Magnetic Resonance Imaging (MRI) is a scan that takes cross-sectional images of the body using a strong magnetic field and radio waves. It can produce detailed images of the human body for diagnosis or treatment planning. Some examples include the brain, spine, blood vessels, and the heart.
Although radiation is not used, the very strong magnetic field may interact with some metallic and electronic implants, or metallic foreign bodies (FB), causing injury to the patient, or damage to the implants. Therefore, it is important that we gather any medical history for the above-mentioned items from you before proceeding with the scan.
Most MRI scanners are large, donut-shaped equipment that open on both ends. During the scan, patients will be required to lie down inside the scanner and keep still throughout the scan. It can get rather noisy during the scans due to the magnetic interactions between various parts of the scanner, producing loud "humming", "thumping" or "knocking" sounds. Earplugs and headphones will be provided to minimise the noise.
In certain procedures, injection of an MRI contrast media into the veins (intravenous) or the joint (intra-articular) may be required for better visualisation. MRI contrast media rarely cause allergic reactions. However, do inform your doctor or MRI staff if you have kidney failure or any renal function impairment, or have had a previous allergic reaction to MRI contrast media. Decisions on whether to proceed with the contrast agent will be made on a case-by-case basis.
To help us achieve the best results and experience for you, some preparations may be required. Below are some preparations that will ensure a smooth and successful MRI scan appointment.
You must inform your doctor or our staff before scheduling an appointment if you:
Are pregnant, or there is a chance you may be pregnant.
Are unable to lie down for 30 to 60 minutes.
Have a history of claustrophobia (fear of being in enclosed spaces).
Have a history of reduced kidney function (renal impairment).
Have had a previous allergic reaction to an MRI contrast agent.
Any other surgery or procedures where you are unsure if you had an implant.
In case it is unsafe to proceed with the MRI due to the nature of the implant or location of the metallic foreign body, the scan may have to be rescheduled or cancelled, in discussion with your referring doctor. For your safety, you must provide us with accurate information.
Fasting and medicationsIn certain abdomen scans, fasting for four hours before the scan is required. You will be advised accordingly if there is a need to fast. Otherwise, there is no dietary restrictions and you should continue with any medication before the scan.
Outfit and external accessoriesIt is best to leave all jewelry and metallic accessories and valuables at home as you will be asked to remove them before the MRI scan. Please do not apply make-up, hair-sprays, or use coloured contact lens as these may affect the images.
You will be asked to change into a hospital gown, regardless of the region being scanned and the clothes you arrive in. This is because certain materials used in streetwear may affect the scan.
All metallic items have to be removed, including any jewelry, removable dentures, hearing aids, hairpins, or any other objects that may interfere with the MRI procedure.
Our Radiographer will go through the MRI safety screening checklist with you one more time before starting. This is to ensure it is safe for you to have an MRI.
If MRI contrast administration may be required for your scan, an intravenous cannula (a thin tube for collection of sample and delivery of fluid into a vein) will be inserted into one of the veins on your hand or arm before the scan.
Please inform the staff performing the cannulation if you have had an allergy to MRI contrast before.
In case a blood test was ordered to be done before the MRI scan, the blood will be drawn at our department and sent to the laboratory for testing.
You will be accompanied into the scan room by an MRI-trained Radiographer.
The procedure will be explained to you and your cooperation is very important for the success of the scan.
Earplugs and headphones will be provided to minimise the noise during the scan.
Depending on the region of scan, the Radiographer will position you accordingly.
You must keep still throughout the scan. Therefore, please let the Radiographer know to make you as comfortable and relaxed as possible.
MRI scans generally take between 30 and 60 minutes depending on the nature of the procedure requested by your doctor.
You will be given a call bell which you can press at any time should you need assistance or feel unwell during the procedure.
However, rest assured that most people can go through with the scans, and the Radiographer will be observing you at all times from outside the scan room. This is done through a window in the adjoining room as well as closed-circuit television (CCTV).
The Radiographer will also communicate with you along the way through an inter-comm to let you know the scan progress.
If you had a cannula inserted, it shall be removed by our staff before you can change back to your clothes.
In case you do not feel well after the scan, for whatever reasons, please let the Radiographer know immediately. It is possible to get our department doctor to review your condition.
Our radiologists will review and report your scan images. The scan results will be sent electronically to your referring clinician, who will discuss with you on your next appointment.
There is generally no special care needed after an MRI and you should be able to resume your usual diet, activities and all medication, if any.
In exceptional cases such as MR arthrograms (MRI with injection of contrast into the joint) and MR Enterography (MRI of the small intestines), you will be informed of the post-scan care separately.
On the rare occasion of delayed contrast reaction after you leave the department, you may:
Visit a general practitioner (GP) clinic nearest you for mild symptoms such as itch, hives, or rashes.
Visit the nearest Emergency Department or call 995 only if you have severe, life-threatening symptoms such as difficulty in breathing.
In any of the above scenarios, do inform the doctor that you have had an injection of an MRI contrast media earlier in the day.
If you notice any pain, redness, or swelling at the IV injection site, you may visit your GP or come back to our department to get it checked by our doctor.
If MRI is so good, why do I still have to go through other imaging procedures such as x-ray or CT scan?While MRI produces detailed images of the body, it is not able to answer all or all aspects of the diagnostic question at hand. Your doctor will order the most appropriate imaging method based on the diagnostic question and your medical history.
Are there any limitations imposed by the MRI scanners?Our MRI scanners have the physical limitations:
Maximum patient weight: 250kg
Maximum diameter / width: 70cm (including both arms)
Contributed by Department of Radiology.