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Purpose: To compare objective and subjective assessment of the distribution of emphysema in unselected patients with chronic obstructive pulmonary disease (COPD)., Material and Methods: 167 patients were computed tomography (CT) scanned, and the relative area (RA-910) of emphysema in each CT slice was plotted against table position. The craniocaudal distribution was calculated as the slope of the regression line, and grouped as upper-lung-zone predominance (ULP), lower-lung-zone predominance (LLP), or mild/homogeneous distribution (MHE). CT scans were also classified as ULP, LLP, and MHE based on visual assessment of three high-resolution CT (HRCT) slices, and the leading pattern of emphysema was classified as centrilobular (CLE), paraseptal (PSE), panlobular (PLE), or no emphysema (NE)., Results: By objective classification, scans were divided into almost equal numbers of ULP, LLP, and MHE, whereas visual evaluation classified more scans as ULP (P<0.001) and very few as LLP (P<0.0001). In patients with CLE, 49% had ULP by objective classification, whereas LLP was the commonest leading pattern in PSE, PLE, and NE., Conclusion: We found significant discrepancies between the objective and subjective distributions of emphysema in various morphological patterns, which may be of clinical importance in, for instance, lung-volume-reduction surgery.

Purpose: To study the short-term reproducibility of lung density measurements by multi-slice computed tomography (CT) using three different radiation doses and three reconstruction algorithms., Material and Methods: Twenty-five patients with smoker's emphysema and 25 patients with alpha1-antitrypsin deficiency underwent 3 scans at 2-week intervals. Low-dose protocol was applied, and images were reconstructed with bone, detail, and soft algorithms. Total lung volume (TLV), 15th percentile density (PD-15), and relative area at -910 Hounsfield units (RA-910) were obtained from the images using Pulmo-CMS software. Reproducibility of PD-15 and RA-910 and the influence of radiation dose, reconstruction algorithm, and type of emphysema were then analysed., Results: The overall coefficient of variation of volume adjusted PD-15 for all combinations of radiation dose and reconstruction algorithm was 3.7%. The overall standard deviation of volume-adjusted RA-910 was 1.7% (corresponding to a coefficient of variation of 6.8%). Radiation dose, reconstruction algorithm, and type of emphysema had no significant influence on the reproducibility of PD-15 and RA-910. However, bone algorithm and very low radiation dose result in overestimation of the extent of emphysema., Conclusion: Lung density measurement by CT is a sensitive marker for quantitating both subtypes of emphysema. A CT-protocol with radiation dose down to 16 mAs and soft or detail reconstruction algorithm is recommended.

Purpose: To determine how to adjust lung density measurements for the volume of the lung calculated from computed tomography (CT) scans in patients with emphysema., Material and 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., Conclusion: 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.