Magnetic Resonance Imaging (MRI) is a scanning procedure used in medicine for examining the interior of the human body. An MRI machine is a large, cylindrical machine, that creates a powerful magnetic field around a patient. The magnetic field combined with radio wave pulses alters the natural alignment of hydrogen atoms in the body. When the radio waves stop, the atoms realign themselves and emit a radio signal. These signals are received and interpreted by a computer that converts the information into 2-D or 3-D images to be examined by a radiologist.
MRI is unique to other imaging systems such as X-ray or CT scans, because it does not require any harmful ionizing radiation. In addition, in most instances MRI is the most sensitive imaging test and provides the highest quality images.
MRI Contrast vs. Non-contrast
There are two major types of MRI scans; contrast and non-contrast. When a patient is undergoing a contrast MRI, a dye that is gadolinium-based is given to the patient intravenously. A contrast agent will only be used when ordered by a physician, allowing the radiologist to more accurately report on how the patient’s body is working and whether any disease or abnormality is present. The gadolinium contrast medium enhances and improves the quality and clarity of the MRI images.
However, in most cases a non-contrast MRI is an effective exam for imaging the body’s organs. Even without the intravenous contrast, MRI can detect pathology in most organs and in some cases the pathology is made less visible on a contrast MRI than a non-contrast scan. For example, non-contrast scans provide greater images of blood vessel activity to detect aneurysms and blocked blood vessels.1 The results of an MRI procedure without contrast are just as valuable and relevant as those done with the use of a contrast agent.
MRI contrast is required when a very detailed image is necessary to evaluate the problem area of the body. Gadolinium contrast is used in about one in three MRI scans, to improve the diagnostic accuracy of the scan. Adding contrast to the image enhances the visibility of inflammation, tumors, blood vessels and the blood supply of certain organs.2 The decision of whether to use contrast during a scan depends on the type of problem and the health history of the patient.
The three main differences between a contrast and non-contrast scan are:
- Typically, if an MRI procedure is done with a contrast agent then there will be no need for additional MRI procedures due to the high resolution of the resulting image. A non-contrast scan may require additional procedures to clarify any abnormalities.
- MRI with contrast is superior at measuring and assessing tumors. Contrast helps detect even the smallest tumors, giving the surgeon more clarity regarding the location and size of the tumor and other tissues involved.
- MRI images with contrast are clearer and better quality than the images without contrast.
What does MRI Contrast Show?
When the gadolinium dye is injected into a patient’s bloodstream the contrast agent circulates through the bloodstream and is absorbed in certain tissues, making them stand out more on the scan. In an MRI image of the body, air and hard bone do not give off an MRI signal, so these areas appear black or dark on the scan. However, bone marrow, spinal fluid, blood, and soft tissues vary in intensity from black to white, depending on the amount of fat and water present in each tissue and the specific machine settings for the scan. The radiologist then compares the size and distributions of the bright and dark areas to asses normal and abnormal tissue.3 When contrast is utilized during a scan, the targeted tissues will glow a bright white on the final image, making them easy to detect and assess.
Common uses of MRI with contrast are:
- The head and neck- Contrast agents can help detect brain tumors, traumatic brain injury, developmental anomalies, multiple sclerosis, stroke, dementia, and infection.
- Arteries and veins- Contrast dye injected into the bloodstream helps the computer “see” arteries and veins, so that a radiologist can detect aneurysms, blockages of the blood vessels, carotid artery disease, and arteriovenous malformations.
- Spine- Contrast MRI is sensitive to changes in cartilage and bone structure, making it easier to detect herniated discs, pinched nerves, spinal tumors, spinal cord compression, and fractures.
Opting for Contrast MRI
A surgeon will order an MRI with contrast based on the problem area being imaged and the health history of the patient. In most cases, a contrast MRI will not be ordered unless deemed absolutely necessary. Sports injuries, work related injuries and back pain do not usually require intravenous contrast exams.
The main usage of intravenous contrast in MRI is in the detecting of benign or malignant tumors and for the staging of tumors of the central nervous system and major body organs.4 While many conditions can be examined with a non-contrast scan, ordering a contrast scan initially can provide the clarity needed to rule out certain conditions. For example, a non-contrast MRI scan is capable of diagnosing a stroke. However, when examining a stroke patient, by performing an MRI scan with a gadolinium-based agent first, a physician can rule out a brain tumor or aneurysm as well as diagnose the stroke. Pituitary disease, acoustic neuromas, central nervous system aneurysms, vascular malformations and causes for seizures are also more completely evaluated with contrast MRI exams.4
Possible Health Concerns with Gadolinium Contrast
Gadolinium-based contrast agents are considered generally very safe. There is no clinical evidence directly linking gadolinium to adverse health effects in patients.4 However, in a small percentage of patients, there is the possibility for some side effects caused by the dye.
In approximately 1 in 1,000 patients, minor allergic symptoms may appear a few minutes after the injection. This side effect usually manifests as an itchy skin rash and settles down by itself within an hour or so. Severe allergic reactions to the gadolinium have happened but are extremely rare, occurring in approximately 1 in every 10,000 patients.2
Nephrogenic Systemic Fibrosis
Nephrogenic systemic fibrosis (NSF) is a rare disease that has occurred in some patients with pre-existing severe kidney function abnormalities. In patients with normal kidney function, most of the gadolinium substance (over 90%) is passed out of the body within 24 hours. However, patients with kidney disease may not be able to process the contrast agent, resulting in skin contractures and internal organ damage.2
In late 2014, a study was released showing that very small amounts of gadolinium-based contrast agents used in MRI (about 1% of the injected dose) are retained in the tissues.2 Most of the retention happens in the bones, with tiny amounts in the brain. Currently, no clinical evidence has shown that there are adverse effects caused by the gadolinium retention, but radiologists are increasingly more careful to recommend a contrast MRI only when necessary.
If a patient is pregnant or thinks she may be pregnant a physician's recommendation for a gadolinium injection is very unlikely unless deemed absolutely essential.1 Studies show that gadolinium dye should be avoided during pregnancy, as it is associated with increased risks to the fetus.5 If an injection is recommended, the patient’s physician will discuss the contrast substance before the procedure.
While there are a few minor risks associated with gadolinium-based contrast agents, the benefits of using the contrast injections typically outweigh them immensely. By enhancing the quality and clarity of MRI images, gadolinium injections help increase diagnostic accuracy, thus increasing the confidence and abilities of radiologists; ultimately improving patient care.
1. "What is an MRI with contrast? Why do I need contrast? Is it safe?". Orthopaedic & Spine Center. Web. 01 August 2018. <https://www.osc-ortho.com/services/open-mri/mri-frequently-asked-questions/what-is-an-mri-with-contrast-why-do-i-need-contrast-is-it-safe/>.
2. Ferris, Nick. "Gadolinium Contrast Medium (MRI Contrast agents)". Inside Radiology. 26 July 2017. Web. 01 August 2018. <https://www.insideradiology.com.au/gadolinium-contrast-medium/>.
3. "MRI (magnetic resonance imaging) and MR angiography". Mayfield Brain & Spine. April 2018. Web. 01 August 2018. <https://www.mayfieldclinic.com/PE-MRI.htm>.
4. A1 Medical Imaging. "Guidelines for Ordering Intravenous Contrast with MRI Examinations." A1 Imaging Centers, LLC. 01 March 2013. Web. 01 August 2018. <https://a1mri.com/blog/guidelines-for-ordering-intravenous-contrast-with-mri-examinations/>.
5. "Gadolinium in Pregnancy: Can gadolinium be given to pregnant women?" MRIquestions.com. 28 September 2015. Web. 14 January 2019. <http://mriquestions.com/gd-in-pregnancy.html>.