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Comparative Study
. 2015 May-Jun;16(3):632-40.
doi: 10.3348/kjr.2015.16.3.632. Epub 2015 May 13.

Quantitative Assessment of Global and Regional Air Trappings Using Non-Rigid Registration and Regional Specific Volume Change of Inspiratory/Expiratory CT Scans: Studies on Healthy Volunteers and Asthmatics

Eunsol Lee  1 , Joon Beom Seo  1 , Hyun Joo Lee  1 , Eun Jin Chae  1 , Sang Min Lee  1 , Sang Young Oh  1 , Namkug Kim  1
Affiliations
Comparative Study

Quantitative Assessment of Global and Regional Air Trappings Using Non-Rigid Registration and Regional Specific Volume Change of Inspiratory/Expiratory CT Scans: Studies on Healthy Volunteers and Asthmatics

Eunsol Lee et al. Korean J Radiol. 2015 May-Jun.

Abstract

Objective: The purpose of this study was to compare air trapping in healthy volunteers with asthmatics using pulmonary function test and quantitative data, such as specific volume change from paired inspiratory CT and registered expiratory CT.

Materials and methods: Sixteen healthy volunteers and 9 asthmatics underwent paired inspiratory/expiratory CT. ΔSV, which represents the ratio of air fraction released after exhalation, was measured with paired inspiratory and anatomically registered expiratory CT scans. Air trapping indexes, ΔSV0.4 and ΔSV0.5, were defined as volume fraction of lung below 0.4 and 0.5 ΔSV, respectively. To assess the gravity effect of air-trapping, ΔSV values of anterior and posterior lung at three different levels were measured and ΔSV ratio of anterior lung to posterior lung was calculated. Color-coded ΔSV map of the whole lung was generated and visually assessed. Mean ΔSV, ΔSV0.4, and ΔSV0.5 were compared between healthy volunteers and asthmatics. In asthmatics, correlation between air trapping indexes and clinical parameters were assessed.

Results: Mean ΔSV, ΔSV0.4, and ΔSV0.5 in asthmatics were significantly higher than those in healthy volunteer group (all p < 0.05). ΔSV values in posterior lung in asthmatics were significantly higher than those in healthy volunteer group (p = 0.049). In asthmatics, air trapping indexes, such as ΔSV0.5 and ΔSV0.4, showed negative strong correlation with FEF25-75, FEV1, and FEV1/FVC. ΔSV map of asthmatics showed abnormal geographic pattern in 5 patients (55.6%) and disappearance of anterior-posterior gradient in 3 patients (33.3%).

Conclusion: Quantitative assessment of ΔSV (the ratio of air fraction released after exhalation) shows the difference in extent of air trapping between health volunteers and asthmatics.

Keywords: Air trapping; Asthma; Quantitative assessment; Registration; Specific volume change.

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Figures

Fig. 1
Fig. 1. Automatic non-rigid lung registration and subtraction map.
Original CT scans of paired inspiratory (A) and expiratory (B) CT show different volumes of lung parenchyma. After non-rigid registration, expiratory CT is expanded and matched to inspiratory CT (C). Using inspiratory CT scan and registered expiratory CT scan data, subtraction color map (D) was generated.
Fig. 2
Fig. 2. ΔSV color map of healthy volunteer.
Transverse and sagittal plane maps (B, C) show anterior-posterior gradient of ΔSV. Coronal map (A) also shows difference between upper and lower lung. Rainbow color scale: red and yellow represent high values of ΔSV - large air fraction difference between paired inspiratory and registered expiratory CT. Purple, blue, and green represent low values of ΔSV - small air fraction difference between paired inspiratory and registered expiratory CT.
Fig. 3
Fig. 3. ΔSV color map of asthmatic.
Transverse and sagittal plane maps (B, C) show disappeared normal anterior posterior gradient of ΔSV, and all plane maps (A-C) show multifocal wedge-shaped air trapping areas (arrows).
See this image and copyright information in PMC

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