| Subject: Braces and MRIs, CTs |
Author:
Katie
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Date Posted: 12:16:11 07/07/04 Wed
In reply to:
drrick
's message, "Re: Dr. Rick...I have a question for you" on 08:00:50 07/07/04 Wed
Interesting question... I know people who have had successful MRIs performed with a permanent retainer in place, but it took several tries to get a scan of the brain that did not have significant artifacts, even when the piece of metal was small and only present in the lower jaw.
The artifacts in an MRI are caused by the fact that, in the presence of the magnetic field produced by the MRI machine, a piece of metal (even one that's not usually attracted by a magnet, such as stainless steel or titanium) will respond by producing its own magnetic field. This can lead to blurry MRI pictures, as may be happening in your case.
Metal objects can also cause artifacts in CT scans, but for a different reason. A CT scan is performed by taking X-rays from many different directions and compiling them into a 3D model of your body. With each scan the X-rays travel through a part of your body and reach a detector on the other side. Since metal is opaque to X-rays, it can cast a shadow between the X-ray source and the detector, blocking the view of any tissue there. This causes bright lines to radiate from the metal object in the final image - see Figure 4, here:
<a rel=nofollow target=_blank href="http://www.research.ibm.com/hc/ARTIFACT/artifact.html">http://www.research.ibm.com/hc/ARTIFACT/artifact.html</a>
However, the object there was very large (a hip joint replacement) - it's likely that your braces will not cast a large enough shadow to interfere with the imaging process. So a CT scan may produce a good picture... unfortunately I am not familiar with the diagnosis techniques for MS, so I don't know whether a CT scan will be able to identify the symptoms with the same degree of accuracy as an MRI would. A CT scan distinguishes tissues only on the basis of how opaque they are to X-rays, whereas an MRI distinguishes them based largely on water content.
I'd talk to your doctor about alternate techniques for diagnosis, but it may be that an MRI is your best shot. It's up to you whether the trouble of braces removal/replacement is worth it compared to finding out sooner about the MS. If more MRIs are in your future, you might consider getting your brackets replaced with ceramics - then the ortho would only have to remove the archwire.
I hope this helped some, and hope that everything goes well for you.
Katie
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