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Jang, Sun, Kang, Park, and Park: Emphysema Quantification Using Low Dose Chest CT: Changes in Follow-Up Examinations of Asymptomatic Smokers
Chest Radiology

Journal of the Korean Society of Radiology 2012; 66(1): 35-42.

Published online: 10 August 2015

DOI: https://doi.org/10.3348/jksr.2012.66.1.35

Emphysema Quantification Using Low Dose Chest CT: Changes in Follow-Up Examinations of Asymptomatic Smokers

Eun Ho Jang, MD1, Joo Sung Sun, MD1, Doo Kyoung Kang, MD1, Kwang Joo Park, MD2, Kyung Joo Park, MD1

1Department of Radiology, Ajou University School of Medicine, Suwon, Korea.

2Department of Pulmonary Medicine, Ajou University School of Medicine, Suwon, Korea.

Corresponding author: Kyung Joo Park, MD. Department of Radiology, Ajou University School of Medicine, 164 Worldcup-ro, Yeongtong-gu, Suwon 443-749, Korea. Tel. 82-31-219-5852, Fax. 82-31-219-5862, kjpark@ajou.ac.kr

Received 29 August 2011       Accepted 5 October 2011

Copyright © 2012 The Korean Society of Radiology

Abstract

Purpose

To evaluate the changes of emphysema quantification in a follow-up low dose CT compared with pulmonary function test (PFT) results in asymptomatic smokers.

Materials and Methods

We selected 66 asymptomatic smokers (> 40 years old) who underwent a follow-up low dose CT at least one year after the first CT as well as PFT within the same time period. Emphysema quantification was performed using an automated measurement software and an emphysema index (EI) was calculated using multiple threshold values (-970--900 HU). The interval change of EI (ΔEI) was compared with the change in the PFT values.

Results

Mean follow-up %forced expiratory volume in 1 second (88.1), %forced vital capacity (FVC) (89.5) and forced expiratory flow between 25 and 75% of vital capacity (3.21) were significantly lower compared with the values of initial tests (93.3, 93.1, 3.48). The mean EIs (2.4-25.6%) increased on follow-up CTs compared with initial EIs (2.1-24.5%), though the increase was not statistically significant. In a group with a follow-up period of 2 years or more (n = 32), EI significantly increased when using -900 HU as the threshold. The ΔEIs were poorly correlated with the ΔPFT values, but significantly correlated with ΔFVC (r = -0.32--0.27).

Conclusion

Emphysema quantification using low dose CT was not effective for the evaluation of short-term changes in less than a 2-year period, but may be used for long term follow-up series in asymptomatic smokers.

Keywords: Pulmonary Emphysema, Tomography, Spiral Computed, Follow-Up Studies, Pulmonary Function Tests

Figures and Tables

Fig. 1

Example of emphysema quantification in a 47-year-old smoker.

A. Reconstructed coronal image shows highlighted pixels in both lungs indicating lower attenuated areas with the threshold of -950 HU.
B. Volume rendering image shows automatically segmented lungs and airways in different colors.
C. Histogram analysis demonstrates calculated lung volumes, emphysema volumes and emphysema indices.
jksr-66-35-g001
Fig. 2

Box plot of EIs with the threshold of -900 HU at initial and follow-up low dose CT in a group of patients with a follow-up period of 2 years or more. Follow-up mean EI (31.5%) are significantly increased comparing with initial mean EI (27.7%) (p = 0.02). Upper and lower margins of box plot indicate 75 and 25 percentile values of EI.

Note.-EI = emphysema index
jksr-66-35-g002
Table 1

Changes in PFT Parameters at Initial and Follow-up Examinations (n = 66)

jksr-66-35-i001

Note.-*By Wilcoxon signed rank test.

FEF25-75% = forced expiratory flow between 25 and 75% of vital capacity, FEV1 = forced expiratory volume in 1 second, FVC = forced vital capacity, PFT = pulmonary function test

Table 2

Changes of EI at Initial and Follow-up Low Dose CT Scans using Various Threshold Values

jksr-66-35-i002

Note.-*Group of patients with follow-up period for 2 years or more.

†By Wilcoxon signed rank test.

EI = emphysema index

Table 3

Correlation Coefficients by Spearman Rank Correlation between Changes of PFT Parameters and EI in All Patients (n = 66)

jksr-66-35-i003

Note.-Numbers in parentheses are p values.

EI = emphysema index, FEF25-75% = forced expiratory flow between 25 and 75% of vital capacity, FEV1 = forced expiratory volume in 1 second, FVC = forced vital capacity, PFT = pulmonary function test

Table 4

Changes of PFT Parameters in Current and Former Smokers

jksr-66-35-i004

Note.-*By Wilcoxon signed rank test.

†Mean values of calculated annual change of PFT parameters.

FEF25-75% = forced expiratory flow between 25 and 75% of vital capacity, FEV1 = forced expiratory volume in 1 second, FVC = forced vital capacity, PFT = pulmonary function test

Table 5

Changes of EI in Current and Former Smokers

jksr-66-35-i005

Note.-EI = emphysema index

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