# Dual-energy CT based low flow rate, low dose CTPA and lung perfusion in the pulmonary diagnosis of post-COVID-19 syndrome

## TL;DR

This study shows that low-dose CT scans combined with blood tests can accurately detect lung issues in post-COVID-19 patients.

## Contribution

The study introduces a low-dose DECT method for diagnosing post-COVID-19 lung abnormalities with high accuracy.

## Key findings

- Low-dose DECT showed excellent inter-observer agreement and detected more perfused abnormal lung tissue in positive cases.
- Combining DECT with D-dimer and mMRC scores achieved a high diagnostic accuracy (AUC of 0.969).
- Positive cases had higher median age and D-dimer values but no severe symptoms beyond mMRC grade 3.

## Abstract

To investigate the diagnostic value of low flow rate, low dose DECT in combination with D-dimer values and mMRC scores, in the assessment of lung lesions in patients with post-COVID-19 syndrome who have been infected with Omicron strains.

A retrospective analysis was conducted on patients who underwent low-dose DECT pulmonary angiography (CTPA) between February 2023 and May 2024. Patients were categorized into positive or negative groups based on respiratory signs of post-COVID-19 syndrome, as determined by a respiratory physician, along with their corresponding mMRC scores. Demographic data (e.g., gender) were compared using the Chi-Square test. The Mann-Whitney U test was used for D-dimer, mean CT value, etc. The independent samples t-test was used for quantitative data (e.g., total lung volume). Inter-observer agreement for DECT parameters was assessed using the intraclass correlation coefficient (ICC). Diagnostic performance was evaluated using receiver operating characteristic (ROC) curves, with comparisons made via the Delong test.

A total of 92 cases were included. The positive group had a significantly higher median age and median D-dimer value. A higher mMRC score was associated with a greater likelihood of abnormal D-dimer values. No positive cases exceeded an mMRC grade of 3, and no severe clinical symptoms were observed. Inter-observer agreement for DECT parameters was excellent (ICC 0.8∼1.0). DECT perfusion revealed a significantly larger volume of perfused abnormal lung tissue and a lower mean iodine density in these areas in the positive group compared to the negative group (P < 0.001). The combined diagnostic model achieved a superior area under the curve (AUC) of 0.969, significantly outperforming individual parameters (P < 0.001).

The low flow rate, low dose DECT enhances patient safety and accurately identifies functional lung abnormalities not easily detected by conventional CT or CTPA. When combined with clinical data such as mMRC scores and D-dimer levels, it significantly improves diagnostic accuracy for post-COVID-19 syndrome. This approach provides an objective basis for clinical diagnosis and can help guide appropriate treatment planning.