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Optimal threshold of subtraction method for quantification of air-trapping on coregistered CT in COPD patients

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Abstract

Objectives

To investigate the optimal threshold of subtraction method for quantification of air trapping on co-registered CT in COPD patients in correlation with pulmonary function parameters.

Methods

From June 2005 to October 2010, 174 patients were included in our study. Inspiration and expiration CT were performed followed by non-rigid registration using in-house software. The subtraction value per voxel between inspiration and registered expiration CT was obtained, and volume fraction of air trapping (air trapping index, ATI), using variable thresholds was calculated. ATI, expiration/inspiration ratio of mean lung density (E/I MLD) and the percentage of lung voxels below −856 HU on expiration CT (Exp−856) were correlated with FEF25–75% and RV/TLC.

Results

The highest correlation coefficient with FEF25–75% was −0.656, using the threshold of 80 HU. As for RV/TLC, the highest correlation coefficient was 0.664, using the threshold of 30 HU. When plotting the relationship between subtraction thresholds and FEF25–75% and RV/TLC, the threshold of 60 HU was most suitable (r = −0.649 and 0.651). Those correlation coefficients were comparable to the results with E/I MLD (r = −0.670 and 0.657) and Exp−856 (r = −0.604 and 0.565).

Conclusions

The optimal threshold for quantification of air trapping was 60 HU and showed comparable correlations with pulmonary function parameters.

Key Points

• The optimal CT threshold of subtraction method for air trapping was 60 HU.

• ATI with 60 HU threshold was comparable to E/I MLD and Exp −856 .

• Emphysema may substantially contribute to air trapping with statistical significance (P < 0.001).

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Abbreviations

ATI:

Air trapping index

COPD:

Chronic obstructive pulmonary disease

DLco:

Diffusing capacity of lung for carbon monoxide

E/I ratio:

Expiration/inspiration ratio of the mean lung density

Exp−856 :

Percentage of lung voxels with attenuation below −856 HU on expiration CT

FEV1 :

Forced expiratory volume in 1 s

FEF25–75% :

Mid-expiratory phase of the forced expiratory flow

FVC:

Forced vital capacity

GOLD:

Global Initiative for Obstructive Lung Disease

KOLD:

Korean Obstructive Lung Disease

PFT:

Pulmonary function test

RV:

Residual volume

RV/TLC:

Ratio of residual volume to total lung capacity

TLC:

Total lung capacity

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Acknowledgments

The scientific guarantor of this publication is Dr. Joon Beom Seo. The authors of this manuscript declare no relationships with any companies whose products or services may be related to the subject matter of the article. This study has received funding by a grant of the Korea Healthcare Technology R&D Project, Ministry for Health and Welfare, Republic of Korea (Grant number: HI11C1552 and HI10C2020). No complex statistical methods were necessary for this paper. Institutional review board approval was obtained. Written informed consent was obtained from all subjects (patients) in this study. Some study subjects or cohorts have been previously reported in Kim et al.’s study (Eur Radiol 2015;25:541–549). Methodology: retrospective, diagnostic or prognostic study, performed at one institution.

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Authors and Affiliations

  1. Department of Radiology and Research Institute of Radiology, University of Ulsan College of Medicine, Asan Medical Center, 88 Olympic-ro 43 Gil, Songpa-gu, Seoul, 138-736, Korea

    Sang Min Lee, Joon Beom Seo, Sang Min Lee, Namkug Kim & Sang Young Oh

  2. Department of Pulmonary and Critical Care Medicine, and Clinical Research Center for Chronic Obstructive Airway Diseases, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea

    Yeon-Mok Oh

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  1. Sang Min Lee
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Correspondence to Joon Beom Seo.

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Lee, S.M., Seo, J.B., Lee, S.M. et al. Optimal threshold of subtraction method for quantification of air-trapping on coregistered CT in COPD patients. Eur Radiol 26, 2184–2192 (2016). https://doi.org/10.1007/s00330-015-4070-z

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  • DOI: https://doi.org/10.1007/s00330-015-4070-z

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