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Home > Archive > Radiology interventional > October 2005 > MRI magnetic resonance imaging display, sounds
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MRI magnetic resonance imaging display, sounds
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| dsaklad@gnu.org 2005-10-13, 6:02 pm |
| a.
What does the digital display on the MRI mean exactly?... 123 mm ?
b.
What causes the sounds that are heard when entering the room with the
MRI ?...
c.
What causes each of the sounds that are heard inside the MRI ?...
d.
More appropriate hearing protection needed. Earplugs should expand to
properly fit the ear canal. Earplugs should be of the \
appropriate rating, appropriate density.
e.
Okay or not to blink, to open and close eyes during MRI ?...
f.
Regarding the CD, how do you get the PC AutoPlay DICOM Viewer to work
on an iMac Apple Computer?
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| GeoffS 2005-10-20, 6:50 pm |
| > What does the digital display on the MRI mean exactly?... 123 mm ?
If you're talking about the readout on the front of the magnet, I
believe it's the distance from landmarked point and the magnet
iso-center. The "landmark" is the spot on the patient that the
technologist chooses as a reference for the scan - usually a prominent
anatomical spot like the bridge of the nose.
> What causes the sounds that are heard when entering the room
> with the MRI ?...
Most likely the compressor (aka "cold head") attached to the magnet
used to reliquify the Helium that boils off keeping the magnet cold (we
used to call it the "the ka-chunk, ka-chunk machine").
> What causes each of the sounds that are heard inside the MRI ?...
Basically, an MRI is a really big loudspeaker. There is a large static
magnetic field with a coil-magnet (the gradients) inside it. When the
current in the gradient coils is changed (especially rapidly) they
create very large forces which cause the coil structure to move (very
slightly); just like a speaker cone that motion generates sound. In
designing the machine, every effort is made to make all the parts stiff
so they won't flex, but the forces are quite high.
> More appropriate hearing protection needed.
What? Huh? Could you speak a little louder? I can't hear you...
Seriously, good ear protection is an absolute requirement, especially
with the high-speed scans these days.
People are working on the problem:
http://www.rps.psu.edu/jun95/mri.html
> Okay or not to blink, to open and close eyes during MRI ?...
It depends on the scan. For an extreme example, if you're having a
chest or abdominal scan, then you can blink as much as you want. If
you're having a head scan, then blinking (or even moving your eyes
behind closed eyelids) can cause a motion artifact to blur the slices
that include the eyes. Some scan types are more sensitive to motion
artifacts than others, too. Personally, I always close my eyes, find a
comfortable position, relax, and lay still when I'm in the magnet (and
I've spent *many* hours being scanned).
> Regarding the CD, how do you get the PC AutoPlay DICOM Viewer
> to work on an iMac Apple Computer?
Beats me, sorry.
Cheers,
Geoff S.
http://geoff-s.net/
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