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, noninvasive 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 ED setting.
Furthermore, the DeFACTO and NXT trials reported that imaging-based estimation of FFR demonstrated only moderate diagnostic accuracy (73-80%) compared with catheter-based FFR measurement. A recent systematic review has revealed that the accuracy of FFR-CT measurement decreases as the degree of stenosis increases when compared to the gold standard catheter-based FFR measurement (Cook et al. (2017) Diagnostic accuracy of computed tomography-derived fractional flow reserve. A systematic review. JAMA Cardiol; 2(7):803-810. Accordingly, there is a continuing need for alternative methods and systems for 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. Coronary blood flow, fractional flow reserve (FFR), flow friction and 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 (luminal narrowing) is functionally significant to inform decision-making on interventional reperfusion treatment. Assessment of shear stress across an atherosclerotic plaque can provide useful insight 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, hence a more comprehensive diagnosis of coronary artery disease can be achieved. This technique can potentially be generalized for studying diseases in other organs such as assessing the hemodynamics of the carotid arteries in stroke patients.
– TRD-ACT facilitates the clinical use in both outpatients and emergency departments as it is computationally less intensive (about 1-2 minutes per patient study, minimal assumption for the calculation, based largely on real dynamic data measured) than FFR-CT (usually takes more than 24 hours per patient study, estimates drop across a coronary artery plaque based on extensive assumptions on many physiologic parameters)
– TRD-ACT is capable of simultaneously assess the large (epicardial) and small (microvascular) coronary arteries
– Hemodynamic parameters such as shear stress across a plaque can be estimate, which may lead to a more reliable prediction of the risk of plaque rupture
– A new system and method for dynamic angiographic imaging
– Non‑invasive diagnosis of coronary artery diseases
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 favorably with current CCTA techniques.
Lawson Health Research Institute are seeking partners who will either develop the method into a stand-alone software for image processing or incorporate the method into a software package that integrates with existing imaging scanners.