Late Gadolinium Enhancement (LGE) is a specialized magnetic resonance imaging (MRI) technique used to visualize and characterize specific types of damage or scarring within the heart muscle. This advanced imaging method provides detailed insights into the heart’s tissue composition, helping medical professionals identify areas affected by various conditions.
What Late Gadolinium Enhancement Is
LGE is part of a cardiac MRI scan, using strong magnetic fields and radio waves to create detailed images without ionizing radiation. During an LGE MRI, a gadolinium-based contrast agent (GBCA) is administered intravenously. Gadolinium is a paramagnetic substance that alters the magnetic properties of water molecules in tissues, enhancing the signal intensity on MRI images.
In healthy heart muscle, gadolinium quickly washes out, remaining in the extracellular space. However, in damaged or scarred heart tissue, such as areas of myocardial fibrosis or necrosis, the extracellular space is expanded or cellular membranes are disrupted, allowing gadolinium to accumulate and be retained for a longer period. Images are typically acquired 10 to 20 minutes after injection, a “late” phase, allowing healthy tissue to clear the gadolinium while affected areas retain it. These regions with retained gadolinium appear bright white on MRI, contrasting with darker, healthy myocardium.
Why LGE is Used in Heart Imaging
LGE helps diagnose and characterize heart conditions by revealing specific patterns of myocardial damage. It provides detailed information on the nature and extent of cardiac disease.
A primary use of LGE is assessing myocardial infarction (heart attack). LGE accurately identifies and quantifies scar tissue from a previous heart attack. This technique helps determine myocardial viability, indicating which heart muscle segments are still alive and could benefit from revascularization. If the LGE occupies less than 50% of the myocardial thickness, the segment is generally considered viable, while more than 50% LGE suggests non-viable tissue.
LGE is also instrumental in detecting myocarditis, an inflammation of the heart muscle. In myocarditis, LGE often presents as patchy enhancement, frequently in the mid-myocardial or subepicardial layers, particularly in the basal inferolateral wall. Its presence and extent can indicate inflammation severity and provide prognostic information.
LGE is also widely used for various cardiomyopathies. In hypertrophic cardiomyopathy (HCM), LGE can reveal intramyocardial fibrosis, associated with increased risk of adverse events. For dilated cardiomyopathy (DCM), LGE may show mid-wall linear, patchy, or diffuse patterns, aiding diagnosis. LGE can also help diagnose infiltrative diseases like cardiac sarcoidosis or amyloidosis, where it shows characteristic, often diffuse, patterns of enhancement. Identifying LGE helps predict future cardiac events and guides treatment strategies.
What to Expect During an LGE MRI
Before the scan, you will remove all metal objects like jewelry and watches due to the strong magnetic field of the MRI machine. You might also receive specific instructions regarding food and drink intake, though fasting is not always required.
During the scan, you will lie on a movable table that slides into a large, tunnel-like MRI machine. The machine can be quite loud, producing knocking or thumping sounds, so you may be offered earplugs or headphones. The gadolinium contrast agent is usually injected into a vein in your arm midway through the scan. You might feel a temporary sensation of coolness or warmth at the injection site.
Throughout the procedure, it is important to lie as still as possible and, at times, you may be asked to hold your breath for short intervals to ensure clear images of your heart. The entire cardiac MRI, including the LGE portion, typically takes between 45 to 90 minutes. After the scan, you can usually resume your normal activities immediately, and drinking extra fluids may be recommended to help your body excrete the contrast agent.
Understanding Your LGE Results
Interpreting LGE findings involves recognizing how damaged or scarred heart tissue appears and what different enhancement patterns signify. On LGE MRI images, areas of myocardial injury or fibrosis appear bright white, standing out against darker, healthy heart muscle. This contrast allows radiologists and cardiologists to pinpoint the location and extent of tissue abnormalities.
The pattern of LGE provides specific diagnostic clues. For example, subendocardial or transmural enhancement (extending from the inner lining to the full heart wall thickness) characterizes a previous heart attack. In contrast, a mid-myocardial or patchy enhancement often suggests non-ischemic conditions like myocarditis or dilated cardiomyopathy. An epicardial pattern, involving the outer layer of the heart, can indicate certain inflammatory conditions such as myocarditis. Diffuse enhancement, spread throughout the myocardium, may be seen in infiltrative diseases like cardiac amyloidosis.
The location, pattern, and extent of LGE offer information for diagnosis, assessing disease severity, and guiding treatment. A specialized radiologist or cardiologist will interpret these images in conjunction with your other clinical data to provide a comprehensive assessment.
Safety of Gadolinium Contrast
Gadolinium-based contrast agents (GBCAs) used in LGE are generally considered safe for most patients. Common side effects are typically mild and temporary, including sensations of coldness or warmth at the injection site, mild nausea, or headache. More serious allergic reactions are rare but can occur.
A rare but serious complication associated with GBCAs is nephrogenic systemic fibrosis (NSF), which primarily affects patients with severe kidney dysfunction. With the development of newer GBCAs and stricter screening protocols for kidney function, the incidence of NSF has significantly decreased. Small amounts of gadolinium can be retained in tissues like the brain and heart. However, current research indicates this retention has no clear health consequences for most patients, and the diagnostic benefits of LGE MRI typically outweigh these potential risks. Always inform your healthcare provider about any history of kidney problems or allergies before an LGE MRI.