Tracheal index on chest computed tomography: association
with lung function and CT-quantified measures of COPD
Poster No.:
C-0592
Congress:
ECR 2015
Type:
Scientific Exhibit
Authors:
E. Pompe , L. Gallardo Estrella , B. van Ginneken , H. J. de
1
2
3
4
2
2
1
Koning , M. Oudkerk , E. M. van Rikxoort , P. A. de Jong ,
1
1 1
F. A. A. Mohamed Hoesein , J. W. J. Lammers ; Utrecht/NL,
2
3
4
Nijmegen/NL, Rotterdam/NL, Groningen/NL
Keywords:
Lung, CT, Computer Applications-Detection, diagnosis
DOI:
10.1594/ecr2015/C-0592
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Page 1 of 7
Aims and objectives
Chronic obstructive pulmonary disease (COPD) has been associated with tracheal shape
changes. However, knowledge on the relation with lung function tests and CT-quantified
smoking related changes is lacking. Therefore, the aim of this study was to associate
the shape of the trachea on inspiratory CT with CT-quantified emphysema, air trappping
and airway wall thickness.
Methods and materials
Participants from the Dutch - Belgian Lung Cancer Screening Trial (NELSON) were
included. All participants underwent inspiratory and expiratory CT and pre-bronchodilator
pulmonary function testing. The shape of the trachea was assessed by the tracheal index
(TI), which represents the ratio of the coronal and sagittal length of the trachea. TI was
measured on each axial slice from 2.5 cm above the bifurcation of the main bronchi up
to the top of the trachea. The smallest TI was used for analyses.
th
CT-quantified emphysema was assessed by the 15 percentile (Perc15) method.
Perc15 represents the Hounsfield Unit (HU) number below which 15% of all voxels are
distributed. The closer the Perc15 is to -1000, the more emphysema is present. Airway
wall thickness was calculated by the square root of wall area for a theoretical airway with
an internal perimeter of 10 mm (pi10). Air trapping was defined as the ratio of expiratory
to inspiratory mean lung density, Expiratory/Inspiratory-ratioMeanLungDensity (E/I-ratioMLD).
One-way ANOVA tests were used to assess differences between quintiles classified by
TI.
Images for this section:
Page 2 of 7
Fig. 1: The tracheal index (TI) is computed for every axial slice from 2.5 cm above the
bifurcation of the main bronchi up to the top of the trachea. The centroid of the trachea
is computed, after which two orthogonal axes are drawn. TI is computed as the radio of
the coronal and the sagittal line.
Fig. 2: Graph showing attenuation histograms for the inspiratory and expiratory CT. The
15th percentile (Perc15) is calculated as the Hounsfield Units (HU) number below which
15% of the voxels are distributed (green area). The E/I-ratio is calculated as the ratio of
the mean lung density (MLD) on the expiratory and inspiratory image.
Page 3 of 7
Fig. 3: Pi10 is calculated after segmentation of the bronchial tree (a). Inner (yellow) and
outer (orange) wall boundaries are calculated for all bronchial cross-sections (b). From
these sections the wall area is calculated. (c) shows a line graph in which the square root
of the wall area is plotted against the internal perimeter. A regression line (dashed line) is
drawn though the measurements, from which the square root of wall area for a theoretical
bronchus with 10 mm lumen perimeter (i.e. Pi10) was calculated (dotted lines).
Page 4 of 7
Results
1,109 participants were included in this study. Based on lung function tests 437
participants were classified as COPD, of which 277 were classified as GOLD 1, 135 as
GOLD 2 and 25 as GOLD 3.
No difference was found in the number of COPD patients between the quintiles, based on
TI (p = 0.2). Our results showed that the lowest and highest TI quintiles had significantly
higher Pi10 values (p = 0.001) and E/I-ratioMLD measurements (p = 0.04) compared with
the other quintiles. Perc15 was also significantly different between the quintiles (p = 0.03).
FEV1 and FEV1/FVC were lower in the quintile with the lowest TI and in the quintile with
the highest TI (p = 0.001 and p = 0.02, respectively).
Images for this section:
Page 5 of 7
Fig. 4: Four graphs showing results of lung function tests and CT-measurements divided
by quintiles classified by the tracheal index (TI), with a) FEV1, b) Pi10, c) Perc15 and
d) E/I-Ratio.
Page 6 of 7
Conclusion
Our results show that participants with either a small or a large TI have lower lung function,
more large airway disease and more air trapping. This suggests that both a large and a
small TI can be abnormal. Further research is needed to assess the normal range of TI
and to evaluate its clinical application.
Personal information
References
1. Eom JS, Lee G, Lee HY, et al. The relationship between tracheal index and lung volume
parameters in mild-to-moderate COPD. Eur J Radiol 2013;82:e867-e872.
2. Lee HJ, Seo JB, Chae EJ, et al. Tracheal morphology and collapse in COPD:
correlation with CT indices and pulmonary function test. Eur J Radiol 2011;80(3):e531-5.
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