[FieldTrip] signal patch size measurement

[GEE Laura]

Dear Jan-Mathijs,

Thank you for your reply.
In the end I decided to use the formulas in table 1 of the paper Comparison of noise-normalized minimum norm estimates for MEG analysis using multiple resolution metrics (DOI:10.1016/j.neuroimage.2010.09.053) which allow me to calculate the dipole localization error and the spatial dispersion. If I'm not satisfied with these values, I will definitely look into your idea.
Best wishes,
Laura
________________________________
From: fieldtrip <fieldtrip-bounces at science.ru.nl> on behalf of Schoffelen, J.M. (Jan Mathijs) via fieldtrip <fieldtrip at science.ru.nl>
Sent: Thursday, March 10, 2022 8:29 AM
To: FieldTrip discussion list <fieldtrip at science.ru.nl>
Cc: Schoffelen, J.M. (Jan Mathijs) <janmathijs.schoffelen at donders.ru.nl>
Subject: Re: [FieldTrip] signal patch size measurement

Dear Laura,

I am not sure whether it makes much sense scientifically to measure the extent of an arbitrarily thresholded blob of reconstructed MNE-reconstructed signal, but if you insists I would use the triangular surface area for this (i.e. compute the area for each of the triangles in the mesh, and then assign to each vertex 1/3 of the summed triangle areas of the triangles that the given vertex belongs to). There is no dedicated FieldTrip functionality to compute this, but since it would be some relatively straightforward 3D vector voodoo using the sourcemodel.tri and sourcemodel.pos arguments I think that Mr. Google might already help you on your way (https://www.mathworks.com/matlabcentral/answers/271797-surface-area-of-a-3d-surface<https://fra01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.mathworks.com%2Fmatlabcentral%2Fanswers%2F271797-surface-area-of-a-3d-surface&data=04%7C01%7Claura.gee%40icm-institute.org%7Cadacd7b9f1ea46c51ec008da0267b92f%7C9df7cf1718fa41508b00dc5e754777d8%7C0%7C0%7C637824941765834799%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=Kdg0fgDSqCXuVeLCHF4b%2F6QnFWK4%2Bxrbb6CAphnzOtQ%3D&reserved=0>)

Best wishes,
Jan-Mathijs


On 7 Mar 2022, at 13:14, GEE Laura via fieldtrip <fieldtrip at science.ru.nl<mailto:fieldtrip at science.ru.nl>> wrote:

Hello everyone,

I am currently working on source reconstruction using minimum norm estimation (just like in the following tutorial https://www.fieldtriptoolbox.org/tutorial/minimumnormestimate/<https://fra01.safelinks.protection.outlook.com/?url=https%3A%2F%2Furldefense.com%2Fv3%2F__https%3A%2F%2Fwww.fieldtriptoolbox.org%2Ftutorial%2Fminimumnormestimate%2F__%3B!!HJOPV4FYYWzcc1jazlU!7aDum4j9lnD6EqpLub4_WWLz5Z28MYiMGa0dfS09Z4IK1aK5MKVwU5nQlyLV5imZ33y6_Q9ssBc0USvOTJRWXdMcJwif9qy1rY3MVg%24&data=04%7C01%7Claura.gee%40icm-institute.org%7Cadacd7b9f1ea46c51ec008da0267b92f%7C9df7cf1718fa41508b00dc5e754777d8%7C0%7C0%7C637824941765834799%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=1A8%2FKaBr8ag36Hyu8z0q3LEPVfKSAPJkBq3q9hHRL6Y%3D&reserved=0> ). I have managed to get to the visualization part and I am able to plot my source and the signal around it (see attached file).

I would like to measure the size of the patch. I thought about starting off by implementing a threshold (all cells with values above 50% of the source value would be put to 1 and the rest to 0) and then finding the furthest point away from the source (so by measuring the length between the source and each cell that is within the threshold and choosing the maximum length).

My questions are the following :


  *   Is there any function in the fieldtrip toolbox that already does this or something similar that will allow me to measure the size of the patch?
  *   If not, has anybody ever implemented something close to this and would be willing to share their thoughts/ideas?

Thank you in advance!
Laura

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