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Assessment of Regional Progression of Pulmonary Emphysema with CT Densitometry

¹ Division of Image Processing, Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands ² Department of Medical Statistics, Leiden University Medical Center, Leiden, the Netherlands ³ Department of Pulmonology, Leiden University Medical Center, Leiden, the Netherlands ⁴ Department of Respiratory Medicine, Gentofte University Hospital, Hellerup, Denmark ⁵ Department of Pulmonary Medicine and Allergology, Malmö University Hospital, Malmö, Sweden ⁶ Pulmonology Division, University Hospital Zurich, Zurich, Switzerland

M.E.Bakker{at}lumc.nl

Abstract

BackgroundLung densitometry is an effective method to assess overall progression of emphysema, but generally the location of the progression is not estimated. We hypothesized that progression of emphysema is the result of extension from affected areas towards less affected areas in the lung. To test this hypothesis, a method was developed to assess emphysema severity at different levels in the lungs in order to estimate regional changes.

MethodsFifty subjects with emphysema due to -1-antitrypsin deficiency (PiZ group) and sixteen subjects with general emphysema (non-PiZ group) were scanned with CT at baseline and after 30 months. Densitometry was performed in 12 axial partitions of equal volumes. To indicate predominant location, craniocaudal locality was defined as the slope in the plot of densities against partitions. Regional progression of emphysema was calculated after volume correction and its slope identifies the area of predominant progression. The hypothesis was tested by investigating the correlation between predominant location and predominant progression.

ResultsAs expected, the PiZ patients showed more basal emphysema than the non-PiZ group (craniocaudal locality, -40.0 g/L versus -6.2 g/L). Overall progression rate in PiZ patients was lower than in non-PiZ subjects. A significant correlation was found between craniocaudal locality and progression slope in PiZ subjects (R = 0.566, p<0.001). In the non-PiZ group no correlation was found.

ConclusionsIn the PiZ -group, the more emphysema is distributed basally, the more progression was found in the basal area. This finding suggests that emphysema due to -1-antitrypsin deficiency spreads out from affected areas.

Key Words: Emphysema • distribution • locality • regional progression • CT • densitometry