Image quality assessment in low-dose COVID-19 chest CT examinations.

Background: Low-dose thoracic protocols were developed massively during the COVID-19 outbreak.

Purpose: To study the impact on image quality (IQ) and the diagnosis reliability of COVID-19 low-dose chest computed tomography (CT) protocols.

Material And Methods: COVID-19 low-dose protocols were implemented on third- and second-generation CT scanners considering two body mass index (BMI) subgroups (<25 kg/m and >25 kg/m). Contrast-to-noise ratios (CNR) were compared with a Catphan phantom. Next, two radiologists retrospectively assessed IQ for 243 CT patients using a 5-point Linkert scale for general IQ and diagnostic criteria. Kappa score and Wilcoxon rank sum tests were used to compare IQ score and CTDI between radiologists, protocols, and scanner models.

Results: In vitro analysis of Catphan inserts showed in majority significantly decreased CNR for the low dose versus standard acquisition protocols on both CT scanners. However, in vivo, there was no impact on the diagnosis: sensitivity and specificity were ≥0.8 for all protocols and CT scanners. The third-generation scanner involved a significantly lower dose compared to the second-generation scanner (CTDI of 1.8 vs. 2.6 mGy for BMI <25 kg/m and 3.3 vs. 4.6 mGy for BMI >25 kg/m). Still, the third-generation scanner showed a significantly higher IQ with the low-dose protocol compared to the second-generation scanner (30.9 vs. 28.1 for BMI <25 kg/m and 29.9 vs. 27.8 for BMI >25 kg/m). Finally, the two radiologists had good global inter-reader agreement (kappa ≥0.6) for general IQ.

Conclusion: Low-dose protocols provided sufficient IQ independently of BMI subgroups and CT models without any impact on diagnosis reliability.