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This page provides information on examinations using contrast agents in MRI. It is intended for use by patients (or their families or carers) who have been referred to our service for imaging requiring contrast agents.

If you have any questions about this, a member of the neuroradiology team will be happy to answer them for you.

Contrast agents are used to enhance specific blood vessels, tissues or body cavities during your scan or procedure. Contrast agents can come in many different forms; in neuroradiology these can be injected, or on occasion swallowed. Contrast agents are made of different compounds depending on what they are being used for. They are not dyes that permanently discolour internal organs. They are substances that temporarily change the way x-rays or other imaging tools interact with the body.

In MRI we use gadolinium-based contrast agents (GBCAs). When GBCA’s are present in the body, they alter the magnetic properties of nearby water molecules, which enhance the quality of MR images.

Contrast agents are used to improve and enhance the images produced when you are having a scan or procedure; helping distinguish selected areas of the body from surrounding tissues. This helps the radiologist diagnose medical conditions or plan and carry out treatments.

The scans and procedures using contrast agents have helped in the diagnosis and treatment of many patients with various diseases and injuries. It is important however, that the benefits of having a contrast enhanced scan or procedure outweigh the risks associated with the use of contrast. The radiographers performing your examination will ask you some questions and/or review your medical records in order to ensure it is appropriate for you to have contrast agents.

In neuroradiology we follow current published guidance and use contrast agents with the lowest possible associated risks. If you have known kidney problems, renal failure or ever been on dialysis please contact neuroradiology prior to your appointment.

Problems that may happen straight away

Contrast agents are safe drugs; however as with all drugs, they have the potential to cause an allergic reaction. Mild reactions include:

  • nausea and/or vomiting
  • warmth or flushing
  • mild rash
  • mild swelling of the skin/tissues
  • perspiration
  • altered taste
  • anxiety
  • nasal congestion
  • slight itchy throat
  • sneezing

Mild reactions are common and occur between 1 in 10 and 1 in 100 patients.

Moderate reactions happen occasionally and include:

  • wide-spread rash
  • wide-spread skin redness
  • facial swelling
  • throat tightness or hoarseness
  • wheezing
  • chest pain

Moderate reactions are uncommon and occur between 1 in 100 and 1 in 1,000 patients. 

Severe life-threatening reactions are extremely rare and include:

  • wide-spread swelling
  • severe swelling of the throat
  • difficulty breathing or swallowing
  • irregular heartbeat
  • anaphylaxis (low blood pressure and fast heartbeat)
  • death

Severe reactions are rare and occur between 1 in 1,000 and 1 in 10,000 patients. The department is equipped to deal with reactions in the rare event of this happening.


Extravasation is when a drug has accidentally leaked from the vein (the injection site) into the surrounding skin. Extravasation is very rare but if left untreated it could lead to serious damage to the skin. It is important that you follow the advice given to you by the radiographer. If this happens you would have reddening and a stinging sensation in your limb, a possible swelling of the arm or hand and some pain which usually wears off after about 30 minutes.

Sometimes you may need another injection of contrast and if necessary, this will be discussed with you. We will give you an information sheet to take home with you should this occur.

Problems that may happen later

Some patients may experience delayed reactions in the hours following exposure to contrast, this is usually associated with milder reactions. Patients should seek medical advice from NHS 111, their GP, or local emergency department if necessary. Patients should also notify neuroradiology if they experience any reactions on 020 344 83440.

Gadolinium Deposition

There is recent evidence that tiny traces of gadolinium may be retained in different organs of the body, including the brain following an injection of GBCA’s. While there are no known negative effects from this, your doctor may take gadolinium retention into account when referring you for a contrast enhanced MRI.

Problems that are rare, but serious

In people whose kidneys are working normally contrast very rarely causes kidney problems. If you have a history of kidney disease you should contact neuroradiology before attending for your scan as you may require a blood test to assess your kidney function. We may not be able to complete your scan if the required blood test results are not available. 

In people who have severe kidney disease and who are given a contrast injection there is a very small risk of developing Nephrogenic Systemic Fibrosis (NSF) which is an extremely rare, but serious and potentially life-threatening condition affecting the skin and other organs. People with acute kidney injury (AKI) and chronic kidney disease (CKD) are also at higher risk. The condition has not been reported in people with mild kidney damage or normal kidney function. The condition can develop within 24 hours and up to around 3 months after having a GBCA.

Symptoms and signs of NSF include:

  • Burning, itching, swelling, scaling, hardening and tightening of the skin
  • Red or dark patches on the skin
  • Stiffness in joints with trouble moving, bending or straightening the limbs
  • Pain in the hip bones or ribs; or muscle weakness

If your kidneys are not working normally the referring doctor may advise extra precautions before your scan, such as extra fluids. If your kidney function is particularly low, the risk of NSF is higher, and we may not give you a contrast injection. In neuroradiology we use low risk contrast agents. We may perform, where possible an alternative scan whereby GBCA’s are not needed. There are no proven treatments for NSF, but symptoms may gradually improve over time. New medications are showing promising results but preventing the symptoms in the first place remains most important.

If you are asked to attend for a GBCA enhanced scan and you have already had a scan with GBCA within the last 7 days, please contact neuroradiology or your doctor or clinical nurse specialist who referred you. If you wish to discuss why you need to have contrast, or if you have any concerns about possible risk factors, you can do so with your referring doctor or clinical nurse specialist. If you do need to have contrast then make sure you follow any instructions before, during or after the procedure.

If you do not wish to have contrast, this is your choice, and you will not be treated any differently. Contrast is given to help distinguish between normal and abnormal tissues and organs; this will give your doctors the best opportunity to make a diagnosis and to plan your future management and care.

Your doctor or clinical nurse specialist will have taken into account the potential risks and benefits of having a scan or procedure involving contrast when referring you to neuroradiology. There are some alternative scan methods in MRI or ultrasound that do not use contrast agent, the possibility of these should be discussed with your referring doctor or clinical nurse specialist first.

Please contact neuroradiology prior to your scan should you have:

  • Kidney problems
  • Kidney failure
  • Ever been on dialysis

Eating and drinking guidance

  • Before your scan or procedure please see your specific appointment letter
  • Gently increase your intake of fluids starting the day before your scan and continuing for another 24 hours after the scan to ensure you are well hydrated

Medication guidance

  • Take other medications as normal, before and after contrast, unless advised otherwise
  • Contact neuroradiology if you are unsure about any of your medications.

If possible, aim to arrive shortly before your appointment to give the staff time to prepare you for your scan or procedure. The length of your scan or procedure will vary depending on which type of scan you are having, please see your appointment letter or associated information leaflet for further information.

We want to involve you in all the decisions about your care and treatment. If you decide to go ahead with a contrast scan or procedure, by law we must ask for your consent. This confirms that you agree to have the procedure and understand what it involves. Staff will explain all the risks, benefits and alternatives before they ask you to verbally consent to contrast.

If you are unsure about any aspect of your proposed scan or procedure, please don’t hesitate to speak with a senior member of staff again.

You will be given contrast before or during your scan or procedure. If we are giving GBCAs during an MRI scan, then we will give this through a cannula or small plastic tube placed in your vein in the hands, arms or feet. This cannula will remain in the vein for the duration of your scan. The radiographer will observe you throughout the duration of your scan and inform you when they are about to inject the contrast through the cannula, this may be done by hand or by an automatic pump injector.

If you have had an injection of gadolinium-based contrast, we will ask you to remain in the neuroradiology department for up to 30 mins after your injection unless you are an inpatient where you will return to the ward.

We will keep the cannula in place during this time in case we need to give you any further medication. After this, our staff will check you feel well enough to leave the department.

UCLH cannot accept responsibility for information provided by other organisations.

Lysholm Department of Neuroradiology
National Hospital of Neurology and Neurosurgery,
Queen Square, London

Direct line: 020 344 83440
Switchboard: 020 3456 7890
Extension: 83440/ 83103
Fax: 020 344 84723

The Lysholm Department of Neuroradiology reception is located in Chandler wing, on the lower ground floor of the National Hospital for Neurology & Neurosurgery, Queen Square. Please turn left when you exit the Chandler wing lifts on the lower ground floor to find our main neuroradiology reception.

Page last updated: 09 May 2024

Review due: 30 September 2024