Volume adjustment of lung density by computed tomography scans in patients with emphysema.
OBJECTIVE
To determine how to adjust lung density measurements for the volume of the lung calculated from computed tomography (CT) scans in patients with emphysema.


METHODS
Fifty patients with emphysema underwent 3 CT scans at 2-week intervals. The scans were analyzed with a software package that detected the lung in contiguous images and subsequently generated a histogram of the pixel attenuation values. The total lung volume (TLV), lung weight, percentile density (PD), and relative area of emphysema (RA) were calculated from this histogram. RA and PD are commonly applied measures of pulmonary emphysema derived from CT scans. These parameters are markedly influenced by changes in the level of inspiration. The variability of lung density due to within-subject variation in TLV was explored by plotting TLV against PD and RA.


RESULTS
The coefficients for volume adjustment for PD were relatively stable over a wide range from the 10th to the 80th percentile, whereas for RA the coefficients showed large variability especially in the lower range, which is the most relevant for quantitation of pulmonary emphysema.


CONCLUSIONS
Volume adjustment is mandatory in repeated CT densitometry and is more robust for PD than for RA. Therefore, PD seems more suitable for monitoring the progression of emphysema.
Department of Respiratory Medicine, Gentofte Hospital, Hellerup, Denmark. saher@dadlnet.dk
S B
SB
Shaker
A
A
Dirksen
L C
LC
Laursen
L T
LT
Skovgaard
N H
NH
Holstein-Rathlou
D015502:Absorptiometry, Photon / Q000379:methods; D000368:Aged; D000402:Airway Obstruction / Q000503:physiopathology; D005260:Female; D005500:Follow-Up Studies; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D001239:Inhalation / Q000502:physiology; D008168:Lung / Q000000981:diagnostic imaging* / Q000503:physiopathology; D008176:Lung Volume Measurements / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011653:Pulmonary Diffusing Capacity / Q000502:physiology; D011656:Pulmonary Emphysema / Q000000981:diagnostic imaging* / Q000503:physiopathology; D012907:Smoking / Q000009:adverse effects; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014109:Total Lung Capacity / Q000502:physiology; D014797:Vital Capacity / Q000502:physiology; D019896:alpha 1-Antitrypsin Deficiency / Q000150:complications