchography and virtual bronchoscopy. Complementary CT evaluation at suspended or continuous full expiration is mandatory to detect air trapping that is a key finding for depicting an obstruction on the small airways. Indications for CT evaluation of the airways include: (a) detection of endobronchial lesions in patients with an unexplained hemoptysis; (b) evaluation of extent of tracheobronchial stenosis for planning treatment and follow-up; (c) detection of congenital airway anomalies revealed by hemoptysis or recurrent infection; (d) detection of postinfectious or postoperative airway fistula or dehiscence; and (e) diagnosis and assessment of extent of bronchiectasis and small airway disease. Improvement in image analysis technique and the use of spirometrically control of lung volume acquisition have made possible accurate and reproducible quantitative assessment of airway wall and lumen areas and lung density. This contributes to better insights in physiopathology of obstructive lung disease, particularly in chronic obstructive pulmonary disease and asthma.

Computed tomographic imaging of the airways: relationship to structure and function

“…These scoring systems have been applied in several diseases [35][36][37][38][39][40][41][42][43][44][45]. Scoring systems rely on the subjective detection and grading of direct and indirect signs of airway disease, such as airway wall thickening, bronchiectasis, mosaic perfusion and/or gas trapping [46][47][48][49][50]. However, qualitative studies are sensitive to the display settings (window width and level) of the images, are prone to inter-and intra-reader variability, and are time consuming and, therefore, expensive.…”

“…Although such ''gas trapping'' is apparent even in asymptomatic individuals who have normal lung function [86], it is markedly increased in patients with asthma and the degree of gas trapping is related to abnormalities of lung function [33,34,48,70,87].…”

Imaging Studies in Emphysema

“…A recent paper suggests a novel approach, using the intermediate density voxels (2900 to 2950 HU) as a measure of air trapping on expiratory scans compared with inspiratory scans, without the diluting effect of the lowattenuation voxels below 2950 HU that are presumed to show fixed emphysema (40). Reviews of the literature on CT in emphysema have recently been reported and may be useful as additional background information (25,(45)(46)(47)(48)(49).…”

Modern imaging of the tracheo-bronchial tree

“…The tracheal index can be calculated as a ratio of the coronal diameter (mm) by the sagittal diameter (mm). The normal value is approximately one [6] . The angle of the tracheal bifurcation, also called the carinal angle, can vary widely even in normal individuals.…”

“…It can result from a wide variety of causes. MDCT with 3-D reformations from the isotropic data acquisitions allows excellent imaging of the entire tracheabronchial tree in one breath hold and is capable of demonstrating clinically significant outflow obstruction using inspiration and expiration imaging in combination, as well as the full extent of the disease process with additional applications like cine-CT and virtual bronchoscopy [6,[32][33][34] .…”