How Does an MRI Work?

How Does an MRI Work?

If you’ve broken a bone, or at least thought you have, you might’ve needed to go for an x-ray, or an MRI, depending on the injury.

There’s no difference between the two, right? They both have the ability to ‘see through’ the human body, allowing doctors to determine if something just ain’t right about you.

Actually, despite similar functionalities and purposes, they are significantly different from one another.

X-rays are primarily employed for diagnostic scans, such as CT imaging, mammograms, or standard x-rays. The high energy photons or light particles used in x-rays allows the light to pass through the tissues of the human body, allowing us to peek inside. But this light exposure must be limited; x-rays are ionizing, meaning they charge atoms (positive or negatively charged) by losing or gaining electrons. Overexposure to ionizing radiation eventually damages the structure of the cell. You can learn about radiation doses here.

MRI machine CT imaging mammorgrams

An MRI, conversely, doesn’t utilize this form of radiation. An MRI operates through magnets and radio frequencies, which are completely harmless to the human body.

The magnet used in an MRI is no ordinary elementary school, science class magnet – this one’s strong enough to pick up a car if it were used in a standard electromagnet! But, the MRI machine employs that potent magnetic field in an alternative way.

The Science Behind MRIs

Hydrogen, the most abundant element in the universe, plays a crucial role in MRIs.

For every water molecule, there are two hydrogen atoms (there’s a point to this, we promise), and remember water makes up 70% of your body. At its nucleus, water molecules have one, positively-charged proton.

These protons are magnetized, and can therefore have what’s known as a ‘magnetic moment’: when the north and south pole spin on its axis, like our planet Earth.

This is where the aforementioned magnetic field, generated by the MRI scan, comes into play. The magnetism causes the protons in the body’s water molecules to line up, and spin at a certain frequency.

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A secondary magnet then makes the molecules turn in different, new directions, and then the MRI machine is switched off. This allows the water molecules to realign, with the rate of realignment dependent on the type of tissue the molecule is found in. That radio frequency of the molecules adjusting is picked up by coils placed on your body beforehand, and from there, that information is relayed to a computer, where the image is visualized.

It’s ridiculously accurate, illustrating everything from soft tissue, to bones, and organs like the heart or brain.

What truly differentiates an MRI from an X-ray, besides the cool use of magnets vs. radiation, is the MRI process has no known side effects.

Are all MRI scanners that noisy?

differences between MRIs and x raysIf you’ve had an MRI, you know that thing can get loud.

That noise from the scanner is from the electrical current running through a coiled wire that’s making the magnetic field. When the scanner is on, the energy pushes the coil outward, and vice versa when it’s switched off.

It’s not uncommon for a machine to turn on and off rapidly to measure the changes in proton spins, hence the all ‘click’ noises.

If there are no known side effects, why do I have to lie still and hold my breath?

MRI scans are so precise, that they even pick up the smallest of sub-atomic movements in your body.

So for a truly accurate scan, any movement outside of the magnetic field it’s creating must be minimized. Lying still, as well as holding your breath for a few seconds, allows for the most correct scan possible.

If you’re worried about an upcoming scan, read 6 ways to keep calm during your MRI scan.

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