Posted: 10/26/2007 8:53:54 AM EDT
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So, I had another scan of my knee today. Just what in the hell is inside of those damn things that they make so much noise? Sounds like at least one garbage truck, a cement mixer, couple of leaf blowers, 12 midgets with hammers, all mixed on an old Pink Floyd album.  I thought I worked around noisy stuff, but pound for pound, I think those take the cake. |
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A MRI is a complicated system, there is the BIG super conducting magnet (which you are in) and the gradient coils (which you are in also) that are there to bend or shape the magnetic field to give slice selection for the images. This is the part of the MRI system that makes all the noise. The magnetic field has to be moved like an electron beam inside of a TV CRT. And it is this part that makes all the noise by flexing the magnet a bit, is like you are inside of a very large speaker. Remember that this will be a magnet that is so powerful that small steel abject that gets sucked in can fly so fast that it can kill someone. And will trash cell phones and hearing aids. kychas |
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Yep, gradient coils. These are big electromagnets that are switched rapidly to alter the main magnet field (Bo) . While the coils are ridigidly mounted inside the tube, the forces generated are considerable and thus there is relative movement. Remember, nothing conductive or magnetic can be used to mount these gradient coils. And because the suitable materials are of lower modulus, there is some relative movement and subsequent noise. Yes, the issue of material fatigue in these materials is considered in design. Having a gradient coil rip out during a scan would be a really bad thing. |
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The magnetic field is so powerful that it alters the spin of the protons in your tissues. It is the difference in spin that is detected and then reconstructed as images that the radiologist sees. If you haven't seen the images MR produces, look at your films. The detail is astounding. It looks very much like an anatomic specimen. |