Trouble generating hand motor CST tracts using TMS points as ROI

[Aesha Jain]

Dear Frank,
I’m trying to track the hand motor (M1 hand knob) corticospinal fibers, using TMS points but I’m not getting a convincing hand bundle. What I consistently see is mainly the leg-related CST, and the hand seeds either don’t generate enough streamlines or don’t descend reliably into the brainstem.
What I’ve tried:

• Dilating the TMS points ROI to increase coverage
• Adding a second ROI/waypoint around the internal capsule
• ROI near/within the brainstem
• Used TMS points as seeds, ran all the tracts. 
• Adjusting these ROIs in a few ways,  the hand streamlines remain sparse compared to leg fibers
• Adjusted parameters to different angles, step size, threshoold and tried running on all three three models, DTI, GQI and QSDR.

This has been consistent across 3 subjects. Could you recommend a more reliable ROI strategy or parameter settings to isolate the hand CST?

Thanks a lot for your help.

Regards,
Aesha 

[Frank Yeh]

The hand location is usually much harder to map. I would increase the
step size and not specify the seed region to see if it works.

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[Aesha Jain]

Thank you very much for the suggestion, Frank. It works when I increase the step size to above 5. Do you think it is okay for the step size to be this large?

Regards,

Aesha

[Frank Yeh]

It is a bit large, but if the trajectories look correct, it should be fine.
Frank

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