[FieldTrip] ft_sourceinterpolate

[RICHARDS, JOHN]

I figured part of it out.

The functional data, computed from a tetra source, is not on a regular grid and so is "unstructured".  We had a dim member in the source structure which defined it in ft_sourceinterpolate as regular grid.  The anatomical 1mm data was structured hex.  

However, its still not exactly correct.  The output MRI volume based on the interpout data seems to be on discrete voxels.  Perhaps it’s the "nearest" interp method which is the only interp allowed for non-grid functional?   The 3mm regular hex sources allow "spline" interp, that might be it?

John




***********************************************
John E. Richards
Carolina Distinguished Professor
Department of Psychology
University of South Carolina
Columbia, SC  29208
Dept Phone: 803 777 2079
Fax: 803 777 9558
Email: richards-john at sc.edu
https://jerlab.sc.edu
*************************************************

-----Original Message-----
From: RICHARDS, JOHN 
Sent: Saturday, March 6, 2021 10:50 AM
To: fieldtrip at science.ru.nl
Cc: CONTE, STEFANIA <CONTES at mailbox.sc.edu>
Subject: ft_sourceinterpolate

We are trying to use ft_sourceinterpolate.

1--We have a tetra source model, do source analysis with eLORETA, ERP data, etc.  The source model is based on a tetrahedral mesh on gm rather than a hex mesh.

2--We have a 1mm hex mesh on gm

3--The goal is to interpolate the "sparse" tetra mesh with the functional data, onto the 1 mm hex mesh, in order to create MRI volumes with the activation.

4--The ft_sourceinterpolate(cfg,sourcewithtetrameash,hex1mmmesh) does not work.  It does not result in the same no of "inside" voxels as the 1mm hex mesh

e.g., like 25K voxels in the tetra, 855K in the 1 mm grid, but only 15K voxels in the interpout.inside(:).

Alternatively
1--using a 3 mm hex mesh, source analysis, the source model is based on a 3 mm hex mesh on gm.
2--1mm hex
3--same goal
4--ft_sourceinterpolate(cfg,sourcewith3mmhexmesh,hex1mmmesh) works.  It has 855K voxels in the interpout.inside(:).  It also correctly saves to the gm of the MRI volume.


Any ideas on this?
We have tried int32(pos) on both tetra3mm ahd hex1mm; used only overlapping  tetra3mm and hex1mm voxels; etc

John


***********************************************
John E. Richards
Carolina Distinguished Professor
Department of Psychology
University of South Carolina
Columbia, SC  29208
Dept Phone: 803 777 2079
Fax: 803 777 9558
Email: richards-john at sc.edu
https://jerlab.sc.edu
*************************************************