The CT part of hybrid imaging has an excellent ability to rule out anatomic CAD, but an abnormal CCTA (or an abnormal conventional angiography) is a poor predictor of ischemia. Therefore, MPI testing is recommended to identify patients who might benefit from a revascularization procedure, i.e., those with an ischemic burden >10% [26, 27]. The technologic refinements implemented in the latest generation of CT scanners have reduced the number of non-evaluable coronary segments, and further improvements may be expected. However, the two pieces of information obtained with perfusion imaging versus morphology are difficult to compare and will likely remain complementary. By contrast, the receiver operator characteristic analysis for detecting perfusion defects (by SPECT) has been shown to result in a similar area under the curve for the reference standard (conventional angiography) as for CCTA, documenting the comparable performance and limitations of both anatomic and morphologic techniques [28].

Results from a multicenter study emphasize the value of a combined functional and anatomical approach even without image fusion, i.e., without creating a hybrid image, showing that this combination allows improved risk stratification [29]. The added value of hybrid imaging seems most pronounced for functionally relevant lesions in distal segments and diagonal branches and in vessels with extensive coronary lesions of heavy calcification on CCTA. The prognostic value of cardiac hybrid imaging has been confirmed, and matched defects on hybrid imaging have been shown to be a strong predictor of major adverse cardiovascular events [30]. Cardiac hybrid imaging in CAD evaluation may have the potential to optimize the downstream resource utilization [25].