Quantitative and semi-quantitative computed tomography analysis of interstitial lung disease associated with systemic sclerosis: A longitudinal evaluation of pulmonary parenchyma and vessels

Abstract

Objectives: To evaluate interstitial lung disease associated with systemic sclerosis (SSc-ILD) and its changes during treatment by using quantitative analysis (QA) compared to semi-quantitative analysis (semiQA) of chest computed tomography (CT) scans. To assess the prognostic value of QA in predicting functional changes.

Materials and methods: We retrospectively selected 35 consecutive patients with SSc-ILD with complete pulmonary functional evaluation, Doppler-echocardiography, immunological tests, and chest CT scan at both baseline and follow-up after immunosuppressive therapy. CT images were analyzed by two chest radiologists for semiQA and by a computational platform for texture analysis of ILD patterns (CALIPER) for QA. Concordance between semiQA and QA was tested. Traction bronchiectasis severity was scored. Analysis of ROC curves was performed.

Results: Seventy CT scans were analyzed and QA failed in 4/70 scans. Thus, the final population included 31/35 patients (51.3±12.1 years). QA had a weak-to-good concordance with semiQA (ICC reticular:0.275; ICC ground-glass:0.667) and QA correlated better than semiQA (r = -0.3 to -0.74 vs r = -0.3 to -0.4) with functional parameters. Both methods correlated with traction bronchiectases score and pulmonary artery diameter at CT. A pulmonary artery diameter ≥29mm distinguished patients with lower lung volumes and ILD extent greater than 39% (p<0.001). Changes in QA patterns during treatment were not accurate (AUC: 0.50 to 0.70; p>0.05) in predicting disease progression as assessed by functional parameters, whereas variation in total lung volume at QA accurately predicted changes in the composite functional respiratory endpoint with FVC% and DLco% (AUC = 0.74; 95%CI: 0.54 to 0.93; p = 0.03).

Conclusions: Pulmonary QA of CT images can objectively quantify specific patterns of ILD changes during treatment in patients with SSc-ILD. Changes in QA patterns do not correlate with functional changes, but variation in total lung volume at QA accurately predicted changes in the composite functional respiratory endpoint with FVC% and DLco%. Pulmonary artery diameter at CT reflects the interstitial involvement, identifying patients with more severe prognosis.

Fig 1. 44 years-old woman showing an improvement of ILD at QA after therapy with rituximab.

PFT revealed an increase in FVC% (87% to 101%) and a decrease in DLco% (69% to 50%). Axial chest CT scans at the same level at baseline (A) and follow-up (B) show reduction of the diffuse and bilateral ground-glass opacities with a complete disappearance of the superimposed subpleural reticulation in the lower lobes. QA analysis performed by Imbio LTA shows an increase in total lung volumes (3.8L to 4.6L) and in %Normal pattern (74% to 97%) with a reduction in %GG (20% to 1%) and %Reticular (6% to 2%) patterns, as shown in the glyphs (C).

Fig 2. 46 years-old woman showing a progression of ILD at QA after therapy with rituximab.

PFT revealed a mild increase in FVC% (90% to 97%) and a stability in DLco% (27%). Axial chest CT scans at the same level at baseline (A) and follow-up (B) show increase of the diffuse and bilateral ground-glass opacities more evident in the subpleural regions in both lower lobes associated with fine intralobular reticulation. QA analysis performed by Imbio LTA shows a reduction in total lung volumes (4.4L to 3.9L) and in %Normal pattern (83% to 61%) with an increase in %GG (15% to 35%) and %Reticular (2% to 4%) patterns, as summarized in the glyphs (C).

Fig 3. ROC curve of lung volume at QA to predict the FVC and DLco composite end-point.

The variation in total lung volume calculated by Imbio LTA accurately predicted the composite functional respiratory endpoint with FVC% and DLco% (AUC = 0.74; 95%CI: 0.54 to 0.93; p = 0.03), but not changes in FVC% and DLco% alone (see also Table 6).