title: A new quantitative index of lobar air trapping in chronic obstructive pulmonary disease (COPD): comparison with conventional methods.
abstract: OBJECTIVE
  To determine the usefulness of newly-proposed index (attenuation-volume index, AVI: increase in mean value of lung attenuation (MVLA) divided by volume decrease ratio (VDR)) for quantitative assessment of lobar air trapping (LAT) using expiratory/inspiratory (E/I) computed tomography (CT) by minimizing influence of respiratory level.
  
  
  METHODS
  Institutional review board approved study protocol. Twenty-one moderate or severe COPD (group A), 16 mild COPD (group B) and 26 normal volunteers (group C) underwent both E/I scans via 320-row CT and pulmonary functional test (PFT). Volume image data were automatically segmented into six lung lobes with minimal manual intervention. AVI, pixel index (PI), air trapping ratio (ATR) and relative volume change (RVC860-950) were calculated in total lung (TL) and each lobe. Four indices in TL were correlated with both PFT result and VDR and those in TL and each lobe were compared between three groups.
  
  
  RESULTS
  Similar to ATR, AVI correlated with both FEV1/FVC (r=0.772, p<0.01) and RV/TLC (r=-0.726, p<0.01) and demonstrated a significant difference between three groups in both TL (group A: 1.69±0.45, group B: 2.21±0.45 and group C: 2.80±0.44) and five lobes except for left lingular segment. In a lobe-based analysis regarding relationship with VDR, AVI was much less dependent than ATR, although regression lines of groups A and C were separated for AVI as well as ATR. Coefficient of variation of either PI or RVC860-950 was significantly larger than that of AVI.
  
  
  CONCLUSIONS
  AVI can be a more suitable CT index for quantitative evaluation of LAT, minimizing influence of respiratory level.
authors: Department of Radiology, Shiga University of Medical Science, Seta-tsukinowa-cho, Otsu, Shiga 520-2192, Japan. Electronic address: yatsushi@belle.shiga-med.ac.jp.
authors: Yukihiro
authors: Y
authors: Nagatani
authors: Department of Radiology, Shiga University of Medical Science, Seta-tsukinowa-cho, Otsu, Shiga 520-2192, Japan.
authors: Kiyoshi
authors: K
authors: Murata
authors: Department of Radiology, Shiga University of Medical Science, Seta-tsukinowa-cho, Otsu, Shiga 520-2192, Japan.
authors: Masashi
authors: M
authors: Takahashi
authors: Department of Radiology, Shiga University of Medical Science, Seta-tsukinowa-cho, Otsu, Shiga 520-2192, Japan.
authors: Norihisa
authors: N
authors: Nitta
authors: Division of Respiratory Medicine, Department of Internal Medicine, Shiga University of Medical Science, Seta-tsukinowa-cho, Otsu, Shiga 520-2192, Japan.
authors: Yasutaka
authors: Y
authors: Nakano
authors: Department of Radiology, Shiga University of Medical Science, Seta-tsukinowa-cho, Otsu, Shiga 520-2192, Japan.
authors: Akinaga
authors: A
authors: Sonoda
authors: Department of Radiology, Shiga University of Medical Science, Seta-tsukinowa-cho, Otsu, Shiga 520-2192, Japan.
authors: Hideji
authors: H
authors: Otani
authors: Department of Clinical Laboratory, Shiga University of Medical Science, Seta-tsukinowa-cho, Otsu, Shiga 520-2192, Japan.
authors: Hidetoshi
authors: H
authors: Okabe
authors: Health Administration Center, Shiga University of Medical Science, Seta-tsukinowa-cho, Otsu, Shiga 520-2192, Japan.
authors: Emiko
authors: E
authors: Ogawa
mesh_terms: D000368:Aged; D045853:Exhalation; D005260:Female; D006801:Humans; D001239:Inhalation; D008168:Lung / Q000000981:diagnostic imaging*; D008176:Lung Volume Measurements; D008297:Male; D011237:Predictive Value of Tests; D029424:Pulmonary Disease, Chronic Obstructive / Q000000981:diagnostic imaging* / Q000503:physiopathology; D012720:Severity of Illness Index; D014057:Tomography, X-Ray Computed / Q000379:methods
keywords: Chronic obstructive pulmonary disease; Computed tomography; Expiratory/inspiratory scanning; Lobar air trapping; Respiratory level