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Improving Quality of Dynamic Airway Computed Tomography Using an Expiratory Airflow Indicator Device

Hahn, Lewis, D., MD*; Sung, Arthur, W., MD; Shafiq, Majid, MD, MPH; Guo, Haiwei, Henry, MD, PhD*

doi: 10.1097/RTI.0000000000000325
Original Articles

Purpose: Dynamic computed tomography (CT) of the airways is increasingly used to evaluate patients with suspected expiratory central airway collapse, but current protocols are susceptible to inadequate exhalation caused by variable patient compliance with breathing instructions during the expiratory phase. We developed and tested a low-cost single-use expiratory airflow indicator device that was designed to improve study quality by providing a visual indicator to both patient and operator when adequate expiratory flow was attained.

Materials and Methods: A total of 56 patients undergoing dynamic airway CT were evaluated, 35 of whom were scanned before introduction of the indicator device (control group), with the rest comprising the intervention group. Lung volumes and tracheal cross-sectional areas on inspiratory/expiratory phases were computed using automated lung segmentation and quantitative software analysis. Inadequate exhalation was defined as absolute volume change of <500 mL during the expiratory phase.

Results: Fewer patients in the intervention group demonstrated inadequate exhalation. The average change in volume was higher in the intervention group (P=0.004), whereas the average minimum tracheal cross-sectional area was lower (P=0.01).

Conclusions: The described expiratory airflow indicator device can be used to ensure adequate exhalation during the expiratory phase of dynamic airway CT. A higher frequency of adequate exhalation may improve reliability and sensitivity of dynamic airway CT for diagnosis of expiratory central airway collapse.

*Stanford University Department of Radiology, Division of Thoracic Imaging

Stanford Department of Medicine, Division of Pulmonary and Critical Care Medicine, Stanford, CA

Johns Hopkins Department of Medicine, Division of Pulmonary and Critical Care Medicine, Baltimore, MD

The authors declare no conflicts of interest. This work was self-funded.

Correspondence to: Haiwei Henry Guo, MD, PhD, 300 Pasteur Dr. S-074B, Stanford, CA 94305 (e-mail:

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