Veterinary Imaging of the Chesapeake
808 Bestgate Road
Annapolis, MD 21401

Phone: (410) 224-0121 - ext 8

MRI Contrast: A Clinical Approach to Understanding Gadolinium

It’s likely that most of us have come across the term “MRI contrast gadolinium” either in a report, in the news, or when we or someone we know have received an injection for an MRI exam. The vast majority of us don’t have a good grasp on what it is and/or why it is necessary for imaging studies.

First, MRI contrast gadolinium is not iodine-based contrast. This is important to note, because an iodine-based contrast agent used during a CT scan, Intravenous Pyelogram (IVP) or heart catheterization study can cause an allergic reaction. This raises concerns when the term “contrast” is used. The term describes any substance used in an imaging study to reveal abnormal tissue, in opposition to normal tissue, and also opposed to how that tissue presented prior to the administration of a contrast agent.

In MRI, we utilize a specific agent called gadolinium. This clear, viscous liquid is administered intravenously to the patient at a pre-calculated amount, usually during the second half of the study. Unlike the iodine contrast, the gadolinium itself is not visualized, but rather the changes it causes in the tissue. As the gadolinium molecules interact with the body, they change the nuclear precession of the hydrogen molecules in the tissue. (For more information on Nuclear Precession please check out the Technology section on our website). This change in precession causes an augmentation in the signal echo that is read out, causing it to show up hyper-intense (bright) on the images. Because of this interaction, only a few types of sequences are viable for post-contrast imaging. The most widely-used sequences are T1 weighted images, sometimes with the addition of Fat Saturation. The T1 images are done before and after the administration of gadolinium to reveal any abnormalities.

So why does gadolinium only affect abnormal tissue? Though there are some normal tissues that are affected by the gadolinium contrast, it is most often passed through the circulatory system and then dispersed into the interstitial space or filtered out by the kidneys. Because of the hydrophilic nature of gadolinium contrast, it will not have an effect on normal healthy tissue. However, if there is degradation of the blood-brain barrier, the contrast is allowed to leak through and invade the abnormal pathology.

In the images below, you will see that on the pre-contrast images, the brain tissue looks mostly uniform and cohesive in shape, contrast and density. However, after the administration of the gadolinium, we see that there are large tumors within the normal tissue of each of these cases. Based on the characteristics of the post-contrast imaging, we are able to gain valuable information on the pathology involved. With this information, the turn-around of a diagnosis becomes faster and treatment can begin almost immediately in some cases.

Figure 1. "Dixie," a 12-year-old FS Golden Retriever presented for seizures and mentation changes. Axial T1 pre-contrast imaging at the level of the TMJ shows a mass that is hypointense centrally with isointense to normal gray matter.

Figure 2. Shows fairly uniform, avid enhancement following contrast administration with dural tail dissecting dorsally and ventrally. Given the characteristics, a large meningioma with a necrotic center is considered most likely. Severe edema and mass effect are noted. MR characteristics are highly suggestive of a large extradural meningioma with necrotic central zone.

This patient is scheduled for surgery with an expected positive outcome.

Figure 3. “Lexis,” an 11-year-old FS Lab cross, came to us after having several seizures within the previous 4 months. Coronal T1 weighted image shows a large 2.7 x 2.7 x 1.7 cm mass in the right olfactory/ frontal lobe with extension into the nasal cavity. The mass bulges laterally and appears to just break through the bone into the right orbit.

Figure 4. Coronal post-contrast imaging reveals intense enhancement and several fluid-filled cavities within the mass. A dural tail is noted extending from the mass along the falx cerebri. There is moderate mass effect and perilesional edema with compression on the third ventricle and mild lateral ventriculomegaly. Diagnosis includes meningioma with nasal extension; olfactory blastoma; left subclavian artery (LSA) or histiocytic sarcoma; or nasal carcinoma with brain invasion.

The patient is scheduled for surgery in late December for removal of this mass.

Gadolinium-based contrast is utilized for a multitude of different exams and indications in MRI. It is essential in accurately diagnosing conditions of the brain and central nervous system including, but not limited to, small lesions, white matter demyelination, infarcts, infection, and differentiating between benign and malignant tumors. In orthopedic imaging, it is utilized to evaluate for the presence of abnormal pathological growths and the evaluation of ligament and tendon ruptures. Patients who have undergone spinal surgery within the past 3-5 years are given a contrast injection to show the difference between post-surgical scar tissue and degeneration of the intervertebral disks. Contrast is used in the circulatory system to visualize arterial and venous conditions such as clots, stenosis, aneurysms, anastomosis and rupture.

Over the past several years, gadolinium has been getting some bad press because of a condition called NSF (Nephrogenic Systemic Fibrosis). This condition has been proven to be caused by the administration of gadolinium contrast agents to patients with severely compromised renal function prior to the injection. These patients lack the ability to filter out and eliminate the contrast from their blood stream, leading to severe fibrosis of the skin, joints, eyes and organs. Though this is generally known as a human condition, and not much is known about NSF in animals, we take every precaution to evaluate the condition of our patients prior to the MRI exam to prevent this and many other conditions.