What is Cardiac Magnetic Resonance Imaging?
Cardiac magnetic resonance imaging (CMR), also known as cardiac MRI, is a non-invasive diagnostic imaging technique that provides detailed information about the structure and function of the heart. It utilizes a powerful magnetic field and radio waves to create high-resolution images of the heart, allowing healthcare professionals to evaluate cardiac anatomy, assess myocardial function, and detect various cardiovascular conditions.
CMR works by aligning the hydrogen atoms in the body’s tissues using a strong magnetic field. When radio waves are applied, the hydrogen atoms emit signals that are captured by specialized detectors, enabling the creation of detailed images. By manipulating different imaging parameters, such as magnetic field strength and timing, CMR can provide a wealth of information about the heart’s structure and function.
One of the main applications of CMR is the assessment of myocardial function. It can accurately measure the heart’s pumping capacity, known as the ejection fraction, and evaluate the movement of the heart muscle during each cardiac cycle. This information is invaluable in diagnosing conditions such as heart failure, cardiomyopathies, and myocardial infarction.
CMR is also highly effective in evaluating cardiac anatomy. It can provide detailed images of the heart’s chambers, valves, and blood vessels. This allows for the detection of structural abnormalities, such as congenital heart defects, valve disorders, and the presence of tumours or masses. Additionally, CMR can assess blood flow patterns, making it useful in evaluating conditions like aortic aneurysms, pulmonary hypertension, and congenital heart diseases involving abnormal blood flow.
According to leading cardiovascular surgeon Dr Ramji Mehrotra, one of the unique strengths of CMR is its ability to provide tissue characterization. With specialized techniques, such as late gadolinium enhancement (LGE), CMR can identify areas of scar tissue or fibrosis within the heart muscle. This is particularly useful in assessing myocardial viability after a heart attack or identifying the extent of fibrosis in conditions like hypertrophic cardiomyopathy or cardiac amyloidosis.
CMR is a safe procedure with minimal risks. Unlike other imaging techniques that use ionizing radiation, such as computed tomography (CT), CMR does not expose patients to radiation. However, it is important to ensure that patients do not have any metallic objects or devices in their body, as the strong magnetic field can interfere with or cause damage to these objects. Dr Ramji Mehrotra cautions that patients with pacemakers, certain metallic implants, or severe claustrophobia may not be suitable candidates for CMR.
The benefits of CMR extend beyond diagnosis. It is also valuable in treatment planning and monitoring. CMR can help guide interventional procedures, such as transcatheter valve replacements, by providing detailed anatomical information. Additionally, it enables the assessment of treatment response and the monitoring of disease progression over time, allowing doctors to customise therapies for better patient outcomes.
