How does an MRI scan work?

An MRI scan is one of the most fascinating diagnostic tools of modern medicine, as it works by taking advantage of the composition of the human body, using both radio waves and magnetic fields to produce highly detailed images of what’s happening inside the patient. Most of the human body is made up of water; the exact percentage can vary from person to person, as fat doesn’t hold quite as much as lean tissue, but most adults will be around 55 to 60% H2O. Those hydrogen atoms are what makes the MRI scan work – at their center is a small particle called a proton, and it’s these magnet-like particles that make the scan an effective diagnostic tool.

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If you have ever played with a magnet, you will know that you can pull a compass needle away from where it would point without interference. The magnets in the scanner work in conjunction with the radio waves to create pictures – just as the magnet changes the direction of a compass needle, the magnets in the scanner pull all the protons in the same direction. The radio waves knock the protons out of alignment again, and short on-off bursts in areas of the body requiring examination form the pictures required to make a diagnosis.  Additionally, different types of tissue produce different signals, so the scan can be particularly useful in distinguishing healthy tissue from potentially cancerous areas, and even how deeply the tumor might be seated within the body. This is an invaluable tool in determining whether cancer surgery has been successful or not.

 

Having an MRI scan can make some people feel anxious, but familiarity with the procedure can help to take away a lot of the fear. The duration of the scan will depend entirely on the size of the area to be covered, but even a full-body scan is unlikely to take longer than 90 minutes. If you are very claustrophobic, you can ask for a sedative to help you relax whilst the scan is taking place, and it’s usually possible to bring your own music to be played into the scanner to pass the time. The scanner can be very noisy, and you will be given earplugs and headphones to wear to protect your hearing.

 

Because of how it works, an MRI scan is unfortunately not for everyone – even though it is unlikely to hurt your baby, do mention if you are, or if you might be pregnant. Metal objects can interfere with the scan too; remove piercings, dentures, glasses and wigs with metal clips, and try to arrive for your appointment in clothes that don’t have metal fastenings. Before your scan, you will be given a questionnaire to fill in, so don’t forget to mention any metal implants, including fillings and IUDs. It won’t mean you can’t have your scan, but the medical staff carrying out the procedure can make allowances if they are aware in advance.

 

Image courtesy of [stockdevil] at FreeDigitalPhotos.net

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