The use of contrast dyes in medical imaging is extremely common. Typically injected into a vein in the hand or arm during the scan, contrast is used to enhance the appearance of certain structures within the body.
Dyes are not always essential – when looking at bones, ligaments and tendons, contrast dyes are rarely needed. However, they are regarded to be very important when trying to get a good look 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 pick up things that would otherwise not be visible. For certain conditions, contrast can effectively highlight areas of interest and help in making a more accurate, and more specific diagnosis.
Do contrast agents have any side effects?
The particular type of contrast dye used in an MRI scan is different to other x-ray based tests. In MRI, the contrast used contains a naturally occurring substance called Gadolinium, which is typically attached to other compounds so that it can be used in the human body without causing any harm. Contrast dyes are designed so that healthy kidneys recognise the contrast as something the body does not need, and excrete the agent before the complex bonds of the contrast itself have a chance to break down.
For this reason, gadolinium is generally considered to be very safe, and due to the design of modern day contrast agents, allergic-type reactions to gadolinium are very rare indeed. The vast majority of patients will feel nothing after receiving an injection of contrast and only a very small number of people will have any adverse effects.
As with all injections, whatever the substance being injected, doctors and radiology staff are always conscious of the risks versus the benefits of performing the injection. A contrast dye injection is only ever used if certain information is required which cannot otherwise be obtained using non-contrast imaging techniques.
Gadolinium in the News
A quick Google search will show you that Gadolinium has been in the news recently, and you may have come across statements about gadolinium based contrast dyes leaving behind deposits in the body. These statements have been made by highly regarded medical research institutions who are rightly tasked with spending a great deal of time investigating possible risks or side effects from the use of all medicines, including contrast dyes.
Research has identified that gadolinium has the potential to remain in the body after the scan is complete, although the risk is deemed to be low and avoidable, and the presence of remaining gadolinium is not thought to have any adverse effect on a patient’s health.
Recently, the Medicines Healthcare Products Regulatory Agency (MHRA) has concluded that while there is no evidence that gadolinium deposition causes harm, they have ordered manufacturers to measure patient tissue for deposition, and advised that it should only be used when “essential” to improve imaging, and at “the lowest effective dose”.
In response, doctors and radiology departments have altered their techniques to ensure that these possible risks are reduced as much as possible. In order to avoid gadolinium lingering in the body after the scan, more emphasis is now being placed on the exact volume of contrast that is really needed, and how necessary it really is for each individual patient. These stricter guidelines enforce the rule that contrast is only ever used when it may provide crucial, even life-saving, medical information.
As explained by Dr Giles Roditi, a consultant radiologist and spokesman for the Royal College of Radiologists, “the benefits of accurate MRI scanning far outweigh the small risk of an adverse reaction”.
He said: “The risks from gadolinium contrast, as long as we are giving them to the right patient for the right indication are very, very low, and you have to balance the risks of not knowing the diagnosis you have come to find out against the risk of not having the scan at all.”
Gadolinium and the Kidneys
For some years, radiology departments have also been aware of very rare cases where patients who have received Gadolinium contrast agents have developed a condition called nephrogenic systemic fibrosis. The first case identified was in Denmark in 2006 and this rare complication is now recognised to exist mainly in conjunction with older generations of MRI contrast (now no longer in use), and only in patients with very poor kidney function who are unable to excrete the contrast agent prior to the gadolinium bonds breaking down, allowing unbounded gadolinium to persist within the body.
As a result, it is now routine that all patients who may need contrast dye as part of their MRI scan to be screened as part of the initial safety questionnaire, to make sure that their kidneys are working properly, that they are not at high risk of kidney impairment, and that they haven’t had allergic reactions in the past. This screening is not complicated and many centres, including our own, are able to measure kidney function on the spot with a simple pin prick blood test if necessary.
Again, whilst a possible side effect has been identified, there are simple ways in which the risk can be avoided so that contrast dye may be used safely in order to reveal crucial information.
If you have a question, just ask. Patient safety is the number one priority.
If you are concerned about having MRI contrast, then don’t be afraid to bring it up with your doctor or the radiographer, who will both be able to advise you and if necessary, perform a simple blood test to confirm your kidney function. We are also able to conduct a simple pin prick test to show your kidney function in the department if necessary.