Magnetic resonance imaging (MRI)
What is magnetic resonance imaging (MRI)?
Magnetic resonance imaging (MRI) is a non-invasive imaging technique that uses a combination of powerful magnetic fields and radio waves to produce detailed images of the body.
What is an MRI scanner?
A MRI scanner is a large tube containing powerful magnets (see picture). It provides a very detailed image of the inside of the body.
Why would I have an MRI scan?
An MRI scan can be used to examine almost any part of the body, including the blood vessels, internal organs and musculoskeletal structures. Benefits of choosing MRI imaging compared to other similar imaging modalities, such as computed tomography (CT), include the lack of exposure to radiation and better imaging assessment of muscular structures; particularly relevant for thoracic outlet or popliteal entrapment syndromes.
How does an MRI scan work?
The majority of the human body consists of water molecules; hydrogen and oxygen atoms. Within each hydrogen atom there is a smaller particle called a proton. Protons act like tiny magnets and are very sensitive to magnetic fields. When you lie within the MRI magnetic field, the protons in your body align in the same direction, much like a magnet influencing the direction of the needle of a compass. Bursts of radio waves are then focussed on the body region of interest to knock the protons out of alignment. When the radio waves are turned off, the protons realign emitting a radio signal that is detected by the scanner providing information about the exact location of the protons in the body. Protons in different tissues realign at variable speeds producing distinct signals allowing the MRI scanner software to distinguish between different types of tissues. In the same way that millions of pixels on a computer screen can create complex pictures, the signals from the millions of protons in the body are combined to create a detailed image of the inside of the body.
What happens during an MRI scan?
This examination is performed as an outpatient. During an MRI scan you are positioned on a moveable examination table that slides into the MRI scanner tube for the duration of the scan. You hear a loud tapping noise when images are being acquired. You may require an injection of contrast into a vein in the arm. This contrast material does not contain iodine and is thus less likely to cause an allergic reaction than the contrast agents used during a CT angiogram (CTA). Depending on the body region and type of scan being performed, the duration of the scan can vary from 15 minutes to 1 hour. Once the scan is completed, the radiologist will check the images to ensure no additional pictures are required and then you will be able to leave.
Is an MRI scan uncomfortable?
An MRI scan is not painful. Occasionally people who suffer with claustrophobia find the process of lying still within the MRI scanner disconcerting; where required a light sedative can be arranged but this is rarely required.
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Are there any risks from MRI scans?
An MRI scan poses very little risk; the main one, albeit extremely rare, is nephrogenic systemic fibrosis that is believed to be caused by the injection of high doses of gadolinium-based contrast material in patients with very poor kidney function. Everyone having an MRI scan with contrast (MRA) undergoes kidney function assessment prior.
What happens after an MRI scan?
The scans are individually reported by our radiology team and reviewed with each client’s lead surgeon. You will then be reviewed in clinic to discuss the scan findings and how we may be able to help.