Hong Kong Imaging and Diagnostic Centre

Magnetic Resonance Imaging (MRI)


If you have never had an MRI scan before, you might not know what to expect. This brief guide is designed to answer any questions you may have:

What is an MRI Scan?

Magnetic Resonance Imaging (MRI) is a special radiology technique that uses a powerful magnet, radio waves and computers to produce detailed images (or scans) of the inside of the body.

MRI can detect very small changes in the body’s structures, which helps make a proper diagnosis and allows close monitoring of different medical conditions.

It's suitable for every part of the body, including the bones and soft tissue (such as blood vessels, ligaments and muscles) and the brain. MRI doesn’t use X-rays.

What to expect

Having an MRI isn’t painful or uncomfortable, although some patients may feel a little anxious or claustrophobic. If this is the case, please tell the technician beforehand.

Once you check in at reception, you will be shown to a small private changing room where you will be given a gown to cover yourself (depending on the area to be scanned). You will be asked to remove all necklaces, earrings and metallic objects. You will be provided with a secure locker to place your valuables. Once you have changed, the technician will bring you to a private area to discuss the scan and ask you some questions.

The whole procedure should take between 15 minutes to two hours – depending on the specific parts of the body being examined.

How is an MRI done?

The MRI scanner is a tube made up of a giant circular magnet, attached to which is a moveable bed that glides inside the magnet.

The technician will ask you to lie on top of the bed on your back and will make sure you are comfortable. The bed will then be gently glided inside the scanner and the part of your body that is to be examined will be positioned in the middle of the scanner. It is open ended so you will not be completely enclosed at any time.

You won't feel anything at all, but you may hear some mechanical noises produced by the scanner – we can provide you with ear defenders or earplugs.

Several scans will need to be taken, each lasting a few minutes with a short pause in between. It is very important to lie still and breathe gently during this process. If you move, it can affect the images, and they may need to be taken again. The technician will guide you on when to remain motionless.

The technician will be able to see and hear you clearly during the scan. You will also be given an alarm call button to hold which you can press to get your radiographer's attention at any time.

If you are extremely nervous, or claustrophobic, speak to your doctor in advance. They may offer you a sedative to help you relax during the scan.

Contrast Agents

In some cases it may be necessary to view certain tissues and blood vessels more closely. This is achieved by using a contrast agent.

The contrast material used for MRI is called gadolinium. It is less likely to produce an allergic reaction than the iodine-based materials used for x-rays and CT scanning. However, very rarely, patients can experience an allergic reaction, although these are usually mild and can easily be controlled by medication. Severe reactions are rare.

Nephrogenic systemic fibrosis (NSF), is a rare complication that can occur when gadolinium-based contrast agents are given to patients with severe kidney disease. For this reason, this contrast may be withheld in some patients with severe kidney disease. Please advise the technician if you suffer from any form of kidney disease.

The gadolinium is injected into a vein in your hand or arm. You may initially experience a cool sensation, which this should pass within a few seconds.

If you have past sensitivity to any contrast dyes, or have any allergies, please let the technician know before you have this procedure.

What to expect afterwards

You will usually be able to go home directly after the scan. However, if you have been sedated, it's best not to drive, drink alcohol, or sign any legal documents for 24 hours afterwards. In these instances, you should ask a friend to accompany you home.

Your radiologist will examine your MRI scans and will send the film and report to your referring doctor.

What to tell us

MRI scans aren’t usually done on pregnant women, however they can be done after the first three months of pregnancy if absolutely necessary. If you you are, or if there is any chance you could be pregnant, please tell your radiographer before your MRI appointment.

Preparing for your MRI

Most MRI scans don’t require any special preparation in advance, however, for ease:
  • Eye make-up shall be avoided on the day of examination
  • If you're having an abdominal or pelvic scan, you are required to fast for 2 to 4 hours and you may keep drinking water as normal
  • If you’re having an MRCP scan, you are required to fast for 2 to 4 hours and no drinking is allowed
  • Bring any previous films, discs or reports for comparison.
As the MRI scanner produces strong magnetic fields, it's important to remove any metal objects from your body, including:
  • Watches
  • Jewellery, such as earrings and necklaces
  • Piercings, such as ear, tummy and nose rings
  • Dentures (false teeth)
  • Hearing aids
  • Underwire bras
  • Glasses
  • Wigs (some wigs contain traces of metal)
It's important that you tell us before the scan if you:
  • Are (or might be) pregnant
  • Have a heart pacemaker or an artificial heart valve
  • Have any electro-mechanical devices used for drug delivery
  • Have any surgical clips
  • Have a cochlear implant, a neurostimulator or a programmable hydrocephalus shunt
  • Have had any operations
  • Have had any dental implants or have braces
  • Have any metal implant in your body
  • Have had any injury to your eyes involving metal or metal fragments
Contrast Examination
Your doctor will advise you in advance of the examination
  • Fast for 4 hours prior to the scheduled examination
  • Please inform our staff if you have any kind of allergies