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Quantitative Assessment of Air Trapping in Chronic Obstructive Pulmonary Disease Using Inspiratory and Expiratory Volumetric MDCT

¹ Department of Radiology, St. Marianna University School of Medicine, 2-16-1 Sugao, Miyamae-Ku, Kawasaki City, Kanagawa 216-8511, Japan.
² Present address: Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, 75 Francis St., Boston, MA 02115.
³ Division of Respiratory and Infectious Diseases, Department of Internal Medicine, St. Marianna University School of Medicine, Kanagawa, Japan.

OBJECTIVE. The purpose of our study was to determine the attenuation threshold value for the detection and quantification of air trapping using paired inspiratory and expiratory volumetric MDCT scans and to assess whether the densitometric parameter can be used for the quantification of airway dysfunction in chronic obstructive pulmonary disease (COPD) regardless of the degree of emphysema.

MATERIALS AND METHODS. This study included 36 patients with COPD who underwent 64-MDCT. The entire lung volume with attenuation between –500 and –1,024 H was segmented as whole lung. The lung volume with attenuation between –500 and –950 H was segmented as limited lung, while the lung volume of less than –950 H was segmented as emphysema and eliminated. The relative volumes for limited lung (relative volume_n–950) with attenuation values below thresholds (_n) ranging from –850 to –950 H, and relative volume for whole lung (relative volume_<n) were obtained on inspiratory and expiratory CT. Then the differences of relative volumes after expiration in whole lung (relative volume change_<n) and limited lung (relative volume change_n–950) were calculated. Patients were classified into two groups according to mean relative volume less than –950 H. Correlations between densitometry parameters and pulmonary function tests (PFTs) reflecting airway dysfunction were evaluated.

RESULTS. The highest correlation with PFTs was observed at the upper threshold of –860 H. In the moderate to severe emphysema group (relative volume_<–950 > 15%), relative volume change_860–950 significantly correlated with the results of PFTs, whereas no significant correlations were seen between relative volume change_<–860 and PFTs. In the minimal or mild emphysema group (inspiratory relative volume_<–950 < 15%), all densitometric parameters correlated with PFTs.

CONCLUSION. The densitometric parameter of relative volume change calculated on paired inspiratory and expiratory MDCT using the threshold of –860 H in limited lung correlated closely with airway dysfunction in COPD regardless of the degree of emphysema.

Keywords: air trapping • chronic obstructive pulmonary disease • CT • emphysema • lung

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				M. Akira, K. Toyokawa, Y. Inoue, and T. Arai Quantitative CT in Chronic Obstructive Pulmonary Disease: Inspiratory and Expiratory Assessment Am. J. Roentgenol., January 1, 2009; 192(1): 267 - 272. [Abstract] [Full Text] [PDF]