Computed Tomography (CT)
What is computed tomography? Computed tomography (CT) is a way of using X-rays to take pictures or images in very…Read more
Iodine-containing contrast medium (ICCM), sometimes called contrast or contrast medium, is a chemical substance used in medical X-ray imaging. When injected into the body, ICCM shows what is happening inside the hollow parts of the body (like blood vessels, the stomach, bowel or even the fluid around the spinal cord) on X-ray images or pictures. When injected into a blood vessel, which can be either an artery or a vein, it not only shows the inside of the blood vessel, but it can give information about how the organs supplied by that blood vessel are working. Good examples of this are the kidneys, brain and lungs.
It is important to note that ICCM does not produce radiation: it is a chemical substance that harmlessly interacts with X-rays.
The radiologist (a specialist doctor) who carries out and interprets your medical imaging procedure or test will read what your doctor has written on your radiology referral. The referral tells the radiologist what your doctor thinks might be wrong and what your doctor wants to know from the test or procedure. This information enables the radiologist to decide if the use of ICCM will provide the necessary images to help them give your doctor the answer.
Types of tests that nearly always use ICCM include angiograms/angiography (which are X-rays of blood vessels), arthrography (which is an X-ray of the inside of a joint (like the shoulder)) and myelography (which involves injection of contrast medium into the fluid around the spinal cord).
Some, but not all, computed tomography (CT) scans require you to have ICCM either by drinking it or by injection into a vein in the arm.
ICCM is given by injection into a vein in the back of your hand or on the front of your arm or elbow, or by drinking it. If the test you are having is to investigate a problem in the lower part of the bowel (the colon or rectum), a soft plastic tube might be put into your rectum (or back passage) and the ICCM will be put in through the tube.
For an arthrogram (a type of X-ray of a joint), the ICCM is injected directly into the joint (like your knee, shoulder or wrist) using X-rays or ultrasound to guide the needle into the correct position.
A myelogram (a type X-ray of the spine) requires ICCM to be injected into the lower part of your spine while you lie on your stomach.
For angiography, a catheter (thin plastic tube) will be put into an artery or vein, most often in your groin, and the ICCM will be given through the catheter.
The type of problem or symptom you have will determine which way the ICCM must be given. Sometimes, you will need ICCM to be given two different ways for the same test. For example, many CT scans will require that you have ICCM to drink as well as having an injection into a vein.
If you need an ICCM injection, this might be given by a radiologist, nurse, or radiographer (medical imaging technologist) injecting it manually or through a thin plastic tube inserted into a vein or artery. The tube might also be connected to a small electric pump that will inject the ICCM. A pump is commonly used to inject the ICCM for CT scanning and angiograms (X-rays of blood vessels).
What you might feel will depend on how the ICCM is given.
The most common way it is given is into a vein during a CT scan or into an artery for an angiogram. Most patients will notice a very warm feeling that spreads throughout their body for about 20 seconds during and after the injection. This is often concentrated around the groin area and you might think that you are passing urine, but you are not. This is very common, very normal, nothing to worry about and the feeling goes away quickly (10–20 seconds). Some people feel nauseous (like vomiting) for a short time during and after the injection (see the section on risks below). It is, however, very uncommon for this feeling to be severe enough that you actually vomit (see the ‘Risks’ section below).
If you are given ICCM to drink, you generally will not notice any of the things described above. The taste is not unpleasant, and you usually need to drink a couple of cups followed by some water.
If you are given ICCM into a joint for an arthrogram, you might feel some temporary aching or ‘pressure’ in the joint as it fills up with fluid. If you have ICCM into a tube in your rectum, it might feel temporarily uncomfortable, as if you need to go to the toilet.
Most patients will not usually notice anything abnormal after being given ICCM. Some patients might have some allergies or side effects, which are discussed below. The ICCM will leave your body through your urine in the hours after your test or procedure. You can help this by drinking plenty of fluids. If you are not allowed to drink due to your medical condition, the fluids will be given to you in an intravenous drip. The main after effects you need to be aware of are listed in the ‘Risks’ section below.
This depends on the type of test or procedure you are having and how you are to be given the ICCM. It is best to ask the staff this question when you are being prepared for your procedure.
All medical tests, procedures and medications are associated with risks. There are some risks that you need to know about before you have ICCM. If you know about these risks, and are in anyway concerned, then contact your doctor or the hospital or X-ray centre where you are having the test. You can do this when you make your appointment, and again when you arrive to have your test or procedure.
If there is a chance that you will be given ICCM, then you will be asked several questions at the time of your appointment or when you arrive for your test. These will include:
If you do not know the answers to these questions or are unsure, then your referring doctor should be able to help you. If you have any other known medical condition, please ask your doctor or the X-ray practice where you are having the test to make sure that there is no reason why you can’t have ICCM if required.
As with all medical procedures, the risks need to be weighed against the benefits in every case. Your doctor will work with the radiologist to assess whether the risk of a procedure involving ICCM is outweighed by the benefits of the test.
This is an individual medical judgment that is different for every patient and every situation or problem. Where the ICCM might provide additional information to the radiologist who is going to interpret your imaging (the pictures taken when you have your X-ray procedure), this can often lead to a more accurate diagnosis that, in turn, will allow your doctor to better understand what is wrong and to give you the right treatment.
These occur in less than 3% of all people who have ICCM. Reactions are unpredictable, and anyone can have a reaction. Even if you have had ICCM before and had no problem, it does not mean you could not have a reaction the next time you have an injection of ICCM. For this reason, all radiology practices and hospital radiology departments are prepared at all times to treat moderate and severe allergic reactions with appropriate medication. These reactions respond, in almost all cases, very well to emergency drug treatment.
If you have had a mild, moderate or severe allergic reaction to ICCM in the past, you MUST tell the radiology facility when you are making your appointment. If you need to have ICCM again, the radiologist might decide to do a different test that does not need ICCM. If it is impossible to avoid giving ICCM, you might require medication (tablets taken by mouth) every few hours for several hours before the procedure to decrease the chance of you having a moderate or severe reaction. These tablets are corticosteroids (or cortisone), which might reduce, but will not eliminate, the chance of another reaction to ICCM. The tablets take a few hours to have any effect and do not work if you take them right before you have ICCM.
Allergic type reactions to ICCM can be divided into mild, moderate and severe types.
Mild reactions occur in 1–3 in every 100 patients who receive ICCM. These reactions include:
Almost always these types of reactions do not require any special treatment and generally take only minutes to go away.
Moderate reactions consist of severe or prolonged vomiting, a generalised rash, or swelling of the face, mouth or throat, making it harder to breathe and swallow. These reactions often need drug treatment, typically with adrenaline, antihistamines and sometimes corticosteroids (or cortisone), as well as a period of observation (2–3 hours) before you are allowed to go home. They occur in less than 1 in every 3000 people who has ICCM.
Severe reactions are rare, and occur in less than 1 in every 25,000 people who have ICCM. They require emergency medical treatment and admission to hospital for a period of observation. A severe reaction might consist of any of the following:
These side effects are treated with emergency medication including adrenaline, and you will be admitted to hospital after this treatment for a period of monitoring.
Less than 1 in every 170,000 people who have ICCM injected will die as a result of a very severe allergic-type reaction, even if emergency medical treatment is provided.
Rarely, salivary gland swelling (under and behind the jaw bone) can occur a few days after ICCM, as can generalised joint aches and pains. These seem to be more common in patients with abnormal kidney function.
For people with normally functioning kidneys, ICCM is quite safe. If your kidney function is severely reduced before you have ICCM injected into an artery or vein, you are at an increased risk of temporarily worsening your kidney function if you have a large amount of ICCM. Larger amounts of contrast are typically given for an angiogram, especially of the heart. You might also have a large amount of contrast in a short time if you have a number of tests or procedures that use ICCM within a few hours or days.
Your kidney function will not be affected by the very small volumes of ICCM that are given for arthrograms or myelograms. There is also little or no effect on kidney function if you are given the ICCM to drink or through a tube placed into your rectum, stomach or bowel.
Occasionally, the kidney function reduction that occurs after ICCM is prolonged or even permanent, and you might need dialysis (purification of the blood by dialysis machine as a substitute for normal kidney function). This generally occurs in people who already have a severely reduced amount of kidney function.
you will probably need to have the results of your most recent kidney function test available when you schedule your test or procedure if the test or procedure involves ICCM.
This is a simple blood test that your doctor can organise. If your kidney function is found to be very poor (or low), the radiologist might decide to give you some extra fluids through an intravenous drip before and after your procedure to help your kidneys get rid of the ICCM through your urine. This is why it is helpful to know this information when you schedule your procedure, if it is not an emergency.
Side effects that can occur in people taking certain medical conditions
Myaesthenia gravis: If you have myasthenia gravis and you have ICCM there is a small chance that your muscle weakness will temporarily get worse. As the muscles involved in breathing are affected in this condition, like all of the other muscles, this could mean you experience more difficulty in breathing. If you must have ICCM, you will be closely monitored to ensure that if you do develop breathing problems or increasing weakness this is recognised promptly and treated.
Phaeochromocytoma and paraganglioma: It is not believed there is an increased risk of raising your blood pressure using ICCM as part of a routine CT scan. There is an increased risk during an angiogram where ICCM is directly injected through a tube (catheter) into the blood vessels supplying or draining either of these tumours.
As a general rule, giving any drug to a pregnant woman, including injecting ICCM, needs to be carefully considered. There is no medical evidence that ICCM can harm the unborn foetus or baby, but at the same time there are no large studies that conclusively prove that it is safe. There might be a small risk of reduced functioning of the thyroid gland of the foetus or newborn if its mother has ICCM while pregnant. For this reason, it has been suggested that the thyroid function of the newborn be tested in the first week of life if the mother needed to have ICCM while pregnant. Testing of thyroid function in newborns is now a routine procedure for all babies born in Australian and New Zealand hospitals, so this will occur, along with other newborn screening tests, if your baby is born in a hospital in Australia or New Zealand.
Less than 1/1000th of the contrast dose given to the mother is excreted into the breast milk, so there is no reason to stop breast-feeding or to discard your breast milk by expressing, if you need to have ICCM, as your milk will not harm your baby.
This occurs to varying degrees in approximately 2% of patients. It is more common with larger amounts of ICCM, when a mechanical pump injector is used and when the patient is very young, very old, or has difficulty with communication or is confused or unconscious.
Usually, the pain and redness that leakages might cause can be treated with ice or warm compresses, and it will disappear quite promptly. Rarely, the pain, swelling, and redness can increase and be associated with pins and needles in the hand (if you had the injection in your arm) or in the foot (if the injection was around the ankle). If this happens to you after you have gone home, you must see your GP urgently or your nearest hospital emergency department, as you might need treatment to prevent long-term complications. This complication is rare and is called ‘compartment syndrome’. It generally occurs after fairly large amounts of contrast have leaked into the soft tissues beneath the skin.
The ICCM that you might be given to drink is usually known as Gastrografin. It is different to the ICCM that is given by injection.
The risks of severe reaction with ICCM that you drink are much lower than the already low risk of injected ICCM. A few cases of moderate allergic reactions have been described in the medical literature. Again, these seem to be much less common than if the ICCM is injected.
The main risk with ICCM that is swallowed, such as Gastrografin, is in people who cannot swallow properly because they are confused, very old, very young or not fully conscious. The ICCM can produce severe breathing problems that are occasionally fatal if enough of it reaches the lungs. Great care is taken in giving ICCM to people who cannot swallow properly, for this reason. The ICCM might not be given at all in this situation, or a different type of ICCM that is safe if it gets into the lungs might be given instead.
Diabetes and medications containing metformin
Metformin is often taken for diabetes. Medications containing metformin include:
If you are taking metformin or other medications containing metformin (see list above), your doctor is probably checking your kidney function regularly. You will need to have the most recent result available when you schedule your test or procedure, and the hospital or imaging practice might want it checked again closer to the time of your appointment. If you are having an emergency imaging procedure involving ICCM, your kidney function might be checked after the procedure to save time.
If your kidney function is very poor or very low, you might need to stop taking metformin after you have your imaging procedure if this test or procedure involves injection of ICCM into an artery or vein. You will need to wait a few days before having your kidney function re-tested. If your kidney function is back to your normal level when you have it re-tested, your doctor will generally advise you that it is safe to restart your metformin at that time.
If your kidney function is shown to be normal before the ICCM injection and you are taking metformin, there is no need to stop taking metformin after your ICCM injection.
The radiologist, in consultation with your referring doctor and you if necessary, will have decided that the benefits of having ICCM outweigh the risks outlined above, which are uncommon in most healthy people. Radiologists use ICCM to make the images clearer and therefore to allow the most accurate answer to be given to your doctor. Some types of tests and procedures, such as CT angiograms, cannot be carried out without ICCM.
Depending on the kind of procedure you are having, a radiologist (a specialist doctor) or a radiology nurse or a radiographer (medical imaging technologist) will give you the injection. For CT scanning and angiography, often a small electrical pump will be used to inject the ICCM.
This will be done in the CT scanning room or the angiography suite or in the fluoroscopy room while you are on the examination table having your scan or test (fluoroscopy is the process of viewing X-ray images on a screen rather than taking and developing X-ray pictures). If you are required to drink ICCM, you might be asked to do this an hour or two before your CT scan (in the waiting room or in your hospital bed if you have been admitted).
RANZCR 2016 ICCM guideline
Information for Patients, Patient Questionnaire
Page last modified on 26/7/2017.
RANZCR® is not aware that any person intends to act or rely upon the opinions, advices or information contained in this publication or of the manner in which it might be possible to do so. It issues no invitation to any person to act or rely upon such opinions, advices or information or any of them and it accepts no responsibility for any of them.
RANZCR® intends by this statement to exclude liability for any such opinions, advices or information. The content of this publication is not intended as a substitute for medical advice. It is designed to support, not replace, the relationship that exists between a patient and his/her doctor. Some of the tests and procedures included in this publication may not be available at all radiology providers.
RANZCR® recommends that any specific questions regarding any procedure be discussed with a person's family doctor or medical specialist. Whilst every effort is made to ensure the accuracy of the information contained in this publication, RANZCR®, its Board, officers and employees assume no responsibility for its content, use, or interpretation. Each person should rely on their own inquires before making decisions that touch their own interests.