Magnetic Resonance Imaging (MRI) is a non-invasive examination designed to produce detailed images of the human body by utilising a strong magnetic field and radio waves. MRI is suitable for imaging most body parts (such as musculoskeletal and neurological systems) and is useful for check-up, medical diagnosis, staging of disease and follow-up without exposing the body to radiation.
The MRI machine uses a strong magnetic field and radio waves to generate signals from hydrogen nuclei (protons) in your body. Protons can be found in water molecules, which is abundant in human. The signals received would then be used to generate images of your body.
Preparation for your MRI starts at home with the following few points to keep in mind:
When you arrive for your examination, you will be asked to change into clothes provided by us to ensure there would not be any ferromagnetic items on your clothes. For female patients, please kindly remove your bra as well since there may be metallic wires inside.
For female patients, please inform the staff before the examination if you are or may be pregnant. Since the long term or delayed biological effects of MRI examinations on foetus are not fully known, pregnant patients in the first trimester are not recommended to have MRI scan, and exams are only performed if your doctor has decided that the benefit of an MRI scan outweighs the risk.
For your own safety, it is advised that you inform us before the scan if you:
Due to the strong magnetic field of MRI scanners, it is crucial not to bring along any loose ferromagnetic items with you into the examination room, such as glasses, watches, jewellery, safety pins, hair-pins etc, and items which may be damaged by the strong magnetic field such as credit cards, Octopus card, hearing aids, smartphones etc. Other accessory items such as braces and corsets need to be taken off as well because they may contain ferromagnetic substances.
The MRI scanner is a cylinder shaped machine with an inner tube surrounded by a strong magnet. Patients lie on a moveable table which glides in and out of the magnet for examination.
Our MRI staff will help you lie on the table in a comfortable position. The table will glide in the machine gently until the examined body part is in the middle of the scanner. The tube is open on both ends so you can be relaxed during the examination. A call bell will be provided during the examination for you to inform radiographers if you are feeling unwell or need to be attended.
Examination time varies depending on the body part imaged and the exam type (ranging from 15 minutes to more than an hour). Please be patient and keep still throughout the examination, as any movement during the scan will produce blurred images (just like taking a photograph) and will prolong the scan time as images would need to be reproduced.
Throughout the examination, the scanner will generate some noise.
You should breathe normally unless instructed by the radiographers to hold your breath for certain examinations.
Some MRI examinations require administration of contrast agent (Gadolinium) to provide more detailed information for precise diagnosis. When contrast agent is administered via the IV catheter, you may feel a cool sensation. Our radiographers will inform you beforehand. Please try to be calm and keep still.
Gadolinium-based contrast agents are in general safe pharmaceuticals and are less likely to produce an allergic reaction compared with the iodine-based contrasts used in X-ray and CT examinations. However, undesirable side effects may still occur:
Mild reactions: Temporary metallic taste in mouth, coldness/warmth/pain at injection site, itchy skin, nausea, headache etc. (less than 1/100 patients)
Severe reactions: Bronchospasms, hypotension or other severe adverse effects or even death is extremely rare (less than 1/130,000 patients)
In 1-7% of patients with severely impaired kidney function kidney or undergoing dialysis treatment, administration of gadolinium would cause nephrogenic systemic fibrosis (NSF), and deaths have been reported. However, this is very rare.
If you have been allergic to any MRI contrast agents before, please inform our staff prior to your examination.