CT and MRI techniques have also been developed to evaluate myocardial perfusion. Currently, in MPI, MR is more widely used than CT. Both are performed with the patient at rest and the results are compared to perfusion under adenosine stress. MR perfusion imaging provides dynamic information on the wash-in of gadolinium-based contrast agents into the myocardium. Ischemia will be visualized during stress MR perfusion as a perfusion defect (“cold spot”). CT perfusion is more static and provides perfusion information mostly at a fixed time point in a non-dynamic manner. The difference between ischemic and normal myocardium is far greater on MR than on CT imaging.

Cross-sectional CT and MR imaging are well suited to assess the gross morphology of the heart and large vessels. CT is currently routinely applied to evaluate acute chest pain (life-threatening coronary occlusion, aortic dissection, and pulmonary embolism should initially be excluded). However, it should be noted that the differential diagnosis of acute chest pain is quite extensive and many other causes may be incidentally diagnosed by CT (e.g., pneumonia, lung disease, chest wall disease, pericardial disease). In many hospitals “excluding pulmonary embolism” is a very common and sometimes misused indication for urgent CT of the chest. In the emergency setting, CT is a preferred technique due to its speed availability, robust image quality, and ease of use in acutely ill patients who may require assisted ventilation and direct supervision. The complications of ischemic heart disease may be well shown by CT and/or MR imaging (e.g., scar, aneurysm, contained rupture, thrombus).

MR imaging is a versatile technique for evaluating many aspects of ischemic and non-ischemic heart disease. In stable patients with suspected CAD, imaging will mostly focus on the detection of coronary stenosis and defining the functional significance of the stenosis. The focus of imaging will be different in patients with suspected acute coronary syndromes (acute infarction, unstable angina pectoris). In the acute setting it will be important to use imaging tools to diagnose or exclude coronary occlusion, especially when the clinical signs and symptoms are inconclusive. CCTA is an excellent gatekeeper for excluding CAD in the emergency room setting and thereby decrease the length of stay of patients in the hospital. MR MPI has also successfully been employed as a gatekeeper in the emergency room setting for the exclusion of ischemia due to coronary artery stenosis. After coronary artery occlusion, the dependent myocardium distal from the occluded coronary artery is at risk of necrosis, thus mandating early and timely intervention. The area at risk may be visualized on T2-weighted MR sequences, which will show a region of high signal intensity due to developing edema in the area at risk. Early intervention may prevent myocardial necrosis in the area at risk (“aborted” infarction). The necrosis develops over several hours, starting as a wavefront at the endocardial site within the confines of the area at risk that, when not halted by intervention, then progresses over time and may fill the entire area at risk. There is some discussion as to whether T2-weighted techniques are reliable enough for quantification of the risk area, because of potential imaging artifacts. Nonetheless, MR-based estimates of the area at risk have been incorporated as end-points in several cardiology trials.

The wave front of progressing necrosis can be defined very accurately by late gadolinium enhancement (LGE). Combining LGE and T2-weighted MR images is an option to assess the infarct:risk ratio as an important clinical parameter. LGE has been used for over 25 years to characterize myocardial necrosis, in both the acute setting and chronic setting. T2-weighted MR techniques may be useful to distinguish acute from chronic infarcts. Acute infarcts will show LGE in conjunction with high myocardial signal (acute edema) in the area at risk, whereas chronic infarcts will show LGE in the absence (no edema present) of high signal intensity in the myocardium at risk.

The epidemic growth of the number of patients suffering from heart failure constitutes a diagnostic and therapeutic challenge. CT and MR imaging are playing an increasingly important role in the work-up and follow-up of patients with heart failure. The diagnostic challenge in heart failure is to identify its most likely cause. First and foremost, it is important to exclude CAD, e.g., by using CCTA to exclude coronary stenosis and plaques. However, it may also be important to evaluate the myocardium directly, to assess the presence of myocardial scar and infarction, because in a small number of patients infarction may be present after recanalization of a previously occluded coronary artery. In this respect LGE by MR imaging has a central role in the identification of ischemic myocardial scar (i.e., subendocardial LGE).

The MR protocol in the evaluation of patients with heart failure includes functional imaging (global and regional function), velocity-encoded MR to assess mitral flow, T2-weighted sequences to assess edema, T1-weighted sequences (T1 mapping with techniques such as Look-Locker technique or modified Look-Locker inversion recovery sequences) to assess diffuse fibrosis and other diffuse myocardial infiltration unseen with LGE, and LGE sequences to assess scar location, size, and distribution. The combined assessment of the location and extent of ischemic scar, the presence and severity of secondary mitral regurgitation, and precise estimates of left ventricular volumes provide a surgical road-map for planning scar resection in conjunction with mitral valve repair (e.g., Dor procedure).