Can MRI Fringe Fields be Mapped in a 3D Space?

[arashazizi]

Hello everybody, I am working on a project that require to have map of an MRI machine fringe field in 3d space. I basic idea is to measur it in one plane parallel to radius of machine and then by assuming that field is axissymetric make my map. does anybody have any idea on doing that or on my work?

 

[Dale]

The manufacturers of MRI machines are required to publish various field maps in their official documentation. Why don't you just use the published maps?

 

[arashazizi]

Thanks, but they just publish safe zone around machine and in Cartesian plans. I am going to use fringe field for navigation purpose and I need to have a more exact map of magnetic field in proximity of machine. the gradient in this region is bigger than inside the machine and also we have more freedom there.

 

[Dale]

They publish quite detailed plots of the field, the field gradient, and sometimes other quantities also.

The distance of the 5 Gauss line is often published in the marketing material. I think that is what you are talking about, but the actual system documentation and manuals contain much more detailed maps.

Look for the MRI Compatibility Data portion of the manual.

 

[Vanadium 50]

Why would you think the fringe field is axisymmetric when the MIR machine is not - for example, it is supported on the bottom, but not on the top. Furthermore, if you are going to the trouble of measuring the field, why not measure it everywhere?

 

[Dale]

The main field producing elements are axisymmetric, so it is a pretty good approximation. But you are right that there are slight deviations from axisymmetric. Particularly if the room has steel structural members.

 

[Vanadium 50]

Inside the bore, the symmetry is good. But outside, all bets are off. Particularly if there is little or no iron for the return flux (common in these magnets) and, like you say, something ferrous in the room.

If you've ever mapped a magnet, you'll know that the vast majority of the time is in setup. Once you get going, it's pretty quick - so more points is the way to go for sure.

 

[Dale]

I do agree with that. I would either use the published plots or I would do a full mapping.

 

[arashazizi]

Your comments made my way more clear. I appreciate your guidance.

 

[Andy Resnick]

Hello everybody, I am working on a project that require to have map of an MRI machine fringe field in 3d space. I basic idea is to measur it in one plane parallel to radius of machine and then by assuming that field is axissymetric make my map. does anybody have any idea on doing that or on my work?

I'm confused- are you asking how to measure the magnetic field in a plane, or are you asking how to make the planar measurement axisymmetric?

 

[arashazizi]

My aim is to have a spatial measurement of fringe magnetic field in a 1^3 cubic space. If I want to have a 1 cm resolution I would have to take 10^3 measurement on exact points. I believe simulation does not work hear because geometry and all sources of uncertainty. I thought that if I take measures in a plane and then extend it to a cylindrical space I would have the map but distortion and lots of cables and other stuff around the machine make this assumption wrong.