Initial Registration of fiducial points (NAS/LPA/RPA)

[mkfzdmr]

Hey Everyone,

I want to automate the manual definition of fiducial points (NAS/LPA/RPA) on the Anatomical MRI (instead of clicking on related points on the MRI).

MRI files were analyzed by FreeSurfer before uploading to Brainstrom.

We have accurate fiducial points (NAS/LPA/RPA) defined during TMS navigation by Brainsight software.

Below, the "bst_process" function uses "nas," "lpa," and 'rpa' parameters as input:

bst_process( ...
            'mrifile',     {AnatDir, 'FreeSurfer'}, ...
            'nas', [127, 213, 139], ...
            'lpa', [  52, 113,   96], ...
            'rpa', [202, 113,   91]);

Everything is OK. But, the fiducial points (NAS/LPA/RPA) defined by Brainsight provide those points locations in different spaces.

I want to transform one of the below coordinate systems to the coordinate system that is used by bst_process function. However, I couldn't find any transformation matrix or function.

Please see below the coordinate systems' names and exported fiducial points (NAS/LPA/RPA) examples by Brainsight. All are indicated same points in different spaces.

Brainsight Location System

'Nasion' 'Session 2'     97.3729000000000   36.5679000000000   116.260500000000
'RPA'    'Session 2'    169.700900000000   140                  80.3649000000000
'LPA'    'Session 2'     24                136.624600000000     96.9871000000000

Nifti Scanner

'Nasion' 'Session 2'      0.130100000000000  111.879100000000    -25.2005000000000
'RPA'    'Session 2'    -72.1979000000000      8.44700000000000  -61.0961000000000
'LPA'    'Session 2'     73.5030000000000     11.8224000000000   -44.4739000000000

LOCATOR (.elp/.hsp)

//Position of fiducials X+, Y+, Y- on the subject
%F  0.105419     1.42109e-17 0
%F  0.00344251   0.0732616 0
%F -0.00344251  -0.0732616 0

BESA (.sfp)

FidNz    0.00 10.53  -0.00
FidT9   -6.84  0.00  -0.00
FidT10   7.83  0.00  -0.00

I also added not exact but approximate positions of fiducial points (NAS/LPA/RPA) as defined by manual clicking on the MRI viewer of Brainstorm (desired approximate locations on Brainstorm x,y,z):
(NAS/LPA/RPA)

NAS: MRI:  130 220 109  - World:   2.5  111.45  -32.46
RPA  MRI:  202 139  95  - World:  74.5   30.45  -46.46
LPA  MRI:   48 108  96  - World: -79.50   0.55  -45.46

Could you please help me transform one of the above coordinate systems to the Brainstrom coordinate system?

This issue has discussed before, but I think never solved:

Import the fiducial file

Hellow, Thanks for support to BST users. I would like to know about how to import fiducial file marked by brainsight, and will match 3 points (NAS/LPA/RPA). I read Brainstorm tutorial, then we can match head localization between MRI and MEG (CTF) using Polhemus device when put *.pos file on the MEG data set. BrainSight doesn't export *.pos (it can export *.txt, *slp/.hsp, *sfp, *.mat). We cannot import these data from degitized head points>add point in Brainstorm. Thank you. Regards Nojima

Matching fiducials selection

Hello, Thanks for continued support to BST user We have EEG and structural scan acquired for each subject. Surface segmentations are performed using BRAINSUITE. Inside EEG file we have electrode positions measured on individuals head w.r.t NAS, LPA, RPA points using Brainsight. As per tutorial on your website using NAS, LPA, RPA points inside EEG channel file, BST will convert existing coordinates to BST coordinate system while importing. However when we import anatomy, we ma…

Here, the defined brainsight coordinate system.

Best,
Mehmet

[Raymundo.Cassani]

Hi Mehmet,

@mkfzdmr

Everything is OK. But, the fiducial points (NAS/LPA/RPA) defined by Brainsight provide those points locations in different spaces.

Is it possible to export the location of the fiducial points in MNI space coordinates instead of the Brainsight internal system?

Does the manual indicates a transformation in Brainsight to go from MRI voxels to their location system?

Best,
Raymundo

[mkfzdmr]

Hi Raymundo,

Thanks for your reply. It is not possible to export locations in the MNI space by Brainsight. But I think the best way to use Brainsight coordinates is to export them in world space, then convert them to MRI space for Brainstorm.

Thanks again for your time.
Best,
Mehmet