Photon-Counting CT Improves ARDS Chest Imaging

Chest CT plays a central role in the diagnosis and monitoring of acute respiratory distress syndrome (ARDS), particularly when clinicians need to assess lung parenchyma, pulmonary perfusion and possible complications such as pulmonary embolism. A retrospective observational analysis published in Emergency Radiology compared photon-counting detector CT (PCD-CT) with conventional energy-integrating detector CT (EID-CT) in contrast-enhanced chest imaging of patients with ARDS. The comparison focused on image quality and radiation exposure in a critically ill population undergoing routine clinical care. PCD-CT produced higher subjective and objective image quality than EID-CT, while radiation dose metrics showed no significant difference between the two CT technologies.

Patient Cohort and Imaging Approach

The cohort came from a specialised supra-regional ARDS centre and included patients with confirmed ARDS who underwent chest CT between April 2023 and May 2025. Among 531 patients with ARDS who received chest CT, 80 underwent PCD-CT. Of these, 59 received contrast-enhanced examinations. The median age was 51.7 years and 62.7% were male. In 32 patients, contrast-enhanced scans were available for both PCD-CT and EID-CT during the same hospital stay, with a maximum interval of four weeks between examinations.

All included patients had pneumonia at admission or during hospitalisation. Severe ARDS was present in 88.1% of the contrast-enhanced PCD-CT cohort, while 11.9% had moderate ARDS. Sepsis was present in 88.1% of patients and 74.6% underwent extracorporeal membrane oxygenation therapy. Overall mortality reached 67.8%.

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Contrast-enhanced chest CT used an arterial mixed phase intended to provide simultaneous enhancement of the pulmonary arteries, aorta and lung parenchyma. The indication covered lung parenchymal assessment, pulmonary perfusion assessment and exclusion of pulmonary arterial embolism.

Higher Image Quality Across Key Measures

PCD-CT achieved higher subjective image quality scores than EID-CT in the 32-patient intraindividual group. Two radiologists independently assessed sharpness, contrast, noise, artefacts and overall diagnostic acceptability using a six-point Likert scale. PCD-CT achieved significantly higher scores for sharpness, contrast and overall diagnostic acceptability, as well as for noise. Artefact scores did not differ significantly between PCD-CT and EID-CT.

Median PCD-CT scores reached the highest category for sharpness, contrast and overall diagnostic acceptability. Noise and artefact ratings also remained high. EID-CT also achieved acceptable diagnostic quality, but median scores were lower for sharpness, contrast, noise and diagnostic acceptability. Inter-reader agreement was moderate overall.

Objective assessment also favoured PCD-CT. Signal and signal-to-noise ratio values were significantly higher with PCD-CT across all evaluated anatomical regions. The thoracic aorta, pulmonary trunk and lung parenchyma all showed higher signal-to-noise ratios with PCD-CT than with EID-CT. Noise values did not differ significantly in these regions. The objective pattern therefore reflected higher signal intensity rather than a major difference in measured noise.

Pulmonary embolism was detected in 18.6% of patients in the broader contrast-enhanced PCD-CT cohort. Most emboli were peripheral. No pulmonary emboli appeared on PCD-CT that had not been detected on EID-CT.

Radiation Exposure Shows No Significant Difference

Radiation exposure did not differ significantly between PCD-CT and EID-CT in the intraindividual comparison. Median CT dose index volume was 8.2 mGy for PCD-CT and 7.7 mGy for EID-CT. Median dose-length product was 435 mGycm for PCD-CT and 297 mGycm for EID-CT. Although median values were numerically higher with PCD-CT, the differences were not statistically significant.

Organ dose estimates were available for a subset of examinations through dose monitoring software. In 17 patients, effective dose and organ dose estimates were available for both PCD-CT and EID-CT, enabling paired comparison. Median effective dose was 4.09 mSv for PCD-CT and 3.81 mSv for EID-CT. Effective dose and organ doses showed no significant difference between the two modalities.

The analysis also recorded the wider CT burden in this population. Most patients who underwent contrast-enhanced PCD-CT received more than one CT examination during the same hospitalisation, with a median of three chest CT scans per patient. This reflects repeated imaging in a clinically complex population with high rates of severe ARDS, sepsis, ECMO therapy and complications.

The retrospective design, single-centre setting and relatively small intraindividual sample limit generalisability. The interval between paired examinations could also introduce variation related to disease progression or treatment.

In contrast-enhanced chest CT for ARDS, PCD-CT provides higher image quality and diagnostic acceptability than conventional EID-CT without a significant difference in radiation dose. The advantage appears across subjective radiologist ratings and objective signal-to-noise measurements, while artefact burden and dose metrics remain comparable. In a critically ill cohort with frequent severe ARDS, sepsis, ECMO use and pulmonary complications, improved image quality may support diagnostic assessment under challenging clinical conditions. Further evaluation would need to clarify whether image quality gains affect clinical management or outcomes.

Source: Emergency Radiology

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