Non-invasive functional assessment using computed tomography: When will they be ready for clinical use?

Coronary computed tomography (CT) angiography is a noninvasive and accurate diagnostic tool to detect coronary artery disease (CAD), and is increasingly utilized in clinical practice. However, anatomical information from coronary CT angiography does not always provide accurate insight into whether the stenosis causes clinically significant ischemia. With a concern that widespread use of coronary CT angiography may result in excess referral of patients to invasive coronary angiography and unnecessary revascularization of non-ischemic coronary lesions, novel methods were developed to evaluate both anatomic and functional aspects of coronary stenosis. Several studies suggested that CT assessment of myocardial stress perfusion is feasible and improves the diagnostic accuracy of coronary CT angiography in the detection of hemodynamically significant stenosis. Cardiac CT protocol including both coronary CT angiography and stress/rest myocardial perfusion can simultaneously evaluate anatomical CAD and its physiological consequences. However, significant radiation exposure and a larger volume of iodinated contrast administration are required for additional perfusion imaging. Computational fluid dynamics, as applied to coronary CT angiography, enables prediction of blood flow and pressure in coronary arteries, and calculation of lesion-specific fractional flow reserve (FFR). CT-derived FFR (FFRCT) was reported to have a high diagnostic performance for detection and exclusion of ischemia-causing stenosis. Since the calculation of FFRCT is performed on simulated hyperemia, it does not require modification of typical coronary CT angiography protocols, does not require the administration of additional medication and does not confer any additional radiation. CT myocardial perfusion imaging and CT-derived computed FFR represent significant advances in the field of cardiac CT, with the ability to combine anatomical data from CT angiography together with the physiologic significance of anatomical stenosis. Such non-invasive anatomic-functional testing prior to intervention may improve patient outcomes and reduce costs. Further clinical studies are needed prior to widespread clinical adoption of these diagnostic techniques.