title: Quantitative computed tomography measurements to evaluate airway disease in chronic obstructive pulmonary disease: Relationship to physiological measurements, clinical index and visual assessment of airway disease.
abstract: OBJECTIVE
  To correlate currently available quantitative CT measurements for airway disease with physiological indices and the body-mass index, airflow obstruction, dyspnea, and exercise capacity (BODE) index in patients with chronic obstructive pulmonary disease (COPD).
  
  
  METHODS
  This study was approved by our institutional review board (IRB number 2778). Written informed consent was obtained from all subjects. The subjects included 188 current and former cigarette smokers from the COPDGene cohort who underwent inspiratory and expiratory CT and also had physiological measurements for the evaluation of airflow limitation, including FEF25-75%, airway resistance (Raw), and specific airway conductance (sGaw). The BODE index was used as the index of clinical symptoms. Quantitative CT measures included % low attenuation areas [% voxels≤950 Hounsfield unit (HU) on inspiratory CT, %LAA-950ins], percent gas trapping (% voxels≤-856HU on expiratory CT, %LAA-856exp), relative inspiratory to expiratory volume change of voxels with attenuation values from -856 to -950HU [Relative Volume Change (RVC)-856 to -950], expiratory to inspiratory ratio of mean lung density (E/I-ratioMLD), Pi10, and airway wall thickness (WT), luminal diameter (LD) and airway wall area percent (WA%) in the segmental, subsegmental and subsubsegmental bronchi on inspiratory CT. Correlation coefficients were calculated between the QCT measurements and physiological measurements in all subjects and in the subjects with mild emphysema (%LAA-950ins<10%). Univariate and multiple variable analysis for the BODE index were also performed. Adjustments were made for age, gender, smoking pack years, FEF25-75%, Raw, and sGaw.
  
  
  RESULTS
  Quantitative CT measurements had significant correlations with physiological indices. Among them, E/I-ratioMLDhad the strongest correlations with FEF25-75% (r=-0.648, <0.001) and sGaw (r=-0.624, <0.001) while in the subjects with mild emphysema subsegmental WA% and segmental WA% had the strongest correlation with FEF25-75% (r=-0.669, <0.001) and sGaw (r=-0.638, <0.001), respectively. The multiple variable analyses showed that RVC-856 to -950was an independent predictor of the BODE index showing the highest R2(0.468) as an independent variable among the QCT measurements.
  
  
  CONCLUSIONS
  Quantitative CT measurements of gas trapping such as E/I-ratioMLD, correlate better with physiological indices for airway disease than those of airway such as WA% or LD. In mild emphysema, however, quantitative CT measurements of airway correlate better with the physiological indices. RVC-856 to -950is a predictor of the BODE index.
authors: Department of Radiology, National Jewish Health, 1400 Jackson Street, Denver, CO, 80206, USA. Electronic address: nambu-a@gray.plala.or.jp.
authors: Atsushi
authors: A
authors: Nambu
authors: Department of Radiology, National Jewish Health, 1400 Jackson Street, Denver, CO, 80206, USA. Electronic address: ZachJ@NJHealth.org.
authors: Jordan
authors: J
authors: Zach
authors: Department of Radiology, National Jewish Health, 1400 Jackson Street, Denver, CO, 80206, USA. Electronic address: Joyce.schroeder@stanfordalumni.org.
authors: Joyce
authors: J
authors: Schroeder
authors: Department of Radiology, National Jewish Health, 1400 Jackson Street, Denver, CO, 80206, USA. Electronic address: gyjin@chonbuk.ac.kr.
authors: Gongyoung
authors: G
authors: Jin
authors: Department of Radiology, National Jewish Health, 1400 Jackson Street, Denver, CO, 80206, USA. Electronic address: haneul88@hanmail.net.
authors: Song Soo
authors: SS
authors: Kim
authors: Department of Medicine, National Jewish Health, Denver, CO, USA. Electronic address: kyionly@chonnam.ac.kr.
authors: Yu-Il
authors: YI
authors: Kim
authors: Department of Medicine, National Jewish Health, Denver, CO, USA. Electronic address: SchnellC@NJHealth.org.
authors: Christina
authors: C
authors: Schnell
authors: Division of Pulmonary Medicine, Department of Medicine, National Jewish Health, USA. Electronic address: BowlerR@NJHealth.org.
authors: Russell
authors: R
authors: Bowler
authors: Department of Radiology, National Jewish Health, 1400 Jackson Street, Denver, CO, 80206, USA. Electronic address: LynchD@NJHealth.org.
authors: David A
authors: DA
authors: Lynch
mesh_terms: D000368:Aged; D015992:Body Mass Index; D004417:Dyspnea / Q000000981:diagnostic imaging / Q000503:physiopathology*; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000000981:diagnostic imaging* / Q000503:physiopathology; D011656:Pulmonary Emphysema / Q000000981:diagnostic imaging* / Q000503:physiopathology; D011857:Radiographic Image Interpretation, Computer-Assisted; D012189:Retrospective Studies; D012720:Severity of Illness Index; D012907:Smoking; D014057:Tomography, X-Ray Computed / Q000379:methods
keywords: Air trapping; Airway disease; CT; Chronic obstructive lung disease (COPD); Quantitative CT