Coronary inflammation read from noncontrast CT: a fat attenuation index score sharpens risk in people with zero calcium
Synopsis
Coronary inflammation could previously be measured only on contrast-enhanced coronary CT angiography, while routine calcium scoring uses low-dose noncontrast CT. A deep-learning pipeline trained and externally validated in a multicenter cohort computes a pericoronary fat attenuation index (FAI) score from noncontrast CT; the score performed comparably to the contrast-based FAI and further separated cardiovascular death and major adverse cardiovascular events among people with a calcium score of zero.
Interpretation
Coronary inflammation can be read from the noncontrast cardiac CT already acquired for calcium scoring, without a second contrast-enhanced scan. The FAI score previously depended on contrast coronary CT angiography to delineate the coronary wall, while noncontrast CT served only to compute the Agatston calcium score. In the 19,110-person external validation cohort, adding the noncontrast FAI score to the calcium score raised the area under the curve for cardiovascular death from 0.76 to 0.80, and adding the contrast FAI score raised it to 0.81, with no statistically significant difference between the two.
The method first segments the interface between the coronary lumen and perivascular fat on noncontrast CT, then computes the value under the existing FAI definition. Segmentation is guided by artificial contrast generated on the noncontrast phase to help delineate the lumen and perivascular fat interface, after which a research version of the CaRi-Heart device computes the FAI. The algorithm was developed in a 6,818-person derivation cohort from three hospitals in England and validated in consecutive patients from 10 geographically separate UK hospitals scanned for suspected coronary artery disease between 2010 and 2021, with median follow-up of 6.7 years.
The inflammation score stratifies most strongly in the people with the least calcium, precisely the group usually judged low risk. A calcium score of zero is often treated as reassuring, yet in this cohort people with a score below 100 still accounted for 42.3% of cardiovascular deaths and 50.8% of major adverse cardiovascular events. Among people with a calcium score of zero, those above the 75th percentile of the noncontrast FAI score had cardiovascular mortality rise from 1.4 to 4.0 per 1000 person-years and major adverse cardiovascular event rates rise from 5.9 to 13.3 per 1000 person-years.
Perspective
The conclusions rest on symptomatic patients with a clinical indication for coronary CT angiography, among whom the noncontrast FAI score performed comparably to the contrast FAI score; extending it to subclinical primary prevention populations requires further investigation.
Noncontrast calcium scans are commonly reconstructed at 2 to 3 mm slice thickness versus 0.6 to 0.75 mm for contrast coronary CT angiography, giving lower spatial resolution and greater partial volume effects; the role of the FAI score in selecting patients for targeted anti-inflammatory treatment remains to be explored in a clinical trial setting.