[Homer-users] Probabilistic Spatial Resgistration

[Huppert, Ted]

Hi Drew-

I have some code that does the opposite of what you asking; given the location of optodes in 3d Cartesian space registered to a brain, it projects the points (and brain image) into the 10-20 space for display.

The code was easy to write so you can probably just do something similar.  I took the landmark points (ear, nasion, top of head) and fit it to an ellipse/sphere.  Then it's easy to map from the nearest Cartesian coordinate to spherical (theta/phi) positions and vice versa.  Its not perfect but its an easy way to do it.  You could do the same from the parameter measurements (over top and around the head) to define the width/height/length and registration of the ellipse.  SPM has a similar function in their M/EEG tools (I think it is spm_meeg_register.m or something like that).

-Ted

Theodore Huppert, PhD
University of Pittsburgh
Department of Radiology

On Feb 1, 2013, at 2:08 PM, "Drew Halliday" <drewh at uvic.ca<mailto:drewh at uvic.ca>> wrote:

Hello NIRS community,

Has anyone successfully used gross anatomical landmarks (e.g., nasion, inion, left and right preauriculars) to computer probabilistic spatial registration using either Homer 2, or another program (e.g., fNRI Tools from Ippedia Dan’s group)? My understanding is that this can be done without MRI or 3D Digitizer data, however the disconnect for me is in computing 10-20 or MNI coordinates based simply on distances from nasion-inion, left-right preauriculars, and other combinations of distances between these landmarks.

As the AltasViewer GUI in Homer 2 is not yet available, I have been using fNRI Tools, and to a lesser extent NIRS_SPM.  An ‘origin’ and ‘others’ spreadsheet (.csv) are called during this process, however these spreadsheets contain x, y and z axis coordinates, presumably computed using either 3D digitizer data, MRI scans, or gross anatomical measurements.

Does anyone know how to use a probe geometry file, combined with gross anatomical measurements, and produce said origin and others spreadsheets?  All thoughts are welcomed!

Thanks,
Drew
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