Korean J Radiol.  2015 Jun;16(3):632-640. 10.3348/kjr.2015.16.3.632.

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

Affiliations
  • 1Department of Radiology and Research Institute of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul 138-736, Korea. seojb@amc.seoul.kr

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. DeltaSV, which represents the ratio of air fraction released after exhalation, was measured with paired inspiratory and anatomically registered expiratory CT scans. Air trapping indexes, DeltaSV0.4 and DeltaSV0.5, were defined as volume fraction of lung below 0.4 and 0.5 DeltaSV, respectively. To assess the gravity effect of air-trapping, DeltaSV values of anterior and posterior lung at three different levels were measured and DeltaSV ratio of anterior lung to posterior lung was calculated. Color-coded DeltaSV map of the whole lung was generated and visually assessed. Mean DeltaSV, DeltaSV0.4, and DeltaSV0.5 were compared between healthy volunteers and asthmatics. In asthmatics, correlation between air trapping indexes and clinical parameters were assessed.
RESULTS
Mean DeltaSV, DeltaSV0.4, and DeltaSV0.5 in asthmatics were significantly higher than those in healthy volunteer group (all p < 0.05). DeltaSV 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 DeltaSV0.5 and DeltaSV0.4, showed negative strong correlation with FEF25-75, FEV1, and FEV1/FVC. DeltaSV 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 DeltaSV (the ratio of air fraction released after exhalation) shows the difference in extent of air trapping between health volunteers and asthmatics.

Keyword

Air trapping; Specific volume change; Quantitative assessment; Registration; Asthma

MeSH Terms

Adult
Aged
Asthma/*physiopathology
Exhalation/physiology
Female
Healthy Volunteers
Humans
Lung/*physiopathology/radiography
Male
Middle Aged
*Respiratory Function Tests
Tomography, X-Ray Computed/methods

Figure

  • 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 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 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).


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