# Quantitative spectral computed tomography detects different patterns of airway wall thickening and contrast enhancement in infective lung disease: a feasibility study

## TL;DR

Spectral CT can detect different airway patterns in healthy people and those with pneumonia, including signs of inflammation and new blood vessels in COVID-19.

## Contribution

This study shows spectral CT can distinguish airway inflammation and neovascularization in pneumonia subtypes.

## Key findings

- Arterial phase wall thickness was increased in both pneumonia groups compared to controls.
- Airway contrast enhancement was significantly higher in COVID-19 compared to non-COVID-19 and controls.
- Spectral CT can detect airway inflammation and neovascularization in pneumonia.

## Abstract

We aimed to show that spectral computed tomography (CT) can identify different patterns of airway wall thickening and contrast enhancement in lung-healthy controls, coronavirus disease 2019 (COVID-19), and non-COVID-19 pneumonia patients, reflecting airway inflammation in both pneumonia subtypes and airway neovascularization in COVID-19.

331 subjects (age 58.9 ± 17.2 years) with 218 arterial and 113 venous phase spectral CT acquisitions were retrospectively recruited: 119 lung-healthy controls, 45 with COVID-19 and 167 with non-COVID-19 pneumonia. Scientific software was used for segmenting the airway tree. Wall thickness (WT5-10) and the difference in median maximum airway wall attenuation (slope of the spectral attenuation curve) between 40 keV and 100 keV display energy were calculated and aggregated for subsegmental airway generations 5–10 (λHU5-10). Descriptive statistics, correlations, t-tests, and ANOVA analyses were performed.

Arterial phase WT5-10 was similarly increased in COVID-19 (1.70 ± 0.44 mm) and non-COVID-19 (1.64 ± 0.53 mm) pneumonia compared to controls (1.18 ± 0.34 mm, p < 0.001). Arterial phase λHU5-10 was significantly higher in patients with COVID-19 pneumonia (3.09 ± 2.27 HU/keV) than in non-COVID-19 pneumonia (2.18 ± 1.54 HU/keV, p < 0.01) and lung-healthy controls (2.06 ± 1.11 HU/keV, p < 0.01).

Spectral CT shows significant differences in segmental wall thickness and airway contrast enhancement between COVID-19 and non-COVID-19 pneumonia and lung-healthy controls. Airway contrast enhancement may be a feasible measure to detect airway inflammation in pneumonia and neovascularization in COVID-19 pneumonia.

Question
Is spectral CT airway contrast enhancement a feasible quantitative method to detect airway inflammation or neovascularisation?

Findings
Spectral CT shows significant differences in segmental wall thickness and airway contrast enhancement between COVID-19 and non-COVID-19 pneumonia, and lung-healthy controls.

Clinical relevance
Spectral CT can be used to assess inflammatory airway diseases such as cystic fibrosis, COPD, asthma and bronchiectasis.