Having an MRI scan done is certainly a strange experience. You’re asked to remove all jewelry and credit cards, questioned about any metal objects you may have inside your body, and asked to lay down on a table where you have to be perfectly still as your body is guided into the opening of what essentially looks like a giant donut tube.
But what’s inside the giant donut tube? Why were the removal of metal objects and credit cards so important? Wonder no more, because below we’ll answer those questions and more.
Giant donut tube unmasked: What makes an MRI so different and unique in comparison to other imaging sources is its magnet. The tube the patient enters that runs through the magnet is called the bore. The MRI magnet is rated using a unit of measure called a tesla (named after the famous scientist Nikola Tesla,) although another common unit of measure used is gauss. (1 tesla = 10,000 gauss.) Extremely powerful, the magnets used in an MRI are stronger than the Earth’s magnetic field, which measures 0.5 gauss. Typical MRI machines are 5,000 to 20,000 gauss!
In order for the MRI machine to work, a magnetic field has to be created. This happens for MRI machines that use superconducting magnets when a current of electricity is passed through the many coils of wire inside of it. It creates a magnetic field of up to 2.0 tesla. Then the magnetic field has to be maintained. That’s where superconductivity comes in!
Superconductivity is reducing the resistances in the coils of wire to almost zero. In order for this to happen, the coils of wire are continually bathed in liquid helium at 452.4 degrees below zero. The cold is insulated by a vacuum. Superconductive magnets are super expensive, but it’s worth it for the excellent image quality and economical value created by superconductivity.
Besides the large superconductive magnets, there are five other magnets that come into play inside the MRI machine. Resistive magnets, permanent magnets, and three gradient magnets.
Resistive magnets are similar to superconductive magnets, but don’t have liquid helium, which means they require a large amount of electricity and will be expensive to operate above 0.3 tesla.
When it comes to permanent magnets, they have a constant magnetic field, but don’t have a large one due to them being so heavy.
Then there are the three gradient magnets as well. These magnets aren’t as strong as the main magnetic field, but are used to create a variable field in order to scan different parts of the body.
So many magnets! Now you know why you have to remove all metal objects and credit cards. The metal is a given, but the magnets in the MRI would strip your credit cards of their own magnet strip.
Another part of the MRI machine is a set of coils that correlate to different parts of the body: knees, heads, necks, etc. They transmit radiofrequency waves into the patient’s body, and conform to the contour of the body part being imaged.
Other parts of the MRI machine include the powerful computer system and the patient table which slides into the bore. Also fun to note is that the exact center of the MRI machine is called the isocenter, and it’s where the patient’s body has to be in order for the scan to begin.
Now you know what’s in that giant machine you hear so much about. If you are getting ready to have an MRI scan be sure to speak with your radiologist about precautions and safety measures that need to be taken. Contact Clermont Radiology today to schedule your appointment!
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