Validation of computed tomographic lung densitometry for monitoring emphysema in alpha1-antitrypsin deficiency.
BACKGROUND
Lung densitometry derived from computed tomographic images offers an opportunity to quantify emphysema non-invasively, but a pathological standard cannot be applied to validate its use in longitudinal monitoring studies. Consequently, forced expiratory volume in 1 second (FEV1) remains the standard against which new methods must be judged. We related progression of densitometry (15th percentile point and voxel index, threshold -950 Hounsfield units) to disease stage and FEV1 decline in two studies of subjects with alpha1-antitrypsin deficiency (PiZ).


METHODS
Consistency of progression, measured using densitometry and FEV1, was assessed in relation to disease stage in a 2 year study of 74 subjects grouped according to the FEV1 criteria employed in the GOLD guidelines. In the second study of a subgroup of subjects with extended data (n=34), summary statistics were applied to measurements performed annually over 3 years and the rate of progression of densitometry was related to FEV1 decline.


RESULTS
The progression of percentile point was consistent across a wide spectrum of disease severity, but voxel index progression varied in association with disease stage (p=0.004). In the second study, FEV1 decline correlated with progression of lung densitometry (percentile point: rS=0.527, p=0.001; voxel index: rS=-0.398, p=0.012).


CONCLUSIONS
15th percentile point is a more consistent measure of lung density loss across a wide range of physiological impairment than voxel index. However, both methods are valid for use in longitudinal and interventional studies in which emphysema is the major outcome target.
Parr
D G
DG
Lung Investigation Unit, First Floor, Nuffield House, Queen Elizabeth Hospital, Birmingham B15 2TH, UK, and Department of Radiology, Leiden University Medical Centre, The Netherlands.
Stoel
B C
BC
Stolk
J
J
Stockley
R A
RA
D015502:Absorptiometry, Photon; D000328:Adult; D018450:Disease Progression; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D011656:Pulmonary Emphysema / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology; D012680:Sensitivity and Specificity; D012907:Smoking / Q000473:pathology / Q000503:physiopathology; D014057:Tomography, X-Ray Computed / Q000592:standards*; D019896:alpha 1-Antitrypsin Deficiency / Q000150:complications*