Fractional Flow Reserve Measurement with Dynamic Angiographic Computed Tomography
Coronary artery disease (CAD) is one of the leading causes of death in the world and is caused by the development of atherosclerotic plaques in the coronary arteries. Management of CAD patients depends on the functional significance of CAD. The clinical gold standard metric for assessing the functional significance of CAD is fractional flow reserve (FFR), which is defined as the flow pressure gradient across a stenosis (lumen narrowing) during maximal hyperemia. A coronary stenosis with a FFR value less than 0.75 to 0.80 is considered as functionally significant. FFR is traditionally measured with a specialized pressure wire during cardiac catheterization. In the past decade, non-invasive FFR assessment from coronary computed tomography (CT) images based on computational fluid dynamics (CFD) has emerged as a promising alternative approach to the invasive FFR technique. However, there are several limitations associated with the current CFD-based CT methods in estimating FFR, such as the need of centralized processing center, long computation time (hours), reduced diagnostic accuracy in stenoses with heavy calcification and intermediate degree of lumen narrowing.
A novel analytic algorithm has been developed for non-invasive FFR assessment from CT images without the aforementioned limitations. This approach requires only one bolus injection of contrast solution and a short dynamic CT acquisition of the heart. The contrast-enhanced CT images acquired over multiple time frames are used to monitor the temporal changes of signal enhancement in the coronary arteries, from which functional variables such as absolute coronary flow velocity and flow pressure are derived, the latter is used to estimate FFR as the ratio of flow pressure distal to proximal of a stenosis. The calculation is entirely based on personalized functional information present in the dynamic CT images and no CFD simulation is used.
A prototype software has been developed based on our novel analytic algorithm. This software facilitates rapid and onsite FFR analysis of CT images to inform clinical decision making. Since intensive computer simulation is not required, there is no need to send CT images to a remote image processing center for analysis. Furthermore, this software can compute FFR for any given stenosis within a minute, which permits a much faster patient triage. Another advantage is its ability to estimate FFR for stenosis with heavy calcification. Our approach estimates FFR based on the dynamic functional information proximal and distal to a stenosis, thus is unaffected by the “blooming” artifact arising from calcification at the stenosis. Our preliminary validation data also suggests the functional assessment of intermediate coronary stenoses with our new approach is highly accurate against invasive FFR and MRI perfusion measurements.
Fractional flow reserve; Computed tomography (CT); Dynamic imaging; Coronary artery disease
Entered national phase in Canada, China, Europe, Japan, Korea and US
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