Tessellation Alignment GUI - reporting wrong coordinates??

[wchua]

Hi there,

I am trying to align the CTF sensors with the tessellation file of one subject. The result shows that the superior region of the head touches some of the sensors, which I think it is impossible. After careful checking the marker positions. I find out that the size of the head reported by the tessellation alignment GUI is not consistency with the MR images. According to the MR images, the subject's head should be about 20cm from anterior to posterior; however, the distance reported from the alignment GUI is just 16cm. I created the tessellation file based on the dsgl file from BrainSuite. I don't know whether it is a bug in the BrainStorm or in the BrainSuite. Any comment?

cheers,
-- Wilkin

[Sylvain]

Hi Wilkin,

Sorry for this late answer. CTF sensor locations are supposed to be expressed in a reference system defined from the Nasion and left & right preauricular points. One you get your tessellated enveloppes from BrainSuite, when using BrainStorm's tessellation alignement tool, you need to point at these locations in 3D and get the selected surfaces aligned properly in this reference system.

Now, if you get sensors that are too close to head surface, please double check that you have properly pointed at the right anatomical locations using the alignement tool. Another possibility is that localization coils during acquisition were not placed at the proper anatomical locations you're looking for on the surface envelopes.

Hope this helps - Let me know how things are doing.

[wchua]

Hi Sylvain,

Thanks for the reply. I just find out that the problem was due to the fact that the tessellation file was created with the anisotropic MR images. The problem is gone after I recreated the file using the isotropic images.

-- Wilkin