Potential Risks and Side Effects of MRI Scans

An MRI, or magnetic resonance imaging, scan is a type of medical scan that can be used to diagnose different types of diseases and conditions. MRI scanners can be used to scan almost all parts of the body and can help doctors diagnose conditions and disease that affect:

• The heart, brain and blood vessels, such as a brain aneurysm 

• The bowel, for example, Crohn's disease

• The back, such as degenerative disc disease

• The brain, for example a stroke or Alzheimers’ disease 

• The joints, ligaments or muscles

• The organs including the liver and kidneys 

They’re also very effective at detecting different types of cancer affecting different parts of the body. 

MRI scans are usually carried out on an outpatient basis in the radiology department of a hospital or clinic. You will be given all the information you need for the day of your appointment, and you’ll be provided with a hospital gown to wear for the duration. MRI scans are performed by a radiographer and the results read and analysed by a radiologist. You can normally go home the same day and begin to carry out your normal activities the following day. 

If you have a private MRI scan, you can expect the results within a few days to a week. It may take several weeks to get your results if you have an NHS MRI scan, but the technology used is the same. 

Is There a Risk When Having an MRI Scan?

To have an MRI scan, you’ll be required to lay on a bed that slowly moves into an MRI scanner, a long tunnel-like machine that contains powerful magnets. The scan itself utilises a strong magnetic field and radio waves to create detailed images of the inside of the body. 

The human body is made up of around 70% water, and these water molecules are made up of tiny atoms of hydrogen and oxygen. Each hydrogen atom contains even tinier particles called protons, and these protons react to magnetic fields. 

During an MRI scan, an electric current is used to turn the strong magnets on (causing the protons to line up, rather like the hands on a compass) and the radio waves are then given in short, intermittent bursts (causing the protons to scatter and then realign). 

The movement of the protons sends out radio signals that special receivers in the machine detect. Like pixels on a TV or computer screen, the location of the protons detected by the receivers then creates an image that allows specialist radiologists to distinguish between bones, organs and soft tissues, and whether or not there’s presence of disease. 

Unlike X-rays or CT scans, MRI scans don’t use ionizing radiation, so the risk of harmful radiation exposure isn’t a consideration. (This doesn’t mean that X-rays and CT scans aren’t useful. They’re an important part of diagnosing different types of disease; their use just needs to be limited.)

You won't feel anything during an MRI scan, however, there are some MRI scan side effects and safety considerations that will affect some people. If you’ve been told you need an MRI scan, or you’re thinking about having one, here’s what you might need to consider.

Discomfort From Lying Still for an Extended Period

An MRI scan can last for around 30 minutes, sometimes longer (up to 90 minutes) and during this time, you will need to remain very still. The only movement you will be asked to make is to potentially take deep breaths and hold them for a few seconds. 

If you have mobility issues or problems keeping still or holding your breath for any length of time, let your medical team know as they may be able to make alternative arrangements. 

Claustrophobia or Anxiety in the Confined Space

Feeling nervous about having any kind of test or medical procedure is completely normal. But some people who have claustrophobia or who struggle with being in a small space, may develop anxiety around having an MRI scan. Your medical team may be able to provide a sedative to help calm your thoughts which can be very beneficial. 

Temporary Dizziness or Lightheadedness After the Scan

Prior to most MRI scans, you can eat and drink normally beforehand, but in some cases, you’ll be asked not to eat or drink in the hours prior to your scan. Your medical team will let you know in advance. If you haven’t had anything to eat or drink, you may feel dizzy or lightheaded afterwards. You may also feel this way if you have a contrast dye MRI (see below) or if you’ve become very worried and anxious about your scan or the results. 

If you feel faint, tell your radiographer, who will help you up into a seated position and help you to your feet when you feel able. 

Loud Noises Causing Temporary Discomfort

The electric currents used to turn the magnets on and off in an MRI scanner cause a loud banging or knocking sound throughout the duration of the scan. To many, this can be understandably worrying and frightening, especially as you’ll also be in a confined space. 

You’ll be given ear plugs or headphones to wear that will help to muffle out some of the sound and you may also be able to listen to music. Throughout your MRI scan, you will be able to talk to your radiographer who can also help to put your mind at ease.

Twitching Sensation from Muscle or Nerve Stimulation

Although you won’t be able to feel the effects of the strong magnetic field on the protons in your body, you may feel a mild twitching sensation in your muscles as your nerves are stimulated. This is nothing to be concerned about, but if you’re worried, let your radiographer know. 

Allergic Reaction to Contrast Dye

Some types of MRI scans require the use of a contrast dye in order to get more detailed images. A contrast dye is a chemical that’s injected into the body through a vein in the arm or groin. 

Some people have a mild allergic reaction to this dye, because it contains a substance called gadolinium that can cause symptoms including:

• Nausea and sickness

• Lightheadedness

• A skin rash

• Headaches

These symptoms tend to be mild and will usually disappear after a day or two. You’re at a higher risk of developing these MRI scan side effects, and potentially more severely, if you have kidney disease or a known allergy to gadolinium. Speak to your medical team if you’re concerned. 

Metallic Taste in the Mouth 

If a contrast dye is used during your scan, you may also experience a metallic taste in your mouth. This will be temporary, and can be helped by drinking water afterwards to help take the taste away and to flush the contrast dye from your body via your kidneys. 

Bruising or Discomfort at the Injection Site 

If a contrast dye is injected into a vein, you may develop bruising, swelling or pain at or around the injection site. If you bruise easily or you’ve developed bruising from having blood tests or injections in the past, you may be more likely to experience the same after a contrast MRI. 

While uncomfortable, this is usually nothing to be concerned about, and will disappear after a few days. However, if the pain or bruising gets worse, it doesn’t disappear or the area feels numb, speak to your medical team. 

Interference With Medical Implants or Devices

There’s no evidence that the strong magnetic fields and radio waves used in an MRI cause damage to the human body, and for this reason, they’re considered very safe. But if you have metal objects or implants, you may be unsuitable as they may be affected by the powerful magnets. Let your medical team know if you have any of the following:

• Cochlear implant 

• Pacemaker or any other kind of electrical implant 

• A drug implant 

• Surgical clips, valves, shunts, stents, coils or filters 

• Metal plates, rods or screws 

• Artificial joints or implants 

• Extensive dental work 

Bullets, metal shrapnel and other kinds of metal fragments (such as those caused by working with metal) in your body (especially near your eyes) can also mean that you’re unsuitable for an MRI scan. 

Heating, Burns and Thermal Injuries

The bed used in an MRI scanner is layered with an insulating pad to prevent heating or burns. If this moves out of place, you may feel a burning sensation. If so, speak to your radiographer immediately. 

Most tattoos and permanent makeup are considered safe in an MRI scanner, however some contain metal fragments. If you’re concerned or you start to feel any heat on or around a part of your body that has a tattoo, tell your radiographer straight away. 

Sedation and Anesthesia

As mentioned above, you may be given a sedation prior to having an MRI scan, to help you manage the process emotionally. It isn’t often that anaesthetic is used before an MRI scan, but babies and young children may well be anaesthetised so that they remain still.

Sedation and anaesthesia medications can cause MRI scan side effects such as dizziness, lightheadedness and tiredness. Your medical team will discuss this with you and help you slowly return to seating and standing positions when you’re ready. 

Magnetic Objects in MRI Scanners

You should remove any jewelry, hair clips, piercings and external devices that are safe to remove before entering the MRI scanning room. You should also leave keys, other metallic objects, bank cards and mobile phones outside of the room too, as they can be attracted to the magnets in the MRI scanner. 

Find an MRI Scan

In the majority of cases, having an MRI scan is considered safe, but you should let your radiographer know if you’re pregnant or breastfeeding. 

As we’ve detailed in this article, there may be some instances where you’re unsuitable for an MRI scan, or you may experience discomfort or an allergic reaction. If you’re unsure if an MRI is right for you, book an appointment to see one of our private consultants who can advise you and put your mind at ease. If you’d like to have an MRI scan because you’re concerned about a certain aspect of your health, book a private scan with us today. 

References

Website, N. (2022a, August 5). MRI scan. nhs.uk. https://www.nhs.uk/conditions/mri-scan/

Risk factors. (n.d.). Stanford Health Care. https://stanfordhealthcare.org/medical-tests/m/mri/risk-factors.html

Harvard Health. (2021, September 30). Radiation risk from medical imaging. https://www.health.harvard.edu/cancer/radiation-risk-from-medical-imaging