J Korean Soc Radiol.  2012 Jan;66(1):35-42. 10.3348/jksr.2012.66.1.35.

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

• Jang EH
• Sun JS
• Kang DK
• Park KJ
• Park KJ

• KMID: 2208868
• DOI: http://doi.org/10.3348/jksr.2012.66.1.35

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 (DeltaEI) 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 DeltaEIs were poorly correlated with the DeltaPFT values, but significantly correlated with DeltaFVC (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.

MeSH Terms

Emphysema
Follow-Up Studies
Pulmonary Emphysema
Respiratory Function Tests
Thorax
Tomography, Spiral Computed
Vital Capacity

Figure

• 

  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.

• 

  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

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