Hybrid imaging in diagnostics and therapy of chronic myocardial ischemia. Clinical value

Clinical studies have consistently shown that there is only a very weak correlation between the angiographically determined severity of coronary artery disease (CAD) and disturbance of regional coronary perfusion. On the other hand, the results of randomized trials with a fractional flow reserve (FFR)-guided coronary intervention (DEFER, FAME I, FAME II) showed that it is not the angiographically determined morphological severity of coronary artery disease but the functional severity determined by FFR that is critical for prognosis and the indications for revascularization. A non-invasive method combining the morphological image of the coronary anatomy with functional imaging of myocardial ischemia is therefore particularly desirable. An obvious solution is the combination of coronary computed tomography angiography (CCTA) with a functional procedure, such as perfusion positron emission tomography (PET), perfusion single photon emission computed tomography (SPECT) or perfusion magnetic resonance imaging (MRI). This can be performed with fusion imaging or with hybrid imaging using PET-CT or SPECT-CT. First trial results with PET CCTA and SPECT CCTA carried out as cardiac hybrid imaging on a 64 slice CT showed a major effect to be a decrease in the number of false positive results, significantly increasing the specificity of CCTA and SPECT. Although the results are promising, due to the previously high costs, low availability and the additional radiation exposure, current data is not yet sufficient to give clear recommendations for the use of hybrid imaging in patients with a low to intermediate risk of CAD. Ongoing prospective studies such as the SPARC or EVINCI trials will bring further clarification here.