Cardiac magnetic resonance (CMR) is a very versatile imaging modality. In this video from our Cardiac MRI Essentials course, cardiologist Dr Andrew Houghton will teach you when CMR is useful—and when it isn’t!
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[00:00:00] Before we look at how CMR studies are performed, we should take a moment to consider what makes an appropriate indication for a CMR study. This will allow you to use CMR to its best advantage, choosing CMR when it can offer you the best answer to whatever clinical question you may have. In this module we will be looking at CMR indications and when CMR is useful and when it isn't. So let's take a look at some of the indications that use CMR to its best advantage.
[00:00:30] CMR is an imaging modality that has developed greatly over the last 20 years and now offers an unrivaled way of assessing cardiac structure and function. Although there are, of course, other noninvasive imaging techniques such as echocardiography and nuclear imaging that can offer similar information to some aspects of CMR—CMR offers the huge advantage of combining the best aspects of these studies into a single examination.
[00:01:00] Moreover, CMR offers some significant advantages over these other imaging techniques. For example, CMR faces no restrictions to the choice of imaging planes and that offers us a great deal more flexibility to obtain exactly the views that we want of the heart. In addition, CMR doesn't face the same limitations from body habitus that we see with echocardiography. For example, in patients of a high body mass index,
[00:01:30] CMR offers us the chance to assess many different aspects of cardiac structure and function all in a single imaging study. It also offers us a high spatial and temporal resolution, which can be invaluable in assessing cardiac anatomy such as in this example here of a patient with a pseudo bicuspid aortic valve. Unlike nuclear cardiology and cardiac CT,
[00:02:00] CMR does not use ionizing radiation or radioactive isotopes. And the versatility of CMR is immense. It can assess ventricular size, both of the left and right ventricles including morphology and function. It allows us to assess myocardial mass with an accuracy that is second to none. And we can also use CMR to assess both left and right atrial size and
[00:02:30] structure. We can assess the morphology of all four heart valves. And we can also use CMR to assess blood flow, which means we can quantify the severity of stenotic valve lesions and regurgitant valve lesions. And we can also quantify the severity of any intracardiac shunts. Using late gadolinium enhance, we can assess myocardial infarction. And as part of that
[00:03:00] we can also assess myocardial viability. CMR is also valuable in assessing myocardial perfusion and we can also use CMR to assess myocardial infiltration and fibrosis. We can also use CMR to perform tissue characterization. And we can also use it to perform angiography. CMR clearly then has a wide range of applications but there are some key
[00:03:30] applications that are used most commonly. One of these is the assessment of heart failure and CMR gives us valuable information about left ventricular size and function and also helps us identify the etiology of heart failure. CMR results are commonly used to assess the cardiomyopathies including ischemic cardiomyopathy, dilated cardiomyopathy, and as in this example here, hypertrophic cardiomyopathy.
[00:04:00] CMR is also commonly used in the assessment of myocardial ischemia, as in this myocardial perfusion study in a patient with LAD disease, shown here. CMR offers a high degree of sensitivity and specificity in ischemia assessment. The use of late gadolinium enhancement imaging allows us to identify areas of myocardial infarction, as shown here, and also to assess residual myocardial viability.
[00:04:30] The right ventricle can be notoriously challenging to assess on echocardiography but with CMR it's much easier and CMR offers a gold standard way of assessing right ventricular size and function. CMR is also commonly used in the assessment of valve disease where it can assess the etiology of the valve problem. It can quantify the severity and also look for any consequences
[00:05:00] such as aortic or left ventricular dilatation. CMR also plays a valuable role in the assessment of congenital heart disease, as in this example here, that shows an atrial septal defect. And CMR can also be used to assess the structure and dimensions of the aorta, as in this case of an aortic coarctation. So, we've seen the huge
[00:05:30] versatility of CMR and what it can offer across a wide range of cardiac conditions. But what about its limitations? Well, one of the problems is that of claustrophobia. CMR scanning does take place inside quite a confined environment in the bore of the scanner and a small percentage of patients are simply unable to tolerate this. CMR does, of course, use powerful magnetic fields and this can pose a problem with certain metallic
[00:06:00] implanted devices. Patient Safety is, of course, paramount and it's therefore essential to identify any metallic objects that the patient may have implanted and to judge whether this poses any problems for the proposed CMR study. CMR studies commonly involve the use of gadolinium contrast agents and these can pose a rare but serious risk of nephrogenic systemic fibrosis
[00:06:30] in patients with underlying renal impairment. As long as these limitations are kept in mind and patient safety maintained at all times, CMR offers us a uniquely wide-ranging imaging modality that can help us address a wide range of clinical issues in cardiology. If you'd like to read more about the indications for CMR, then take a look at this 2010 expert consensus document published in the
[00:07:00] Journal of the American College of Cardiology. So in this module, you've learned how useful CMR is and how we can use it most effectively. Now you'll be able to test what you've learned in our quiz section. The quiz section is a selection of multiple choice questions and is intended to playfully reinforce what you have learned from a module. Oh, and don't miss out on the videos explaining the solution to each question. You'll learn a lot from them.