Slope of emphysema index: an objective descriptor of regional heterogeneity of emphysema and an independent determinant of pulmonary function.
OBJECTIVE
The purpose of this study was to compare quantitative and visual assessments of regional heterogeneity of emphysema and to investigate the influence of regional heterogeneity on pulmonary function in smoking-related emphysema.


METHODS
We developed an automatic computerized algorithm to quantitatively assess heterogeneity in the upper-lower, anterior-posterior, and central-peripheral directions. The emphysema index was plotted with a linear function (emphysema index slopes: slope of emphysema index in upper-lower direction, slope of emphysema index in anterior-posterior direction, and slope of emphysema index in central-peripheral direction) for consecutive 1-pixel-thick slices using volumetric CT data of 59 patients (58 men and one woman; mean age, 65.7 years). Emphysema index was defined as the percentage area of lung with attenuation values below -950 HU. Visual assessment was performed using a 5-point scoring system. Quantitative and visual assessments were compared. Multiple linear regression was performed to evaluate the influence of emphysema index and emphysema index slopes on the pulmonary function test.


RESULTS
Quantitative and visual assessments were significantly correlated in both upper-lower (r(2) = 0.40 and r(2) = 0.67 for observers 1 and 2, respectively) and central-peripheral (r(2) = 0.51 and r(2) = 0.47, respectively) directions. Multiple linear regression revealed that emphysema index, slope of emphysema index in upper-lower direction, and slope of emphysema index in anterior-posterior direction were independent determinants of forced expiratory volume in 1 second (FEV(1)) (r(2) = 0.30; p < 0.001). Emphysema index and slope of emphysema index in upper-lower direction were independent determinants of the ratio of FEV(1) to forced vital capacity (FEV(1)/FVC) (r(2) = 0.32; p < 0.001). In addition to higher emphysema index, lower and posterior lung dominance was associated with a decrease in FEV(1) and FEV(1)/FVC.


CONCLUSIONS
Computerized, quantitative assessment using the emphysema index slope is comparable to visual assessment in the evaluation of regional heterogeneity of emphysema. In addition to the emphysema index, regional heterogeneity of smoking-related emphysema contributes to impairment of pulmonary function.
Chae
Eun Jin
EJ
Department of Radiology and Research Institute of Radiology, University of Ulsan College of Medicine, Asan Medical Center, 388-1, Poongnap-dong, Songpa-gu, Seoul 138-736, Korea.
Seo
Joon Beom
JB
Song
Jae-Woo
JW
Kim
Namkug
N
Park
Bum-Woo
BW
Lee
Young Kyung
YK
Oh
Yeon-Mok
YM
Lee
Sang Do
SD
Lim
Seong Yong
SY
D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D011656:Pulmonary Emphysema / Q000000981:diagnostic imaging* / Q000209:etiology / Q000503:physiopathology*; D011857:Radiographic Image Interpretation, Computer-Assisted; D012129:Respiratory Function Tests; D012907:Smoking / Q000009:adverse effects*; D014057:Tomography, X-Ray Computed