What is the Fat Attenuation Index (FAI)?

FAI visualised around the Right Coronary Artery, displaying attentuation of perivascular fat in the area surrounding the artery,

A novel imaging biomarker of coronary inflammation

Caristo’s new technology utilises artificial intelligence and deep-learning derived image processing algorithms to quantify arterial inflammation from data obtained from routine coronary CT angiography (CCTA).


Developed by scientists at the University of Oxford, Caristo’s novel imaging biomarker, the Fat Attenuation Index (FAI), is a measure of adipose tissue attenuation in the perivascular space caused by intra-arterial inflammation. FAI can be used to identify at-risk atherosclerotic plaques at the earliest stages of development, prior to the development of coronary calcification or a significant coronary stenosis.  FAI can be combined with other known risk factors and imaging characteristics to create a new Cardiac Risk (CaRi) score, which provides a greater level of prognostic insight compared to any existing risk-assessment biomarker.

The Science Behind FAI

Signals released from inflamed coronary arteries diffuse into the perivascular space, inhibiting local adipogenesis and adipocyte differentiation. This changes the composition of perivascular fat from the lipid to aqueous phase, causing attenuation which can be detected on CCTA. FAI is a measure of the average attenuation of signal from a volume of adipose tissue of interest on reconstructed CT. It is inversely correlated with the amount of intracellular lipids within the adipocytes. For more information, please read our publication from Science Translational Medicine.

Comparison of identical vessels with normal and abnormal FAI
Kaplan-Meier curves of all-cause and cardiac mortality with high vs low FAI

FAI is predictive of future cardiac mortality

FAI has been validated in a landmark study involving approximately 4,000 consecutive patients undergoing CCTA. Published in the Lancet, the CRISP-CT study showed even after adjusting for known cardiac risk factors, an abnormal FAI was associated with at least a 5-fold increased risk of future cardiac mortality.


Caristo’s technology can assist clinicians in making personalized treatments decisions related to a patient’s future cardiac management.