title: Improved CT-based estimate of pulmonary gas trapping accounting for scanner and lung-volume variations in a multicenter asthmatic study.
abstract: Lung air trapping is estimated via quantitative computed tomography (CT) using density threshold-based measures on an expiration scan. However, the effects of scanner differences and imaging protocol adherence on quantitative assessment are known to be problematic. This study investigates the effects of protocol differences, such as using different CT scanners and breath-hold coaches in a multicenter asthmatic study, and proposes new methods that can adjust intersite and intersubject variations. CT images of 50 healthy subjects and 42 nonsevere and 52 severe asthmatics at total lung capacity (TLC) and functional residual capacity (FRC) were acquired using three different scanners and two different coaching methods at three institutions. A fraction threshold-based approach based on the corrected Hounsfield unit of air with tracheal density was applied to quantify air trapping at FRC. The new air-trapping method was enhanced by adding a lung-shaped metric at TLC and the lobar ratio of air-volume change between TLC and FRC. The fraction-based air-trapping method is able to collapse air-trapping data of respective populations into distinct regression lines. Relative to a constant value-based clustering scheme, the slope-based clustering scheme shows the improved performance and reduced misclassification rate of healthy subjects. Furthermore, both lung shape and air-volume change are found to be discriminant variables for differentiating among three populations of healthy subjects and nonsevere and severe asthmatics. In conjunction with the lung shape and air-volume change, the fraction-based measure of air trapping enables differentiation of severe asthmatics from nonsevere asthmatics and nonsevere asthmatics from healthy subjects, critical for the development and evaluation of new therapeutic interventions.
authors.affiliation: Department of Mechanical and Industrial Engineering, The University of Iowa, Iowa City, Iowa; IIHR-Hydroscience & Engineering, The University of Iowa, Iowa City, Iowa; Department of Biomedical Engineering, The University of Iowa, Iowa City, Iowa;
authors.forename: Sanghun
authors.initials: S
authors.lastname: Choi
authors.affiliation: Department of Biomedical Engineering, The University of Iowa, Iowa City, Iowa; Department of Radiology, The University of Iowa, Iowa City, Iowa; Department of Internal Medicine, The University of Iowa, Iowa City, Iowa;
authors.forename: Eric A
authors.initials: EA
authors.lastname: Hoffman
authors.affiliation: Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh, Pittsburgh Pennsylvania; and.
authors.forename: Sally E
authors.initials: SE
authors.lastname: Wenzel
authors.affiliation: Departments of Internal Medicine and Pediatrics, Washington University School of Medicine, St. Louis, Missouri.
authors.forename: Mario
authors.initials: M
authors.lastname: Castro
authors.affiliation: Department of Mechanical and Industrial Engineering, The University of Iowa, Iowa City, Iowa; IIHR-Hydroscience & Engineering, The University of Iowa, Iowa City, Iowa; ching-long-lin@uiowa.edu.
authors.forename: Ching-Long
authors.initials: CL
authors.lastname: Lin
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D001249:Asthma / Q000000981:diagnostic imaging / Q000503:physiopathology*; D005260:Female; D005541:Forced Expiratory Volume; D005652:Functional Residual Capacity; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008176:Lung Volume Measurements / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed; D014109:Total Lung Capacity; D014132:Trachea / Q000503:physiopathology
keywords: air trapping; asthma; lung mechanics; protocols; quantitative computed tomography
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