MRI With Contrast: What to Expect

What is MRI contrast?

Most MRI contrast agents contain the element gadolinium.

Free gadolinium itself would not be suitable for injection.

In MRI contrast agents, gadolinium is tightly bound to another molecule called a chelate, which allows it to be administered safely.

These substances are known as gadolinium-based contrast agents — GBCAs.

They temporarily alter the magnetic behaviour of nearby water molecules.

This changes the signal produced by tissues on certain MRI sequences and can make particular abnormalities easier to see.^[1,2]

Is MRI contrast a dye?

People often call contrast a “dye”, but that description can be misleading.

Gadolinium contrast is usually a clear, colourless liquid.

It does not permanently colour or stain your organs.

Instead, it temporarily alters the way tissues appear on MRI.

Is gadolinium the same as CT contrast?

No. They are different types of contrast media.

• —MRI contrast: usually contains a gadolinium-based contrast agent.
• —CT contrast: usually contains iodine.

Having had a reaction to CT contrast does not automatically mean that you will react to MRI contrast.

However, you should always tell the radiology team about any previous contrast reaction.

Why do I need contrast?

The radiologist or referring clinician may need contrast to answer a particular clinical question.

Gadolinium can highlight areas where blood vessels or tissue characteristics differ from their surroundings.

It may help when assessing conditions involving:

• —the brain
• —spinal cord
• —tumours
• —inflammation
• —infection
• —multiple sclerosis
• —blood vessels
• —the liver
• —heart
• —pelvis
• —joints
• —postoperative changes.

For example, after gadolinium is injected, areas with abnormal blood flow or disruption of normal tissue barriers may become brighter on certain MRI sequences.

This is known as enhancement.

What does “enhancement” mean?

Enhancement simply means that a tissue or lesion becomes more conspicuous after contrast administration.

Different patterns of enhancement can provide useful diagnostic information.

For example, enhancement can sometimes help radiologists distinguish between:

• —active inflammation and old scarring
• —solid tumour and cystic tissue
• —viable tumour and treatment-related change
• —abscess and surrounding inflammation
• —normal and abnormal blood vessels.

Enhancement does not automatically mean cancer.

Many benign and inflammatory conditions also enhance.

Does every MRI need contrast?

No.

Many MRI examinations are performed successfully without any contrast at all.

Examples may include many:

• —knee MRI scans
• —lumbar spine MRI scans
• —shoulder MRI scans
• —screening examinations
• —other specific protocols.

Whether contrast is required depends on:

• —the body part
• —your medical history
• —previous imaging
• —the clinical question.

Sometimes the decision is made before the scan.

Sometimes the radiologist may decide during the examination that contrast would provide useful additional information.

How is the contrast given?

A small plastic tube called a cannula is placed into a vein, usually in your hand or arm.

The contrast is then injected:

• —by hand
• —or using an automatic injector.

The cannula usually stays in place until the relevant part of the MRI is finished.

You may have some images before the injection and additional images afterwards.

What does the injection feel like?

Many people feel very little beyond the sensation of the cannula and injection.

Possible temporary sensations can include:

• —coolness at the injection site
• —warmth
• —a metallic or unusual taste
• —mild nausea
• —headache
• —dizziness.

These effects are usually brief.

In many people, there is no noticeable sensation at all.

Is MRI contrast safe?

For the vast majority of patients, gadolinium-based contrast agents have an excellent safety record.^[2,3]

Hundreds of millions of doses have been administered worldwide.

However, important potential risks include:

• —allergic-like reactions
• —contrast leaking outside the vein
• —nephrogenic systemic fibrosis in specific high-risk circumstances
• —retention of very small amounts of gadolinium in the body.

Modern contrast practice is designed to minimise these risks.

Can you be allergic to gadolinium?

Yes, but reactions are uncommon.

Most people receive gadolinium without difficulty.

Possible mild reactions include:

• —rash
• —itching
• —hives
• —nausea.

More serious reactions can include:

• —difficulty breathing
• —swelling
• —severe allergic-type reactions.

These are rare.

A previous reaction to a gadolinium-based contrast agent is one of the most important risk factors for another reaction.^[4]

Tell the MRI team before your scan if you have previously reacted to MRI contrast.

What happens if I have a reaction?

MRI departments administering contrast are equipped to recognise and treat acute contrast reactions.

If you experience symptoms such as:

• —itching
• —rash
• —breathing difficulty
• —throat tightness
• —facial swelling
• —significant dizziness

tell the radiographer immediately.

You are monitored during the examination and can communicate with staff throughout the MRI.

Can contrast leak outside the vein?

Occasionally.

This is called extravasation.

It means some of the contrast has leaked from the vein into the surrounding soft tissues.

This may cause:

• —swelling
• —discomfort
• —tenderness around the injection site.

Most cases settle without serious problems.

The radiology team will assess you and provide appropriate advice if this occurs.

Does gadolinium damage the kidneys?

For most people with normal kidney function, gadolinium contrast does not cause the same type of kidney concern historically associated with iodinated CT contrast.

However, kidney function matters because most gadolinium agents are removed from the body predominantly through the kidneys.

The main historic concern in patients with severe renal impairment was a rare condition called:

nephrogenic systemic fibrosis — NSF.

What is nephrogenic systemic fibrosis?

NSF is a rare but serious condition causing fibrosis and thickening of tissues, particularly involving the skin and connective tissues.

It was linked mainly to certain older, less stable gadolinium contrast agents in people with severe kidney failure.

Modern practice has changed significantly.

Higher-risk agents have been restricted or avoided, and lower-risk agents are now widely used.

As a result:

• —NSF has become extremely rare.
• —Recent evidence and specialist guidance indicate that the risk from modern lower-risk gadolinium agents is extremely low even in many patients with chronic kidney disease when contrast is clinically necessary.^[2,3]

Will I need a kidney blood test?

Not everyone does.

The department may check your renal function depending on:

• —your medical history
• —age
• —known kidney disease
• —the type of contrast agent being used
• —local policy.

You should tell the MRI team if you:

• —have chronic kidney disease
• —have kidney failure
• —are on dialysis
• —have previously required dialysis
• —have recently had significant kidney problems.

The radiology team can then determine whether contrast is appropriate.

What is eGFR?

You may hear the term:

eGFR — estimated glomerular filtration rate.

This is calculated from a blood test and provides an estimate of how well your kidneys are filtering blood.

If there is concern about significantly reduced renal function, the MRI team may review the eGFR before giving contrast.

What happens to gadolinium after the scan?

In people with normal kidney function, most of the administered contrast is removed from the bloodstream and passed into the urine.

Different gadolinium agents have different chemical structures and stability.

Research has shown that very small amounts of gadolinium can remain in tissues after contrast administration, even in people with normal kidney function.^[2,5]

This is known as gadolinium retention or deposition.

Should I worry about gadolinium staying in the body?

This topic has received a lot of attention.

Research has demonstrated trace retention of gadolinium in tissues including:

• —brain
• —bone
• —other organs.

Retention appears to be greater with some older linear agents than with more stable macrocyclic agents.^[2,5]

Importantly:

• —To date, convincing evidence has not demonstrated harmful clinical effects from this trace retention in people with normal kidney function.
• —Radiology practice nevertheless follows the principle that gadolinium should only be used when it provides meaningful diagnostic benefit.

What is the difference between linear and macrocyclic gadolinium?

Gadolinium-based contrast agents differ in how the gadolinium ion is chemically bound.

• —Linear agents: the chelating molecule has a more open structure.
• —Macrocyclic agents: the gadolinium is enclosed within a more cage-like molecular structure.

Macrocyclic agents are generally more stable and are associated with less tissue retention than many linear agents.^[2,5]

Several linear agents have therefore been restricted in Europe.

The specific contrast agent used depends on the examination and local radiology policy.

Can I ask which gadolinium agent is being used?

Yes.

If you are concerned, you can ask the MRI department:

• —which agent they use
• —why contrast has been recommended
• —whether there are alternatives.

The aim should be an informed conversation rather than simply refusing a clinically useful examination because the word “gadolinium” appears online.

What if I am pregnant?

Tell the radiology team if you are:

• —pregnant
• —think you may be pregnant.

MRI itself does not use ionising radiation.

However, gadolinium-based contrast crosses the placenta.

Current UK guidance advises considering non-contrast MRI or another appropriate imaging strategy first where feasible.

Gadolinium may still be used during pregnancy if it is clinically essential and the anticipated benefit outweighs the potential risk, using the lowest effective dose.^[6]

This is therefore an individual risk-benefit decision.

Can I breastfeed after MRI contrast?

Yes.

Current Royal College of Radiologists and Society of Radiographers guidance states that breastfeeding can continue normally after administration of gadolinium contrast.^[7]

Only a very small proportion of the contrast enters breast milk, and only a tiny fraction of that is absorbed through the infant's gastrointestinal tract.

Routine interruption of breastfeeding or “pumping and dumping” is not required after gadolinium contrast.

If you remain concerned, discuss this with the radiology team.

Can gadolinium affect fertility?

There is no established evidence that clinically used gadolinium contrast impairs human fertility.

If you have specific concerns related to:

• —pregnancy
• —fertility treatment
• —breastfeeding

tell the radiology team beforehand so the examination can be planned appropriately.

Should I drink lots of water afterwards?

For people who are allowed to drink normally, staying normally hydrated is reasonable.

You do not need to force yourself to drink excessive amounts of water to “flush the gadolinium out”.

If you have:

• —heart failure
• —kidney disease
• —a fluid restriction

follow the advice from your own healthcare team rather than deliberately increasing fluid intake.

Do I need to avoid driving?

Gadolinium contrast itself does not usually prevent you from driving.

However, you should not drive if you have also received:

• —sedation
• —anti-anxiety medication

or if your healthcare team specifically advises you not to.

What happens after the injection?

Most patients can leave shortly after the examination once the MRI team is satisfied that they are well.

Some departments may ask you to remain for a short observation period after contrast.

Your cannula is removed before you leave unless it is needed for another part of your care.

Can I refuse contrast?

Yes.

You should be given enough information to make an informed decision.

If you are worried, ask:

• —Why is contrast needed?
• —What additional information will it provide?
• —What are the risks in my circumstances?
• —Could the scan be performed without it?
• —Would a non-contrast examination be less accurate?

Declining contrast may sometimes mean that the examination cannot answer the clinical question as confidently.

The radiologist can help weigh the risks and benefits.

Why did my previous MRI not need contrast but this one does?

Because the clinical question may be different.

For example, a routine MRI looking for:

• —degenerative change

may not require contrast.

A scan looking for:

• —infection
• —active inflammation
• —tumour
• —postoperative recurrence
• —blood-vessel abnormality

may benefit substantially from it.

Contrast use is therefore driven by the question being asked, not simply by the body part being scanned.

Why might contrast be added halfway through my scan?

Some MRI protocols include:

• —images before contrast
• —contrast injection
• —additional post-contrast images.

Comparing the appearances before and after gadolinium can provide important diagnostic information.

This is entirely normal.

Five things to remember

• —MRI contrast usually contains gadolinium, not iodine.
• —Not every MRI requires contrast.
• —Allergic-like reactions are possible but uncommon.
• —Tell the MRI team if you have significant kidney disease or a previous gadolinium reaction.
• —Breastfeeding does not normally need to be interrupted after gadolinium contrast.

Questions you can ask before your scan

If you are concerned about contrast, useful questions include:

• —Why do I need contrast for this MRI?
• —What would you miss if contrast were not given?
• —Do I need a kidney-function blood test?
• —Which gadolinium contrast agent do you use?
• —I reacted to contrast previously — does that affect this scan?
• —I am pregnant or breastfeeding — does that change the plan?

The key message

Gadolinium contrast can provide important information that cannot always be obtained from a non-contrast MRI.

Modern gadolinium-based contrast agents have a strong overall safety record.

The important thing is not whether gadolinium is completely risk-free — very few medical interventions are.

The important question is:

Does the additional diagnostic information justify the small potential risk in this individual patient?

That is the decision your radiology team makes when contrast is recommended.