A brain Magnetic Resonance Imaging (MRI) with contrast is a medical imaging technique that provides detailed images of the brain. This procedure uses a powerful magnetic field and radio waves to create cross-sectional views. A contrast agent is administered during the scan to enhance the visibility of certain tissues or abnormalities, providing a clearer assessment than an MRI without contrast.
How Contrast Enhances MRI Images
The contrast agent used in brain MRIs is a gadolinium-based compound. When administered, this agent alters the magnetic properties of water molecules in the body. Gadolinium is a paramagnetic substance, slightly increasing the signal intensity of tissues where it accumulates. This leads to brighter signals on MRI images in areas where the contrast agent has gathered.
The contrast agent highlights areas with increased blood supply or a compromised blood-brain barrier. In healthy brain tissue, the blood-brain barrier restricts the passage of substances from the bloodstream into the brain. However, in certain disease states, this barrier can be disrupted, allowing the gadolinium contrast to leak into affected brain tissue. This accumulation makes abnormalities stand out more clearly on the scan.
Specific Conditions Identified
The use of contrast improves the detection and characterization of various neurological conditions.
Brain Tumors
Brain tumors often have abnormal blood vessels and a disrupted blood-brain barrier, causing them to “enhance” brightly after contrast injection. This enhancement helps delineate the tumor’s size, shape, and extent, distinguishing it from surrounding healthy brain tissue or edema. It also aids in identifying new or recurring tumor growth following treatment.
Infections
Infections within the brain, such as abscesses or encephalitis, show characteristic enhancement patterns with contrast. These infectious processes involve inflammation and breakdown of the blood-brain barrier, leading to gadolinium accumulation. This allows radiologists to pinpoint the location and extent of the infection, guiding appropriate medical or surgical treatment. Contrast can help differentiate active infection from other brain lesions.
Inflammatory Conditions
Inflammatory conditions, like active lesions in multiple sclerosis (MS), are well-visualized with contrast. Active MS plaques represent areas of ongoing inflammation and demyelination, where the blood-brain barrier is temporarily compromised. These active lesions enhance brightly on contrast-enhanced MRI images, helping clinicians identify new disease activity and monitor treatment effectiveness. Vasculitis, an inflammation of blood vessels, can also be detected as it causes vessel wall enhancement.
Vascular Abnormalities
Contrast-enhanced MRI is valuable for identifying certain vascular abnormalities. Arteriovenous malformations (AVMs), tangles of abnormal blood vessels, show prominent enhancement due to their high blood flow. Aneurysms, weakened bulges in blood vessel walls, are better characterized with contrast, though other specialized MRI techniques like MRA are often preferred. Contrast can also help evaluate subacute or chronic stages of stroke by highlighting areas of evolving tissue damage or scar tissue.
Post-Surgical Evaluation
Contrast is used to evaluate post-surgical changes, especially in patients who have undergone brain tumor resection. It helps differentiate between post-operative changes like scar tissue, which shows minimal or no enhancement, and recurrent tumor, which enhances brightly. This distinction is important for guiding subsequent patient management and determining the need for further intervention.
What to Expect During the Procedure
Before a brain MRI with contrast, patients are asked to remove all metal objects, including jewelry, eyeglasses, and certain dental work, due to the strong magnetic field. Patients may also be asked to refrain from eating or drinking for a few hours prior to the scan, depending on specific clinic protocols. Upon arrival, an intravenous (IV) line will be inserted, into a vein in your arm or hand, through which the contrast agent will be administered during the scan.
During the procedure, you will lie on a movable table that slides into a large, tube-shaped MRI machine. The machine produces loud knocking or buzzing noises as it operates, so earplugs or headphones are provided. Remaining as still as possible throughout the scan is necessary to ensure clear images, and you may be given a call button to communicate with the technologist. The entire scan, including the contrast administration, takes between 30 to 60 minutes.
Safety and Risks of Contrast Agents
Gadolinium-based contrast agents are considered safe, and adverse reactions are uncommon. Many people experience no side effects, or only mild sensations like a cold feeling at the injection site. Other mild reactions can include temporary nausea, a metallic taste in the mouth, or a headache, which resolve quickly. These minor effects are not cause for concern.
More serious reactions are rare but can occur, including allergic reactions ranging from hives to anaphylaxis. Patients with severe kidney impairment face a specific risk called nephrogenic systemic fibrosis (NSF), a serious condition affecting the skin and other organs. For this reason, healthcare providers will assess kidney function before administering gadolinium, often through a blood test. Patients must disclose their full medical history, especially any kidney problems or allergies, to their healthcare team before the procedure.