Air Trapping: A Cause of Heterogeneous Attenuation

Keiko Morikawa, Fumito Okada, Yumiko Ando, Asami Ono, Hiromu Mori

Department of Radiology, Faculty of Medicine, Oita University, Yufu, Japan.

DOI: 10.4236/ojrad.2012.23017                

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.

Keywords

Air Trapping; CT Examination; Lung Attenuation

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	A. Devakonda, S. Raoof, A. Sung, W. D. Travis and D. Naidich, “Bronchiolar Disorders: A Clinical-Radiological Diagnostic Algorithm,” Chest, Vol. 137, No. 4, 2010, pp. 938-951. doi:10.1378/chest.09-0800
[2]	E. J. Stern, N. L. Müller, S. J. Swensen and T. E. Hartman, “CT Mosaic Pattern of Lung Attenuation: Etiologies and Terminology,” Journal of Thoracic Imaging, Vol. 10, No. 4, 1995, pp. 294-297.
[3]	H. Arakawa, P. A. Gevenois, Y. Saito, H. Shida, V. De Maertelaer, H. Morikubo and M. Fujioka, “Silicosis: Expiratory Thin-Section CT Assessment of Airway Obstruction,” Radiology, Vol. 236, No. 3, 2005, pp. 1059-1066. doi:10.1148/radiol.2363041611
[4]	E. S. Lee, M. B. Gotway, G. P. Reddy, J. A. Golden, F. M. Keith and W. R. Webb, “Early Bronchiolitis Obliterans Following Lung Transplantation: Accuracy of Expiratory Thin-Section CT for Diagnosis,” Radiology, Vol. 216, No. 2, 2000, pp. 472-477.
[5]	H. Arakawa and W. R. Webb, “Air Trapping on Expiratory High-Resolution CT Scans in the Absence of Inspiratory Scan Abnormalities: Correlation with Pulmonary Function Tests and Differential Diagnosis,” American Journal of Roentgenology, Vol. 170, No. 5, 1998, pp. 1349-1353.
[6]	C. F. Yang, M. T. Wu, A. A. Chiang, R. S. Lai, C. Chen, W. M. Tiao, T. C. McLoud, J. S. Wang and H. B. Pan, “Correlation of High-Resolution CT and Pulmonary Function in Bronchiolitis Obliterans: A Study Based on 24 Patients Associated with Consumption of Sauropus Androgynous,” American Journal of Roentgenology, Vol. 168, No. 4, 1997, pp. 1045-1050.
[7]	D. M. Hansell, A. U. Wells, M. B. Rubens and P. J. Cole, “Bronchiectasis: Functional Significance of Areas of Decreased Attenuation at Expiratory CT,” Radiology, Vol. 193, No. 2, 1994, pp. 369-374.
[8]	A. Busacker, J. D. Newell, T. Keefe, E. A. Hoffman, J. C. Granroth, M. Castro, S. Fain and S. Wenzel, “A Multivariate Analysis of Risk Factors for the Air-Trapping Asthmatic Phenotype as Measured by Quantitative CT Analysis,” Chest, Vol. 135, No. 1, 2009, pp. 48-56. doi:10.1378/chest.08-0049
[9]	D. M. Hansell, M. B. Rubens, S. P. Padley and A. U. Wells, “Obliterative Bronchiolitis: Individual CT Signs of Small Airways Disease and Functional Correlation,” Radiology, Vol. 203, No. 3, 1997, pp. 721-726.
[10]	H. R. Roberts, A. U. Wells, D. G. Milne, M. B. Rubens, J. Kolbe, P. J. Cole and D. M. Hansell, “Airflow Obstruction in Bronchiectasis: Correlation between Computed Tomography Features and Pulmonary Function Tests,” Thorax, Vol. 55, No. 3, 2000, pp. 198-204. doi:10.1136/thorax.55.3.198
[11]	P. A. Gevenois, P. de Vuyst, M. Sy, P. Scillia, L. Chaminade, V. de Maertelaer, J. Zanen and J. C. Yernault, “Pulmonary Emphysema: Quantitative CT during Expiration,” Radiology, Vol. 199, No. 3, 1996, pp. 825-829.
[12]	A. A. Bankier, C. Schaefer-Prokop, V. de Maertelaer, D. Tack, P. Jaksch, W. Klepetko and P. A. Gevenois, “Air Trapping: Comparison of Standard-Dose and Simulated Low-Dose Thin-Section CT Techniques,” Radiology, Vol. 242, No. 3, 2007, pp. 898-906. doi:10.1148/radiol.2423060196
[13]	O. Lucidarme, P. A. Grenier, M. Cadi, I. Mourey-Gerosa, K. Benali and P. Cluzel, “Evaluation of Air Trapping at CT: Comparison of Continuousversus Suspended-Expiration CT Techniques,” Radiology, Vol. 216, No. 3, 2000, pp. 768-772.
[14]	E. J. Stern, W. R. Webb, M. L. Warnock and C. J. Salmon, “Bronchopulmonary Sequestration: Dynamic, Ultrafast, High-Resolution CT Evidence of Air Trapping,” American Journal of Roentgenology, Vol. 157, No. 5, 1991, pp. 947-949.
[15]	A. A. Bankier, M. Estenne, D. Kienzl, C. Müller-Mang, A. Van Muylem and P. A. Gevenois, “Gravitational Gradients in Expiratory Computed Tomography Examinations of Patients with Small Airways Disease: Effect of Body Position on Extent of Air Trapping,” Journal of Thoracic Imaging, Vol. 25, No. 4, 2010, pp. 311-319.
[16]	S. P. Padley, B. D. Adler, D. M. Hansell and N. L. Müller, “Bronchiolitis Obliterans: High Resolution CT Findings and Correlation with Pulmonary Function Tests,” Clinical Radiology, Vol. 47, No. 4, 1993, pp. 236-240. doi:10.1016/S0009-9260(05)81129-8
[17]	M. C. Sweatman, A. B. Millar, B. Strickland and M. Turner-Warwic, “Computed Tomography in Adult Obliterative Bronchiolitis,” Clinical Radiology, Vol. 42, No. 2, 1990, pp. 116-119. doi:10.1016/S0009-9260(05)80142-4
[18]	P. A. Grenier, A. C. Beigelman, C. Fétita, F. Prêteux, M. W. Brauner and S. Lenoir, “New Frontiers in CT Imaging of Airway Disease,” European Radiology, Vol. 5, No. 12, 2002, pp. 1022-1044. doi:10.1007/s00330-002-1342-1
[19]	S. A. Worthy, N. L. Müller, T. E. Hartman, S. J. Swensen, S. P. Padley and D. M. Hansell, “Mosaic Attenuation Pattern on Thin-Section CT Scans of the Lung: Differentiation among Infiltrative Lung, Airway, and Vascular Diseases as a Cause,” Radiology, Vol. 205, No. 2, 1997, pp. 465-470.
[20]	American Thoracic Society, “Standardization of Spirometry—1994 Update,” American Journal of Respiratory and Critical Care Medicine, Vol. 152, 1995, pp. 1107-1136.
[21]	R. S. Fraser, L. M. Nestor, C. Neil and P. D. Pare, “Deacreased Lung Dencity: Fraser and Pare’s Dianosis of Diseases of the Chest,” 4th Edition, W. B. Saunders Company, Philadelphia, 1999.
[22]	M. L. Goris, H. J. Zhu, F. Blankenberg, F. Chan and T. E. Robinson, “An Automated Approach to Quantitative Air Trapping Measurements in Mild Cystic Fibrosis,” Chest, Vol. 123, No. 5, 2003, pp. 1655-1663. doi:10.1378/chest.123.5.1655
[23]	J. G. Im, Y. W. Choi, H. D. Kim, Y. K. Jeong and M. C. Han, “Thin-Section CT Findings of the Lungs: Experimentally Induced Bronchial and Pulmonary Artery Obstruction in Pigs,” American Journal of Roentgenology, Vol. 167, No. 3, 1996, pp. 631-636.
[24]	P. S. Hasleton and A. Curry, “Anatomu of the Lung: Hasleton PS. Spencer’s Pathology of the Lung,” 5th Edition, McGraw-Hill, New York, 1962.
[25]	T. J. Vrtiska, R. P. Hartman, J. M. Kofler, M. R. Bruesewitz, B. F. King and C. H. McCollough, “Spatial Resolution and Radiation Dose of a 64-MDCT Scanner Compared with Published CT Urography Protocols,” American Journal of Roentgenology, Vol. 192, No. 4, 2009, pp. 941-948. doi:10.2214/AJR.07.2679
[26]	D. M. Michael and J. S. Sally “Cardiopulmonary Function Testing: Jennifer AP, Barbara AW. Phisiotherapy for Respiratory and Cardiac Problems,” 2nd Edition, Churchill Livintstone, London, 1993.
[27]	J. A. Verschakelen, K. Scheinbaum, J. Bogaert, M. Demedts, L. L. Lacquet and A. L. Baert, “Expiratory CT in Cigarette Smokers: Correlation between Areas of Decreased Lung Attenuation, Pulmonary Function Tests and Smoking History,” European Radiology, Vol. 8, No. 8, 1998, pp. 1391-1399. doi:10.1007/s003300050558