Why MRI Scans Are So Loud: The Science Behind MRI Sounds

This article takes a look inside an MRI scanner to show you what makes the different MRI sounds produced during a scan. The loud MRI sounds are produced by 3 MRI components: the coldhead, rf coil, and gradient coil. Learn more about what makes MRI sounds with the helpful resources below.

What Makes the Loud MRI Sounds?

Table of Contents

• What Makes the Loud MRI Sounds?
• What Makes The Loud Noises During an MRI Scan?
  • What makes the chirping sounds in MRI?
  • What Makes The Scan Sounds During MRI Scans?
  • Why Does an MRI Make a Loud Knocking Noise?
• Conclusion
  • Related Resources

What Makes The Loud Noises During an MRI Scan?

Recommended Read: MRI Scanner Components Explained

What makes the chirping sounds in MRI?

The rhythmic chirping heard in the background of MRI scans is produced by the liquid helium recondenser, known as the coldhead. MRI uses a powerful superconductive magnet that requires liquid helium to keep primary magnetic field coils in a supercooled state. The main purpose of the coldhead is to convert helium gas inside the MRI scanner back into liquid helium. It minimizes helium loss and helps to counter pressure created by the sublimation of liquid helium in MRI scanners. 

So what actually makes the chirping sound in MRI scans? If we slow down the audio of the coldhead assembly, we hear two distinct sounds coming from the coldhead compressor. See video above.

The first sound is the coldhead components expanding into a low pressure state as helium gas enters the coldhead chamber.

Secondly, we can hear the coldhead components contracting to compress the helium gas.

This two-stage liquid helium recondenser operates at temperatures near absolute zero to successfully convert helium gas back into liquid state.

What Makes The Scan Sounds During MRI Scans?

One of the questions we most often receive is what makes an MRI scan so loud? An MRI scan consists of a symphony of sounds working together to produce crisp, clear images of the anatomy. While there are many different noises that can be heard during MRI scans, there are two main components that make the loud noises in MRI. 

MRI sounds begin as a small RF source signal of less than 5 volts produced by the exciter assembly in the MRI systems cabinet. The radio frequency pulse makes its way to the RF cabinet where the signal is amplified and directed into the RF coil. You may notice the MRI sounds of one machine may sound different from another. That’s because the operating frequency and RF power output required varies according to the strength of the magnetic field.

As a good rule of thumb, higher magnetic fields requires higher RF output at a higher operating frequency. The RF coil inside the MRI scanner acts as a speaker and transmits the amplified radio frequency signal at the angle prescribed by the MRI technologist.

Why Does an MRI Make a Loud Knocking Noise?

The MRI gradient coil houses three sets of wire coils that produce a strong time-varying secondary magnetic field. Gradient coils modulate the primary magnetic field during MRI scans.

Gradient amplifiers supply each axis with rapid pulses of high voltage electricity. This contracts and expands the coils inside the MRI scanner.

The loud knocking noise in MRI scans is the sound of the gradient coils interacting with the primary magnetic field causing the coils to vibrate against the fiberglass mountings.

Additionally, the loud resonant noise produced by the gradient coil can reach noise levels in excess of 100 db. Ensure all patients are outfitted with hearing protection before starting MRI scan.

Conclusion

Are you feeling nervous about your upcoming MRI scan? Click here to read the best tips to stay calm during MRI scans. This helpful resource is a compilation of the top tips provided by some of our amazing community members.

The different noises associated with MRI scans work in sync to provide a safe, non-invasive diagnostic imaging procedure. Additional resources related to sound in MRI scans available below.

Want to learn more? Click here to learn how MRI works or visit our MRI knowledge center for a full catalogue of resources.

Related Resources

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