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/m2 and >25 kg/m2). 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 CTDIvol 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 (CTDIvol of 1.8 vs. 2.6 mGy for BMI <25 kg/m2 and 3.3 vs. 4.6 mGy for BMI >25 kg/m2). 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/m2 and 29.9 vs. 27.8 for BMI >25 kg/m2). 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.

New image quality and dose reduction technique for pediatric digital radiography.

PURPOSE: The purpose of this study was to test a new post-processing and denoising engine for patient dose reduction while maintaining diagnostic image quality (IQ) in pediatric digital radiography (DR). MATERIALS AND METHODS: Pediatric DR images of the thorax, pelvis, abdomen and spine obtained in 174 patients (102 males, 72 females; mean age, 2±1.8 [SD] years; age range: 6 months-9 years) were retrieved. Artificial noise was added to the images to simulate acquisitions at 50%, 32% and 12.5% of the routine dose levels. A total of 696 images corresponding to four dose levels were post-processed using S-Vue™ and further blindly scored by three pediatric radiologists using a scoring grid of 4-6 criteria specifically defined per anatomical area. The mean score was assessed for each area and weight class (5-15 and 15-30kg) and compared across the simulated low dose images. Paired Wilcoxon test was used with a threshold difference of 0.5 (half a criterion) between scores to highlight a significant reduction in image quality. Inter-rater reliability was assessed using intraclass correlation coefficient (ICC). RESULTS: Only the 50% reduced dose images showed non-inferiority when compared to routine images for all of areas and weight classes (P<0.01). Very good inter-rater reliability of the overall scores was observed for the pelvis in the 5-15kg weight class (ICC=0.85) for images at full dose, 50% and 32% reduced dose. For the remaining areas (thorax, abdomen and spine) and weight classes, inter-rater reliability was moderate (ICC: 0.3-0.6). CONCLUSION: S-Vue™ post-processing software allows a two-fold radiation dose reduction while maintaining satisfactory IQ in pediatric DR.