MRI is a diagnostic scanning technique which uses no radioactivity or X-rays and thus is why it's often described as being a safe modality.
The human body is predominately made of water molecules which contain hydrogen protons. When you are placed in a strong magnetic field, the tiny magnetic fields of the hydrogen protons (which normally move around randomly) are aligned to the magnetic field.
A brief radio pulse is rapidly switched on and off. This makes the protons' magnetic fields spin round in unison and emit a weak radio signal. By altering the timing of the radio wave applications it's possible to produce images which show up the various body tissues as shades of grey. The contrast on MRI images is very good and the operator can change the parameters to give images that demonstrate the anatomy of the area and also, in many cases, highlight common disease processes.
An MRI must not be performed on people with certain implants in their bodies due to the powerful magnet that's used in the scanner.
Because of this, when you arrive at the scan department, you'll be asked to fill out a safety questionnaire to verify your personal safety. Please ensure that you answer the questions carefully and accurately. It's absolutely essential that you don't enter the scan room if you have a heart pacemaker.
It’s important that you tell us before the scan if you:
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 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.
In some instances, you may need an injection to enhance the images. The injection is unlikely to have side effects but you should have a blood test (U&E) in advance with your GP to check your renal (kidney) disease. Please tell the MRI staff if there was any problem with this U&E test before any injection.
Traditional X Ray contrast media often contains iodine; MRI contrast media usually contains gadolinium or iron oxide combined with other products to reduce toxicity and make them safer to inject. However, if you have any concerns about your injection or have any serious allergies, particularly to previous injections of MRI contrast media (gadolinium or iron) please let us know in advance.