Elsevier

Academic Radiology

Volume 21, Issue 10, October 2014, Pages 1262-1267
Academic Radiology

Original Investigation
Airflow Limitation in Chronic Obstructive Pulmonary Disease: Ratio and Difference of Percentage of Low-attenuation Lung Regions in Paired Inspiratory/Expiratory Computed Tomography

https://doi.org/10.1016/j.acra.2014.05.020Get rights and content

Rationale and Objectives

The purpose of this study was to analyze the relationship between airflow limitation and two types of computed tomography (CT) measurements: expiratory/inspiratory (E/I) ratio and E/I difference of percentage of low-attenuation lung regions (LAA%).

Materials and Methods

Thirty patients who underwent inspiratory and expiratory CT scans were included in this study. The CT data were used to calculate the LAA% E/I ratio and E/I difference. Other types of CT measurements were also obtained, including the E/I ratio and E/I difference of lung volume, mean lung density, standard deviation, skewness, and kurtosis. LAA% was calculated at 20 thresholds (−990 to −800 HU). Pearson's correlation between the measurements and forced expiratory flow in 1 second was used to determine the efficacy of LAA% E/I ratio and E/I difference. P values of <5.88 × 10−5 were considered statistically significant with Bonferroni correction.

Results

The LAA% E/I ratio and E/I difference significantly correlated with forced expiratory flow in 1 second. The best correlation coefficient for the LAA% E/I ratio was −0.699 (P = 1.75 × 10−5) and for the LAA% E/I difference was −0.723 (P = 6.53 × 10−6). The best correlation coefficient for the LAA% E/I difference was stronger than that for the other types of CT measurements.

Conclusions

The LAA% E/I ratio and E/I difference significantly correlated with airflow limitation in chronic obstructive pulmonary disease.

Section snippets

Materials and methods

The institutional review board of our hospital approved this study. Written informed consent was obtained from all patients for the use of their data.

Results

The pulmonary function test results and CT measurements are summarized in Table 1, Table 2. The correlation coefficients between LAA% and FEV1 in inspiratory and expiratory CT are shown in Table 3. The correlation coefficients of LAA% in inspiratory CT ranged from −0.517 to −0.193, and the corresponding P values ranged from .00344 to .307. In expiratory CT, the correlation coefficients of LAA% ranged from −0.644 to −0.370, and the corresponding P values ranged from 1.24 × 10−4 to .0443. In

Discussion

In the present study, we observed that the LAA% E/I ratio and E/I difference significantly correlated with airflow limitation measured by the pulmonary function test and that the LAA% E/I difference showed stronger correlation with the pulmonary function test results than the other types of CT measurements.

Airflow limitation in COPD is caused by lung parenchymal destruction and small airway disease. According to previous reports, LAA% in inspiratory CT reflected airflow limitation in the

Conclusion

The LAA% E/I ratio and E/I difference were significantly correlated with airflow limitation in patients with COPD. The LAA% thresholds in paired inspiratory/expiratory CT caused a large variability in the correlation with airflow limitation. Although it is necessary to confirm these results in a larger patient cohort, the LAA% E/I ratio and E/I difference are expected to be useful for assessing airflow limitation in COPD.

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