Asthma and COPD are the principally prevalent of lung diseases and contribute an enormous load of morbidity in North America and globally.

Asthma and COPD are the principally prevalent of lung diseases and contribute an enormous load of morbidity in North America and globally. In the couple conditions, inflammation leads to airway remodeling, which contributes to airway narrowing. To date, airway remodeling has sole been assessed using histological examination of airways. However, it may now be possible to assess and quantify the length of airway remodeling in vivo using high-resolution CT (HRCT) The aim of this article is to review the use of HRCT in the investigation of airway remodeling. A number of investigators have reported techniques to make measurements of airway dimensions using CT and an increasing number of quantitative systems are being developed. Using these techniques, airway dimensions have been examined in patients with asthma and COPD In patients with asthma, the airway wall area was increased without a decrease in luminal area, whereas in patients with COPD the airway luminal area was decreased and airway wall area was increased. The different pattern of remodeling may think fundamental differences in the inflammatory processe in asthma and COPD and could influence the reversibility of the narrowing. It has also been shown that, by dint of quantifying both the extent of emphysema and of airway remodeling, CT is useful in differentiating COPD patients who have primarily parenchymal disease from those who have primarily airway pathology. With additional advances in technology, it is likely that quantitative assessment of airway wall dimensions will ultimately provide a valuable tool for the reflection of airway disease.

tonic words: airway remodeling; asthma; COPD; comput tomography

Abbreviations: Aaw = airway wall area; Ai = airway luminal area; HRCT = high-resolution CT; HU = Hounsfield units; LAA% = depressed attenuation area/total lung area x 100; WA% = Aaw/(Aaw + Ai) X 100

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Asthma and COPD are the greatest in quantity prevalent of lung diseases, and they contribute an enormous carrying capacity of morbidity in North America and globally. (12) Schema outlining the pathophysiologic mechanisms underlying asthma and COPD are shown in Figures 1 and 2 In as well-as; not only-but also; not only-but; not alone-but disorders, environmental factors such as allergens, viruses, and bacteria as well as personal, occupational, and atmospheric pollution cause an exaggerated immune/inflammatory rejoinder in genetically susceptible individuals. The inflammatory answer leads to airway remodeling, which contributes to airway narrowing. There is also accumulating evidence that airway remodeling plays a part in the pathogenesis of other airway diseases like as bronchiectasis, cystic fibrosis, and bronchiolitis. (3) Although airway remodeling has not been precisely defined, we present the following description: (a) Airway remodeling is characterized by the agency of changes in the composition, quantity, and organization of the cellular and molecular constituents of the airway wall. (b) Remodeling is a chain of cause and effect of chronic injury and repair. (c) Remodeling may be reversible or irreversible. (d) Remodeling leads to functional changes.

[FIGURES 1-2 OMITTED]

To date, airway remodeling has been assessed using simply histologic examination of airways. However, with the refinement of the precision and resolution of high-resolution CT (HRCT) it may now be possible to assess and quantify the length of airway remodeling in vivo. In this article, we provide a brief review of latter advances in the assessment of airway disease using HRCT and a certain quantity of examples of the application of these techniques to the research of COPD and asthma. Diseased airways have been assessed in a qualitative or semiquantitative fashion using chest radiographic films and conventional CT HRCT has allowed visualization of airways and parenchyma in frequently greater detail than conventional CT and plain radiography. HRCT has also made possible the investigation of the site and the magnitude and distribution of airway narrowing in vivo. (4) Technical improvements have increased the spatial resolution of HRCT making it theoretically possible to examine small airways. However, qualitative and semiquantitative measures of airway wall remodeling are expand to subjective bias and have been shown to be les accurate. (5) An increasing number of quantitative orders are being developed, and it is these studies we will review herein because of the enormous potential provided on the digital data on which this imaging modality is based.

A number of investigators have reported techniques to make measurements of airway dimensions using CT In principally of these studies a visual assessment was used. (6-12) Visual assessment is time-consuming and, as mentioned above, eventuates in the potential for keeper bias and considerable intra- or interobserver error. Because CT data are based onward the variable absorption of radiographs by way of tissue, which is measured by means of Hounsfield units (HU), a more direct and objective manner to measure airway dimensions is preferable. There are several quantitative rules reported that used CT data directly. McNitt-Gray and coworkers (13) touchstoneed an analysis method in which a commencement number was used to bring to light the airway luminal area (Ai); all pixels with values below this start were designated as lumen. They originate that a threshold value of -500 HU yielded the in the greatest degree accurate measurements of the lumen of a bronchial phantom. This outset is consistent with the findings of other studies. (1214) thicket and co-workers (15) made quantitative measurements of airway wall and luminal areas from spiral CT data. The first degree in their analysis was to re-create the asymmetric CT voxels into cubic dimensions (isotropic voxels) The voxel were re-createed to approximately 0.4 x 04 x 04-mm voxel from interpolation in the longitudinal axis. This manipulation allowed the images to be rebuilded in any orientation. They then defined the central axis of the airway and re-established the airway lumen in a plane perpendicular to this axis. This analysis technique overmasters the major limitation to the use of HRCT in quantitative analysis, which is that accurate or authentic Ai and airway wall area (Aaw) can be measured solitary from airways that are oriented approximately perpendicular to the plane of scanning.

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