The role of coronary CT angiography and cardiac MR imaging is expanding at a rapid pace for evaluating the many facets of ischemic heart disease. In a series of review articles, the current state-of-the-art applications of CT and MR imaging in cardiac disease are highlighted in this special symposium issue of the journal, with an emphasis on coronary artery disease and myocardial ischemia.
The basic concept of hibernating myocardium is central to understanding the potential role of non-invasive imaging for assessing myocardial viability. The pathophysiology, clinical implications, available imaging techniques and, in particular, the various MR imaging techniques for evaluating myocardial viability are highlighted in the first article in this symposium by Bogaert et al.1 Late gadolinium enhancement by MR imaging has gained a central role in myocardial viability imaging, but other imaging strategies are also discussed for their utility in assessing myocardial cell integrity.
The utility and potential of parametric T1 and T2 mapping of the myocardium is attracting widespread attention and is a topic of active research. T2 mapping appears useful to characterize myocardial edema in acute infarcts, to identify the area at risk after coronary artery occlusion, and to detect acute inflammation. T1 mapping attracts much clinical interest as a technique for characterizing diffuse myocardial fibrosis, which plays a major role in many cardiac diseases that may result in heart failure and arrhythmias. In the second article in this symposium by Ferreira et al, the state-of-the-art applications of myocardial T1 and T2 mapping are summarized.2
Multidetector coronary CT angiography has made great strides and has become a widely accepted clinical tool for non-invasive coronary imaging over the last several years. It is interesting to note that whole-heart coronary MR angiography has also made great strides for reliable coronary artery imaging using high field strengths and multichannel technology. In the third article by Ishida and Sakuma, the diagnostic performance of coronary MR angiography is shown to be at a similar level as that of multidetector CT imaging.3 The added advantage of coronary flow measurements by MR techniques shows promise for characterizing the functional significance of a coronary artery stenosis.3
A paradigm shift has occurred in assessing coronary artery disease, moving away from an isolated emphasis upon lumenography to also include an estimation of the functional significance of a stenosis. Combining the assessment of the anatomic degree of coronary artery stenosis and the downstream effect on coronary flow and myocardial perfusion under resting and stress conditions is now pivotal in guiding therapy. In the fourth article by Loewe and Stadler, the state-of-the-art CT applications for determining the functional significance of a stenosis are summarized.4 For this purpose, interesting CT techniques, such as CT perfusion imaging, CT contrast gradient assessment along a coronary vessel, as well as computing the fractional flow reserve, are under active investigation.
Traditionally, cardiac CT has focused on assessing structural abnormalities and in particular anatomic visualization of coronary arteries. However, cardiac CT also allows one to assess functional aspects of cardiovascular disease. Apart from assessing the functional consequences of coronary artery stenosis, cardiac CT also provides prognostic information on global cardiac function, such as left ventricular ejection fraction, time-volume curves of ventricular filling, and aortic distensibility. The role of cardiac CT for evaluating structural and global functional heart disease is summarized in the fifth article by Sala et al.5
The versatility of multiple MR techniques for measuring heart function and flow is a particular strength of cardiac MR imaging. Functional MR imaging has become the gold standard for assessing global and regional heart function. The utility of velocity-encoded MR imaging has not only been shown for assessing the functional consequences of coronary artery disease, but also for large vessel flow estimates in valvular stenosis and regurgitation. Four-dimensional (4D) flow acquisition is broadening the scope of clinical flow imaging applications and is reviewed in the final symposium article by Calkoen et al.6 4D MR flow imaging provides improved flow quantification across cardiac valves as well as large vessel flow. Post-processing techniques are required to extract the wealth of flow information from 4D flow data sets. A number of displays are providing more insight into cardiovascular physiology and pathology. These types of display can, for example, be presented as a glyph (velocity vector field), color coding of the glyph to represent velocity magnitude, streamlines to indicate flow direction, or particle tracing to show the path line of flowing blood over time.
The authors have done a superb job in discussing and reviewing the established as well emerging cardiovascular applications in the field of non-invasive cardiac CT and MR imaging. I would like to thank all of the contributing authors, along with editor-in-chief Phil Boiselle and editorial coordinator Emily Senerth for their contributions toward initiating and completing this symposium in a timely and efficient manner.
1. Bogaert J, Gheysens O, Dymarkowski S, et al..Comprehensive evaluation of hibernating myocardium: use of noninvasive imaging.J Thorac Imaging.2014;29:134–146.
2. Ferreira VM, Piechnik SK, Robson MD, et al..Myocardial tissue characterization by magnetic resonance imaging: novel applications of T1 and T2 mapping.J Thorac Imaging.2014;29:147–154.
3. Ishida M, Sakuma H.Magnetic resonance of coronary arteries: assessment of luminal narrowing and blood flow in the coronary arteries.J Thorac Imaging.2014;29:155–162.
4. Loewe C, Stadler A.Computed tomography assessment of hemodynamic significance of coronary artery disease: CT perfusion, contrast gradients by coronary CTA, and fractional flow reserve review.J Thorac Imaging.2014;29:163–172.
5. Sala ML, Bizino MB, Amersfoort J, et al..Computed tomography evaluation of cardiac structure and function.J Thorac Imaging.2014;29:173–184.
6. Calkoen EE, Roest AA, van der Geest RJ, et al..Cardiovascular function and flow by 4-dimensional magnetic resonance imaging techniques: new applications.J Thorac Imaging.2014;29:185–196.