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MRI Phantom 2

by SCaruthers, published

MRI Phantom 2 by SCaruthers Apr 11, 2013

Description

Intended to be used as a "resolution phantom" in a magnetic resonance imaging system to verify that the size of objects in the image matches the real world dimension. Could also be used as a "jig" to verify 3D print dimensions are accurate.

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Interesting. I guess, I'm just used to seeing signal dropout from prosthetic hips, i.e. lots of metal, and calling that a susceptibility artifact. While I can see the artifact that you are referring to, I would think that it is a SNR issue due to the voxel size. Of course I'm not an MRI guy, so that needs to be taken into consideration. Regardless, thanks for putting these phantoms up!

That's a great question. So PLA and ABS have magnetic properties similar to water, so as you point out, a solid piece of plastic should not create an artifact in an MR image (though, it would also give no signal, and therefore show up as dark in the image). HOWEVER, if you print this thing with an infill other than 100%, then there is air inside the block. Air does not have the same magnet properties as water or plastic, and therefore this difference in materials (air/water) create a border between two things of different magnetic properties (this is called magnetic susceptibility heterogeneity). This heterogeneity creates tiny fluctuations in the local magnetic field of the MRI scanner which ultimately causes artifacts in the images. Look at the MRI images of Phantom 1 (http://www.thingiverse.com/thi... to see an example of the susceptibility artifact surrounding the phantom printed with 10% in fill; whereas the phantom printed with 100% in fill has nice sharp edges.

Why would there be susceptibility artifacts is not solid? Lack of ABS isn't ferromagnetic, to my knowledge.

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Instructions

If to be used as intended (for MRI in a water bath), best to be printed with 100% infill. Otherwise, there will be significant susceptibility artifacts ( mritutor.org/mritutor/suscept.htm ). See drawing for original dimensions of "pegs".

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tgfisher on Apr 11, 2013 said:

Why would there be susceptibility artifacts is not solid? Lack of ABS isn't ferromagnetic, to my knowledge.

SCaruthers on Apr 11, 2013 said:

That's a great question. So PLA and ABS have magnetic properties similar to water, so as you point out, a solid piece of plastic should not create an artifact in an MR image (though, it would also give no signal, and therefore show up as dark in the image). HOWEVER, if you print this thing with an infill other than 100%, then there is air inside the block. Air does not have the same magnet properties as water or plastic, and therefore this difference in materials (air/water) create a border between two things of different magnetic properties (this is called magnetic susceptibility heterogeneity). This heterogeneity creates tiny fluctuations in the local magnetic field of the MRI scanner which ultimately causes artifacts in the images. Look at the MRI images of Phantom 1 (http://www.thingiverse.com/thi... to see an example of the susceptibility artifact surrounding the phantom printed with 10% in fill; whereas the phantom printed with 100% in fill has nice sharp edges.

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