Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand.
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Keywords: Cardiovascular Magnetic
Page: 846 - 848
Cardiovascular magnetic resonance (CMR) is a new promising technique in the field of cardiovascular disease.ÿCMR can provide information in many aspects including myocardial systolic function and regional wall motion, myocardial perfusion, viability, and anatomy of the coronary arteries in a one-stop fashion.
CMR has been considered the gold standard for the assessment of global and regional cardiac function.ÿ Because of its high spatial resolution, 3-dimensional image acquisition and the derivation of left ventricular ejection fraction without geometric assumption of the left ventricle (Fig 1), information from CMR is very accurate and had little variation compared to those derived from echocardiogram.1ÿ Therefore, CMR is suitable not only for clinical use but also for research purposes, since it needs smaller sample size.2
Evaluation of myocardial ischemia by CMR can be performed either by assessment of myocardial perfusion reserve and dobutamine stress magnetic resonance imaging (MRI).ÿ Both dipyridamole and adenosine can be used to assess myocardial perfusion reserve.ÿ Perfusion MRI can be performed by the use of multi-slice first pass technique with gadolinium injection (Fig 2 and 3).3ÿ Semi-quantitative post-processing analysis can also be performed by comparing the upslope of increasing signal intensity of first pass images during stress and during rest.4ÿ With its high spatial resolution, this method has been reported to have high accuracy in the diagnosis of coronary artery disease.ÿ Recent studies showed that, by the use of 3-slice technique, sensitivity, specificity and accuracy of perfusion MRI in the diagnosis of CAD was 88%, 90% and 89%.5
CMR is currently the gold standard for the assessment of myocardial viability.ÿ Gadolinium enhances in the area of scar tissue and can be visualized by CMR (Fig 4).ÿ Increased signal intensity on delayed-enhancement MRI images is related to the altered sarcolemmal membrane integrity during acute injury and extracellular matrix structure and an expanded volume of distribution of gadolinium in scar tissue late after injury.6,7ÿ Although infarct mass calculated from delayed-enhancement MRI may be slightly decreased early after MI,8 this technique has been shown to be highly reproducible.9,10ÿ Among 181 segments with subendocardial infarction identified by MRI, SPECT can detect abnormality in only 47%.11ÿ Myocardial scar by MRI has a good correlation with scar by pathology.12ÿ Reversibility of myocardial dysfunction in patients with ischemic cardiomyopathy is highly correlated with information from delayed-enhancement MRI.13
Despite the progress in prevention and early diagnosis, coronary artery disease remains the leading cause of death in both men and women.ÿ Invasive X-ray coronary angiography remains the ‘gold standard’ for the diagnosis of significant coronary artery disease.ÿ Although numerous noninvasive tests are available to help discriminate between those with and without significant angiographic disease, up to 40% of patients referred for X-ray angiography are found to have no significant stenosis.ÿ Despite the absence of the disease, these individuals remain exposed to the cost, inconvenience, and potential morbidity of X-ray angiography.ÿ Because mechanistic revascularization of proximal coronary disease has the greatest impact on survival, it would be desirable to have a noninvasive method that allows direct visualization of the proximal segments of coronary arteries for the accurate identification, exclusion, or both of significant atherosclerotic disease.
Coronary artery anatomy can also be visualized by MRI without the need for contrast agent administration (Fig 5).14,15 Coronary artery MRI has been reported to correlate well with coronary angiography.ÿ Although image resolution of coronary artery MRI is less than that of coronary angiography, complementary information of functional, ischemia and viability data make MRI a promising and robust tool for the assessment of patients with coronary artery disease especially those with left ventricular systolic dysfunction. Not only in the aspect of differentiation of ischemic cardiomyopathy and dilated cardiomyopathy,16 but also in the aspect of whether revascularization procedure should be performed in patients with ischemic cardiomyopathy.13ÿ Although beneficial information of CMR has been documented in the assessment of myocardial perfusion, viability and coronary anatomy separately, one-stop examination concept of CMR should make it even more beneficial.ÿ
The practice of cardiology includes a number of noninvasive imaging techniques that provide means by which to diagnose and evaluate the impact of treatment for cardiovascular disease.ÿ Unfortunately, it has been difficult for practitioners to keep up with the technological advancement.ÿ Naturally, diagnostic evaluation begins with a comprehensive history and a physical examination.ÿ However, the application of advanced imaging techniques allows substantially more information to enhance diagnostic precision and generate additional patho-physiological insight.ÿ Conventional radiographic, radionuclide, and echocardiographic techniques are firmly established as important diagnostic tools; and, clinicians generally have a good understanding of the physical principles on which they are based and the indications for their applications.ÿ Techniques of CMR have emerged over the past 2 decades as cost-effective methods of diagnosing and making prognoses in cardiovascular diseases. ÿÿ CMR, however, is a new field in cardiology.ÿ It has enormous potential because of its major attributes of high image quality and resolution combined with non ionizing radiation and versatility.ÿ With recent major technological advances there has been a quantum leap in acquisition speed and image quality that makes its use in ischemic heart disease robust and clinically valuable.
Physicians should be aware of the clinical utility of CMR in view of its advantages over other modalities.ÿ Substantial growth in the applications of MRI should be anticipated during the early part of this new millennium.ÿ Nevertheless, CMR methods continue to be somewhat of a mystery to most practitioners.ÿ This is related to a number of questions such as the complexity of the technology and the lack of systems capable of generating cardiovascular studies.
In conclusion, CMR has the potential to combine all aspects of non-invasive cardiac diagnostics.ÿ It already offers greater sensitivity and specificity than other techniques, with precisely reproducible slice planes, and good spatial and temporal resolution.ÿ In its present form, CMR offers significant advantages in studies of cardiac function and anatomy.ÿ CMR can also be used to assess myocardial perfusion and allow accurate detection of significant coronary artery disease.ÿ It may be used to screen patients with suspect coronary artery disease and avoid cardiac catheterization.ÿ
Figure 1. Magnetic resonance images of the end-diastolic (upper) and end-systolic (lower) phases of the 3 short axis slices at the apical (left), mid (middle) and basal (right) part of the left and right ventricles including the measurement of volumes and masses.
Figure 2. First-pass contrast (Gd-DTPA) study to assess myocardial perfusion in short axis view of mid level of left ventricle. The images show 4 different phases during the passage of contrast agent. The left upper image is the image during contrast enter right
Figure 3. First-pass gadolinium images showed delayed perfusion in anteroseptal wall reflected by a decrease in signal intensity in the ischemia area (arrow) compared to other regions.
Figure 4. Delayed-enhancement images showed increased signal intensity in area of myocardial scar in anterior wall.
Figure 5. Transverse slice at the level of aortic route showed left anterior descending artery (LAD) on the left, left circumflex artery (LCX) in the middle and right coronary artery (RCA) on the right.
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