Discordant Quantitative and Visual CT Assessments in the Diagnosis of Emphysema

Abstract

Purpose: Visual assessment of computed tomography (CT) of the lung is routinely employed in the diagnosis of emphysema. Quantitative CT (QCT) can complement visual CT but must be well validated. QCT emphysema is defined as ≥5% of lung volume occupied by low attenuation areas ≤-950 Hounsfield units (LAA-950). Discordant visual and QCT assessments are not uncommon. We examined the association between visual and quantitative chest CT evaluation within a large cohort of subjects to identify variables that may explain discordant visual and QCT findings.

Materials and methods: Volumetric inspiratory CT scans of 1221 subjects enrolled in phase 1 of the COPDGene study conducted at the University of Iowa were reviewed. Participants included never smokers, smokers with normal spirometry, preserved ratio impaired spirometry, and Global Initiative for Obstructive Lung Disease (GOLD) stages I-IV. CT scans were quantitatively scored and visually interpreted by both the COPDGene Imaging Center and the University of Iowa radiologists. Individual-level visual assessments were compared with QCT measurements. Agreement between the two sets of radiologists was calculated using kappa statistic. We assessed variables associated with discordant results using regression methods.

Results: There was a fair agreement for the presence or absence of emphysema between our center's radiologists and QCT (61% concordance, kappa 0.22 [0.17-0.28]). Similar comparisons showed a slight agreement between the COPDGene Imaging Center and QCT (56% concordance, kappa 0.16 [0.11-0.21]), and a moderate agreement between both sets of visual assessments (80% concordance, kappa 0.60 [0.54-0.65]). Current smoking and female gender were significantly associated with QCT-negative but visually detectable emphysema.

Conclusion: The slight-to-fair agreement between visual and quantitative CT assessment of emphysema highlights the need to utilize both modalities for a comprehensive radiologic evaluation. Discordant results may be attributable to one or more factors that warrant further exploration in larger studies.

Clinical trial registration: ClinicalTrials.gov Identifier NCT000608764.

Trial registration: ClinicalTrials.gov NCT00608764 NCT00608764.

Keywords: Akaike information criterion; chest imaging; chronic obstructive pulmonary disease; interobserver agreement.

Figure 1

Overlap of discordant groups from comparisons of University of Iowa radiologists versus quantitative computed tomography (QCT) and COPDGene radiologists versus QCT. (A) Visual-only emphysema. (B) Quantitative-only emphysema.

Figure 2

Continued.

Figure 2

Examples of discordant assessments. (A) The computed tomography was visually interpreted as negative for emphysema but emphysema was identified quantitatively; axial multiplanar reformat (MPR) (upper left), low attenuation area (LAA) percentages by lung lobe (upper right), axial MPR with LAA overlay (lower left), and topographic MPR (lower right) provided. Quantitative measures correlated with spirometry in this participant. (B) Visual-only identified emphysema. Small areas identified quantitatively but were not above the LAA ≤950 Hounsfield units 5% threshold; axial MPR (upper left), LAA percentages by lung lobe (upper right), axial MPR with LAA overlay (lower left), and topographic MPR (lower right) provided. Quantitative measures also correlated with spirometry. Images courtesy of VIDA, Coralville, Iowa, USA.

Figure 3

Factors associated with discordance (multivariable stepwise logistic regression) Adjusted analysis comparing quantitative-only emphysema and visual-only emphysema (University of Iowa). Variables tested but not retained in the final model: functional residual capacity percent predicted and chronic bronchitis.

Figure 4

Sensitivity of visually-detected emphysema at various quantitative computed tomography diagnostic thresholds.