Fully automatic quantification of pulmonary fat attenuation volume by CT: an exploratory pilot study

Abstract

Background: Non-malignant chronic diseases remain a major public health concern. Given the alterations in lipid metabolism and deposition in the lung and its association with fibrotic interstitial lung disease (fILD) and chronic obstructive pulmonary disease (COPD), this study aimed to detect those alterations using computed tomography (CT)-based analysis of pulmonary fat attenuation volume (CTpfav).

Methods: This observational retrospective single-center study involved 716 chest CT scans from three subcohorts: control (n = 279), COPD (n = 283), and fILD (n = 154). Fully automated quantification of CTpfav based on lung segmentation and HU-thresholding. The pulmonary fat index (PFI) was derived by normalizing CTpfav to the CT lung volume. Statistical analyses were conducted using Kruskal-Wallis with Dunn's post hoc tests.

Results: Patients with fILDs demonstrated a significant increase in CTpfav (median 71.0 mL, interquartile range [IQR] 59.7 mL, p < 0.001) and PFI (median 1.9%, IQR 2.4%, p < 0.001) when compared to the control group (CTpfav median 43.6 mL, IQR 16.94 mL; PFI median 0.9%, IQR 0.5%). In contrast, individuals with COPD exhibited significantly reduced CTpfav (median 36.2 mL, IQR 11.4 mL, p < 0.001) and PFI (median 0.5%, IQR 0.2%, p < 0.001).

Conclusion: The study underscores the potential of CTpfav and PFI as imaging biomarkers for detecting changes in lung lipid metabolism and deposition and demonstrates a possibility of tracking these alterations in patients with COPD and ILDs. Further research is needed to validate these findings and explore the clinical relevance of CTpfav and PFI in lung disease management.

Relevance statement: This study introduces a fully automated method for quantifying CTpfav, potentially establishing it as a new imaging biomarker for chronic lung diseases.

Key points: This retrospective observational study employed an open-source, automated algorithm for the quantification of CT pulmonary fat attenuation volume (CTpfav). Patients with fibrotic interstitial lung disease (fILD) showed a significantly higher CTpfav and pulmonary fat index (PFI), i.e., CTpfav/CT lung volume, compared to a control group. Patients with chronic obstructive pulmonary disease (COPD) showed significantly lower CTpfav and PFI compared to the control group. CTpfav and PFI may each serve as imaging biomarkers for various lung diseases and warrant further investigation.

Keywords: Body composition; Lung diseases (interstitial); Lung volume measurements; Pulmonary disease (chronic obstructive); Tomography (x-ray computed).

Fig. 1

Depiction of the entire cohort and its subgroups. The investigated cohort of 716 patients comprised 279 patients in the control group, 283 patients with advanced COPD, and 145 patients with fILDs. COPD, Chronic obstructive pulmonary disease; fILD, Fibrotic interstitial lung disease; fNSIP, Fibrotic non-specific interstitial pneumonia; PFI Pulmonary fat index

Fig. 2

Comparison of the PFI among the different entities. Advanced COPD patients exhibited a significantly lower median CTpfav (36.2 mL, IQR 36.5–53.4 mL, p < 0.001 (a)), while patients with fILDs showed a significantly higher median CTpfav (71.5 mL, IQR 50.0–111.9 mL, p < 0.001 (a)). Compared to the control group, COPD patients had a significantly higher CT lung volume (6,765 mL, IQR 5,922–8,155 mL, p < 0.001 (b)). Conversely, patients with fILDs displayed a lower CT lung volume (3,626 mL, IQR 2,959–4,680 mL, p = 0.012 (b)). The PFI was significantly higher in patients with fILDs (2.0%, IQR 1.1–3.6%, p < 0.001 (c)). Conversely, a significantly lower PFI was observed in COPD (0.5%, IQR 0.5–0.6%, p < 0.001 (c)). Whiskers represent the 10th and 90th percentile. Only statistical significance compared to control is reported. *p < 0.05, ***p < 0.001. CTpfav, Computed tomography pulmonary fat attenuation volume; COPD, Chronic obstructive pulmonary disease; fILD, Fibrotic interstitial lung disease; PFI, Pulmonary fat index

Fig. 3

Exemplary 3D presentation of the CTpfav for one patient of each group. 3D-representation of the CTpfav for the different groups: a Control (42.1 mL), (b) COPD (36.1 mL), and (c) fILD (74.4 mL). 3D, Three-dimensional; CTpfav, Computed tomography pulmonary fat attenuation volume; COPD, Chronic obstructive pulmonary disease; fILD, Fibrotic interstitial lung disease

Fig. 4

Subanalysis of the PFI among fILD patients. Patients with IPF (CTpfav 78.9 mL, IQR 52.1–124.4 mL, p < 0.001; PFI 1.9%, IQR 1.1–3.6%, p < 0.001 (a + c)), and fNSIP (CTpfav 66.1 mL, IQR 45.1–103.2 mL, p < 0.001; PFI 2.0%, IQR 1.1–3.6%, p < 0.001 (a + c)) had significantly higher CTpfav and PFI compared to the control group (CTpfav 43.6 mL, IQR 36.5–53.4 mL, 1.0%, IQR 0.8–1.4% (a + c) but did not show significant differences among each other. Concerning the CT lung volume, patients with fNSIP (3,178 mL, IQR 2,959–4,680 mL (b)) demonstrated significantly lower values compared to the IPF (3,803 mL, IQR 3,282–4,839 mL, p = 0.016 (b)) and control group (4,228 mL, IQR 3,312–5,259 mL, p < 0.001 (b)). Whiskers represent the 10th and 90th percentile. *p < 0.05, ***p < 0.001. CTpfav, Computed tomography pulmonary fat attenuation volume; COPD, Chronic obstructive pulmonary disease; fILD, Fibrotic interstitial lung disease; fNSIP, Fibrotic non-specific interstitial pneumonia; PFI, Pulmonary fat index