What is an MRI Scan? how does it work?

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MRI scanning

Magnetic Resonance Imaging

MRI scanning is a powerful medical diagnostic tool that uses a strong magnetic field to produce high-quality, images in multiple planes or directions. The images are generated using superconducting magnets and pulsed radio waves. Magnetic resonance imaging uses non ionising radiation, unlike x-rays which uses radiation.
MRI scanning, however, is not suitable for everyone, this article will provide some of the reasons why this type of scan may not be suitable. MRI scanning has been in use since the early 1980s and has no known side-effects. It has become the investigative method of choice for many neurological and musculoskeletal conditions and is used in all areas of the body. It helps identify problems in soft tissue in particular – nerves, muscles, ligaments and tendons. For example, MRI scanning is widely used to investigate the brain, heart, bones, joints, breasts and other organs such as lungs and the liver.

Having an MRI scan

Important things to tell us before having an MRI scan

It's important that you tell us before the MRI 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 on your head
  • have any metal implant in your body
  • have had an injury to your eyes involving metal or metal fragments

Could you have metal fragments in your eyes?

If there is a possibility that you might have metal fragments in the eyes – as a result of a penetrating injury, or from working with metal at high speed – you may need to have an X-ray to ensure that there are no particles present. This is because the MRI scanning magnet can exert a pull on small fragments of metal. Such metal fragments can remain unchanged for many years – so we will need to be absolutely sure, regardless of how long ago a possible injury might have occurred.

Before you arrive

  • We make sure that it’s appropriate for you to have an MRI scan. We’ll ask you some basic health questions when you book and you’ll be required to complete a questionnaire before your appointment. Unless we let you know otherwise, you don't need to make any special preparations before the MRI scan. You can eat and drink as normal and take any prescribed medicine.
  • Please wear clothing without zips or metal buttons, and leave jewellery and watches at home if possible.
  • If requested, please confirm your appointment by phone before your MRI scan and arrive in plenty of time.
  • Please let us know if you have any disabilities so that we can ensure we are able to offer you the highest quality service. You’re welcome to bring a friend or a relative with you, but for safety reasons we won’t allow them into the examination room.

Preparation for the MRI scan

  • Once you’ve checked in at reception (don’t forget to bring your appointment letter), a member of the radiography team will meet you, explain the procedure and go through your safety questionnaire with you.
  • We might ask you to change into a hospital gown. We’ll provide somewhere to store your personal possessions. You’ll be looked after by the radiography team throughout the procedure – they will explain what’s happening and will be there if you experience any discomfort.
  • You’ll have the opportunity to ask any questions about the scanning process.
  • We might need to give you an injection (known as a contrast medium) to increase the amount of information we can get from the MRI scan, depending on the area we're scanning.

During the scan

  • The examination consists of several scans, each lasting a few minutes with a short pause between each. The whole procedure will take between quarter of an hour and one hour – depending on which part(s) of the body we’re scanning.
  • We’ll ask you to lie down on the scanner bed and we'll make sure you're comfortable so you can stay as still as possible. With magnetic resonance imaging you won’t feel anything, but there is some mechanical noise from the equipment –, we’ll provide you with some ear defenders or ear plugs. For safety reasons, we don’t normally allow anyone accompanying you to come into the examination room whilst the scan is in progress.

After the scan

  • There are no restrictions on normal activity – you can eat and drink normally, drive and return to work immediately after the MRI scan.
  • If we’ve given you a contrast injection we will check you before you leave the scanner. A Radiologist will examine the images shortly after your visit and send a report to your Doctor or Consultant, normally within a few days.
  • For ethical and professional reasons, we cannot discuss results with you. Only your Doctor or Consultant can do this.

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