why MRI machines make so much noise.

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My boyfriend got an MRI of his brain the other day and will not stop talking about all the noises it made and has been obsessing over the “Why” of it. Can someone so I can give him the answer he so desperately needs?

In: Engineering

Cause there’s a big spinny supermagnet on rails.

https://m.9gag.com/gag/a6OLpMN

Slightly terrifying without the cover on

Yea nevermind, this is a CT scanner not a MRI

because on the inside of the machine, the large metal coils are vibrating when electricity passes through rapidly, creating a magnetic field, which causes the banging noise. the louder the bang, the more the vibration, the more detailed the scan.

I think ICP said it best. “Magnets, how do they work?”

Got an mri a couple of weeks ago after 2 herniated discs. Was no where near as bad as i had been told it would be

There are multiple coils inside of an MRI that produce magnetic fields for various purposes in various ways.

1) the ‘primary’ coil. This is what is known as a superconducting coil. It’s made of proprietary alloys, cooled to about 4Kelvin (-452°F or -269°C) to prevent loss of current via heat and ‘cannot be turned off’. This is your 1.5, 3, 7, or 12 Tesla magnets (commonly, they do have other levels of tesla). This is the magnetic field that is used to image the body. (Edit: for comparison, the magnetic field of the earth is about 0.5 Gauss… there’s 10,000 Gauss to 1 Tesla!)

2) gradient coils. These are water-cooled electromagnetic coils, inside of a resin shell shaped like a tube, that’s just on the other side of the tube a patient sees. They are powered by about around 600 amps and used to manipulate the primary magnet field in such a way to produce spatial information (x,y and z axis to build the actual image being taken). (Edit: there is typically 1 gradient coil for each axis, so 3 gradient coils in the whole assembly, each sucking up 600amps!)

The primary magnetic field does not make noise. It’s at a constant level, just being shifted around by the gradient coils during a scan.

The gradient coils are basically giant speakers without a diaphragm… well, YOU are the diaphragm. The air is a diaphragm. Absolutely do not do this, but if you took a piece of aluminum sheet into the magnet while the gradients were pulsing, the field and noise actually knocks the aluminum and it feels like it is being physically contacted!

Much has been done to reduce the noise of a machine… after all, they’re scary enough for many patients. But at the end of the day, a 600 amp (x3) speaker tube big enough to fit a large person is going to create some noise

Maybe if we sucked all the air out of room….

Source: clinical imaging engineer