I returned to the Trail (Kootenay Boundary) hospital on Monday night for an MRI. This one was of my lower back, and traces to my original problem with sciatica / sciatic nerve disruption. The X-rays of that back region had shown bone degeneration, but the MRI should also show any nerve involvement.
What I observed: from certain angles, an MRI is truly a very noisy machine.
Past MRIs
I’ve had one or two MRIs in the past, but always of the upper back and neck. I knew what to expect, including how loud the machine can get. But I found the noise for those previous visits to be quite manageable even without ear protection. Loud, yes, but not insufferably so.
It gets louder
But this time it was the lower back being scanned, and that involves being shoved another metre or so into the belly of the machine. I was extremely glad that the technician basically forced me to put in ear protection plugs. The noise the MRI makes is magnified the deeper you go into it, apparently.
Exactly what is making all the noise in an MRI? Its close cousin, the CT scan, is comparatively quiet- so it must be something unique to the MRI process. Apparently it has something to do with how the magnetic coils expand and contract during operation, with sounds being produced in excess of 100 decibels. The switching between positive and negative in the MRI scanning process makes the sound even louder as the coils slam against their mounts.
The intensity of the sound increases the deeper you go into the MRI tube. The tube is about two metres in length on some of the machines like the one I was in. In my case it was my lower back and pelvis being scanned, and I was inserted so that my waist was around the centre of the MRI machine. Basically, my whole body was inside the MRI, toes to top of my head. In that configuration I would say that not wearing ear protection would border on painful.
This is interesting to me because my previous MRI was just of my head and neck, and the loudness was far more tolerable.
MRI loudness is relative
If someone tells you that an MRI is not loud, temper that with the fact that loudness depends on what is being scanned. If their body was mostly outside the scanning tube then the loudness might only be 50 or 60 decibels. It could be double that, however, if their body was deep inside the machine. Unless you are deaf, 100+ decibels is very loud.
There are also different MRI machine designs. The ‘tube’ style design is being surpassed by ‘open’ MRIs which I could imagine would be both quieter (less echo) and less claustrophobic. I doubt that we have many open MRI machines in Canada, but they could be coming.
Boiling it all down, my advice is: listen to your MRI technician, and wear the ear protection if they recommend it.
