Standard CCTA is an excellent purely morphological imaging modality — but it is a poor predictor of reversible myocardial ischemia. Because the anatomic severity of a plaque doesn’t always correlate with its hemodynamic relevance, clinicians traditionally had to rely on separate stress tests to determine whether a lesion actually restricted blood flow.
Fractional Flow Reserve from CT (CT-FFR) bridges that gap — it produces both anatomic and functional/physiological assessments from a single noninvasive scan, with no additional pharmacological stress agent.
1 How the technology works
CT-FFR takes standard anatomical CCTA data and uses cloud-based supercomputers to run Computational Fluid Dynamics (CFD) modeling. The system creates a patient-specific 3D mesh model of the aorta and epicardial coronaries and simulates hyperemia to calculate pressure and flow.
The algorithms rely on three core physical principles:
- Allometric scaling law — baseline coronary blood flow is proportional to left ventricular mass
- Murray’s law & Poiseuille solution — flow rate is proportional to vessel diameter and shear stress, and inversely proportional to blood viscosity
- Hyperemic boundary conditions — model parameters tuned to simulate adenosine-induced maximal vasodilation
Processing is currently done off-site via FDA-approved platforms (e.g. HeartFlow). The CCTA dataset is uploaded; CT-FFR results return in 2–3 hours.
2 Interpreting CT-FFR values
Invasive FFR — measured with a pressure wire in the cath lab — uses a threshold of < 0.80 to indicate a hemodynamically significant lesion requiring revascularization.
CT-FFR provides pressure values throughout the entire coronary tree. Rather than a strict binary, interpret as a continuous variable:
| FFRCT | Interpretation |
|---|---|
| > 0.80 | Not significant for lesion-specific ischemia |
| 0.75 – 0.80 | Borderline for lesion-specific ischemia |
| < 0.75 | Significant for lesion-specific ischemia |
Interpretation pearls:
- A sharp pressure drop across a focal stenosis resulting in FFRCT < 0.75 is highly indicative of lesion-specific ischemia.
- A gradual pressure drop is less specific. Normal vessels experience a natural, gradual pressure drop along their length even in the absence of CAD — e.g. the distal LAD may naturally reach FFRCT > 0.90 in a clean coronary.
- Don’t refer for ICA based solely on a low end-vessel FFRCT — the location and gradient of the pressure drop matter more than the terminal number.
3 Clinical evidence & impact
CT-FFR is most clinically valuable for adjudicating moderate (50–69%) stenoses. Standard CCTA struggles with specificity in this range — particularly when calcification creates blooming artifacts that artificially inflate the appearance of stenosis.
| Trial | Finding |
|---|---|
| NXT & PACIFIC | 86–87% diagnostic accuracy vs. invasive catheterization gold standard |
| PLATFORM | Combining CT-FFR with CCTA cancelled 60% of planned ICAs and reduced invasive procedures on non-obstructive lesions |
| RIPCORD | CT-FFR data changed clinical management (medical therapy vs. PCI vs. CABG) in 36% of patients |
4 Limitations
- Image-quality requirements. Demands an exceptionally high-quality CCTA dataset — slice thickness < 1 mm, strict heart-rate control, and proper nitroglycerin administration. Real-world rejection rates due to motion or noise are around 10%.
- Diagnostic blind spots. Accuracy drops for lesions that fall into the borderline range (0.70–0.80).
- Contraindications. Cannot be reliably used in patients with extensive heavy calcification, prior stents, or surgical bypass grafts — all distort the CFD model.