Dose-aware 5-star image quality rating in CT: Findings from the IAEA-MGH study.

OBJECTIVE: To evaluate the feasibility, reproducibility, and operational impact of a structured, dose-aware 5-star CT image quality (IQ) rating system across multiple institutions and clinical indications. MATERIALS AND METHODS: This retrospective, multinational, IAEA study included 2737 adult (1247 chest, 1490 abdomen) CT examinations across six hospitals in five countries of Europe. Three radiologists per hospital scored CT images using a standardized 5-star system designed to evaluate diagnostic IQ with consideration of radiation dose. Data collected included CT scanner type, clinical indication, patient characteristics, CTDIvol, and DLP. Inter-reader agreement, concordance of star ratings, and dose metrics were evaluated per hospital and clinical indication. RESULTS: The rating framework demonstrated robust reproducibility, with three-reader concordance reaching up to 93% in highly standardized centers and complete discordance remaining exceptionally rare (1.6% cases overall). A compelling inverse correlation between CTDIvol and star ratings was observed, especially for larger patients. Analysis by clinical indication revealed that some intrinsically noise-tolerant exams (for pulmonary nodules and kidney stones) showed high radiation exposure, highlighting an opportunity for optimization. Certain centers used higher-dose protocols, heavily skewing toward 2-star ratings. CONCLUSIONS: The 5-star CT IQ rating system is reproducible and supports dose-aware CT optimization. Noise-tolerant examinations should maintain diagnostic quality at lower radiation dose, supporting wider use of low-dose protocols. The method highlights opportunities for multinational and manufacturer-level protocol harmonization and may guide optimization strategies, including the number of series and reconstruction approaches.