Better Images, Lower Dose: Five-Star CT System Offers a New Path for Patient Safety

CT scans use X-rays to produce detailed views inside the body and have become an essential part of diagnosing many diseases and injuries.

A five-star approach to rating computed tomography (CT) images could give hospitals a practical way to maintain the diagnostic quality doctors need while reducing radiation doses that offer little additional clinical benefit. An IAEA-led study carried out with Massachusetts General Hospital and Harvard Medical School tested the method across six hospitals in five European countries, finding that radiologists could use the system consistently even when working across different scanners, institutions and clinical settings.

Published in the European Journal of Radiology, the study, titled 'Dose-aware 5-star image quality rating in CT: Findings from the IAEA-MGH study,' looked beyond the traditional idea that the sharpest and cleanest CT image is automatically the best. Researchers instead considered whether an image provides enough information for an accurate diagnosis while keeping radiation exposure at an appropriate level for the clinical question being investigated.

Why the Clearest CT Image Is Not Always the Best

CT scans use X-rays to produce detailed views inside the body and have become an essential part of diagnosing many diseases and injuries. Increasing radiation exposure can reduce image noise and create a sharper-looking scan, yet that extra clarity may not provide doctors with any additional information needed to make the diagnosis, leaving the patient exposed to radiation without a corresponding clinical benefit.

The five-star system, first proposed in 2021, changes how image quality is judged by connecting the appearance of the scan with the radiation dose used to produce it. A very crisp, low-noise image created with more radiation than necessary may receive only two stars, while a somewhat noisier scan that still gives the radiologist everything needed for diagnosis at a suitably low dose can earn five stars. This shifts attention from producing visually perfect images toward producing clinically useful images with responsible radiation exposure.

2,737 CT Examinations Put the System to the Test

Researchers evaluated 2,737 adult CT examinations, consisting of 1,247 chest scans and 1,490 abdominal scans covering 23 clinical indications. Three radiologists at each participating hospital independently assessed images using the five-star method, giving the research team an opportunity to see whether different specialists could apply the rating system in a similar way.

Agreement between radiologists reached as high as 93% at centres with highly standardized CT protocols, suggesting that the method can be reproducible when imaging practices are well established. Complete disagreement was uncommon, with examinations in which all three radiologists assigned different ratings representing just 1.6% of the total cases.

Some Scans May Be Using More Radiation Than Needed

The study also uncovered considerable differences in radiation doses between CT scanners and participating centres. Certain examinations were performed at relatively high doses even when the diagnostic task could tolerate more image noise, highlighting opportunities for hospitals to reconsider how their scanning protocols are configured.

Pulmonary nodule, kidney stone and appendicitis examinations were among the examples identified by researchers as situations where greater image noise may still allow radiologists to obtain the information required for diagnosis. A dose-aware rating could help imaging teams recognize when a scan is technically excellent but unnecessarily radiation-intensive, then adjust the protocol without compromising its clinical usefulness.

Madan M. Rehani, lead author of the study at Massachusetts General Hospital and Harvard Medical School, said the findings show how the system could help radiologists identify areas where CT protocols can be optimized while encouraging more consistent practices between hospitals and countries.

A More Patient-Focused Way to Set CT Protocols

Many CT protocols are organised around the part of the body being examined, yet different medical questions within the same body region do not always require identical image quality. A dose-aware approach gives healthcare professionals another way to tailor scans to the specific clinical task rather than relying on a broadly similar imaging standard for every patient and indication.

Vesna Gershan, IAEA Radiation Protection Specialist and study co-author, described the five-star method as a simple way of turning radiologists' subjective assessment of image quality into a structured tool that can guide dose adjustments, particularly when the clinical task can tolerate greater image noise.

Wider adoption could also encourage hospitals, countries and CT scanner manufacturers to work toward more consistent imaging practices. The central principle is straightforward: the best CT scan is not necessarily the one that looks the sharpest, but the one that provides enough diagnostic information while avoiding radiation that the patient does not need.