Abstract
Purpose: To investigate important factors affecting the frequency of air trapping through observation of normal lung attenuation, and propose a cause of heterogeneous attenuation. Materials and Methods: In this ethical committee-approved study, a total of 109 patients (30 males, 79 females; mean age, 58.2 years; range, 27 - 81 years) were included. All patients had undergone inspiratory and expiratory chest thin-section computed tomography (CT) examinations and pulmonary function tests. Air trapping on CT images was graded subjectively. Hounsfield units (HU) lung attenuation value and lung volume were measured on CT images. All variables (age, sex, indices of pulmonary function test results, air trapping score, HU value, and rate of change in lung volume) were compared by diagnoses and air trap- ping findings cohorts. The correlation between lung function test results and expiratory HU attenuation were analyzed. Results: Interstitial pneumonia showed higher and bronchiolitis obliterans showed lower HU attenuation at normal and air trapping regions. The variables affecting air trapping findings were age, a ratio of forced expiratory volume in 1 second to forced vital capacity (FEV1.0/FVC), maximal expiratory flow at 50% of forced vital capacity (MEF50), HU attenuation at normal regions, and rate of change in lung volume. Compared with expiratory HU attenuation, significant positive correlation was shown to FEV1.0/FVC and negative correlation to single-breath diffusion capacity for carbon monoxide, which was confirmed by a simple regression analysis. Conclusion: It can be suggested that lung attenuation can increase when fibrosis is advanced, and this is exaggerated when lungs are compressed.
Highlights
In patients with obstructive airway physiology, highresolution computed tomography (HRCT) scans often display a characteristic finding of mosaic attenuation
We focused on changes in normal lung attenuation; because air trapping, which is characterized by areas of low attenuation, is demonstrated when attenuation of adjacent normal areas increase on expiratory CT images
In the pulmonary function test results, total lung capacity (TLC) and residual volume (RV) were lowest for interstitial pneumonia (p < 0.001 and p < 0.01, respectively), and FEV1.0, FEV1.0/forced vital capacity (FVC), and MEF50 were lowest for bronchiolitis obliterans (p < 0.001)
Summary
In patients with obstructive airway physiology, highresolution computed tomography (HRCT) scans often display a characteristic finding of mosaic attenuation. This is characterized by heterogeneous lung density, with the lower-density lung being abnormal; this is a common element of air trapping [1,2]. Decreased attenuation of lung parenchyma on expiratory CT scans is a major determinant of airflow obstruction, and expiratory HRCT is an established of imaging technique for assessment of air trapping. Abnormal expiratory air trapping may be depicted in patients with normal pulmonary function tests, while end expiratory scans may appear unremarkable with no change in patients with severe and widespread involvement of small airways [17]. To the best of our knowledge, no studies have been published describing a cause of mosaic attenuation
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