The clinical gold standard for assessing the functional significance of a coronary artery stenosis is the invasive fractional flow reserve (FFR) technique, in which a specialized catheter is advanced to the culprit artery with aids of fluoroscopy to measure the flow pressure gradient across a plaque during maximal hyperemia. Recently, non-invasive assessment of FFR using CT coronary angiography (CCTA) images has emerged as a promising avenue for evaluation of higher risk patients requiring anatomical and functional assessment for coronary artery disease (CAD). However, at the present time, FFR evaluation by CCTA requires extensive post-processing and calculation (often greater than 24 hours) and, therefore, is not presently suitable for evaluation of patients in the emergency department setting.
Furthermore, clinical studies (i.e. DeFACTO and NXT trials) reported that imaging based estimation of FFR demonstrated only moderate diagnostic accuracy of 73% to 80% compared with catheter-based FFR measurement. This accuracy decreases as the degree of stenosis increases when compared to the gold standard method. Therefore, there is a continuing need for alternative methods and systems for accurate imaging based assessment of a blood vessel in a subject.
Our researchers have developed a novel time-resolved dynamic angiographic computed tomography (TRD-ACT) method to facilitate the assessment of the hemodynamics in epicardial coronary arteries. Various measurements (e.g. coronary blood flow, fractional flow reserve (FFR), flow friction, turbulence indexes and shear stress) in each coronary artery can be assessed directly from the dynamic contrast-enhanced heart images acquired from myocardial perfusion imaging.
FFR measurement can be used to evaluate whether a stenosis (narrowing of the artery lumen) is functionally significant to inform decision-making on interventional reperfusion treatment. Assessment of shear stress across an atherosclerotic plaque also provide useful insights on the risk of plaque rupture, which may allow earlier prevention of thrombosis. The TRD-ACT technique can facilitate simultaneous assessment of large (epicardial) and small (microvascular) coronary arteries from the same set of dynamic CT images. This enables the physicians to obtain a more comprehensive diagnosis of coronary artery disease. In general, this technique is useful for the study of diseases in other organs such as assessing the hemodynamics of carotid arteries in stroke patients.
The core theoretical basis and methodology of TRD-ACT are established. The method has been tested in several clinical studies. Preliminary results are available and compare favorable with current CCTA techniques.