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MRI Contrast Dye Explained

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What is contrast dye and what is it used for?

The use of contrast dyes in medical imaging is extremely common. They are typically used to enhance the appearance of certain structures within the body on scans and provide more information and clarity. Dyes are not always required; when examining bones, ligaments, and tendons, they are rarely used. They are however, regarded as an extremely useful tool when looking at soft tissue organs and the process of disease itself.

For imaging of the brain, spine, heart and blood vessels and cancers in particular, contrast can help doctors spot important information that wouldn’t be visible without the use of contrast dyes, assisting with a more accurate diagnosis.  

What is contrast dye made of?

The key component used in contrast dye is Gadolinium. Gadolinium contrast dye is a clear and colourless fluid that is used to make images clearer during an MRI scan, aiding the radiologist reviewing your scan in making a diagnosis. The radiologist (the specialist doctor trained in studying diagnostic scans) or a senior radiographer (a specially trained member of the radiology team who performs the MRI scan) will decide whether gadolinium is necessary and will discuss this with you as part of the MRI screening process that will take place at the beginning of your appointment.

How is contrast dye given?

If a contrast dye is necessary, Gadolinium will be injected into a vein in your arm or hand via a cannula (a soft, hollow, plastic tube) during your scan. A needle is used to insert the cannula but once the cannula is in the correct position, the needle is removed. This leaves the plastic tube in the blood vessel. This should not be uncomfortable and will only be in place until your scan is complete.

Does contrast dye cause side effects?

The type of Dye used for an MRI scan differs to the types used for other X-ray based examinations. Gadolinium, used in MRIs, is a naturally occurring substance that is supplemented by attaching it to other compounds to allow it to be used in the human body without causing damage.

Gadolinium is not suitable for everyone and your radiographer or radiologist will decide if it is appropriate for you as part of the MRI screening process. It is designed to ensure that healthy kidneys recognise the contrast as a substance the body does not require and excrete the agent before the complex bonds of the contrast have the chance to break down. Gadolinium should not be used in patients with impaired kidney function or with certain medical conditions where function of the kidneys and liver is reduced. Please tell the radiographer before your scan if you have any history of kidney problems. You will be asked about your kidney function as part of the MRI screening process.

Gadolinium based contrast agents are associated with a very low rate of adverse effects, such as allergic reaction. Guidelines recently published by the Royal College of Radiologists (Guidance on gadolinium-based contrast agent administration to adult patients, 2019) state that mild adverse events happen in less than 1% of all injections. Serious events are even rarer, occurring in an estimated 0.005% of cases. Recently, it has been identified that small amounts of gadolinium may be retained in the body after the use of Gadolinium-based contrast agents. However, there is no evidence that Gadolinium retention from contrast dye is harmful.