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Published in the European Journal of Radiology, the study found that the five-star system can be used consistently to assess CT image quality while taking radiation dose into account. The system was tested across six hospitals in five European countries.
"CT examinations need to provide images of sufficient quality for an accurate diagnosis, while keeping radiation exposure as low as reasonably achievable," said Madan M. Rehani, lead author of the study at Massachusetts General Hospital and Harvard Medical School in Boston, USA. "This study shows that the five-star system can help radiologists identify where CT protocols can be optimized and bring practices more in line across hospitals and countries."
Five-star System for CT Image Quality
CT imaging uses X-rays to create detailed images of the body and plays an important role in diagnosing a wide range of medical conditions. Image quality is closely linked to radiation dose. While a higher dose of radiation can reduce image noise and produce clearer images, it does not necessarily provide additional diagnostic value.
The five-star system was proposed in 2021 as an alternative to conventional rating approaches. Rather than simply rewarding sharper images, it considers whether image quality is sufficient for diagnosis at an appropriate radiation dose. An exceptionally low-noise and crisp image achieved using more radiation than necessary receives a lower rating of two stars in the scoring system, while a somewhat noisier image providing sufficient diagnostic information receives five stars.
The five-star system assesses CT image quality in consideration of radiation dose. (Source: Rehani et al., 2026)
Testing the System Across Europe
Researchers analysed 2737 CT examinations of adult patients, including 1247 chest scans and 1490 abdominal scans, covering 23 different clinical indications. At each participating hospital, three radiologists assessed the CT images using the five-star system.
The results showed that the rating system was reproducible across institutions, with agreement on image quality ratings reaching up to 93% in centres with highly standardized protocols. Cases in which all three radiologists gave different ratings were rare, accounting for 1.6% of examinations overall.
Researchers also found substantial variation in radiation doses between scanners and centres. In some cases, examinations that can tolerate more image noise, such as CT scans for pulmonary nodules, kidney stones and appendicitis, were performed using relatively high radiation doses.
"These findings suggest that the five-star method provides a simple and reliable way to translate subjective radiologist perception of image quality into a structured tool that helps adjust CT protocols at lower radiation doses when the clinical task is noise-tolerant," said Vesna Gershan, IAEA Radiation Protection Specialist and co-author of the study.
Toward Safer and More Consistent CT Imaging
By considering image quality alongside radiation dose, the five-star system could help healthcare professionals make more informed decisions for examinations of different health conditions rather than using the same imaging protocol for all clinical indications within body regions.
It could also support greater harmonization of imaging protocols across hospitals, countries and CT scanner manufacturers, which could help reduce unnecessary radiation exposure and strengthen patient safety.
The study, "Dose-aware 5-star image quality rating in CT: Findings from the IAEA-MGH study," is available online .
IAEA resources for health professionals on radiation protection and optimization in computed tomography can be found here .
