Contrast Medium: Using Gadolinium or Iodine in Patients with Kidney Problems
What is contrast medium? Contrast media are most frequently used in conjunction with CT and MRI. Iodine-containing contrast media are…Read more
Gadolinium contrast media (sometimes called a MRI contrast media, agents or ‘dyes’) are chemical substances used in magnetic resonance imaging (MRI) scans. When injected into the body, gadolinium contrast medium enhances and improves the quality of the MRI images (or pictures). This allows the radiologist (a specialist doctor trained to examine the images and provide a written report to your doctor or specialist) to more accurately report on how your body is working and whether there is any disease or abnormality present.
Gadolinium contrast media consist of complex molecules, arrangements of atoms held together by chemical bonds. The chemical bonds are made between a gadolinium ion and a carrier molecule (a chelating agent). A chelating agent prevents the toxicity of gadolinium while maintaining its contrast properties. Different brands of gadolinium contrast medium use different chelating molecules. The contrast medium is injected intravenously (into a vein) as part of an MRI scan, and eliminated from the body through the kidneys.
Gadolinium contrast medium is used in about 1 in 3 of MRI scans to improve the clarity of the images or pictures of your body’s internal structures. This improves the diagnostic accuracy of the MRI scan. For example, it improves the visibility of inflammation, tumours, blood vessels and, for some organs, blood supply.
Before the scan begins, the radiologist (specialist doctor supervising the scan) will decide, on the basis of the notes sent by your referring doctor, whether gadolinium injection is likely to be helpful and should be recommended for your MRI.
Before any MRI scan, you will be asked a number of questions about your medical history, and any implants you might have, to make sure that you will not be at risk from the strong magnetic fields of the scanner. You will also be asked about conditions that might mean a gadolinium injection would not be recommended (e.g. pregnancy, previous allergic reaction, severe kidney disease). If you have any of these conditions, then you will not be given gadolinium, but if there is no condition preventing injection, you might be asked to sign a consent form in case gadolinium is required.
Usually, you will be advised by the technologist or nurse before you have the MRI scan that it is recommended that gadolinium contrast medium be injected during the examination. As with any medical procedure, you have the right to seek further advice and/or to decline a gadolinium injection. The technologist who carries out the MRI scan, a nurse or a radiologist will give you the injection.
Sometimes, even though gadolinium initially would not have been required based on the referral notes provided by your doctor, the radiologist might decide during your scan that gadolinium would help make the images clearer. If you are told part of the way through your scan that gadolinium will be needed, you should not be concerned that this indicates something serious is wrong. Most often, this is being done to make the images clearer and of a higher quality, so the radiologist can provide your doctor with a more accurate diagnosis of your symptom or condition. If the gadolinium is not given after such a recommendation, another scan may be required later.
Gadolinium contrast medium is given by intravenous injection, that is, through a small needle into a vein in your arm, either by hand injection or by an automated injector.
Most patients do not notice any sensations, although a few patients will report a cold feeling in the arm during the injection, which is of no significance. An even smaller number (between about 1 and 4 in 100) will notice mild nausea or headache. Vomiting can occur, but this is rare (less than 1 in 100 injections).
The injection takes between 10 and 30 seconds. If there is going to be any immediate reaction (such as those mentioned above), it will almost always be apparent within a few minutes; that is, before the end of the scan.
Gadolinium contrast medium is generally very safe. Side effects or reactions are uncommon, but can occur.
In patients with normal kidney function, most of the gadolinium contrast medium injected (over 90%) is passed out in the urine within 24 hours.
The most common adverse reactions are minimal: headache, nausea (feeling slightly sick) and dizziness for a brief time after the injection. A few patients will have a feeling of coldness at the injection site.
Less often, in approximately 1 in 1000 patients, an itchy skin rash might appear a few minutes after the injection. This appears to be due to a mild allergy. It usually settles down by itself within an hour or so, but rarely it might be a warning sign of a more serious allergic reaction developing.
Severe allergic (anaphylactic) reactions to gadolinium contrast medium have occurred, but are extremely rare. These severe reactions, which might involve difficulty breathing and swelling of the lips and mouth, occur in approximately 1 in every 10,000 people who have gadolinium. These severe reactions generally respond very well to standard emergency drug treatment, similar to that given for other severe allergic reactions. These are usually medications that will be given through the tube that was placed in your arm before or during the MRI scan. All radiology facilities where gadolinium injections are given maintain stock of the medications required to treat these reactions, and are equipped to administer them when needed.
Nephrogenic systemic fibrosis (NSF) is a rare debilitating disease resulting in skin contractures (or localised skin thickening and tightening) and internal organ damage. It has occurred with some gadolinium-based contrast media in a minority of patients with pre-existing severe kidney function abnormalities. There are some forms of gadolinium contrast for which there seem to be lower risks of NSF than for others, and these low-risk forms are used in patients with less severe renal disease if the likely benefit (better diagnosis) justifies the very low likelihood of subsequent NSF. Even in those with end-stage kidney disease, the risk of NSF developing after a single injection of a lower risk agent is believed to be well under 1 in 100 injections.
For this reason, you will be asked questions about possible kidney disease as part of the safety screening before the MRI scan. If you have kidney disease, please advise your referring doctor before the procedure, so that you, your doctor and the MRI radiologist can discuss whether or not the possible benefits of a gadolinium injection outweigh the possible risks in your case.
Recently, it has been recognised that very small amounts of at least some forms of gadolinium contrast (about 1% of the injected dose) are retained in the tissues, mostly in the bones, with tiny amounts in the brain. This seems to be more likely with the same forms of gadolinium contrast that have a higher risk for NSF. At this stage, there are no known adverse effects from these very small amounts of retained gadolinium. This finding has made radiologists more careful to recommend gadolinium contrast only where it is likely to assist the diagnosis.
If you are pregnant, or think you might be pregnant, please inform your doctor or radiologist before having the procedure, so that your doctor can consider and talk to you about any risks and benefits of having an MRI scan, and a possible gadolinium injection, for you and your unborn baby. Where relevant, you will be asked about the possibility of pregnancy as part of the safety screening before any MRI scan. If you are pregnant or possibly pregnant, it is unlikely that you will have a gadolinium injection unless it is absolutely essential. If an injection is recommended, this would be discussed with you and your doctor before giving you the injection.
If you are breast-feeding, it is safe to continue normal breast-feeding after the gadolinium contrast medium has been given. There is no requirement to express and dispose of breast milk or to withhold breast-feeding. Although the gadolinium is eliminated from the body through the kidneys, if you are breast-feeding, it has been shown that a tiny part (less than 1 part in 1000) of the injected gadolinium can enter the breast milk. An even smaller amount of gadolinium from the breast milk might be swallowed by the baby and taken into the baby’s bloodstream. The amount received by your baby is so small it is not thought to represent any danger to your child.
If you have any concerns about the use of gadolinium, please discuss these with your referring doctor and/or the staff where you are having this procedure.
Gadolinium MRI contrast injections improve diagnostic accuracy in some conditions, such as inflammatory and infectious diseases of the brain, spine, soft tissues and bones, by making images clearer so that the radiologist can better see what and where the problem is. The nature and extent of some cancers and benign tumours is best seen and assessed after a gadolinium contrast injection.
Scans showing the function of blood vessels in real time can be carried out using gadolinium contrast medium, and many heart abnormalities can only be fully assessed using gadolinium contrast medium.
If a gadolinium injection is required, it will most likely be given by a radiographer or nurse, either by hand injection through a syringe and needle, or occasionally by a mechanical injector connected to the syringe (this allows more precise timing and a more controlled rate of injection).
Normally, after some initial MRI scans have been carried out, the gadolinium injection will be given to you while you are in the scanner, before more scans are taken.
If a gadolinium angiogram is carried out, some preliminary scans might be required immediately before the gadolinium injection, and it is important to lie still between the preliminary scan and the gadolinium injection.
The most common side effects of headache, nausea and dizziness occur in a small minority of patients only, but if they do occur they will be noticed within minutes of the injection. Allergic reactions usually begin within several minutes of the injection, when a patient is most likely still in the scanner, or still in the radiology practice or hospital.
If you have had a history of a previous allergic reaction to a gadolinium contrast injection, or a severe allergic reaction to some other material, please tell your referring doctor and/or the radiology facility where you are having the MRI, as this will affect whether a further gadolinium injection is recommended. If you have had a previous severe reaction to a gadolinium-based agent, the radiologist will also consider whether you might need some preventive medications before any further gadolinium injection.
There is no way to predict which patients will experience minor side effects, such as headache and nausea, and no reliable preventive measures are known. These will usually settle down without treatment, or with a simple analgesic for headache.
If you have a history of severe allergic reactions, some people believe that taking some preventive medications in the hours before the scan can reduce the risk of another reaction, if a gadolinium injection is thought essential to the diagnosis. The evidence that this ‘pre-medication’ actually reduces the risk is not clear-cut.
Nephrogenic systemic fibrosis (NSF) is a rare condition associated with gadolinium contrast medium given to patients with severe renal (kidney) disease. Its onset occurs days, weeks or months after receiving gadolinium, with almost all cases occurring within 6 months of the last dose. Since radiology facilities began routinely screening patients for kidney disease, and withholding gadolinium from those with severe renal disease, NSF has become extremely uncommon. If you do have a history of kidney disease, please be sure to tell the staff at the MRI practice, so that they can check whether the disease is severe enough to mean that you should not receive gadolinium. This might involve a simple blood test of kidney function.
Page last modified on 26/7/2017.
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