Being told by your doctor that you need an MRI scan can feel daunting. What is an MRI scan, will I feel anything, how long does it take? What happens when I get my results? Some of the most daunting questions might be, are they safe, and if I need more than one, how many MRI scans are safe for me to have? It’s understandable to be nervous.
On the whole, an MRI scan is considered one of the safest medical scans for the human body to undergo, as unlike X rays and CT scans, they don’t use radiation. So let’s dig a little deeper and discuss them in more detail, including how many MRI scans are safe.
Is it Safe to Have Multiple MRI Scans?
MRI stands for magnetic resonance imaging, and MRI scans use radio waves and a strong magnetic field to take detailed images of the inside of the human body.
Depending on your symptoms and subsequent diagnosis, you may require multiple MRI scans for the following reasons:
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To clarify the initial findings
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To monitor the progress of a disease
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To monitor the success of treatment
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To follow up after treatment
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To investigate any new or changes in symptoms
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To get a second opinion
As they’re considered one of the safest types of scan for most people, it’s also safe for most people to have more than one.
How Many MRI Scans Can You Have Per Year?
Your medical team will decide how many MRI scans are safe for you to have, depending on your medical condition. On the whole, it’s safe for most people to have multiple MRI scans a year.
How MRI Scans Work
An MRI machine uses short bursts of radio waves and strong magnetic fields to produce many images taken from different perspectives, of the inside of the body.
The human body is around 70% water, and each water molecule has a hydrogen atom. When the strong magnets are turned on and off, these hydrogen atoms scatter and realign. The bursts of radio waves, along with sophisticated computer programming, pick up these patterns to create detailed images. A radiologist then uses these images to distinguish between normal, healthy tissue, and diseased or damaged tissue.
MRI scans can be used to look at soft tissues such as muscles, ligaments and tendons, organs, including the heart, brain, liver and kidneys, the blood vessels and bones. They’re routinely used to scan the:
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Head and neck
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Brain and spinal column
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Back
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Heart
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Breasts
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Prostate
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Liver, kidneys and other organs
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Womb
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Urinary tract
Sometimes, your medical team will use a contrast dye (also sometimes called a contrast agent) that’s injected into a blood vessel (normally in the arm or groin). These dyes help certain areas show up on an MRI scan with more clarity and distinction, such as the blood vessels, organs and breast tissue.
During an MRI scan, you will be required to lay still on a bed that moves into the MRI scanner, and to remain still for the duration. An MRI scan usually lasts between 30 and 90 minutes. You will hear a loud knocking noise as the magnets turn on and off, and you may feel nervous about the closed nature of the tunnel-like MRI machine. You will be provided with a medical gown and ear plugs, and if you struggle with enclosed spaces, your medical team can provide a mild sedative.
Radiation
MRI scans don’t require the use of radioactive materials or radiation to produce images. Therefore, unlike with X rays and CT scans that do, there’s no risk of radiation exposure or sickness.
Magnetic Fields and Their Effects on the Body
An MRI scanner uses strong magnets, but there are no known side effects caused by these magnets at the strength they’re used at in medical practice.
However, the magnets used can cause magnetic metal objects within the body to move and potentially cause serious harm. They may also cause any metal within the body to heat up, again causing harm. We’ll discuss these in more detail in the next section.
General Guidelines for MRI Safety
Most people are suitable for MRI scans, but there are some reasons why some may not be suitable. These include those with the following, that may react with the magnetic field used in an MRI scanner:
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Metal implants such as brain aneurysm clips or any other kind of surgical clips, staples or stents
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Medical devices such as a cochlear implant, pacemaker or defibrillator
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Metal plates, wires, rods or screws
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Glucose monitors and insulin pumps
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Artificial joints
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Dental work that contains metal
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Intrauterine devices (IUDs)
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Metal fragments inside the body, such as lodged bullets or metal shards
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Tattoos or permanent makeup that contain metal
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Piercings that cannot be removed
If you have any of these, or anything else that concerns you, discuss them with your medical team. They may be able to continue with your MRI, whilst being aware of any metal implants or metal fragments inside your body.
Due to the strong magnetic fields used during an MRI, you will also need to leave anything containing metal outside of the scanning room including:
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Keys
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Bank cards
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Mobile phones
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Other electronic devices
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Removable medical devices such as hearing aids
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Jewellery
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Watches
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Hair clips
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Clothing or accessories with zips, buttons and other fastenings
There’s no evidence to suggest that MRI scans are dangerous to an unborn baby. However, if you’re pregnant, let your medical team know. They will weigh up whether to perform an MRI scan or not, depending on the severity of your symptoms.
Factors Affecting MRI Frequency
As we’ve just discussed, there are some people who aren’t suitable for an MRI scan, and this is mainly due to the presence of metal in the body. If you’re unsuitable for one MRI scan, you’ll be unsuitable for multiple or repeated MRI scans. If your medical team thinks they can carry out a scan safely, even if you have some kind of metallic object in your body, they will proceed with caution and may limit the parts of your body that enter the MRI machine.
There are other factors that will also impact how often you may be able to have an MRI scan, including having kidney disease and the prospect of having an allergic reaction to the contrast dye.
Concerns About Contrast Dye
Some MRI scans require the use of a contrast dye. These dyes usually contain a mineral called gadolinium, which is highly toxic. For this reason, it’s combined with a substance called a chelating agent, which makes it safe for most people.
However, some people will experience an allergic reaction to gadolinium, particularly those with kidney disease as the kidneys are responsible for eliminating the dye from the body after your MRI scan. If you have any condition affecting your kidneys, you’re unlikely to be able to have an MRI scan with contrast.
Some people don’t know they have an allergy to gadolinium. If you develop symptoms of an allergic reaction, such as a skin rash or breathing difficulties during your MRI, your medical team will recognise these and will be on hand to help give you treatment.
Potential Effects of Frequent Scans
Some studies suggest that having more than four MRI scans using gadolinium contrast dye may cause a long term build up of gadolinium in the brain that will persist long after a final MRI scan. The effects of this are still being investigated and for now, the benefit of an MRI scan still outweighs the potential risks. If you require four or more, these risks will also be weighed up against the benefits.
Expert Recommendations and Studies
Given the potential for long term build up of gadolinium in the brain following four or more MRI scans with contrast, the American healthcare regulator, the FDA (the Food & Drug Administration) has advised radiologists to “limit gadolinium use to clinical circumstances where the additional information provided by the contrast is necessary”. In other words, your medical team will only use this contrast dye when extra clarity and distinction is required.
Get an MRI Scan
If you’re concerned about a health issue and you think you need an MRI scan, or your doctor has recommended one, you may be worried. But it’s important to keep in mind that the risks of leaving a potential health problem unchecked are greater than the minimal risks posed to most people from having an MRI scan.
In terms of how many MRI scans are safe for you, it will depend on your personal circumstances. In general, MRI scans are considered safe for most people.
Book your private MRI scan through Scan.com and your medical team will discuss all of your options, and the potential risks, with you. If you’d like to see a consultant before deciding whether an MRI scan is right for you, book an appointment with one of our experts.
References
Green, C. (2018, September 27). Is it safe to undergo multiple MRI exams? Healthline. https://www.healthline.com/health-news/is-it-safe-to-undergo-multiple-mri-exams-080415#Limited-Use-of-Tests-Recommended
Risk factors. (n.d.-b). Stanford Health Care. https://stanfordhealthcare.org/medical-tests/m/mri/risk-factors.html
Website, N. (2024c, November 11). Who can have one. nhs.uk. https://www.nhs.uk/conditions/mri-scan/who-can-have-it/
Fletcher, J. (2023, March 6). What to know about MRI contrast side effects. https://www.medicalnewstoday.com/articles/mri-contrast-side-effects
Radiological Society of North America (RSNA) and American College of Radiology (ACR). (n.d.-d). MRI Safety. Radiologyinfo.org. https://www.radiologyinfo.org/en/info/safety-mr
