ABC of Vascular Disease

Magnetic Resonance Imaging

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1. What is an magnetic resonance imaging?
Magnetic resonance imaging (or MRI) is a new method of taking very detailed images of the inside of the body but without using x-rays.  The images are created using sophisticated computer analysis of radiowaves that are directed at the patient, but in order to create useful images the patient must lie inside a very strong magnetic field which is controlled by the computer as the patient is scanned.  The whole process is completely painless and requires no contact with the patient.  Occasionally a special dye is injected into the vein in the arm and allowed to circulate in the blood to enhance the images of the blood vessels.

2. Are there any special precautions to take before having the MRI?
Most MRI machines consist of a tunnel that the patient must lie in during the scan.  You must lie still during the scan to avoid "blurring" the pictures and some patients find this a bit claustrophobic.  The MRI machine uses very, very strong magnetic field which you cannot feel, but if you have any metal on (or in) you, it may be affected by the magnetic field and can be hazardous.  Patients with metal implants may not be able to have an MRI scan.

3. What are MRI scans used for?
MRI scans are very good at looking at the "soft" tissues that do not show up very well on x-rays and often very poorly on ultrasound.  MRI images can be generated by the computer so that you literally can be looked at from all directions!  Modern MRI machines can also detect the flow of blood in the arteries and veins without repeated injections of dye into the artery (as is needed for an angiogram) and these pictures of the blood vessels can be looked at in three dimensions.

S.R.Dodds 2006

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