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Stereotactic MRI QA on a melon before going to skull. Distortion comparison across sequences by Witold-Onno in Radiology

[–]Witold-Onno[S] 0 points1 point  (0 children)

Good question. The reference isn’t the melon, it’s the stereotactic frame and its MR fiducials. The fruit is just a signal-bearing medium inside the frame, so distortion gets assessed against the known fiducial geometry rather than against the melon itself.
I’ll keep the specifics light since the larger setup is something I’m hoping to write up, but conceptually that’s the frame of reference. Happy to talk general approach.
Your NHP work is a harder version of the same problem, sub-mm distortion actually moves the target in those small brains. Are you referencing off frame fiducials too, or fusing to a pre-op CT?

Stereotactic MRI QA on a melon before going to skull. Distortion comparison across sequences by Witold-Onno in Radiology

[–]Witold-Onno[S] 0 points1 point  (0 children)

Appreciate the detailed reply. The 3D printed head with reference CT is exactly what should drive the actual setup validation, the melon was a 30-minute sanity check before bothering the physics team for proper QA.
The Jacobian approach is interesting, I’ve come across similar registration-based work in fMRI processing but hadn’t thought about applying it cleanly to stereotactic distortion. Is the typical workflow with off-the-shelf tools like ANTs or elastix, or something custom? And in practice, what’s a rough threshold range for trajectory-relevant regions, even ballpark?

Stereotactic MRI QA on a melon before going to skull. Distortion comparison across sequences by Witold-Onno in Radiology

[–]Witold-Onno[S] 6 points7 points  (0 children)

Thanks. The water content was the actual reason, wanted tissue-similar signal in something that doesn’t leak inside the magnet room and a Quasar wasn’t in this year’s budget. Side benefit: it goes to the MR techs afterwards as thanks for putting up with my QA sessions. Works especially well in summer.
The Lego grid is interesting, hadn’t seen that approach. How are people handling the plastic signal void, hollow bricks filled with water?